Running Rich

[tref]

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.

 

[barks944]

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.

 

[Alexw]

Hi there,

I've had my car in with Hartech and they've told me the car is running rich under load - the problem is its running a MAF atm so they're not sure if its that and are going to put a standard unit back to see. I'm hoping its not the MAF as I'm struggling to find any info on its setup. So if its not the MAF, what could do that? The car doesn't have a CAT and I'm not sure if it has an O2 sensor? Temperature sensor? Anyone have experience of this?


Cheers

 

[Diver944]

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

 

[barks944]

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?

 

[Alexw]

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 Acceleration is fine, not seen any black smoke. I hammered it round an airfield over the weekend, no smoke that I could see.

 

[barks944]

Yep 12v feed I Expect. Was wondering if they had the issue I have when making theirs.

 

[Neil Haughey]

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.