Technical Report

Recommended Test Procedure

and Supporting Testing Data for the 

Evaporative Emissions Leak Test

by

Peter Smith

Glenn W. Passavant

December 2013

NOTICE

Technical Reports do not necessarily represent final EPA decisions or positions. They are 

intended to present technical analysis of issues using data or testing results which are currently 

available. The purpose in the release of such reports is to facilitate the exchange of technical 

information and to inform the public of technical developments which may form the basis for a 

final EPA decision, position or regulatory action.

Assessment and Standards Division

Office of Air and Radiation

U.S. Environmental Protection Agency
1

I. Introduction

Evaporative emission control systems have been present on new light-duty vehicles since the 

1971 model year. These systems have gone through several generations of upgrades over the years and 

have become more sophisticated and complex as fuel properties have varied, test procedures have 

changed, emission standards have increased in stringency, and new requirements have been added to meet 

greater demands for improved air quality. These onboard systems are currently responsible for capturing 

evaporative emissions produced from gasoline during diurnal, hot soak and running conditions as well as 

in vehicle refueling situations. Toluene and benzene, which currently account for about five percent of 

the tank headspace vapor composition, have been linked to possible adverse health effects.1,2 In addition 

these compounds and others commonly found in gasoline vapor such as butane and pentane are also 

responsible for the creation of photochemical smog. Due to these concerns, EPA has sought to increase 

the capability of these systems to strictly limit the release of these compounds to the atmosphere.

Over the past several months, the Agency has developed an evaporative emissions leak test 

procedure which could be used in both laboratory and field conditions to quickly test the integrity of a test 

vehicle’s evaporative system. Such a test is independent of On-Board Diagnostics (OBD) leak detection 

requirements and as such would not be bound by the limitations and restrictions commonly present in 

such a monitoring system. The leak test as presently envisioned would be a stand-alone test designed to 

find any vapor leaks in the fuel/evaporative system. This test is not designed to indentify leaks outside of 

the fuel and vapor containment portion of the vehicle fuel system.

Past and current work at the Agency has found that not all evaporative emissions leaks are being 

identified by current OBD systems. This is especially important since these emissions are a potentially 

significant portion of the evaporative emissions inventory. This test procedure and accompanying leak 

standard could serve as a means to reduce vapor from system leaks in use. Concurrent with Tier 3 

emissions levels it is being proposed that the leak test emission standard be proposed at a value of 0.02 

inches cumulative diameter orifice. 

This report was published for comment as part of EPA’s NPRM which proposed the leak

standard.

1 No comments were received. The final report details the evaporative emissions leak test 

procedure as presently proposed as well as the vehicle preconditioning necessary prior to undergoing the 

leak test. It also presents the various testing that has been performed at NVFEL both in the creation of the 

test procedure as well as supporting data to ensure that the leak test provides accurate results on as many 

different vehicle configurations as possible. Examples of calculations of relative leak orifice sizes are 

also presented.

II. History of Evaporative Emissions Controls and Standards

Even though present day fuel evaporative emission controls are relatively mature, the

development of the present emission standards and related requirements and the control technology 

applied by the manufacturers has evolved over about 40 years. The activated carbon canister and the 

basics of evaporative system as it is known today for controlling hot soak and diurnal emissions were 

required by the for 1971 model year light -duty vehicles even before the creation of EPA. The purpose 

of this system is to capture fuel vapors created by the presence or operation of the motor vehicle and store 

these hydrocarbon vapors in an onboard activated charcoal media known as the charcoal canister. Until 

recently, most manufacturers placed this canister under the hood where it was responsible for capturing 

the fuel vapors generated when the fuel tank was heated via atmospheric conditions (diurnal cycle) as 

 1 See Appendix 1 of the draft Regulatory Impact Analysis supporting the NPRM. This is available at

http://www.epa.gov/otaq/tier3.htm
2

well as the vapors generated from the carburetor float bowls (hot soak) and fuel tank when the vehicle 

was parked. In uncontrolled vehicles fuel tank and carburetor evaporative emissions were vented to the 

atmosphere. The fuel vapors generated during vehicle operation, known as “running loss” were basically 

not controlled in early designs.

These early systems did not focus on full vehicle evaporative emissions thus early carbon trap test

procedures were deficient in gaining control. Early evaporative systems did not have any type of 

microprocessor interface for controlling vapor loads and purge and were controlled via a series of vacuum 

check valves, mechanical linkages, and/or solenoids. The canister had a finite storage volume, much like 

present day systems, and was purged of stored vapors during vehicle operation. Unfortunately, many of 

these early systems were disconnected or otherwise modified by unknowing motorists thinking these 

systems had a detrimental effect on the performance or running operation of their vehicle. 

