1998 vw tdi questions. lost power under boost

jeremy153624

jeremy153624

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May 10, 2009
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seems like when im running down the interstate and when the engine gets a pretty good load on it. or when its boosting pretty hard. it just falls on its face almost like it blows a intercooler boot off or something. i can let out of it and it still runs the same. but if i pull up to a stop light and shut it off and start it up it comes right back to life and is very peppy. i dunno about these vws. any help i greatly appriciate. thanks. o yeah what kind of oil is best for this car? only has 12300 miles. thanks
 
Do you have a boost gauge installed?

Could be the vanes are sticking closed.
 
Sounds like overboost causing limp mode to me. Could be the van sticking on the turbo causing the turbo to overboost.

First you need to figure out if there are any codes.
 
turbom700 said:
Sounds like overboost causing limp mode to me. Could be the van sticking on the turbo causing the turbo to overboost.

First you need to figure out if there are any codes.
Click to expand...

I had the same thought. My 96 Passat did this.
 
ok 3 codes came up. po380 glow plug/ heater circuit A. po605D internal control module rom malfuntion. and P1550 manufacturer controlled vehicle speed, idle control and auxillary input. i dont think the glow plug code has anything to do with this but i figured id post it.
 
i googled the p1550 code. from what i gather i need to clean the soot out of my turbo. the vanes a sticking and throwing it into limp mode. then when i turn it off and back on it resets everything. guess ill just putt around til it warms up
 
What model is your 98? If it's a beetle, it has the ALH motor with a variable turbo. If its a Jetta, it'll be the AHU with a wastegate turbo. Easiest way to tell is if your valve cover is held on by 3 bolts in the center or 7 bolts around the perimeter.

The diagnosis for the two different engines for a low power complaint is wayyyyy different.
 
Ok! Now we can get somewhere!

First things first, you really should spend the money and buy Vag-Com. It's a necessity when working on these.

Second, join TDIClub and go to the MK3 TDI section


Now we can do some diagnosis. It sounds like you're experiencing limp mode. Usually, it's caused by either under or over boost. Your car uses a waste gated turbo, however the gate is computer controlled by a vacuum solenoid, not boost pressure. Screwy huh?

Seeing as how you said the car runs very well before it hits limp mode, I'm going to say that it's over boost. The very first thing to check are all your vacuum lines. A leak anywhere in the system will cause control problems with the turbo. While you're replacing vacuum lines, be sure to replace the one that runs from your upper charge pipe to the ecu under the raintray. While you're doing that, pull the ecu out and open it up. It has an internal map sensor and the hose inside the ecu loves to leak and cause all kinds of driveability issues.

Get all the lines changed and let me know what happens, we'll go from there if necessary.
 
On my 98 the last line I changed was the 3" line in
ecu, that was the one leaking.
 
i found a a few dry rotted lines im gonna replace them all. there is a line going into the firewall on the passenger side im guessing this is the one going to the ecm? it is also rotted and falling apart
 
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