CANBUS, LPG and fuel needles....

[eltax91]

Hi guys

I have a Gen7 accord 2.4 on a 08 plate. It's the facelift model

I picked it up today from having it lpg converted and everything is perfect, running smoothly as ever.

The only big bear I have is the way the fuel needle reads now. The way the fitter explained it is that the LPG ecu goes in line between the cars ecu and the cars fuel system, reporting back all being well to the ecu and then switching from petrol to lpg injectors once the car warms up.

Now, he also suggested the face lifted CANBUS car calculates it's remaining fuel, economy and range by measuring the air input into the engine and calculating the fuel usage based on this.

The problem I have is that the fuel needle continues to drop, even though the car is running on LPG. I left the car with him 7/8 full and the needle was showing half way when I picked it up. He'd done about 150-200 miles on the runs to/from work to tune the system and the needle was showing about half way.

I then took the car home and within the first 3 miles the fuel needle jumped up to about 6/8 - the fuel level expected.

So, does anyone have a clue how these fuel levels readings are taken? And if the car periodically checks the tank sensor and adjusts the needle accordingly?

Any other triggers I can use to manually force the car to check? Or could a remapper change the check frequency so I get a more accurate reading?

For reference it definitely does not check the tank on every start up. Car was started several times when showing half a tank and then randomly shot up again.

Any help from experts would be very valuable.

[eltax91]

Nobody?

[JordanTurbo]

Cars that do this normally check the fuel quantity in the tank during the self test each time you turn the ignition on.

Our Discovery does this and if you leave the ignition on while fueling it (e.g. radio for passengers) it won't register the extra fuel until you turn the ignition off and on again.

Edit:Your car may do a periodic check based on milage or may not do the startup check if it's been less than a certain amount of time since last switch off.

Edited by JordanTurbo on Sunday 8th December 08:04

[eltax91]

JordanTurbo said:

Cars that do this normally check the fuel quantity in the tank during the self test each time you turn the ignition on. The calculation part is only when underway to drop the needle at the correct rate.

Our Discovery is the same and if you leave the ignition on while fueling it (e.g. radio for passengers) it won't register the extra fuel until you turn the ignition off and on again.

Thanks. Very interesting as this is how I would assume it works. Previously whenever ive done a 'normal' fill up the car has recognised the new fuel level on the first turn of the key. The range is then immediately adjusted accordingly.

However, the car had been run for several journeys and stopped/ started. It was still showing half a tank. I even messed with the fuel filler and pushed the anti tamper in just in case some kind if trigger existed, it remained at half a tank

Then, 2 miles into my journey And approx 150-200 miles since it was run on LPG for the first time, the needle just shot up to 6/8 full.

So either my car is broke or it behaves in a different way

I do lots of long journeys for work so will be able to monitor things more closely and see how it behaves, but I'm baffled!

Edit: just read your edit. That could make sense, maybe it doesn't check the level if you start up soon after shutdown, but relies on the periodic check as a backup

Edited by eltax91 on Sunday 8th December 07:55

[r11co]

I would have thought that the fuel level check is a closed loop feedback that is constantly monitoring the level.

Sounds to me that there is something completely unrelated wrong with the fuel sender/wiring (dry joint that is making contact once things warm up) rather than the LPG installation is interfering with things.

I'm no expert, but when I investigated getting LPG fitted to a Jag X-Type I was told to make sure the fitter knew to incorporate either a fuel re-circulator or a return pipe to the tank for when the car was running on LPG because the fuel pump would continue to run and be pressurised to the point of failure otherwise. This though would have the effect of the car appearing to use petrol even though it wasn't which would confuse the fuel computer, but the gauge would be unaffected.

Also, from what I learned the LPG systems have their own separate gauge so there should be no effect on the system on how the petrol level is monitored.

I'd look for obvious things such as wiring being disturbed as a result of the installation or a poor earth connection on the sender. Even in this day-and-age the fuel sender is just a variable resistor, so a poor/intermittent connection would cause exactly the symptoms you are describing.