Over the past 40 years there have been about five major changes in evaporative emission control 

requirements. These have involved test procedure changes, more stringent numerical standards, control 

of evaporative emissions from other sources on the vehicle, or control of emissions from various other 

operating modes. Following the initial requirements for the 1971 model year, noteworthy changes in the 

regulatory requirements as indicated in the Code of Federal Regulations included: (1) the change from the 

carbon trap to SHED test method in 1978, (2) the numerically more stringent 1981 model year hot soak 

plus diurnal evaporative emission standards, (3) enhanced evaporative requirements which phased-in for 

the 1996—1999 model years and incorporated multi-day hot soak plus test requirements and emission 

standards, fuel spit back standards, and running loss controls,(4) new onboard refueling vapor recovery 

requirements which phased in from model years 1998-2006, and (5) the Tier 2/MSAT requirements for 

2004-2010 model years which further tightened the hot soak plus standards, addressed resting losses, and 

brought in to play consideration of ethanol-blend fuels. New provisions for “zero evaporative” vehicles 

are now in place in California as part of the PZEV allowance in the ZEV program and have recently been 

included in the evaporative emission control standards for California’s LEV III program. EPA expects to 

propose “zero evaporative” emission standards as parts of its Tier 3 rule to include a more stringent multiday hot soak plus diurnal emission standard and a canister bleed emission standard and test procedure.

Computerized emission control system monitoring became necessary when the California Air 

Resources Board (ARB) mandated that all vehicles sold in that state in 1988 have an onboard diagnostic 

system to detect problems in the performance of emission control systems. These early systems were 

known as On Board Diagnostics (OBD) monitored the oxygen sensor, the fuel delivery system, engine 

control module, and the exhaust gas recirculation (EGR) system. If a problem is detected with a vehicle 

or engine system that is monitored by OBD, the OBD monitor illuminates a Check Engine or Malfunction 

Indicator Light (MIL) and stores a diagnostic trouble code in memory which can be later retrieved. While 

some of these codes and problems may be noticed through vehicle drivability changes or other discernible 

problems with the vehicle performance, some are not. Thus, the MIL provides the driver notice of a need 

to check for a problem in the operation or performance of a given vehicle/engine system based on the 

diagnostic trouble code (DTC) set in the OBD system. Vehicle-based computers also created the 

opportunity for more sophisticated and precise control of canister purge and management of the effects of 

canister purge on exhaust emission rates. 

These controls were further refined with the advent of OBDII which was required beginning in 

1996 with full compliance by 1999. OBDII requirements enhanced the requirements of the original OBD 

systems and added specific requirements related to detecting problems in the fuel /evaporative control 

system. Current OBD systems are required to monitor for vapor leaks of various diameters within the 

fuel /evaporative control system and to check for proper operation of the purge system, and other general 

malfunctions related to items such as pressure sensors. It is clear that OBD and the use of the onboard 
3

computer control system has greatly increased the ability of vehicle evaporative and refueling control 

systems to function more precisely and effectively and to monitor for problems in performance. 
4

III. Reasons for Creation of an Evaporative Emissions Leak Test

At certification current evaporative and refueling emission standards provide reductions in excess 

of 95 percent over uncontrolled levels when evaluated over the specified test procedures. While programs 

such as OBD, extended useful life requirements, and in-use verification programs (IUVP) testing have 

improved the overall in-use performance of these systems, full life durability and performance in off cycle 

situations remain important objectives. 

Even with the upgrades in technology and test procedures over the past years, it was possible for 

a vehicle with a small leak in the fuel/evaporative control system to meet the hot soak plus diurnal 

emission standards. This is because leaks are not expected in certification vehicles and more generally 

because the test procedures and standards were not as rigorous and did not require control under all of the 

various in-use conditions which affect evaporative emissions. Some leak emissions could be 

accommodated and the vehicle would still pass the standard. The leak detection requirements of the 

OBDII regulations have helped to focus more attention on preventing leaks over the vehicle life. 

However, from an in-use performance perspective OBD alone is not sufficient for at several reasons. 

First, OBD systems do not operate under all conditions and do not require that the owner/operator seek a 

repair if a MIL is indicated. While repairs are far more likely areas with inspection /maintenance (I/M) 

programs, repairs are not always made and if so they may well wait until the I/M check is due. Second, is 

the issue of OBD system readiness. There are operating circumstances when an OBD system is not 

required to monitor the evaporative system. These are commonly termed global disables and deficiencies. 

For example, global disables include specifications on outside air temperature, elevation (i.e., barometric 

pressure), and tank fuel volume. Deficiencies include manufacturer specific exceptions provided on a 

case-by-case basis when the system cannot meet the OBD monitoring requirements either due to an 

element of fuel/evaporative system design or if there is some operating condition in which the OBD leak 

detection methodology does not operates reliably in the sense of not giving false fails or false passes. If 

the vehicle is operating in one of these “disable” or “deficiency” conditions the OBD system will not run 

and not detect a leak. Third, OBD systems are not required to detect leaks of less than 0.020”. While the 

prevalence of these very small leaks is not known, it is reasonable to project that they are at least as 

prevalent as larger leaks. Limited data indicates that the leak emission rate for vehicles with leaks less 

than a 0.020” diameter orifice is not significantly less than at 0.020”. Thus, they are potentially 

significant.

