Solved. See last post.

This winter I've done some work on my 2001 996 turbo.
After start-up, the engine doesn't behave like expected. I will try to explain the symptoms and what work I have done that might have caused this.

Work done:
- Clutch change with light-weight flywheel installed. Removed tranny with engine in car. I didn't have any problems doing this clutch/flywheel install. Thank you for excellent DIY: https://www.6speedonline.com/forums/...h-install.html
- Pressurized intake by plumbing one side after turbo and pressurizing before the other turbo. Small leaks found at venturi tube #9 leading to brake booster so I have trouble getting pressure above 0.8 - 0.9 bar, but this pressure it will hold for a long time. I have read the topics about this: https://www.6speedonline.com/forums/...-w-pics-7.html ; https://www.6speedonline.com/forums/...ressure-4.html and https://www.6speedonline.com/forums/...re-leak-2.html No difference to the pressure it hold if i pressurize at the 3,5" intake.
- When pressurizing at turbos i have leaks past the infamous #16 check valve that leaks pressure to the pipe before the turbo. This fault is passed for further testing by pressurizing before the pipe #14 leading to the turbo.
- Swapping the cyclic valve, as a precautionary measure since I've been told this fails regularly.
- When pressurizing the system i read 0.8-0.9 bar on my aftermarket boost meter at manifold, but if ignition is on, the car tells me 0,3. Where is the original pressure sensor located? Could this sensor be faulty, or a leak in this line?

Symptoms:
- Engine starts, but not as easily as it should.
- Engine idles, but not very stable, and I really feel idle is lower than usual. Now its high 500 to about 650rpm. Idle is not stable and the engine may stop any time. Seems its more stable when its cold, but after 1-2 minutes when it warms up a bit and idle drops it might stall.
- Super sluggish throttle response. If i hit the throttle there is no initial response, but after a little while(1-2 sec or even as long as 5-10 sec sometimes) it starts to respond, but very sluggishly. If i give some throttle and hold it, I'm able to hold it at fairly stable rpm. At rpm the throttle response is ok.
- If i go off the throttle its sure to stall out.
- Low vacuum reading at idle, as low as 2-3-4 psi - this is much higher if i rev to 3000 and the release the throttle. Normal?
- Usually no fault codes but P0238 and P1250 may appear on different instances.

My theories:
- My initial thought was major vacuum leak so that it pulls air that doesn't pass the maf. However, when i pressurize the system I cant find any vacuum-leaks so major they should cause this. I'm pretty sure there is no major vacuum to atmosphere, but I'll never be 100% on this. Intercooler-pipes seem tight and diverter valves are fairly new forge-billet.
- Could there be a valve-failure in the vacuum system other that the check-valves and the venturi tube?
- Could new flywheel be different than original? Could ignition therefore be off? I wouldn't think the engine would run at all if this was the case. I don't think its at all possible to mount the flywheel incorrectly, but it would be great to rule this out.
- Any electrical failure. Broken sensor or wires? However when i run durametric, sometimes I don't get any fault codes, but i can sometimes get P0238 and other times P1250. When i read actual values, the MAF-reading seem fine although I don't know what the values should actually be. How to go about testing different things here?
- Any thing wrong with my throttle body? How to test this? I have no idea how this e-throttle works or fails.
- Could I possible have damaged anything when I pressurized the system? I'm absolutely sure I've never had input at more than 1,5 bar or ~22 psi trough a car-tire valve.

I have not taken the car out of my workshop and do not know what happens if I put it under load.

I feel I've tested what I can based on my limited knowledge. Now I don't know what to do next.
I'll appreciate any suggestions and any help on where to go from here.

Immages are on loan from delamarearnaud thread, used for reference:



Reason for edit: "Solved!" See last post.

 

welcome to the forum and the check valve leak lol.

i'll be learning from your post(s). rep pts for your first. for sure.

 

Welcome you'll get some good tech help here.

 

It sounds like you've checkout your air supply quite well - how about fuel?

You don't need the MAF for start & idle so that's not your problem. The car should idle at 800 RPM.

 

That's odd as my Audi tt will act up when cold and MAF has always cured it.

 

My car acts about the same at idle with MAF disconnected.
Shouldn't be fuel as the response improves so much at higher rpms?
I have no idea about how to check on fuel. I'm gonna replace the faulty valves but I'm gonna be really surprised if that does anything. But one lead is that the original boost meter doesn't show correct value when engine is under pressure with ignition on?

 

I've never done it on this car, but throttle position sensor re-calibration comes to mind as well. It is really easy on most cars - you may need Durametric for the 996TT. Perhaps someone can chime in who has done it...

 

i dont know why you'd be surprised? if you have bad check valves which are plastic and get brittle and crack, they create leaks that affect boost. just hope its that simple! was for me, once found! lol

hey, dont forget to re-calibrate the TB after disconnecting the MAF. people often do. turn on the key to "on" for 30/45 seconds until you hear the tb reset itself.
then tun off key, and restart normally.

 

smoke test for vacuum leaks pressure test for boost leaks

 

Thanks for the help so far.
Now with leaks eliminated, problem is still the same.

I've now compared actual valuse at MAF-meter with durametric. At 600rpm idle my values are around 40kg/h while 16-20kg/h is specified at ~740rpm idle speed. Together with my very low idle vacuum it makes sense that this reading is correct. The fact that nothing changes when i disconnect the MAF-sensor indicates that its not sending wrong values.

Im now thinking that my flywheel is actually off, so my reference sensor is reading wrong position of the crank and that i therefor have a wrong ignition timing. If ignition is way retarded, the symptoms make sense.

Is it possible to check this without taking out the new flywheel and comparing it to my old one? (its a lot of work)
Is it possible to make the car adapt to the new flywheel?

I would really like to rule out that my flywheel is off, or confirm that its faulty.

 

I'm still thinking throttle calibration would fix this. It Doesn't look too complicated...



EDIT: I would disconnect the battery first to make sure you are starting from scratch.

 

Adaption routine didn't do anything.
Anybody know how to check ignition timing and flywheel?

 

You havent damaged the crank sensor when changing flywheels etc? at least check the gap.

 

After eliminating all other logical explanations for my problems that i could think off, I took the whole car apart. I removed the new alu flywheel and compared it to the original one. This is what i found:



I just didn't expect this could be off, so I didn't check it before putting it in. Next time I'll check and double check all new hardware!!!

Seems I've been running approximately 30 degrees retardation - more than the engine management is able to compensate.

I've turned the reference ring one step and now it's exactly the same as original flywheel. So now I'm just waiting for new bolts and I'll put it all back together.

Been some frustrating weeks all for bad hardware.

 

Wow - so the new part was shipped having been improperly assembled?