Some CANBUS help (again)

[eltax91]

Hi folks

2nd CANBUS question in as many days! I have a Gen7 facelift MY08 Accord Tourer as a daily hack. It has the 2.4 VTEC engine.

Recently, I had an LPG kit fitted, which is working fine. The car warms up, switches over to gas and fails back to petrol as/ when expected. The main issue is the fuel needle for the petrol tank in the car, it appears to be working under CANBUS instruction from the main ECM and as I drive along happily on LPG, the car appears to be using fuel. The needle moves down as the miles tick away, the expected remaining range decreases etc. Then, at some kind of interval which I can't work out (might be aorund 200 miles or 3 hrs driving, not sure), the CANBUS module for the dash obviously does a check with the main ECU to see what the tank level sensor is reporting, and the needle shoots up by about half a tank!

The installer of the LPG kit says they don't know of a solution to stop this.

I throw it out to the masses. This is utterly infuriating as if/ when I switch back to petrol to find an LPG station I don't truly know how much fuel I have left! All I know is I have the current reading "or more". This will be fine if I lugged half a tank+ around with me all the time, but as I mainly run on LPG, I'd prefer to save the weight and run around with 1/4 tank or less.

I've tried opening/ closing the petrol flap and pushing a petrol nozzle in without filling up, to no avail. The car doesn't check the tank at any other time as far as I can tell, not even on startup!

So, is there a solution? Can I somehow have the settings altered to get it to read every few miles? Or something else.

Help please!

[McWigglebum4th]

Expensive solution

Spends lots and lots of time and money trying to reprogram the ECU

Cheap solution

Carry a 5ltr can of fuel in the boot

[Froomee]

All I know is I have the current reading "or more"
[/quote]

Unless I am reading this wrong then the reading is less than what you have in which case you will never run out of fuel... Not much of a problem.

How sure are you that it isn't correct and when it "resets" it isn't resetting to the correct level which again would be a non-issue.

I'd find a way of determining how accurate it is rather than worrying about it changing or carry some spare fuel I.e 5-10L in a can.

Easiest way I can think of to test the gauge is get 10L of fuel in a can. Fill up both tanks (LPG and petrol) and drive until you run out and see where the fuel gauge ends up if it ends on 0 then surely it is an accurate enough reading if it over reads you will know by how much and if it under reads you will know

[Krikkit]

I don't understand why this is an issue - the ECU gives you a fuel level reading when you start the car, you know its general economy at a cruise, so stick a 1/4 or so of a tank in and reset the trip when you run out of LPG.

Or just put some more bloody petrol in it - it's only 30 or 40kg to carry it around, not worth bothering about on a 1500kg car.

Edited by Krikkit on Thursday 2nd January 10:52

[eltax91]

Froomee said:

All I know is I have the current reading "or more"

Unless I am reading this wrong then the reading is less than what you have in which case you will never run out of fuel... Not much of a problem.

How sure are you that it isn't correct and when it "resets" it isn't resetting to the correct level which again would be a non-issue.

I'd find a way of determining how accurate it is rather than worrying about it changing or carry some spare fuel I.e 5-10L in a can.

Easiest way I can think of to test the gauge is get 10L of fuel in a can. Fill up both tanks (LPG and petrol) and drive until you run out and see where the fuel gauge ends up if it ends on 0 then surely it is an accurate enough reading if it over reads you will know by how much and if it under reads you will know

The carrying spare fuel is my last resort if I can't fix the issue. I have not (yet) let the petrol tank empty (keep filling up LPG over xmas), there may be a "final" check with the tank as it hits the reserve. I guess the problem will come when I'm say, 20 miles into a cycle and the "range" hits 0, because the car thinks it has no fuel. I then run out of LPG and I have to drive to find one. I'm 40 miles from home or whatever, I have to detour and find an LPG station, as I don't know if home/ the station near home is within the range of the petrol I have left in the tank. If i'm carrying over half a tank all the time, no problem, if i'm running at/ near reserve, could be a problem!

Does that make sense?

[eltax91]

Krikkit said:

I don't understand why this is an issue - the ECU gives you a fuel level reading when you start the car, you know its general economy at a cruise, so stick a 1/4 or so of a tank in and reset the trip when you run out of LPG.