Tier 3 evaporative emission standards are intended to allow for essentially zero fuel vapor 

emissions over the vehicle useful life. Full life Tier 3 evaporative emission standards coupled with 

upgraded OBD will help to encourage focus on designs and technology which will improve in-use 

durability. However, a vehicle with a vapor leak in the fuel evaporative emission system will emit VOCs 

at a greater rate than anticipated from the “zero evaporative” technology on which the proposed Tier 3 

evaporative emission standard is based. To help insure that the reductions envisioned by proposed Tier 3 

evaporative emission standards are achieved in-use, EPA is considering an evaporative emissions leak test 

procedure and standard. The leak emission standard would help to ensure added focus on efforts to 

improve in-use durability by reducing the diameter and prevalence of leaks.

The remainder of this memorandum covers the following areas. Section IV, which follows next, 

discusses current leak measurement methods and work done by EPA. Following this is a presentation on 

the basics of the recommended test procedure, (section V), a validation of the recommended test 

procedure by testing on some more unusual fuel/evaporative system configurations (section VI), and 

finally an assessment of the leak test procedure results to several key pre-conditioning variables (section 

VII).
5

IV. Measurement Methods

At present, at least two different methods exist for determining evaporative system leaks. The 

first and more commonly used method is via positive pressure and flow measurement of the system. In 

this instance, the evaporative system is pressurized with a gas (normally inert nitrogen) to a set and 

measured pressure. In-line with the test apparatus is a flow meter designed to measure the flow of the test 

gas being introduced to the evaporative system. Once the system is pressurized to a certain level, the

resulting gas flow is measured and compared to that at known conditions and leak sizes. In this manner, 

any resultant leaks on the vehicle’s evaporative system are determined.

The second manner in which leaks are measured and quantified is through a process of measured 

vacuum decay. In this method, a certain amount of pressure or vacuum is placed on the evaporative

system and then monitored as to how long the evaporative system takes to release any such pressure or 

vacuum. By comparing this rate to that of known decay rates for an identical system, any such leak 

present in the test system can be quantified.

a. Pressure and Flow Measurement Systems

The most common devices for finding evaporative leaks are based on the pressure and flow 

measurement basis. There are many versions on the market today with some being used in individual 

states’ I/M programs. Most of these devices will use an external source of inert test gas so as to mitigate 

the combustion hazard of mixing oxygen with flammable hydrocarbon vapors.

i. Current Production Versions

Two examples of current production leak testers are shown in Figures 6 and 7. They are the 

EELD (Evaporative Emissions Leak Detector) 500 tester produced by Snap On and the Delphi 2010 

produced by Delphi. Both devices Operate on the same principle of flow and pressure measurement into 

the test vehicle.

Figure 1 – Snap On EELD 500 Tester Figure 2 – Delphi 2010 Evaporative Tester

The Snap On unit has the capability to also introduce smoke into the test vehicle’s evaporative

system in order to determine not only the resultant leak size but also its location. The Delphi unit also has 

an optional smoke generation feature. Both machines are similar in that they also provide for individual 

calibration of the units. The EELD performs a calibration check each time the unit is switched on, while 

the Delphi unit comes with a test tank and calibrated orifices to perform a field calibration of the unit. 
6

Both devices are portable with onboard rechargeable batteries or 110V power and both devices pressurize 

the evaporative system with up to 18” of water pressure.

The EELD unit was extensively tested by NVFEL staff over the course of several months as well 

as compared to the EPA Test Console created using laboratory grade equipment also designed to measure 

leaks. While we used this tool in our evaluation program and in developing the test procedure, 

manufacturers can use any tool or other method which meets the requirements of the regulations. 

Several tests were conducted so as to ascertain the EELD’s performance. These test units were 

purchased by NVFEL for testing through normal distribution channels. All measurements were 

obtained using a series of stainless or brass orifices obtained from O’Keefe Controls. The orifices tested 

ranged in sizes under 0.010 to over 0.050. Figure 8 shows the relative performance between two different 

EELD units, serial #’s SA 3890 and SA 3888, respectively. In addition # SA 3890 was also tested in the 

same manner on a different day to determine any day to day variability with the units. Upon analysis of 

the results, it was noticed that both SA 3890 and SA 3888 units underestimated the size of the resultant 

evaporative leak on the order of 0.003-0.004” as compared to the orifices obtained from O’Keefe

Controls. Discussion with the parent company Star Envirotech, which produces the unit for Snap On, 

resulted in the procurement on a new prototype test device which did not include the smoke feature. The 

performance of this new version is indicated by the “New Board” data on the graph in Figure 3. Its 

performance was greatly improved versus the production versions. Upon further testing it was realized 

that the flowing of smoke through the test orifice displaced a certain volume of measured test gas which 

caused the units to indicate a leak size less than actual. 

Figure 3 – Production EELD Samples with Smoke vs. Non Smoke Version

As seen in Figure 4, the EELD without the smoke feature was also compared directly to the 

results obtained via the NVFEL Test Console. 
7

Figure 4 – Comparison of EELD Non Smoke Board vs. Test Console

In all instances, the EELD version without the smoke compared favorably to the Test Console. 

