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Got myself a misfire

Yes. It accelerates strongly through the gears and feels to be giving full power until you hit 4000rpm in 4th which is when it starts hesitating.
 
Unplug the hall sensor and try again. By then the engine will run less timing and if the misfire is still there then it may not be ECU-related.
 
sounds like its Pinking to me, not enough fuel or an air leak,

detonation will cause the ECU to retard the ignition timing drastically, not sure you can check the FPR for high revs but when was the fuel filter last changed
 
Fuel filter is 3 years old only done 400 miles. FPR is new.

I will try running it tomorrow with the cam position sensor disconnected and see what happens and if I have the time will take the cat off for an investigation.

My feeling is that something is befuddling the DME within a certain speed and load range. It's got a Promax chip in it so might also change that back to the Porsche one just to see what if any difference that makes.
 
Detonation is why I suggested to disonnect the Hall sensor. By then the engine will run with -6° of advance on the whole ignition map, so if the misfire disappears then perhaps it may indeed be detonation to a "reasonable" extent, as in "manageable" by the ECU.

If the misfire persists then I doubt it may still be detonation, as with 6° less on the ignition map detonation would feel far more an event than just a slight misfire.
 
So, unplugged the hall sensor and took the car for a quick spin. Misfire/hesitation still evident around 4000rpm and I also noticed it in 3rd gear. Other than that, the car ran fine I didn't notice any difference between sensor plugged in vs unplugged. Wondering if that means that the sensor itself has failed?
 
Well, 6° of timing should make quite a bit of difference, so yes I would say there is something wrong.
When were the following either refreshed or replaced :
- Injectors
- Fuel pressure regulator
- Knock sensors

Failed knock sensors will also cause the ECU to pull timing, resulting in a loss of power.
 
Injectors were serviced (ultrasonic cleaned and flow tested) by a Bosch service centre in March 2016. FPR was new at the same time.
Knock sensors have never been replaced so I suppose I could change them (there are two?)

I've ordered a new hall sensor and also a new TPS. I had the plugs out yesterday and their light colour suggested it might be running lean. After reading up about the TPS I found that it contains a switch for wide open throttle which switches onto a different (richer) map in the DME. I bench tested my TPS and it does't seem to be switching at all so I'm thinking this could cause it to be leaning out under wide open throttle condition.
 
Good point regarding the TPS. Perhaps replace it first and the hall sensor later?
 
I've ordered both but yes I will fit TPS first then test then fit hall sensor then test again. Funny that it started and drove out of the garage quite happily this morning while missing both of those components!
 
New TPS arrived so I fitted it and went for a drive (hall sensor disconnected). It has certainly improved things. Car feels like it has a bit more power and feels a bit more responsive. The hesitation at 4000rpm has gone BUT I still felt a slight judder between 4500 and 5000rpm in 4th.

I can't reconnect the hall sensor because I cut the plug off in anticipation of replacing that at the same time as fitting the new sensor. So I now have to wait for that to arrive to see if that is the final piece in the jigsaw. Hopefully tomorrow.
 
So, soldered a new plug onto the engine wiring loom and plugged it into the existing hall sensor. Hey presto! Misfire/hesitation completely gone! Engine feels smoother and more responsive too. Happy days!

So it seems the hall sensor itself and the short piece of wiring to it's plug is OK but that the engine bay wiring loom had a fault and somewhere along the line the TPS had failed too. So with both now working, the DME is a much happier bunny and the car is running the best it ever has done.
 
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Thanks Oli. Seems that the TPS was also guilty of serving up my slightly lumpy idle too. I was blaming the AFM for that but the new TPS has turned out to be a bit of a magic bullet.

I do like those moments when you change a component and immediately know that the thing you've just replaced was indeed coconutted. I think I might have found all of my 211 horse powers now too!
 
Tom,

Yes, precisely! Although I do think you need to be more careful with your terminology; was the old TPS flamingo'd or was it coconutted? There may be a difference ....

A good S2 will produce more than the book-stated 211bhp. Mine managed 219 a while back and that was before it was chipped.


Oli.
 
Congratulations on your fix Tom. You inspired me to stick an oscilloscope on my hall sensor over the weekend. Guess what? It's not working. Looking forward to a few more hp, and at the same time I plan to dial gauge the cam timing and check that is where it should be.
 
Replaced hall sensor over the weekend... what a transformation!
I wonder how many S2's (or S) are driving about with a failed hall-sensor? I will bring an oscilloscope to the next 944 meeting and offer a testing service.
 
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