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RUNNING RICH

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hi all my 1984 944 is running rich, I think someone has turned the fuel up thinking it will be better as they were not using leaded petrol,
how do i turn it down? and does anyone know the standard setting e.g 2 turns out?
thanks ryan
 
Hi Ryan,
Which screw are you referring to? Do you mean the idle screw adjustment?
You might want to look here before doing anything.
As such the fuelling is controlled by the chip in the ECU so it's not easily user adjustable. However 944's will seem very rich compared to most modern cars and that is nothing to be worried about, but if in any doubt I'd get it to a garage and get them to give it the once over.
 
certainly experience of failing an MOT on a temperature sensor that was slightly out of specified resistance when up to temperature, but within spec cold, so it is worth measuring the resistance as per the manual to ensure it is ok.
 
Could be that the MAF is reading high when at high air flows. If by load they mean under heavy acceleration, this is where the most air is flowing through the engine. If the MAF is telling the DME that there is more air flowing into the engine than there actually is then the injection system would inject too much fuel. Although if the S2's injection system is anything like the lux's then it actuall ignores the AFM above 4000rpm and when at wide open throttle. Under those conditions it injects based upon RPM's so the AFM/MAF has no influence. My guess would be that its not the MAF but then I don't really know how the s2's injection system works or quite how load could influence AFR.

Temp sensor could cause it as any error would be more apparent as the air flow rate increased as the air mass calculation would give more and more innacuracy. Could also be overpressure in the fuel rail as this would cause the fuel flow through the injectors to increase. This should show itself under all conditions, again though it might become more apparent as more fuel is being injected into the engine.

 
I know the engine temp sensor failed on my S2 several years ago and it gave a reading that the engine was always cold so the ECU kept it on the cold start setting. Very rich everywhere, lots of black smoke from the exhaust and very juddery acceleration under load
 
There's also the air temp sensor in the AFM/MAF, which is the one I was thinking of.

AlexW how does your MAF wire up. Does it need a 12v supply?
 
its a SciVision unit, it directly replaces the AFM. It has a little box of magic which converts the signal into the something the DME recognises. I don't think it has a 12V supply, although it does connect to a wire in a small box in front of the fuse box, I think it was mentioned as a voltage signal cable in the instructions IIRC. So that could be a 12v line.... I have no idea :p

Acceleration is fine, not seen any black smoke. I hammered it round an airfield over the weekend, no smoke that I could see.
 
So Hartech are saying specifically that the engine is running too much fuel enrichment only under heavy load? not rpm related? Do you have a performance chip? as these tend to not lean out in the midrange as the motor should do with a standard setup (promax chip seems to stay rich). Still though sounds like the MAF output.

Engine temp sensor will cause rich or lean running all the time the engine is at a particular temperature, I suspected this on my 968 as it was running rough at idle and especially so when cold, much better once warmed up.

Fuel pressure regulator can cause all sorts of problems my S2 did run very rich sometimes because the injectors struggled with too much fuel pressure, but in both cases I would suspect an outfit like Hartech would spot a problem with either straight away. Hartech and Jon Mitchell are probably the 2 most respected expert indies for the 944/968 series cars.
 
What are the exhaust gas readings like, and do you have a later car (with a cat and - presumably - lambda), or an earlier one without?


Oli.
 
The car is a late '91, Oli. It has a bridge spoiler (if that helps) and all I can tell you about the exhaust gasses is that they smell rich.
I have considered the lambda sensor but it is running sooo rich that I don't think it would be that. I have a feeling it could be some problem with the injectors but I am hoping it could be something less complicated.
 
My car started running rich a couple of years ago and it turned out to be the air flow meter but I don't know how to test it.
They do go when they get old. Promax diagnosed the problem replaced the AFM and it's been fine ever since.
 

ORIGINAL: bluedexter

The car is a late '91, Oli. It has a bridge spoiler (if that helps) and all I can tell you about the exhaust gasses is that they smell rich.
I have considered the lambda sensor but it is running sooo rich that I don't think it would be that. I have a feeling it could be some problem with the injectors but I am hoping it could be something less complicated.
If it is that rich and lambda is working as it should then lambda will be constantly telling the ECU to go lean.

I'd suspect a lambda fault - are the wires going to it all as they should be? Is the sensor working as it should? (If Lambda is signalling wrongly then it will force the ECU into running rich, which the lambda then won't be able to sort out ... )

You need proper diagnostics (i.e. someone who can probe lambda), NOT a general garage bodge-artist who will just replace bits. (The latter approach will solve the problem by trial and error, but it may be later rather than sooner - to your financial detriment.)


Oli.
 

ORIGINAL: marty
My car started running rich a couple of years ago and it turned out to be the air flow meter but I don't know how to test it.
They do go when they get old. Promax diagnosed the problem replaced the AFM and it's been fine ever since.
They do, and I have a theory about them. (Come with me on this one.)

1. AFM's work by having a flap, which is blown out of position by incoming air.
2. It is held in place by a spring. This spring is what determines how much it moves in the air flow.
3. Springs become weaker with time. (We know this from suspension, speedometers and lots of other things.)
4. Spring weaker = more flap movement = ECU signalled that more air is coming in = more fuel goes in = engine runs rich.

Solution? Tighten the spring up.

Simple - huh?


Oli.
 
Temperature Sensor dodgy which may be sending wrong signals to the ECU or possibly the Air Flow Meter ?
 

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