Anyone familiar with vehicle fuel gauges?  - Page 1
Forum section: electronics / general

author: MrOmnos
author_rank: Frequent Contributor
timestamp: March 24, 2020, 12:47:54 pm
content: Hi, I am trying to make something that can connect to existing fuel gauges in vehicles and display the amount of fuel in percentage. I am guessing all types of fuel gauges used today probably have analogue voltage on the wires coming out of the tank. Is this correct assumption? Anyone here have any knowledge on fuel gauges that would like to share? It would be really help if you could share anything you know about fuel gauges. Meanwhile I am also google.Thank you!

author: vk6zgo
author_rank: Super Contributor
timestamp: March 24, 2020, 01:27:00 pm
content: Quote from: MrOmnos on March 24, 2020, 12:47:54 pmI haven't had anything to do with fuel gauges for a long time, but in the time I did play with them, there were two types:-The really old ones used a resistive sensor in the tank & (I think--it's ages ago) a twin coil meter movement in the dash---It certainly wasn't a permanent magnet, moving coil!These would come up almost instantly to the correct reading when the ignition was turned on.Old tanks had baffles in them so the fuel wouldn't slosh round when driving,(cornering, etc), allowing the reading to remain pretty steady.The "bean counters" saw these baffles as a waste of money, & decreed that they be no more.All good, but now the reading jumped all over the place, which is why the baffles were there in the first place.The answer to this was to make the meter slow to respond.To this end, they used thermal meters-- they apparently used some sort of bi-metal spring.This worked well, except that it was a bit unnerving to fill your near empty tank up, & wait about a km for the reading to go to "full".My car didn't have a low fuel light, so I played around, trying to design one.I ended up with a rough "first draft" which worked, but real life intervened, & it got shelved, never to be seen again.pI would expect modern temperature gauges to do this "damping" function electronically, either analog or digitally.Many fuel gauges rhese days are "rendered" on the dash display, not real electromechanical ones.

author: schmitt trigger
author_rank: Super Contributor
timestamp: March 24, 2020, 01:57:01 pm
content: I remember the thermal meters. They required 10s of milliamps at full scale.As you mention, nowadays everything in vehicles has become electronic and most recently bussed.I haven't poked around in a modern auto, but I suspect that nowadays fuel level data may be transmitted via LIN or CANBUS.

author: PKTKS
author_rank: Super Contributor
timestamp: March 24, 2020, 02:07:14 pm
content: Floating resistor gaugewired to OBDIIlikely may be encapsulated onCAN or other proprietary protocol as wellPaul

author: unknownparticle
author_rank: Frequent Contributor
timestamp: March 24, 2020, 04:13:33 pm
content: Dunno about your issue but I have to fix a problem with reserve fuel indication on my 15 year old MV Agusta motorcycle. Bikes used to have, many years ago, a reserve fuel tap. So, you rode on main tap until the engine started to miss or even stopped, then turned on the reserve tap, whilst still moving, by hand after groping around under the fuel thank! All very ancient tech and clumsy, but you knew where you were!Now, with my MV, there SHOULD be a reserve level indicator light on the dash so you know you have about 20 miles to find fuel. Except, mine stopped working, with obvious consequences. So, I browsed the manual to find out how it worked and it's basically a thermistor capsule on a stick that becomes exposed when the fuel level drops, thus an increase in temp, thus a signal to the dash module, light comes on. So the thermistor is dead, MV can no longer supply the part, so I have to find an alternative. Great! Although, if that part had been available, it would have cost about £150.00!!!

author: MrOmnos
author_rank: Frequent Contributor
timestamp: March 24, 2020, 05:17:04 pm
content: Will I be able to jus bypass all digital stuff and just tap the cables coming out of the tank in modern vehicles??

author: MrOmnos
author_rank: Frequent Contributor
timestamp: March 24, 2020, 05:21:44 pm
content: Quote from: unknownparticle on March 24, 2020, 04:13:33 pmIt's not that ancient. Atleast hereI have this bajaj pulsar NS200 which I bought last year and It still has carburetor no FI and has reserve knob which you turn when your bike starts to miss and stores 2.5 liter haha

author: vk6zgo
author_rank: Super Contributor
timestamp: March 25, 2020, 01:50:52 am
content: Quote from: unknownparticle on March 24, 2020, 04:13:33 pmInterestingly, most of the people I know with vehicles having reserve tanks run on the reserve first, then when that runs out, switch yo the main-------strange!

author: Fred27
author_rank: Unknown
timestamp: March 25, 2020, 09:18:02 am
content: Every biker (over a certain age at least) will have done that once!Thankfully, I haven't ridden a bike with a reserve tap for quite a while. In my experience a warning light with a view of how many miles since it came on seems the most common these days.

author: schmitt trigger
author_rank: Super Contributor
timestamp: March 25, 2020, 01:28:02 pm
content: Quote from: MrOmnos on March 24, 2020, 05:17:04 pmWe can't tell you with certainty. You would have to open up the gas tank and find out the sender to determine that.But most likely everything is encapsulated in hard epoxy, and only the digital bus signals are available.

author: Brumby
author_rank: Unknown
timestamp: March 25, 2020, 01:56:42 pm
content: From my experience, there's no consistent answer across vehicles. You will need to research how the target vehicle is set up.Here is a link to LPG senders used for vehicles which have been converted to LPG:https://bluelpg.com.au/shop/sender-units-lpg-tankNotice the difference of resistance in the empty to full range.These units are supplied to emulate the petrol tank level mechanism, with the vehicle's fuel gauge switched between the LPG tank and the petrol tank. (For some installations, there is a separate LPG gauge, which typically use the 0-90 sender.)

author: unknownparticle
author_rank: Frequent Contributor
timestamp: March 25, 2020, 02:14:55 pm
content: Quote from: Fred27 on March 25, 2020, 09:18:02 amYeah, bikes have adopted automotive practice now and it's all well and good, until, it develops a fault! Bikes are an order of magnitude worse for environmental stress to electronics, wiring etc, compared to cars, so are more likely to develop electrical faults.Unfortunately, with fuel injection systems, a reserve tap is no longer possible. Ah well

author: unknownparticle
author_rank: Frequent Contributor
timestamp: March 25, 2020, 02:17:49 pm
content: Quote from: MrOmnos on March 24, 2020, 05:17:04 pmWell, all the connections are usually on top of the tank sender unit which is typically located inside the car, somewhere under the rear seat, this is on a normal saloon or hatchback. These connections go to a fuel pump and the fuel level sender unit, or sensor.