Some variation was seen at the extreme ends of the orifice sizes, primarily under 0.010” and over 0.045”. 

Since leaks at these ranges were not of concern for the ongoing test program, the EELD was used for 

validation of the test procedure due to its ease of use and fast reporting of test results. The raw data from 

the testing is presented below in Figure 5. It is important to note that in the range of interest 0.010 -

0.030, that both the Test Console and the EELD displayed similar errors in the calculation of the test 

orifice size. This could possibly be due to slightly inconsistent sizing in the test orifices themselves 

leading to even better unit performance once these sizing errors are taken into account. 

Figure 5 – Data Obtained from Comparison of Test Console and EELD
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ii. NVFEL Constructed Device

The EPA constructed test device is also based on the principle of flow and pressure measurement. 

The test device (Test Console) was built using a Honeywell FP200 pressure transducer calibrated in the 

range of 0-2.5 psi as well as Teledyne Hastings HFM-300 flow meter s calibrated in ranges of 0-2 slpm 

and 0-10 slpm. Figure 6 depicts the flow layout and construction of the test console.

Figure 6 – NVFEL Test Console Flow Diagram

The equation presented in the test procedure (see below) was developed through NVFEL testing. 

It allows the calculation of an effective orifice leak diameter in inches based on the type of test gas being 

used, the temperature of the test gas, as well as the measured pressure and flow of the test gas through the 

Test Console. Figure 5 shows the correlation between the test console equation constants and empirical 

data obtained from a wide range of O’Keefe orifices. In all measurements, error was less than 3 percent

from actual to measured values.

The overall equation as presented in the test procedure was then implemented in the control 

software for the Test Console. Flow and pressure values were recorded by flowing N2 gas through the 

test console and test orifice. A variety of orifice sizes were tested ranging from 0.008” to 0.031”. The 

pressure was varied from 0.25 to 1 psi and the corresponding flow recorded at each pressure point. The 

orifice diameter was calculated via software using the supplied equation and plotted in Figure 7. 
9

Figure 7 – Validation of Test Console Equation Constants
10

The actual orifice size is modeled as a straight line and is indicated as the orifice size - TGT on 

the plot legend from Figure 8. For all orifice sizes tested, the equation deviated from the actual value by 

less than 0.001” in actual reading. Good correlation was seen throughout the pressure ranges tested.

 

Figure 8 – Validation of Supplied Test Procedure Equation

b. Vacuum or Pressure Decay Measurement Systems

Most commonly available evaporative test devices operate on the principle of pressure and flow 

measurement to find evaporative system leaks. At the time of the report, initial conversations were 

underway with Mahle Test Systems regarding their new tester for evaporative systems that operated on 

the principle of drawing a fixed vacuum on the evaporative system and measuring the decay over a short 

period of time. Currently such a system is being used in several OEM assembly plants to find leaks prior 

to the vehicles being fueled. According to Mahle, proprietary algorithms allow leak detection down to 

0.010” and smaller can be found on less than 0.5 psig of vacuum. Typical test times are on the order of 

10-30 seconds. No vacuum or pressure decay systems were available for evaluation. 

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0 0.5 1 1.5

Orfice Diameter (in)

Test Pressure (psi)

Evaporative Test Equation Results

0.008

.008_TGT

0.012

.012 TGT

.014 TGT

0.02

.020 TGT

0.025

.025 TGT

0.031

.031 TGT

.008_2
11

V. Recommended Test Procedure

Based on our developmental work with the EPA NVFEL Console and the Snap-On EELD 500 

(no smoke) meter, EPA developed a draft recommended test procedure. The proposed test procedure for 

fuel/evaporative system leak testing provided in Code of Federal Regulation format is as follows. It does 

not require the use of any specific instrument.

§86.167-18 Leak test procedure.

(a) Scope. Verify that there are no significant leaks in your fuel storage system using the leak test 

described in this section. Perform this check as required in the standard-setting part.

(b) Measurement principles. A leak may be detected by measuring pressure, temperature, and flow to 

calculate an equivalent orifice diameter for the system. Use good engineering judgment to develop and 

implement leak test equipment. Your leak test equipment must meet the following requirements:

(1) Pressure, temperature, and flow sensors must be calibrated with NIST-traceable standards. 

(2) Correct flow measurements to standard temperature and pressure of 20 °C and 101.3 kPa.

(3) Leak test equipment must have the ability to pressurize fuel storage systems to at least 4.1 kPa and 

have an internal leak rate of less than 0.20 slpm.

(4) You must be able to attach the test equipment to the vehicle without permanent alteration of the fuel 

storage or evaporative emission control systems.

(5) The point of attachment to the fuel storage system must allow pressurization to test system integrity of 

the fuel tank and fuel and vapor lines reaching up to and including the gas cap and the evaporative

canister. An example of an effective attachment point is the evaporative emission system test port 

available on some vehicles.

