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over fuelling problem again ! any ideas why ?

eddieedmo

eddieedmo

New member
Since I have had the 944 , about 18mths now , it has twice suddenly run very rich causing misfiring etc and stalling at idle - leave to cool off and all ok.It happened again on Sunday driving to Forest Pines for a couple of days golf.
On the M180 started getting lumpy missing etc managed to get there and as soon as low revs then stalled.Restarted ok but very rich ,missing and exhaust dry black soot ! Left until today and all fine when came home this pm ,although running a little uneven but the plugs will be in a mess from the day before .
Any ideas as to finding the problem.The temp sensor has been replaced idle stab valve cleaned out 2 mths ago, throttle housing cleaned out recently.

Nick [:D]
 
FPR?

my 2.7 was running rich ever since I got it , AFM helped then I got the bad running, and idling etc .

Pull off the vacuum pipe, mine had petrol in it!

Had similar problem 20 odd years ago on my old HPEie Lancia.
 
Nick,

Too much fuel - the question is why. Temp Sensor is the obvious candidate, but you say it has been done. Air Flow Meter would be the next thing to look at.


Oli.
 
Id look at temp sensors and the FPR first as theyre both pretty much a consumable. If that doesnt fix it then an air flow meter clean up might be the answer, as Oli suggests.

Google FRWilk for the AFM.
 
Thanks for the ideas I think I will have to try the FPR , the fault is not a constant one just happens v occasionally and then when left to cool all is ok again.It is affecting all cylinders so not an injector isssue so a sticking FPR is likely.If it was the AFM would it not be a problem all the time ?.Only happened 3 times in 18mths and normally the engine runs clean as a whistle plugs light grey , no exhaust deposits.
Is it possible to fit an adjustable FPR and what would be involved ,any benefits ? or should I just go for straight like for like replacement ?

Cheers guys

Nick [:D]
 
FPR isn't cheap for the S2 unfortunately.

One thought - a very intermittent problem might be wiring / connectors ?
 
why didn't you check the fuel pressure before ordering the new FPR ?

Guages only cost £10 or less on fleabay

If the FPR is causing intermittant over-pressure it could force the injectors to leak but other than that it cannot have any direct over-fuelling effect.

Its the rate of electrical pulses from the ECU that determines the rate of fuel delivery from the injectors ,...not the fuel pressure.

so I would check the AFM isn't faulty (check the tracks and for particularly for a sticky flap due to heat ) and of course the engine temperature sensor but my money is on the AFM
 
if it was the AFM would there not be a problem all the time ?
Do you mean the throttle flap ?
Just replaced plugs with a clean set after the over-fuelling on Sunday , the good run back yesterday had cleaned up the electrode/spark bits just dry soot around edge of plug body.Running fine again now just been for a spin.
Cheers

Nick
 

ORIGINAL: eddieedmo

if it was the AFM would there not be a problem all the time ?
Do you mean the throttle flap ?
Click to expand...

the AFM is a flap ????? what do you mean by throttle flap ?

Its the AFM vane(or flap) that registers the quantity of air flow through the intake by the relative position of the vane to the resistive track and sends the data to the ECU in the form of voltage.

It is a possibility that either the vane could stick intermittently due to distortion caused by heat or it could be a poor connection between the AFM vane and the resistance track .
Have a look at the internals of an AFM and failure mode on Clarkes Garage site for a better explanation.


 

ORIGINAL: eddieedmo

.Running fine again now just been for a spin.
Cheers

Nick
Click to expand...

well i wouldn't count your chickens just yet ![;)]

From your description this fault has only occurred twice in an 18 month period ? Hope the problem is solved but it might be a tad early to celebrate just yet .
Glad the car is running well anyway.[:D]
 

ORIGINAL: peanut

why didn't you check the fuel pressure before ordering the new FPR ?

Guages only cost £10 or less on fleabay

If the FPR is causing intermittant over-pressure it could force the injectors to leak but other than that it cannot have any direct over-fuelling effect.
Click to expand...

Are you sure Nick? Surely if the fuel pressure is increased then more fuel flows through as the injector opens. This is why you can increase the fuel pressure in lieu of fitting inreased capacity injectors.

I have seen this done on more than one occasion.


Simon
 
yes you're right there is a very slight increase in flow rate but not sufficient to cause the sort flooding described I shouldn't have thought.
When there is fuel over-pressure situation the ECU should shut down the injector pulsing as a safety feature .

The problem is that this is such an extremely rare intermittant fault according to the OP so I would think it unlikely to be a component going faulty. Perhaps a poor earth or electrical connection or loom short etc causing component malfunction ? maybe an intermittent vacuum change effecting the FPR ? Who knows ! It would be useful to attach a cheap fuel pressure meter and see what happens to the fuel pressure the next time there is an over-fuelling situation.

There is a formula for calculation of the fuel flow quantity relative to fuel pressure but I'll leave that to others my math days are long gone
Q2+Q1 / (P2/P1) I believe thats right ?

 
no not counting any chickens , problem not fixed yet.As before it fixes itself once cooled down .I just replaced plugs today for clean ones and check the mixture was back to normal.
I will check AFM and clean and reset sweep position if needed , and check throttle flap/AFM flap for free movement and that it is actuating TPS ok.
Thanks for all help and thoughts , will post progress.

Nick [:D]
 
good luck Nick.

Everything you learn helps us all to understand our cars better . The more I learn about the 944 the more I realise how complex the fuel and ignition systems on these cars is.
Nick
 
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