Engine not starting
 

My S8 has just started to play up again. The other day while driving on gas it struggled to rev, then the car light came on.

I turned of the engine and it failed to start on petrol, it stalls right away and its not possible to build any revs.
It started on gas and drove ok but now it wont do either.
If i try it on fuel it stalls immediately and bearly starts, if i try it on gas it sometimes works and then stalls after a few seconds.

Its usually fine starting on gas if I need to so there is defiantly something wrong.

I have checked fuel pressure which is flowing.

Im in the middle of no where in france at the moment and dont have access to an error code reader.

I have ruled out the ISV and the TB as its not even staying on if you try to open the throttle.
Does anyone know what this could be?
Maybe the MAF? or the lambdas?

Please help if you can,
Cheers.
Bo

It's possible that it is your immobiliser. Do you have another key?

Sounds like the immobiliser, I get this intermittently too. If that light on the dash is flashing then it will not start, well it will but shut off.

Try taking the key out, put it back in turn the ignition on and see if the light goes out and stays out, if not try again. Can be a pain at the petrol station.

I just checked the light, it goes out about 1 second after the ignition is turned on.

Can someone confirm that its not MAF or Lambda related.


Thanks for your help guys.


Cheers.
Bo

Faulty mafs and lambdas at worst would make it run lumpy, or cause the engine warning light to come on. I cant see it would cause the issues you describe....

I would suspect the immobiliser if it was purely a starting issue, but it sounds like it died whilst running fine ?, which would rule it out.

If both fuels produce similar results, you can rule out fuel supply, which leaves really coils / plugs / timing / wiring

Is it smooth when it runs for a second or two, or a bit lumpy ?

Thanks,
Its pretty smooth although i have now tried it about 20 times and sometimes it also sounds like its not firing on a few cylinders when it starts up.
it sounds like tis really struggling to start. I would suspect if it was the imob it would fire up fine and then stall, which is not the case.
Very bizarre.

Earlier it did start on gas and i managed to get the revs up before it died. I held it at 3k for about 20 seconds then off throttle and it stalled right away..

While it was running it sounded fine but made no attempt to idle.

Ill check the breather hoses maybe one has perished and is coursing unmetered air to come in.

Im presuming fuel should flow in at the pipe which does not have the FPR attached to it?
If i crack the FPR one off its dry....
Also when cracking off the other fuel line it spits as the nut is undone, so there must be air in the fuel rails.

Maybe my fuel gauge is lying, (says its half full) and when i cranked it over to check fuel pressure it was only spitting out.....

Anyway, i have sent someone out to get 30l of 98ron so ill see what happens hen that goes in.


I think its poss that a cold start on gas can be unsuccessful as the liquid gas can freeze the vaporizer..

If all the above are right then thats hopefully the only problem...

Will update later if i get it to work.
Thanks again for your time..
Bo

Could well be, its not uncommon for problems in the fuel tank to stop the bottom half of the tank being drawn off, ie when gauge says half full, it is, but it cant get to it, so might as well be empty.. !

That was it!

Put in 30l and it started second time and runs as normal.

Gauge now reads 4/5 full...

Thanks for your help gents, ill keep this in mind and will keep both tanks brimmed..

When i removed the tank on my other S8, I put 12v to the pump in situ and ran it till the pump was sucking air.
After i removed the tank it still had 12L in it!
Seams to be quite a complicated system inside the tank as it has thoes two legs.
Maybe one of the internal feed pipes on mine is blocked...

Anyway, I'm happy that its working again now!

The system is complex! :Confused: I've played around in the tank when replacing a fuel pump.

The pump sits in a sump of fuel and it is above the level of fuel at less than a quarter of a tank. However, fuel remains in the sump-part of the pump assembly which allows the pump to prime. When in operation the pump drives fuel into the tank to either side to drive 2 turbines that send fuel to the fuel rail. That way each side is being fed fuel so they stay the same level

With me so far?

The low pressure return from the fuel rail goes up to the header tank at the fuel cap and cascades back down into the sump that primes the pump.

If the sump dries out then the pump wont prime. Simples! :)