(c) Leak test procedure. Test a vehicle’s fuel storage system for leaks as follows:

(1) Fill the vehicle’s fuel tank to 40% capacity.

(2) Soak the vehicle for 6 to 24 hours at a temperature of 20 to 30 °C and maintain this temperature 

throughout the leak test.

(3) Before performing the test, purge the fuel storage system of any residual pressure, bringing the system 

into equilibration with the ambient.

(4) Seal the evaporative canister’s vent to atmosphere and ensure that the system purge valve is closed.

(5) Attach the leak test equipment to the vehicle.

(6) Pressurize the fuel storage system with nitrogen or another inert gas to at least 2.4 kPa. Use good 

engineering judgment to avoid over pressurizing the system.

(7) Maintain gas flow through the system for at least three minutes, ensuring that the flow reading is 

stable for an effective leak diameter of ± 0.002 inches.
12

(8) Use the following equation, or a different equation you develop based on good engineering judgment, 

to calculate the effective leak diameter, Deff.

( ) ( )

( )

0.5057

gas

eff

12 12

0.2153

960

459.67

V

D

PP PP

G T

   

= ⋅ −⋅+ ⋅ ⋅ +  

Where:

Deff = Effective leak diameter, rounded to the nearest 0.01 inch. 

Vgas = Volumetric flow of gas (scfh).

P1 = Inlet pressure to orifice (psia).

P2 = Atmospheric pressure (psia).

G = Specific gravity of gas at 14.7 psia and 60°F.

T = Temperature of flowing medium (°F).

(9) You may perform any number of replicate tests; however, you must perform the same number of tests 

at the same attachment points for every vehicle from a given model year. The average value of replicate 

tests is the official result for a given vehicle. 

(10) You may use special or alternative test procedures as described in 40 CFR 1065.10(c). For example, 

a manufacturer may use a vacuum-based instrument or approach if it can demonstrate correlation and 

meet the requirements of the applicable regulations.

(d) Equipment calibration. Use good engineering judgment to calibrate the leak check device.

For example, you may compare measured and calculated values to a calibration orifice such as that 

defined as an O’Keefe Controls Co, Type B precision-machined brass or stainless steel orifice having a 

gas flow path depicted in the following figure:
13

Figure 1 of §86.167

Validation of Test Procedure

There are many minor design and architecture variations, but essentially all vehicle evaporative 

control systems involve the use of a carbon canister to capture vapors from the gasoline tank and a 

vent and purge solenoid system for refreshing the storage capacity. Leak detection approaches as part 

of this system are based on either natural vacuum or an integrated pump and orifice approach. The 

leak detection instruments described above are commercially available and in use in the auto industry 

today; there is a high degree of confidence in their capability to detect leaks when applied properly 

for the intended purpose. This was confirmed during the testing we conducted on a number of 

different production vehicles in developing this recommended practice. For further validation 

purposes, we looked at several unique design and test conditions to confirm the utility of the test 

equipment and test procedure in these applications. These included testing on a Ford F150 with the 

“No Cap” style fuel fill, a Chrysler 300 equipped with both an ESIM valve and a “No Cap” style fuel 

fill, a Ford E350 cargo van with a fuel tank larger than 20 gallons and a Honda Accord. For all the 

vehicles tested, the following EELD tester procedure was used. 

Evaporative Emissions EELD Tester Attachment Procedure

1. Connect EELD Tester to Test Vehicle

a. Locate purge solenoid (typically located under hood nearby intake manifold or throttle 

body)

b. Remove vapor line on fuel tank side of purge solenoid (various clips can be used)

c. Insert hose adapter and modify as necessary to ensure a proper seal to the vapor line

2. Attach Scan Tool to OBD port

a. Verify engine size and details from under hood emissions label

b. Follow options and screens necessary to allow tool to control evaporative vent solenoid

c. Arrive at vent solenoid command screen (typically under special tests or emissions test 

sub-menus)

3. Power up EELD Tester

a. Attach N2 gas to tester (set to 85-100 psi inlet)

b. Select menu for proper gas while tester is booting (must do this at the right time or tester 

will default to AIR for test medium) Menu selection is done by pressing display select on 

the side of the tester until N2 is displayed. Tester can accommodate N2, CO2 and air for 

test gas.

4. Conduct Test

a. Command tester to flow nitrogen to test vehicle.

b. Close vent solenoid on test vehicle using the scan tool
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c. Monitor flow and pressure in tank and read resultant orifice leak size on tester screen. 

(Test value will start off high and stabilize to a final reading as fuel tank is pressurized. 

Test runs for 5 minutes and then tester will turn off. To continue flowing nitrogen simply 

command the EELD to test again)

a. Ford “No Cap” System

The Ford vehicle tested was a 2011 Ford F150 pickup VIN# 1FTFX1CT5BFA93342. The 

vehicle had 252 miles on it at the time of testing. The fuel tank was drained and filled to 40 percent with 

certification fuel. The vent solenoid was commanded by a Genisys OTC scan tool. The system was 

pressurized by disconnecting the evaporative line from the purge solenoid and pressurizing the system via 

this interface point. All testing was done with the updated version of the EELD500 which did not include 

the provision for smoke. The inlet pressure for nitrogen test gas for the EELD was set to 90 psi. 

