ECU inputs under WOT M5.2

[rallygabe]

Alright guys,

Trying to do a little troubleshooting without all my books, so hoping you smarty pants on the forum can help me out.

What sensors does the ECU look at during WOT?

I have some serious stumble/stutter under WOT when I have smooth operation under partial throttle.

Thanks in advance!

[Loren]

On a MY99 Carrera (C2 only) your have the last throttle cable car.

The DME is looking at MAF for air flow, also the MAF for intake air temperature, and the throttle position sensor.

If your problem is only above 4000 RPM I would put my money on the MAF either being dirty or bad.

If you have access to Durametric or a Porsche PST2, (or PIWIS) tester you can also check the WOT percentage (as read by the throttle position sensor). 70-80% is NORMAL - it will never go to 100% (by design).

In a few rare cases I have seen a stretched accelerator cable (required replacing) and a sticky throttle butterfly.

[bzguy]

Loren, I have a similar issue : some stumble on WOT, perfectly fluent under around 4000 rpm.

Checked the MAF (that's the one @ the airbox, right ?), cleaned it, looks ok. I removed it & test drove without MAF : nothing changes :(

If it's a bad MAF, how come that there's no stumble in lower rpm ?

[Loren]

The MAF primarily works at higher RPMs where the air flow is critical in determining the proper mixture. It does much less under 4000 RPM and almost nothing at idle.

The fact that you see no difference with it unplugged leads me to think it is not functioning at all. In most cases like that you also get a CEL and fault code(s).

[bzguy]

Thank you for your reply Loren !

So it might be not a bad idea for both of us to lend a MAF (since they're pretty expensive) to try if there would be any difference ?!

Btw : my MAF has a Mercedes logo on it, I'll check on the item number. Mine is a 1998 C2. Have it for 1 month now, I'll open a separate topic on it.

Greetings from Belgium, this forum has helped me IMMENSELY fixing small issues & doing maintenance :) !

[Loren]

Do not try just any MAF - you will need one from a like car with part number 996 606 123 00.

Do not use a 996 606 124 00 or 996 606 125 01 -- those are not suitable for your car.

[bzguy]

Thanx Loren ; I checked my MAF, it's the right part number.

How can I test/know if it's broken or not ? To avoid buying an expensive new one and finding out afterwards that there was nothing wrong with the previous one ;)

I checked mine : it's 996 606 123 00 (and has a Mercedes logo on the connector connecting to it ;) )

Edited August 1, 2013 by bzguy

[Loren]

You can try cleaning it - but use only MAF sensor cleaner (available at most auto parts stores).

If that does not improve performance then it will likely need to be replaced.

[bzguy]

I had an OBDII reader connected : no fault codes.

Bt since MAF's fail quite some, I ordered a new one. Hope it fixes the issue.

[Loren]

I had an OBDII reader connected : no fault codes.Bt since MAF's fail quite some, I ordered a new one. Hope it fixes the issue.

I suspect that your OBD2 reader does not pickup Porsche specific codes or pending fault codes.

[bzguy]

Can very much be Loren, since it's a universal cheap thingy ;)

I'm awaiting my new MAF sensor, I'll keep you up to date on the news ...

[Silver_TT]

Might be worth picking up a Durametric too while you're at it. Solving problems on these cars is a lot easier and cheaper when you are able to read the codes.

[RFM]

Durametric is provided by a German importer in Belgium which actually triple the US price + taxes. The result is that individuals do not buy because too expensive, you can at least 50 times to the dealer for a check, and you are still better off here. The dealer network (OPC) is also no problem, the maximum distance between costumer and dealer is merely 50 Km.

[RFM]

It must be "CONSUMER" of course. Sorry.

[JasonStern]

Durametric is provided by a German importer in Belgium which actually triple the US price + taxes. The result is that individuals do not buy because too expensive, you can at least 50 times to the dealer for a check, and you are still better off here. The dealer network (OPC) is also no problem, the maximum distance between costumer and dealer is merely 50 Km.

Durametric accepts orders directly and ships worldwide. You would still have to pay customs fees and, likely, a higher shipping and handling rate. But that would hopefully get you around the 300% markup that German importer charges.

[bzguy]

Durametric costs in Europe around 1000 $ (750 EUR)

[rallygabe]

Loren, and others-

If the MAF is not reading at all, as might be the case when unplugged=same performance, have you seen that not CEL-out? I think I am going to go try with mine unplugged as a test as well but curious about CEL as I only get P1123 right now.

I really wish my move was over so that I could get my durametric out and pull some numbers! :D

[JasonStern]

Durametric costs in Europe around 1000 $ (750 EUR)

I think you are referring to the professional kit and not the enthusiast kit. If you own less than three Porsches, it is more cost effective to buy the enthusiast kit, which costs $287, plus likely just under $200 in shipping and customs fees.

[bzguy]

Hi guys,

sorry, bit late with an update, had to wait for the replacement part :(

Got a new MAF sensor, installed it (literally takes 3 minutes), all works perfectly right now : no hesitation anymore above 4000 rpm, all very smooth & linear :) !

Thank you for all the help, the MAF was the culprit ;)

[bzguy]

BTW : I never had any CEL light on !