Code of Maryland Regulations › Title 11 - DEPARTMENT OF TRANSPORTATION › Subtitle 14 - MOTOR VEHICLE ADMINISTRATION-VEHICLE INSPECTIONS › Chapter 11.14.04 - Safety Standards for Trucks, Truck Tractors, Commercial Buses, and Type I School Vehicles › Section 11.14.04.07 - Emission Control System on School Vehicles

Current through Register Vol. 51, No. 14, July 12, 2024
A. This regulation represents the current
				recommendations of the Vehicle Emissions Inspection Panel of the Motor Vehicle
				Manufacturers Association, Inc., regarding engine maintenance inspection
				required to minimize vehicle emissions. This section is advisory and is
				primarily related to 1968 and later models.
B. The inspection of emission control systems
				applies only to spark ignition engines, not to diesels.
C. This regulation is applicable to school
				vehicles only.
D. Crankcase
				Ventilation. The ventilation system of the crankcase is common to engines using
				either an "air injection" system of control or an "engine modification" system.
				The engine should be warm and running at idle before inspection of vent system.
Procedures
Reject Vehicle If:
(1) Crankcase Ventilation Valve: Inspect valve to make
						  sure it is an approved device.
(1) Valve is not designed for the vehicle if originally
						  equipped.
(2) Plumbing Connections: Inspect plumbing connections
						  for tightness and proper routing of blow-by fumes and fresh air.
(2) Plumbing is loose, restricted, broken, leaking, or
						  improperly routed.
(3) Operation: Disconnect crankcase ventilation valve
						  from engine. A definite "hissing" noise is heard if valve is OK, caused by air
						  being "sucked" into the valve and hose. Place finger or thumb over end of valve
						  and feel for suction.
(3) There is no hissing sound or suction.
E.
				Air Injection Type-Idle Speed and Timing. An air injection-type exhaust
				emission control system can be identified by an air pump and a distribution
				system to the exhaust ports. The air pump is normally driven by a belt off the
				crankshaft or water pump pulleys. Only the plumbing, idle speed and ignition
				timing need be inspected. Reference is made to the Idle Setting Limits Table I.
Procedures
Reject Vehicle If:
(1) Installation: With engine stopped, inspect hose
						  connections and belts for tightness and breakage. Inspect ignition wiring for
						  damage or deterioration. With engine running, inspect for air or vacuum
						  leaks.
(1) (a) Belt is loose. (b) Connections are loose, broken,
						  or leaking. (c) Ignition wires are damaged or deteriorated.
(2) Idle Speed: With engine at operating temperature and
						  at idle speed: (a) Automatic Transmission: Check idle speed as recommended by
						  vehicle manufacturer; (b) Manual Transmission: Place transmission in neutral
						  and check idle speed.
(2) Idle speed is beyond limits in Table I.
(3) Basic Ignition Timing: Disconnect vacuum spark
						  advance line(s) and insert plug(s). Connect timing light and check basic
						  ignition timing (when finished replace line(s)).
(3) Basic timing is beyond limits in Table I.
F.
				Engine Modification Type-Idle Speed and Timing. An "engine modification"
				control system may be most easily identified as one without an air pump. The
				emissions are primarily controlled by engine design. The items to be inspected
				are vacuum, idle speed, ignition timing, and idle air-fuel mixture by measuring
				the carbon monoxide (CO) content of the exhaust. Refer to Table II, Idle
				Setting Limits.
Procedures
Reject Vehicle If:
(1) Installation. With engine stopped, inspect vacuum
						  hose connections for tightness, or breakage. Inspect ignition wiring for damage
						  or deterioration. With engine running inspect for air or vacuum leaks.
(1) Connections are loose, broken, or leaking. (2)
						  Ignition wires are damaged or deteriorated. (3) Idle speed is beyond limits in
						  Table II. (4) Basic timing is beyond limits in Table II.
(2) Idle Speed: With engine at operating temperature and
						  at idle speed. (a) Automatic Transmission: Check idle speed as recommended by
						  vehicle manufacturer; (b) Manual Transmission: Place transmission in neutral
						  and check idle speed.
(3) Basic Ignition Timing: Disconnect vacuum spark
						  advance line(s) and insert plug(s). Connect timing light and check basic
						  ignition timing. (When finished remove plug(s) and replace line(s).)
G.
				Engine Modification-Type Fuel Mixture (Carbon Monoxide). The carbon monoxide
				(CO) concentration in the exhaust of most vehicles may not be more than 3
				percent. Be sure that the testing is done by an experienced operator and that
				the exhaust analyzer is properly calibrated.
Procedures
Reject Vehicle If:
(1) Idle Fuel Mixture: With engine at normal operating
						  temperature and idle speed, insert sampling probe into tail pipe and note
						  carbon monoxide (CO) concentrations. (Major leaks in the exhaust system could
						  cause erroneous readings.)
(1) Carbon monoxide concentrations are greater than
						  limits in Table II.
Table IIDLE SETTING LIMITS TABLE (Exhaust Air
				  Injection Systems)
Manufacturer
RPMManufacturer'sSpecifications
Basic Ignition Timing in Degrees
American Motors Corp.
+100
-25
±3
Ford Motor Co.
+100
-50
±3
General Motors Corp.
+100
-50
±3
International Harvester Co.
+100
-25
±3
Jeep Corp.
+100
-25
±3
Other
As specified by the particular
						  manufacturer
Table IIIDLE SETTING LIMITS TABLE (Engine
				  Modification Systems)
Manufacturer
RPMManufacturer'sSpecifications
Basic Ignition Timing in Degrees
Mixture
American Motors Corp.
+100
-25
±3
3% CO Maximum
Ford Motor Co.
+100
-50
±3
3% CO Maximum*
General Motors Corp.
+100
-50
±3
3% CO Maximum
International Harvester Co.
+100
-25
±3
Set with tachometer method
Jeep Corp.
+100
-25
±3
3% CO Maximum
Other
As specified by the particular
						  manufacturer
* or 13.3/1 Air-Fuel Ratio-Minimum.