[willicar]

Hi everyone!
I have this 2001 jetta tdi that has lower than expected power. Here is a list of things done or checked in the past year or so:

regular upkeep (brake, tires, regular oil changes etc...)
fuel pump timing (somewhat scattered but within spec)
intake manifold cleaned.
turbocharger was checked for sticky vanes
new wastegate actuator and its vacuum valve.

None of these really did the trick. With the idea that a weak fuel pump may not deliver as much fuel as it should (the scattered timing as symptom) I replaced the stock nozzles with 205s (generic... i did not read this forum yet).
The power did go up after appropriate re-tuning, but now there's a a positive pressure deviation in the intake manifold. The car performs well until one requests a bit more power, at which it sets the code and shuts off the turbo. Restarting solves the turbo shutoff, and the code is cleared within a day of driving.
From logging the pressure seems to go well above 1200 mbar and the setpoint is 1020 mbar (if I remember correctly).
I have the impression that it is mechanically fine but there's some subtlety in the programming I'm missing:
With more fuel there is the necessity of more airmass delivery, which is easily achieved with higher pressure. If the ECU lookup table remains unvaried the controller will detect an overpressure. (two lines with different slope will eventually diverge beyond tolerance)
I seem not to find a way to access neither lookup table nor pressure setpoint... which tells me my reasoning is wrong somewhere.

Does anybody have an idea? Suggestions?

Thanks

 

[chittychittybangbang]

When dataloging, try a smooth roll and a sudden acceleration. You should notice that the smooth roll has boost requested vs. boost actual close. In a sudden acceleration, you may notice an initial spike and then level off. This is also normal. The question is how big is the spike, and if it doesn't correct that is a problem. Are you using VCDS? If so, it has some helper numbers if you hold the mouse over the measuring block. These are in the label files, the 2001 shouldn't have anything new recently. I don't know where you could find the exact map unless you know how to read the chip mapping, you just have to datalog and see if everything seems right or not.

Some other questions: did you vaccum test where the wastegate actuator moves and that it holds pressure?

Here is the low power checklist, it sounds like you've already done most of the common causes but double check: http://www.myturbodiesel.com/1000q/multi/low-power-fix-TDI.htm

 

[willicar]

Just for reference: it turns out that the dealer I had bought the car from had done a bad job in replacing the timing belt. This in turn created unusual carbon buildup in the intake manifold (after cleaning once it took only 20k miles to go back to clogged), and in the exhaust. Particularly the CAT was clogged and the volumetric efficiency (how well you can empty and fill the cylinders) clearly dropped reducing power.

New timing belt (with special tool) and intake cleaning seem to have done the job.