AAN in T3 Syncro 16 - misfire above 10psi boost

[RS2]

Well... Now the engine runs ok but only boosts to around 11psi. Now and again I'll get 12psi but that's it.

The idle is stable but very slow to return from 2,000rpm down to idle.

It feels somewhat sedate as a result.

But no misfires. Not a surprise as they only occur on higher boost levels than what I have now.

MG

[UrS4boy]

So both of AAN origin. The D is auto and the C manual nesable base neither of which should be effected by a malfunctioning MFTS! I take it the D is not socketed because ideally we would like to start with the OE C sw in the D hw to give us a baseline. The guy you got the 3bar ecu did have an AAN S6 I believe so perhaps we are being a bit overcautious but unless you can verify its origins and suitability then it is a bit of a risk.

From prj:

"AAN Motronic ECU Part Numbers:
551A early UrS4 with pseudo dizzy and 8k boost chip
551AA UrS4 non-immo, Europe and America
551B UrS4 same as 551AA, but auto
551C UrS6 incorporates all software updates from RS2, different codebase, more diagnostics
551D UrS6 same as 551C but auto (see photos at the end of this post)
551E UrS6 has a small tweak to fuel on cold start
551F UrS6 same as 551E but auto.

[twoqu]

So both of AAN origin. The D is auto and the C manual neither of which should be effected by a malfunctioning MFTS!
I take it the D is not socketed because ideally we would like to start with the OE C sw in the D hw to give us a baseline.
The guy you got the 3bar ecu did have an AAN S6 I believe so perhaps we are being a bit overcautious but unless you can verify its origins and suitability then it is a bit of a risk.

[RS2]

I used the AAN loom.

Here are the two ECUs next to each other.



I've just swapped over to the standard ECU and will report back asap.

MG

[UrS4boy]

I also seem to recall that the AAN loom, if thats what you used, does not have any wiring to the pin on the ecu that would get the overheat signal, whereas the ABY obviously does. So thats a bit of a mystery, to me anyway.

That is correct. Hence the need to know what ECU ( and loom) was used.

[twoqu]

One issue with shall we say unusual installation is when packaging causes deviation from what Audi intended, particularly with plumbing of pipework and positioning of the sensors.
Personally if it was my vehicle i would put it back to as stock as possible to troubleshoot it. If you can get it to work as Audi intended then you can upgrade. We don't know the origins of those chips so we cannot confidently say what they were mapped for in terms of injectors/turbos etc.
The earths are important as Audi chose to use the engine to ground the engine harness.

[RS2]

It has the factory Audi earth strap on the engine and another on the gearbox.

If there was an issue with the earth, I would expect that the starter motor would struggle?

MG

[twoqu]

How is the engine earthed to the chassis out of interest?

[twoqu]

Also you mention that with a faulty MFTS you were getting 10-12psi. The overheat signal should disable the boost control so you revert back to the mechanical boost control of the spring in the wastegate. This should be in the 0.4/0.5bar range so 7psi or so. Therefore its possible that you have either a stiffer wastegate spring or the wastegate cap is adjustable. Ideally this should be either a stock spring or adjust the wastegate to achieve the correct value with the wastegate valve disconnected electrically. Of course this assumes an accurate boost guage!
Just something else to check.

I also seem to recall that the AAN loom, if thats what you used, does not have any wiring to the pin on the ecu that would get the overheat signal, whereas the ABY obviously does. So thats a bit of a mystery, to me anyway.

[mike74]

borked lambda?

[Error404]

Why is the ECU is not throwing a lean mixture adaptation code considering the misfire is so consistent?

[mike74]

No idea. If it was purely an ignition fault you'd imagine the plugs would be slightly darker and sootier due to not getting a good, consistent burn...they look the complete opposite like there wasn't enough fuel...

[RS2]

I think that I was running the wrong plugs, hence changing them.

Re flow rate, why would changing over from ignition system to another influence the misfire if it was fuel related?

MG

[mike74]

It may just be the lighting in the picture but, to me those plugs look a little too light ie lean running. You say you've checked the pressure but have you checked the fuel pump for flow rate as well? Maybe even a blocked fuel filter?

[UrS4boy]

The ecu issue can wait. But it sounds like you must have ABY SW as the AAN didn't have use the MFTS as a safeguard. This might be important as USUALLY (for Dave's benefit) it was only the AAN conversions that used a 3 bar map sensor to allow more mid range boost to move the bulk and lardy NA backsides at the same pace as us less obese S2 owners in Europe which had to make do with 2.5 bar map sensor conversions.

The type of ECU being used here (ABY or AAN) needs to be established because of the MFTS issue.

AANs and ABYs both came stock with 2.5 Bar MAP sensors in the ECU. Upgrading to 3 Bar MAP sensor has nothing to do with the size of NAmerican versus European backside, thank you very much.