Guys my second S2 that I'm selling and now probably sold has developed a bad miss. I have had it plugged into an analyzer that interfaces with the fuel side and can check things like throttle position sensors and inductive pickups. It showed all O.K. We also put a scope on the ignition side and it showed little activty to one side of the coil, I found that problem, it was a dodgy coil lead that somebody had soldered, I then changed over all the leads and caps with my other ones from my other car. This stopped it running on four cylinders but still left with underlying problem.

What the car does is idle rough, if you increase the throttle to try and hold a steady 2000 rpm it will just die like it isn't getting any fuel, on that note the car does seem to run rich, making you eyes water but you can't see black smoke as such. The car will have moments when it responds cleanly, also when you drive it it has good power up top. The compression of the engine is good averaging 170 psi per cylinder with a 3% varience. Higher in the rev range response and the sound of the engine is better than lower as a rule.

So what have I changed, I changed all the leads and connectors, both coils, the amplifiers, the roter buttons, the spark plugs, the fuel and ignition computers. The inductive pickup. The injectors have been out and serviced and I also checked the fuel pressure. I also found bad connections on one of the coils, i.e. the low side positive and negative connections both had damage to the insulators around the connections. I have also removed many earth connections and cleaned them. I found bad connections on one amplifier and two on the MAF. I have since cleaned these terminals and traced most wires back to the computers. I only managed to trace 5 out of 6 wires coming from the MAF. I haven't traced any wires coming from the induction sensor.

So I now have very few avenues to go down, I was thing of getting it put back on the analzer now that the coil lead was fixed. Any hints appreciated.

Greg

 

Having a MAF and/or LH to swap in would be nice ....

 

Hi Garth, as I mentioned in my post I did have a LH unit to swap but that made no difference that I could detect, I also believe that the 2.2 version of the LH is quite reliable and doesn't give much trouble at all. I don't have a spare MAF as I recently sold it. I should say that all the componants I swapped over were second hand off my other car which was running perfectly at the time. When I said I have checked some of the wires, I should have added that they were a resistance test only and possible there may be a break in the insulation that may be arcing wires together.

It is really quite rough you would think that it would be so hard to find.

Greg

 

There should only be 5 wires from the MAF.

Was the MAf one of the components you swapped out from the othere car, and seemed OK in there ?

Try unplugging the MAF and see if that improves things. It should at least idle reasonably well on an S2.

 

Greg

PM me - I have a May 2006 JDS Maf you can swap in (although it doesn't immediately jump out as a likely problem)- it's here sat on top of the stereo in the kitchen so no probs for me. Can also liberate known good ign leads if that would help

I'm around tommorow during the day (apart from waiting for the possum catcher) or evening

Jon

 

Just some thoughts;
final stages on front fender (is that what you mean by amplifiers)
major vac leak
the little toothed belt below the twin dist.
and like you said arcing in the top engine harness
open and sand the connections in the multiple thing near the battery jump post
and make sure TB and cams are aligned and intermittent signal from crank position sensor

 

First thanks to all that have responded, TV I have checked, the cam timing and the distributer also, I didn't think this was the problem as I only recently changed the front main seal. Major vac leak is again a good thought, I can't hear anything and I checked the brake booster to ensure that there wasn't a leak there. As for the earth connections, the one I haven't done is the main one under car near the exhaust, I will do that next time I work on the car.

Hi Jon, thanks for the offer! I think I will take you up on that but I have other things that I need to do first as I now only have part of the weekend to work on the car due to renovations that are in progress here. I unforntunatly also missed the concours held last week due to the work commitments.

John I will recount the wires on the car when I get a moment, if you go to the wiring diagram in the workshop manual, the pages I refer to are the wiring diagrams for type 928s model 85 page 7 titled Engine digital engine electronics. There is 6 wires on the diagram. The wire I couldn't work out where it goes was no. 5 Maybe when you refer to 5 wires you aren't counting the ground wire? As to disconecting the MAF I tried that when it was warm and it ran cleanly and at a fast idle of about 1300 rpm. When I started it yesterday from cold it was pretty rough with the MAF disconected.
you couldn't rev the engine easily.

Thanks again.

Greg

 

Hi Greg
Limp home mode isn't temp compensated, so it does appear that it runs better with the MAF disconnected, which could make it a suspect.

Did the MAF come from the running OK car ?

Sorry about my mistake with the # of wires, you are correct.

# 5 is in fact the main MAF output voltage to pin 7 LH ECU. It seems that it is connected as you get a change of behavour when you disconnect the MAF.

The connection from MAF are

1) Burn off volts
2) 12v input
3) ground
4) ground
5) output
6) idle CO pot.

 

Hi John thanks for that update and info, I have contacted Jon and will endeavour to swap in one of your reco MAFs to see if there is any difference. I didn't realise about the temp sensor being disabled while the MAF was disconected, as I mentioned the car ran cleanly when it was hot and just left to idle. So I'm now more than a little suspicious of this MAF.

Thanks Greg

 

Not necessarily a cheerful thought here -- but have you checked compression lately?

 

Hi Sharkskin yes the engine comp was checked at the recent PPI, the big news is that I borrowed a JDS Porsche MAF and it has done the trick, immediate difference, took it for a spin and power was good and not one hesitation. I now wish I hadn't sold my low KMS MAF, if you can believe this it was the only part I didn't have to try for the fault diagnosis!

Thanks to all that reponded.

Greg

 

Glad it was easy, and good thing you were able to borrow that MAF!