Or just put some more bloody petrol in it - it's only 30 or 40kg to carry it around, not worth bothering about on a 1500kg car.

Edited by Krikkit on Thursday 2nd January 10:52

The ECU doesn't give me a level reading when i start the car. The needle returns to where it was when I last shut off. Not a problem if carrying plenty of fuel, but when it's hoverring around the reserve, it's frustrating not knowing how far you can travel.

I have the LPG stations app, and I can always get unleaded granted. However, the car is a tool for my work, I do a LOT of miles, LPG range is only about 300 miles, sometimes I really on unleaded as a range extender.

To be honest, if I can't fix the needle, then I will stick 20 litres or so in every 8 LPG tanks, but I'd prefer not to if possible

[SavanP]

eltax91 said:

Hi folks

I've tried opening/ closing the petrol flap and pushing a petrol nozzle in without filling up, to no avail. The car doesn't check the tank at any other time as far as I can tell, not even on startup!

Help please!

From the above does this mean that if you fill up the tank (petrol) and start the car again, the needle will remain at the same level as before you filled it, until it runs the fuel sensor check - seems highly unlikely so might be something else going on there.

[Krikkit]

eltax91 said:

Krikkit said:

I don't understand why this is an issue - the ECU gives you a fuel level reading when you start the car, you know its general economy at a cruise, so stick a 1/4 or so of a tank in and reset the trip when you run out of LPG.

Or just put some more bloody petrol in it - it's only 30 or 40kg to carry it around, not worth bothering about on a 1500kg car.

Edited by Krikkit on Thursday 2nd January 10:52

The ECU doesn't give me a level reading when i start the car. The needle returns to where it was when I last shut off. Not a problem if carrying plenty of fuel, but when it's hoverring around the reserve, it's frustrating not knowing how far you can travel.

I have the LPG stations app, and I can always get unleaded granted. However, the car is a tool for my work, I do a LOT of miles, LPG range is only about 300 miles, sometimes I really on unleaded as a range extender.

To be honest, if I can't fix the needle, then I will stick 20 litres or so in every 8 LPG tanks, but I'd prefer not to if possible

Ah, that's a bit different then. Sounds like it won't be a solvable issue, I'm assuming there's a piggyback ECU in the LPG kit? Who's the manufacturer? Might be worth getting in touch to see if they have any ideas.

[kambites]

SavanP said:

From the above does this mean that if you fill up the tank (petrol) and start the car again, the needle will remain at the same level as before you filled it, until it runs the fuel sensor check - seems highly unlikely so might be something else going on there.

There must be something that triggers the car to re-sample when it's filled up. If it's not the engine being restarted, possibly there's a sensor on the filler cap? If there is, you can probably tap into that somehow to get the thing to constantly re-sample.

You might be able to query the fuel tank level directly from the ECU via the diagnostics port, but it'll be a manufacturer specific code so working out how could be tricky.

[McWigglebum4th]

How does the car know its been filled up with petrol?

What happens if you take the car into a garage and throw 10ltrs of fuel in it?

I imagine it would respond


So somehow you must fool the car into thinking it has just been refilled

[anonymous-user]

it "knows" it's been filled up when the fuel level readings increase by a certain amount. All the rest of the time the readings will either stay the same or decrease.

[McWigglebum4th]

Max_Torque said:

it "knows" it's been filled up when the fuel level readings increase by a certain amount. All the rest of the time the readings will either stay the same or decrease.

So if you can fool the car into thinking it is empty then it might recheck the fuel tank and get back to the correct reading

I can't imagine the fuel gauge being anything other then a variable resistance

[eltax91]

SavanP said:

eltax91 said:

Hi folks

I've tried opening/ closing the petrol flap and pushing a petrol nozzle in without filling up, to no avail. The car doesn't check the tank at any other time as far as I can tell, not even on startup!

Help please!

From the above does this mean that if you fill up the tank (petrol) and start the car again, the needle will remain at the same level as before you filled it, until it runs the fuel sensor check - seems highly unlikely so might be something else going on there.