Edited by r11co on Sunday 8th December 10:21

[eltax91]

Interesting point r11co

To be honest I don't suspect a wiring fault at all, the issue is there whether the car is cold or hot, ambient temp on the face of it is irrelevant. Started the at today after it standing overnight and the fuel needle returned to the same place it was wen I suit down yesterday. Done 80+ miles on LPG today (less than 3 on petrol before the switchovers) and the fuel needle has dropped about what i normally expect for the journey. It simply cannot be calculating from a permanent feed from the tank

What I am confused about more than anything is how, before the conversion was done, the car would respond to a fill up, by immediately showing the new fuel level and editing the expected range from say 50 miles to 400 miles.

Could there be some sort if mechanism in the fuel filler neck that triggers the car to do a tank read?

[Sump]

eltax91 said:

car calculates it's remaining fuel, economy and range by measuring the air input into the engine and calculating the fuel usage based on this.

LS430s do this so he isn't bs-ing you.

[eltax91]

Sump said:

LS430s do this so he isn't bs-ing you.

I think a lot of cars do! What I need to figure out is how the hell I get the car to permanently read from the tank feed instead.

[Sump]

From what I remember you're fighting a losing battle.

[anonymous-user]

eltax91 said:

Interesting point r11co

To be honest I don't suspect a wiring fault at all, the issue is there whether the car is cold or hot, ambient temp on the face of it is irrelevant. Started the at today after it standing overnight and the fuel needle returned to the same place it was wen I suit down yesterday. Done 80+ miles on LPG today (less than 3 on petrol before the switchovers) and the fuel needle has dropped about what i normally expect for the journey. It simply cannot be calculating from a permanent feed from the tank

What I am confused about more than anything is how, before the conversion was done, the car would respond to a fill up, by immediately showing the new fuel level and editing the expected range from say 50 miles to 400 miles.

Could there be some sort if mechanism in the fuel filler neck that triggers the car to do a tank read?

The dash, which is probably where the gauge conversion is done, only assumes a fill up when the fuel reading "Increases" by a certain amount after a key cycle. It integrates the fuel cons reported by the ems to decrements the estimated fuel quantity during engine running. This avoids the gauge "wobbling around" due to fuel slosh etc. The system probably reads the actual float gauge after every "cold start" (ie engine temp must have fallen below a certain threshold) but only if the car is within certain lat and long g values when stationary (to avoid false readings from being on a slope etc)

[eltax91]

Max_Torque said:

The dash, which is probably where the gauge conversion is done, only assumes a fill up when the fuel reading "Increases" by a certain amount after a key cycle. It integrates the fuel cons reported by the ems to decrements the estimated fuel quantity during engine running. This avoids the gauge "wobbling around" due to fuel slosh etc. The system probably reads the actual float gauge after every "cold start" (ie engine temp must have fallen below a certain threshold) but only if the car is within certain lat and long g values when stationary (to avoid false readings from being on a slope etc)

All sounds very likely and perfectly feasible. Except mine did not give me a true reading after leaving it overnight. Now, my car does park on a slight slope at night on my driveway, bit it was parked for 5 hours on the flat yesterday daytime and still the needle has not increased.

Given the info you provided above, you sound like a bit if an expert. Any opinions in how I can fix it? Could a remapper adjust the interval in which it reads the tank level down to something like every 10 miles?

[AdeTuono]

It may not be relevant in your case, or you may well have taken it into account, but the conversion in my vehicle (Ford F150) always starts from cold in petrol mode, so the level will drop if you do several short journeys from cold.

[eltax91]

AdeTuono said:

It may not be relevant in your case, or you may well have taken it into account, but the conversion in my vehicle (Ford F150) always starts from cold in petrol mode, so the level will drop if you do several short journeys from cold.

Yeh - pretty much all LPG systems (i've driven/ owned a few) spend the first few miles on petrol before moving to LPG. The car has been run approx 160 miles this weekend, all on gas, with the exception of the start of 2 journeys. I'd say it's run under 5 miles on petrol, but the needle has gone from 1/2 - UP to 7/8 and now back to about 5/8 of a tank.

It's an odd sensation not knowing how much actual fuel I have in it. For the moment it's not a massive issue as the tank is full, but i don't want to be carrying aroud 50+ litres of fuel when I have LPG, so I'd want to run it in the region of 1/4 of a tank, I can see this being a problem though, as the moment I'm 30 miles from home and the LPG runs out, I'm not going to have a clue how much fuel is in the car!