C5 Fuel Gauge

[vinrex7]

Hi guys, can someone tell me if my 2001 1.8i c5's fuel gauge is reading from the tank or does it go down automaticly when you drive?

Strange question but my car runs on lpg and the petrol gauge is going down when it's running on gas, and someone told me that some citroens don't read from the tank.

cheers Dan

[kfk]

I'll try to keep this simple, and will start by describing how the fuel gauge works with just petrol:

 

When you turn on the ignition the fuel guage checks its last known setting and how much fuel approximately is in the tank.....in other words if it was registering half a tank when last turned off does it agree that there is half a tank of fuel.....if it see's a significant difference in the quantity of fuel in the tank compared to that last registered it will adjust the fuel gauge accordingly.

 

Once the engine is started the fuel gauge stops checking the fuel level using the float in the tank....instead it uses the information supplied by the fuel injection ecu.....the injection ecu is constantly calculating the amount of fuel to squirt into the engine and using this information it estimates how much it has used.

 

So.....having carried out your journey, you turn the engine off, at this point the instument panel stores the last displayed fuel level.

 

And so the cycle starts again where by you turn on the ignition and the fuel tank compares the last gauge setting with the level in the tank.......the significant difference that will cause the gauge to correct itself is around 10 - 15 litres.....remember the float in the tank is an estimate of fuel level and can be varied by parking at different angles.

 

Should the fuel drop to a critical level the fuel gauge overides the injection ecu to illuminate the low level fuel light.

 

So what happens when you fit an LPG kit?

 

LPG kits are ussually 'spliced' into the original equipment fuel injection system, the lpg system will make use of various sensors that are already fitted to the vehicle, using its own ecu & lpg injectors aswell as the original equipment ECU & petrol injectors.

 

When the engine is running on gas the the fuel gauge isnt going to know, the sensors will be telling the original ecu that the engine is running, and the ecu will be telling the fuel gauge that its using fuel......which means that the fuel gauge will drop while running.

 

Now you may find that if you use the vehicle for long journeys it drops a fair way, but turning of and then back on again would probably get the fuel gauge to resynchronise itself with the level in the tank.....on shorter journeys it may take longer to show up as a discrepancy.

 

Hope that answers your question