Readings were taken approximately four minutes after the start of each test. Seven test repeats were run 

with the tester disconnected and the system allowed to vent for several minutes between tests.

This vehicle was chosen in order to asses any differences in testing necessary to accommodate

Ford Motor Company’s “No Cap” style of fuel tank system. In all cases, a well sealed system was 

indicated. The indicated leak value on the EELD was at .000 at four minutes duration for each of the 

seven tests. It took approximately 3.5 minutes for the tester to pressurize the tank and indicate a .000 

reading. The final pressure indicated by the EELD was relatively consistent as well, with readings 

ranging from 17.3 – 17.6 inches water. No changes to the test procedure were necessary for this 

application. 

b. Chrysler “ No Cap” ESIM System

The next configuration tested was a 2012 Chrysler 300 VIN# 2C3CCACG2CH266160 equipped 

with Chrysler’s version of the “No Cap” fuel filler system as well as the ESIM style of vent valve. The 

vehicle had 1942 miles on it at time of testing. The updated EELD unit (no smoke) was used to test this 

vehicle. The fuel tank was drained and filled identically as the F150 previously tested. Because of the 

year of the vehicle, available scan tool equipment was unable to communicate with the vehicle’s ECM. 

In all testing, the vent line was disconnected from the ESIM valve. The evaporative system was 

pressurized via the line going to the under hood purge solenoid. The ESIM valve and charcoal canister 

were located behind the right hand rear wheel well liner.

This vehicle was chosen in order to asses any differences in testing necessary to accommodate 

Chrysler’s “No Cap” style of fuel tank system as well as any special procedures needed in testing a 

system which did not have a traditional solenoid controlled vent valve. In all cases, a well sealed system 

was indicated. The indicated leak value on the EELD was at .000 at four minutes duration for each of the 

seven tests. It took approximately 2.0 minutes for the tester to pressurize the tank and indicate a .000 

reading. The final pressure indicated by the EELD was relatively consistent as well with readings ranging 

from 17.4 to 17.5 inches water. No changes to the test procedure were necessary for the application with 

the exception of the understanding that sealing the vent line from the ESIM valve acted in a similar 

fashion as commanding the vent valve closed on a traditional system. Figure 9 below shows the “No 

Cap” style of filler system. The Ford system is similar with the exception that it does not have the sealing 

cover for the filler inlet pipe. 
15

Figure 9 – Chrysler 300 “No Cap” Fuel Filler Inlet

d. Fuel Tank Systems Greater Than 20 Gallons

The vehicle tested was a 2012 Ford E350 Passenger Van VIN# 1FBSS3BL3CDA75451. The 

vehicle had 3452 miles on it at the time of testing. The fuel tank was drained and filled to 40 percent 

certification test fuel. The capacity of the fuel tank was 40 gallons as indicated in the owner’s manual and 

via measurement of the external tank dimensions. The vent solenoid was commanded by a Genisys OTC 

scan tool. The system was pressurized by disconnecting the evaporative line from the purge solenoid and 

pressurizing the system via this interface point. Figure 10 shows the EELD attachment point. All testing 

was done with the updated version of the EELD500 which did not include the provision for smoke. The 

inlet pressure for nitrogen test gas for the EELD was set to 90 psi. Readings were taken approximately 

four and a half minutes after the start of each test. Seven test repeats were run with the tester 

disconnected and the system allowed to vent for several minutes between tests.

Figure 10 – Ford E350 EELD Attachment Point

This vehicle was chosen in order to asses any differences in testing necessary to accommodate 

tank sizes larger than 20 gallons. The indicated leak value on the EELD ranged from 0.001 to 0.005 for 

each of the seven test repeats for this vehicle. There was indication that the default five minute test time 

on the EELD was not sufficient for this vehicle to fully pressurize such a large tank volume leading to the 

variation in “found” leak values. In addition, it was seen that the variation in indicated leak values was 
16

affected by the depressurize time between tests. In prior testing, two minutes was allocated between tests 

to allow the evaporative system and fuel tank to equalize to atmospheric pressure with an open vent valve 

and fuel cap. With the larger tank system of 40 gallons two minutes was seen as not enough 

depressurization time. If the subsequent test was started within two minutes, the ramp time down to the 

indicated leak value was faster than that measured between tests with more than a two minute wait time. 

Figure 11 shows this effect. Based on this testing , it is recommended, when testing large tank sizes, to 

wait at least 5 minutes between test intervals if repeated testing is necessary as well as to test longer than 

5 minutes (in the case of the EELD) in order to give larger systems the appropriate pressurization time 

needed to achieve representative results. It should be noted that even though the larger system took 

longer to fill and achieve a final reading, indicated leak values were within .004” of each other after three 

minutes of testing. 

