Your thoughts on what is going on here?

[flyfishing]

My s4 had been rock solid till a couple months ago. Cold start mis-fires and CEL on and eventually it misfired so much at cold start that it would "choke" for air and want to die. Well one day it misfired so bad I couldn't even drive it down the street and it had to be towed to shop.

Shop said coolant leak into wiring harness so wiring harness replaced with also new coolant temp sensor (I believe where leak was), new sparks b/c misfire had fouled them, and new air filters.

I got it back and cold start misfire still. They did tests in VCDS (the measure blocks one where it shows engine rpm, coolant temp etc) and it showed failing MAF b/c the lambdas were in the 25% range. So I got a new MAF.

Still cold misfire. They do fuel pressure test and it shows it low in the 20s instead of 40 lbs. At this point I had been getting p300 (intermittent misfire) and p1136 (too lean). Well, I had a new fuel pump placed in today, new fuel filter and new fuel regulator. They cleared codes, did a cap discharge to reset ECU and now I get lambda measurements of -3% to -7 instead of 25%.

I red lined it in second gear and CEL comes on. Codes show 1136 (too lean) and 1138 (upper limit reached) and I clear it. Go to gas station, floor it again and VCDS shows intermittent misfire and misfire in banks 4, 5, 6. Same lambda measurements.

Any thoughts?? Edit: I've had coil packs replaced previously also. New battery last week also too. And mine is stage 3 with AWE kit and RS4 turbos.

[vavJETTAw36]

Wait. So there is lambda control which is your short term fuel trim. This should alternate positive negative positive negative. You're saying that is not the case? You should be checking measuring blocks 32 and 33. 32 is your long term, additive and idle. What are your 32 values?


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[flyfishing]

Here are my measurements for block 1, 32 and 33. Well block 1 shows quite difference now -- it has been sitting for about 2 hours:

Block one up until today (after fuel pump and fuel regulator was replaced) was showing +25% on both banks. After it was replaced, it dropped to -3% to -7% this afternoon after I checked logs after rev limiting it in 2nd gear. What was interesting today immediately after fuel pump and regulator was replaced was that it initially showed +25% both banks until battery disconnected AND MAF was unplugged and replugged in.

My shop said they initially saw coolant leak to the ECU so maybe it is damaged and has to be "re-prommed" I don't really want to do that b/c I'm sure that costs more and my car is in shop for a week or so b/c it has to be sent off.

[vavJETTAw36]

It is long term, meaning it is keeping a rolling percentage of the fuel trims. That is why it dropped down after you reset the ecu.

You should clear your codes and immediately switch to measuring value 33 and see what it does.

Coolant leak on the ecu? I don't see how that could be. I'd pull your ecu and check the connections myself.


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[waveblaster200]

Have you done a boost leak check? What sort of vac are you pulling at idle with the a/c off.

[flyfishing]

I'll try that and see what it says.

They said long term coolant leak that leaked down wiring and migrated towards the ecu. They cleaned all the coolant and residue off the ecu they said

[vavJETTAw36]

Unless the hoses to your heater core were leaking, i don't see how that could be possible. Your ecu is raised off of rain tray surface by a couple inches it would be some serious pooling. More likely some rain damage.


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[Zba]

I've seen coolant temp sensors leak internally where the coolant migrates up the connector into the ecu. I've also seen oil migrate up through pressure switches into the ecu.

[flyfishing]

What Zba said is exactly what the shop said. It migrated up.

[vavJETTAw36]

That's crazy... I stand corrected. Sounds like an electrical mess!


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[themadscientist]

I've encountered a lot with Mercedes and on a few mk4 Jettas. Fluids under pressure can indeed get pushed through the sensor, into the plug terminals, and then into the wire insulation, and travel to their final destination, wherever that may be. Harnesses, sensors, and plug connectors are designed to keep fluids out, but they're also good at keeping them in.

[vavJETTAw36]

Well since you are having trouble on 4,5,6 (bank 2) try swapping your ICMs to see if your misfires will move to 1,2,3 (bank 1). You probably don't need it now, but when you replace it or find its not the issue you'll need to apply thermal paste (after cleaning mating surfaces with isopropyl alcohol) that you usually apply to cpu chips on computers


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[flyfishing]

Have you done a boost leak check? What sort of vac are you pulling at idle with the a/c off.

How do I check for boost leak? I'll report back what my boost gauge shows with AC off.

[flyfishing]

OK shows it as 18 inHG with AC off at idle.

[waveblaster200]

If you do your own work, every b5 s4 owner should have one of these. http://turboboostleaktesters.com/audi-s4-2-7t/
Or make your own. With the aging vacuum system in these car you should keep a eye out for leaks. I know leaks can effect fuel trims. But maybe someone with more experience can chime in. You will need a decent size air compressor and tank to be able to effectively test for leaks.

[flyfishing]

I did some more testing. The harness was modified to fit my MAF (I forgot if it is Hitachi or Bosch). I removed the electrical tape and it looked like good modification with shrink tube wrapping, but I noticed when I jiggled it all of a sudden the lambda changed to +25%. I then removed it and it dropped to 0%. I wrapped it in electrical tape again and it changed to 7-8% and after more tape to hold it tighter, it changed to -2%.

Hmmmmm.

[vavJETTAw36]

I did some more testing. The harness was modified to fit my MAF (I forgot if it is Hitachi or Bosch). I removed the electrical tape and it looked like good modification with shrink tube wrapping, but I noticed when I jiggled it all of a sudden the lambda changed to +25%. I then removed it and it dropped to 0%. I wrapped it in electrical tape again and it changed to 7-8% and after more tape to hold it tighter, it changed to -2%.

Hmmmmm.

Before doing anything else, swap your ICMs. It will take like 5 minutes. The fact that you have misfires on one whole bank tells me that you have a bad icm. If you swap and the misfires go to 1,2,3, bam there is your problem.

Sure you may have a problem with your maf wiring but why not check your maf readings? If it's reading, your wiring is fine. Can't recall the measuring block for it. If you know your approx horsepower you can also verify the maf is good or bad. You'll have to search for "Ross tech fuel trim info" it is at the bottom of that.


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[flyfishing]

I will read codes more and if i see same cylinders misfiring, I will swap ICMs.

How long do those last? I put new ICMs in about 3 years ago.