I assume, although not testing this until I have less fuel in the tank, that some kind of trigger (say 3l or more added) exists in the ECU to update the CANBUS modules. This may be my only "trick" to make it work, but if that exists, then surely a decent ECU programmer could emulate that trigger ever 10 miles or something....

[VladD]

eltax91 said:

SavanP said:

eltax91 said:

Hi folks

I've tried opening/ closing the petrol flap and pushing a petrol nozzle in without filling up, to no avail. The car doesn't check the tank at any other time as far as I can tell, not even on startup!

Help please!

From the above does this mean that if you fill up the tank (petrol) and start the car again, the needle will remain at the same level as before you filled it, until it runs the fuel sensor check - seems highly unlikely so might be something else going on there.

I assume, although not testing this until I have less fuel in the tank, that some kind of trigger (say 3l or more added) exists in the ECU to update the CANBUS modules. This may be my only "trick" to make it work, but if that exists, then surely a decent ECU programmer could emulate that trigger ever 10 miles or something....

Is there a fuse linked to the fuel guage or system that if you pull and then reinsert will kick off the ECU check? If you can find one you could perhaps wire in a reset button that performs the same function.

[McWigglebum4th]

eltax91 said:

I assume, although not testing this until I have less fuel in the tank, that some kind of trigger (say 3l or more added) exists in the ECU to update the CANBUS modules. This may be my only "trick" to make it work, but if that exists, then surely a decent ECU programmer could emulate that trigger ever 10 miles or something....

Are we trying to find a £1000 solution to a £10 problem?

[anonymous-user]

Check wiring diagram for car, i suspect the fuel level sender will be an analogue device hardwired directly to the instrument cluster. As such, shorting the output pin directly to ground or 5v (depending which way is "full tank" should fool the car into thinking it has been refuelled.

[eltax91]

Zulu 10 said:

Max_Torque said:

Check wiring diagram for car, i suspect the fuel level sender will be an analogue device hardwired directly to the instrument cluster. As such, shorting the output pin directly to ground or 5v (depending which way is "full tank" should fool the car into thinking it has been refuelled.

I agree that the sender may well be a simple analogue resistive device, but it's not that simple:
Despite giving the visual appearance of analogue gauges, very few modern instrument culsters actually contain traditional galvanometers: most seem to be stepper motors, hence ground its input won't help, and may damage the driver...

You mean the CANBUS driver? Or the one in the OSF seat? If the latter, I don't care if it fixes it.

[anonymous-user]

Zulu 10 said:

Max_Torque said:

Check wiring diagram for car, i suspect the fuel level sender will be an analogue device hardwired directly to the instrument cluster. As such, shorting the output pin directly to ground or 5v (depending which way is "full tank" should fool the car into thinking it has been refuelled.

I agree that the sender may well be a simple analogue resistive device, but it's not that simple:
Despite giving the visual appearance of analogue gauges, very few modern instrument culsters actually contain traditional galvanometers: most seem to be stepper motors, hence ground its input won't help, and may damage the driver...

Assuming a std 3wire potentiometer is used for the fuel level float, and that the instrument cluster provides a 5v drive and 0v analogue ground reference, shorting the signal wire briefly to either supply rail will result in the instrument cluster taking a "max range" signal input. The instrument cluster embedded processor will be measuring this signal input with an ADC channel, and this max range input should therefore trigger the cluster into thinking the fuel tank has been refilled. How long you need to apply this trigger signal, and what voltage results in a "full" input without triggering any diagnostic failure (generally, max/min Volts will be reserved for sensor faults. ie short to ground, short to Supply etc.) will take some experimentation.

My recommendation would be to measure the resistance of the level potentiometer, and get a manual potentiometer of a similar rating (say a 10Kohm one), use a 1kohm series resistor on the signal return line (to prevent direct short to the rails) and play around with the pot to see what happens!

[eliot]

Assuming the level sensor in the tank is a varible resistor, you could make my self calibrated fuel gauge by tapping into the output from the level sensor, cost £10 , time 1/2 day
http://www.mez.co.uk/ms13.html

[Froomee]

OP I'd just keep the tank fairly full or completely full.

It will cost £60 or so but you will eventually use it and saves a lot of hassle unless a cheap easy solution is found then £60 and a trip to the petrol garage... Job done