Indicated Leak Value Indicated Leak Value

Test Time (min) w/ 2 Min Wait w/ 5 Min Wait

1 0.014 0.021

2 0.006 0.01

3 0.002 0.006

4 0.001 0.004

5 0 0.002

Figure 11 – EELD Indicated Values on 40 Gallon Test Tank

e. Honda Produced Fuel Systems

The Honda vehicle tested was a 2007 Accord sedan VIN# 1HGCM56727A141399. The vehicle 

had 123821 miles on it at the time of testing. The fuel tank was drained and filled to 40 percent with 

certification test fuel. The vent solenoid was commanded by a Vectronix Mastertech scan tool. The 

system was pressurized by disconnecting the evaporative line from the purge solenoid and pressurizing 

the system via this interface point. All testing was done with the updated version of the EELD500 which 

did not include the provision for smoke. The inlet pressure for nitrogen test gas for the EELD was set to 

95 psi. Readings were taken approximately four minutes after the start of each test. Seven test repeats 

were run with the tester disconnected and the system allowed to vent for several minutes between tests.

This vehicle was chosen based on concerns initially expressed by Honda regarding the interface 

of the leak detection test methodology with their OBD leak detection scheme. We assessed a Honda 
17

vehicle equipped with a Honda evaporative control system using a solenoid controlled vent and purge 

valve. In all cases, a well sealed system was indicated. The indicated leak value on the EELD was at 

.000 at four minutes duration for each of the seven tests. It took approximately 3 minutes for the tester to 

pressurize the tank and indicate a .000 reading. The final pressure indicated by the EELD was relatively 

consistent as well with readings ranging from 17.5 – 17.7 inches water. No changes to the test procedure 

were necessary for this application. 

VI. Tested Vehicle Variables for Preconditioning

Current preconditioning required prior to conducting the evaporative test is as follows:

1. 6-24 our soak at 20-30 °C prior and during testing

2. 40 percent fuel fill capacity using Tier III certification fuel (9 RVP E15)

3. Purge of any residual fuel tank pressure prior to testing

The cold soak and fuel tank fill level is consistent with the preconditioning needed for the FTP test so as 

to minimize any additional testing burden associated with running the leak test. Prior to setting these 

preconditioning requirements, several factors that were thought to possibly influence the leak test results 

were investigated. These factors were the fuel fill level, the fuel tank temperature, test vehicle inclination 

and the leak location relative to the insertion point of the leak tester. These factors were investigated by 

using a first generation Snap On EELD500 tester. The EELD had the provision to introduce smoke into 

the evaporative system but was not filled with the smoke solution for this testing. The vehicle used for all 

of the preconditioning investigation was a 2006 Chevrolet Silverado, VIN# 1GCEK19B6GZ154114. 

This vehicle had approximately 110,056 miles on it and the vent valve was controlled via a GM Tech 2 

service tool. An evaporative test port was located under the hood and was used as an attachment point for 

the EELD tester.

a. Fuel Fill Level

To investigate the influence of fuel fill level on the leak test, the test vehicle was drained and 

filled to various levels of certification test fuel. The levels investigated were 10, 40, 80, and 100 percent 

tank capacity. Each test was performed at a temperature of 25°C. At each fuel level, seven repeat tests 

were performed with the EELD tester. After each reading the tester was removed and the system was

allowed to depressurize for several minutes. A simulated leak was created by tying in a 0.020 stainless 

O’Keefe orifice at the purge valve. The results are presented below in Figure 12. The error bars 

represent the inherent repeatability of the unit. It was felt that the EELD was accurate to a +/- .001” 

reading while operating under the testing conditions. While the 10 percent fill levels had the highest 

indicated leak reading, on average these were .001” or less than what was indicated at the 40 percent fill 

levels. This difference was also within the accuracy of the EELD unit. So based on the collected data, it 

was determined that the fuel fill level had a minimal, if any, effect on the test reading.
18

Figure 12 – EELD Readings for Several Fuel Fill Levels

b. Fuel Temperature

To investigate any fuel temperature effects on the leak test, the same test vehicle was used and 

filled to a 40 percent fill level with certification test fuel. The temperature of the vehicle was varied by 

subjecting it and the fuel to an overnight soak at the prescribed temperature in a VT SHED. The three 

temperatures tested were 25, 30, and 35 °C. Data obtained from the testing is presented in Figure 13. As 

can be seen, most values are within the accuracy of the EELD, however those obtained at 35 °C show a 

slight trend for higher readings. Since the existing FTP preconditioning was from 20-30 °C, it was 

determined to stay within that range. In this range, fuel tank temperature did not affect the EELD 

readings.

