TDI boost problem, please help...

[shox75]

just test drove a 91 Passat with a 00 TDI engine swap today, and it performed very well, however a problem kicks in. I'm new to TDI's, but very familliar with mechanical IDI's and how a turbo should work, i drive one.
At about 2500rpm when i was in 3rd gear 1/4 up a hill all of sudden the engine loses all turbo boost and can barely make the hill going 40kph. Then after slowing a couple of times the engine never regained the turbo. Until i shut the car off and restarted it. Then everything normal till i tryed the hill again, and same thing happens. It seems like something is blowing off the pressure of the turbo and not reseting till the engine is shut off and turned on again. Mechanically everything looked fine. Do these cars have an electronic wastegate that could be malfunctioning? Or is there some sort of safety poppet valve on the intake like IdI's?
I'm sure the turbo is functioning good, you can hear it spool up and the car has very good power, prior to the problem kicking in. For some reason it can't maintain high boost for more then i'm guessing 5-10 sec.

Anybody can help, it owuld be much appreciated. thanks, Sabi.

[zyewdall]

Hmmmm.  Do you have a boost gauge, or does it just feel like the turbo is giving out?  Is it possible that the computer isn't giving it fuel because it doesn't think there is boost, even though there is?  Any check engine light or codes?

[shox75]

i don't really know how this car is wired up, because it is a swap. SO i don't know if the check engine light is functional or not.
However, like i said, this cars runs perfect when first started up, and in the city it will run this way. However when you hit a long hill or the highway where it has to maintain a high boost for a period of time, the boost pressure just drops as if you blew an intercooler hose off. You can really feel the power loss. And then the car will run without the turbo until you turn it off and on again.

[malone]

Sounds like limp mode, possibly due to a boost deviation error. Do you have VAG-COM or have access to one? Check for fault codes in VAG-COM and if possible, log Channel 011 (under Engine > Measuring Blocks) from approx. 1,500 RPM to redline under WOT. Also record/log the same channel during the moment you lost power (i.e. up a hill), if possible.

Do it again while logging channel 003. You can log multiple channels simultaneously but I recommend one channel at a time because if you add another channel the sample rate for each channel will be decreased.

An aftermarket VAG-COM cable is around $50 USD. I used to sell them but I'm out of stock right now. The VAG-COM shareware is free and you'll be able to log said channels for no cost.

[shox75]

thanks for the help, i'll see what i can do and if i figure it out i'll post up again.
BTW: does the vag-com plug into the diagnostic port, i dont think this car has one!

[dubCanuck1]

Check the MAF connection as well. They're known to get a little corroded. Some dielectric silicone compound on the connectors should clear it up if that's the problem.

[malone]

thanks for the help, i'll see what i can do and if i figure it out i'll post up again.
BTW: does the vag-com plug into the diagnostic port, i dont think this car has one!

Yes, the diagnostic/OBD2 port, which looks like this:





Your port may be black in colour. Because you had a TDI swap the OBD2 port may not have been routed to your vehicle's interior. Pop the hood and check the wiring harness - see if you can locate the OBD2 port. It should be there; whoever did the TDI swap would have to be dimwitted to hack off the OBD2 port.

dubCanuck1's suggestion is good. VAG-COM channel 003 that I mentioned earlier will show MAF values to determine its health but seeing as you don't have VAG-COM right now, it won't hurt to physically check the MAF. They do wear out or fail often. In case you need a new one, tdiparts.com carries them: http://www.tdiparts.com/catalog/index.php?cPath=29_90_31&osCsid=4e89f8dd1c58628262121d4c22b7891a

[89gtx]

shox75,
have you resolved this problem?
i purchased an '02 tdi jetta this week, and i had this same problem yesterday. in my case, the car is factory stock, which leaves out the possiblity of any kind of a mistake during a swap. my problem was simmilar to your description. i was on a freeway at speed for over an hour and all was good untill i went to pass a big rig. as i changed lanes under power, i could feel the sudden loss of power. this problem continued as i made my way to a rest area. i left the car running and took a peek under the hood...i found nothing that i could see or smell out of place. i did notice the lack of the noise the turbo makes on spool up as my friend bliped the fuel peddal. once i had shut it off and started it up again, all was back to normal...turbo noise and power back to the way it was previously. i drove the car arround town for hours without problems and then let it sit at home for a few hours. last night i went on a hwy run just for kicks...about 80km out and then return after a coffee. the car ran fine untill about the last 15km (of a total of160ish). then the same thing happened on a hill this time...no boost no power. i cycled the ignition with the car in nutral, and regained both boost and the power it gives. 5 min latter, no boost no power. i cycled the ignition again and the power came back...but with a check engine light.
IF ANY ONE KNOWS WHAT IS CAUSEING THIS, PLEASE HELP.
i don't want to jack your thread shox75...i just want to know how to solve our common problem. thanx all.

[lord_verminaard]

Sounds like either a MAF, N75 valve or coolant temp sensor.  All of the three can make the car act like that, although MAF is most likely.  Good luck!

Brendan

[89gtx]

i had a chance to have my codes pulled up for me today. vag code 16492, manifold absolute pressure or barametric pressure hight input. so then in my case it is a manifold pressure sensor (G71) issue. i looked through the bently and can't find much on the sensor...just its location. anyone out there know how to test the sensor? if my problem is a boost spike, what could be causing it to happen only under the condition i posted above? i did test my wastegate by-pass regulator valve as per the bently...came in a 16 ohms... 14-20 in the bently.
if anyone has had experience with this, please chim in with your 5 cents. thanks all.

[QuickTD]

89gtx, I doubt very much that the pressure sensor is the problem, more likely that actual overboost is triggering the fault. Gunked up N75 valve (the coil resistance can be fine, but the mechanical portion of the valve can be faulty or dirty), sticking VNT vanes or cracked leaking vacuum hoses are likely causes. MAF failure will also trigger "limp mode" but with a code set for overboost I would concentrate my efforts on the boost control system.

[89gtx]

thanks for the heads up quicktd. i'll take a clooser look at it today.