0.012

0.013

0.014

0.015

0.016

0.017

0.018

0.019

0.02

0 1 2 3 4 5 6 7 8

Indicated Orifice Size

Test Point

Fuel Tank Fill Effects (25 C, 0.020")

0.020" Implanted Leak

40% Fill

10% Fill

80% FIll

100% Fill
19

Figure 13 – EELD readings for Various Fuel Temperatures

c. Vehicle and Tank Inclination

Another factor investigated was the inclination of the test vehicle. Again, the same vehicle was 

used and filled to a 40 percent level with certification test fuel. The test vehicle was then placed on a two 

post hoist and the appropriate lift arms positioned to cant the vehicle in various directions. The 

inclinations tested were 5° left and right (roll), as well as 5° front and back (pitch). All readings for the 

EELD were within the accuracy of the unit for the various vehicle inclinations tested. These results can 

be seen in Figure 14.

0.012

0.013

0.014

0.015

0.016

0.017

0.018

0.019

0.02

0 1 2 3 4 5 6 7 8

Indicated Orifice Size

Test Point

Fuel Temperature Effects (25-35°C)

0.020" Implanted Leak

25C

30C

35C

Most measurements within accuracy of unit
20

Figure 14 – EELD Readings for Various Vehicle Inclinations

d. Leak Location

The last possible influencing factor tested was the location of the leak relative to the insertion or 

test point of the EELD. In these tests, the identical test vehicle was used and filled to a 40 percent fuel 

level with certification test fuel. In all cases, the EELD attachment point remained consistent at the under 

hood evaporative test port. The location of the leak was varied between the purge valve (near to the test 

attachment point) and the top of the fuel cap (far from the attachment point). The results are presented in 

Figure 15. Within these results a definitive trend could be observed. The EELD indicated higher leak 

values when the orifice was placed near the test attachment point versus those where the leak was placed 

far away from the attachment point. On average the near leak values were higher than the far leak values 

by 0.002-0.003”. This was outside of the margin of error of the EELD was considered a definitive test 

influence. 

A plausible explanation for this difference was due to the way the EELD and similar devices 

compute the leak values. For the EELD and similar test instruments, the effective leak values are 

calculated via onboard pressure and flow sensors. Normally they are calibrated to provide an accurate 

reading at the instrument or attachment hose. When the instrument is placed on a test vehicle some 

pressure drop is always present as long as there is flow through the evaporative system and attaching 

lines. It is conceivable that the pressure drop present in the evaporative system is greater when the leak 

location is farther away from the test insertion point. In the data obtained in NVFEL testing, leak 

locations farther away from the test point were reported as 0.002-0.003” smaller than those that were 

implanted closer to the test point. Based on this testing it may be advisable to consider multiple test 

points as part of the requirement to show compliance with the requirements 

0.012

0.013

0.014

0.015

0.016

0.017

0.018

0.019

0.02

0 1 2 3 4 5 6 7 8

Indicated Orifice Size

Test Point

Vehicle Inclination Effects (5°cant)

0.020" Implanted Leak

5 deg Front

5 deg Left

5 deg Rear

5 deg Right
21

Figure 15 – EELD readings for Various Leak Locations

VII. Conclusions

This report is the summary of several months of work of NVFEL testing and test procedure 

development. Pressure leak test equipment was both constructed in-house as well as purchased from 

outside vendors for testing. Both types of equipment produced good results and correlation when tested 

against known orifice sizes. In addition the in-house construction of evaporative test equipment gave 

particularly well placed insight on the governing physical properties and equations necessary to 

accurately predict leak sizes from flow and pressure measurements of an evaporative emissions system.

Several influencing factors affecting the outcome of the leak test were investigated. Within tested 

limits, the test temperature, vehicle inclination, and fill level all displayed minor influences on the overall 

test readings obtained. The only influence that was seen among the factors investigated was the leak 

location, which cannot be controlled in a typical testing fashion. In this case, existing instruments can 

under predict the actual leak by a few thousandths of an inch.

The test procedure was validated against known vehicle types which represented a difference 

from the “norm” in evaporative emission system control or construction. In all instances, the test 

procedure was effective either as is or with minor well understood modifications.

Based on the work so far, the test procedure is seen as robust and applicable to many different 

types of vehicles and evaporative emission systems. However, alternative test procedures are allowed as 

per 40 CFR 1065.10(c) for those systems which cannot be tested under the given procedure or if new fuel 

evaporative control system or OBD leak detection methods are developed which are not compatible with 

this methodology.

0.012

0.013

0.014

0.015

0.016

0.017

0.018

0.019

0.02

0 1 2 3 4 5 6 7 8

Indicated Orifice Size

Test Point

Leak Location Effects

0.020" Implanted Leak

.020 Purge

.020 Cap
22

VIII. References

1. “SAE Paper 860086, Composition of Vapor Emitted from a Vehicle Gasoline Tank During 

Refueling, Robert L. Furey and Bernard F. Nagel, 1986.

2. VOC composition of current motor vehicle fuels and vapors, and collinearity analyses for 

receptor modeling”, J. Chin, Chemosphere (Oxford). 2012;86:951-958.

3. “Automotive Evaporative Emissions Systems”, M. Schager, University of Southern Colorado. 

2011, pp.1-5.

4. “Chrysler Evaporative Leak Detection Systems”, Dixon Matthew, 2008. Presentations. Paper 7. 

http://opensiuc.lib.siu.edu/auto_pres/7.