Need some help diagnosing low power/boost problem

[SilveR316]

Recently, my car started performing pretty bad when I would hit the accelerator in the 2k rpm and up range.

I have a boost guage installed and before this problem, the boost would regularly spike up to 20 psi, and settle around 15 for hard acceleration. It would sit at around 5-6 psi when cruising on the freeway.

Now that this problem started, Im finding that the boost has a really hard time going up. On hard acceleration it slowly creeps up until it hits about 9-10psi max at 4k rpm. Regular driving produces no boost at all. Hiting the accelerator anywhere above 2k rpm will do next to nothing and the car will accelerate rather slowly compared to what it used to do, probably because there is almost no boost from the turbo.

I can hear the turbo whistling pretty nicely while accelerating so I don't think theres a problem with it. I also disconnected the MAF, which decreased performance even further.


Does anyone have any ideas as to what it might be?

 

[SilveR316]

I got a chance to pull the codes from the computer, and it returned a P1144 MAF Open/short to ground.

Would that be caused by disconnecting the MAF or by a faulty MAF?

 

[Uncle_Dave]

Why not put the MAF back in, or was it a test?

Toronto? The Don Valley, How about that Don Valley VW? So you are becoming a DIY type also?

Check Engine Light on?

I have the same problem. Have been puting light oil on the Vaccum linkage, seems to have helped, but not fixed it so far.

 

[gt]

low power

What year? how many miles on it? Stick or auto/tr.? It helps to know what we are trying to diagnois. It sounds like real slow timing or clogged intake, but that is just a guess, cause I don't know what we are working on. Could be wastegate solenoid valve. gt

 

[SilveR316]

No stealerships for me, Im a DIY'er. But this one has me a bit puzzled.

CEL was on, but went off after a few trips.

Its a 2000 Golf TDI 5 speed stick, with 213k KM on it. Timing belt is due for a replacement soon, but I just checked the belt and it looks like it is in tip top shape. Looks can be decieving though I guess.

 

[bodycounter]

I would say you might want to check the IP case pressure relief valve. If it starts to sense too much back pressure it will start to walk out of its normal position and this prevents the engine from advancing its timing under acceleration.

Its the ovalish connector that has two flats on it (i thinnk 11mm) at the rearleftish corner of the IP facing it from the front of the car.

Theres a thread on here somewhere. Ill post it if i can find it again.

Lee

 

[Canadian_Grizzly]

Has the intake ever been cleaned? Also does power return after you cycle the ignition? (which would indicate limp mode). Your CEL was probably stored after unplugging it previously. Start with an intake cleaning the link is in the writeup in the link in my signature. Keep us updated.

 

[Curious Chris]

Oh failed MAF will cause the boost to stop or go wierd as it goes governs the turbocharger with a whip. I would highly recommend changing the MAF. Or since you have VagCom do the classic diagnostic: warm engine, straight stretch of road with low probability of law enforcement, logging Specifed MAF, Actual MAF, Specified MAP, Actual MAP, and a field with throttle position (I like having throttle position as you want to analyse the data at 100% throttle as ECM adaptation is lowest there), 3rd or 4th gear 100% throttle from 2000-4200 rpm, repeat 3-5 times. Send the data to chris_idzerda@yahoo.com and I will do the analysis and return to you. I am an engineer/statistician/gearhead.

 

[JBT4]

I'm sorry to jump in on this thread, but as you are undoubtedly pretty damn knowledgeable about TDis, could you please advise me of the necessary groups I need to log with VAG-COM to try to diagnose my 1998 T4 2.5TDi (ACV) lack of power problem (no boost?).
I did post earlier in the week here. The actual log files I've done so far are currently posted in the 'Files' area on the VAG-COM Yahoo Group.
Regards.

JB

 

[SilveR316]

I think it may be the MAF. Power does not return by turning the engine off and on again.

I was coming home from work today and accelerating, when all of a sudden the car seemed to loose the little power it had and the boost instantly dropped from 10psi to next to nothing (like 1-2 psi according to my gauge). Cycling the engine off and on did nothing so I know its not limp mode.

I'll go out in a sec with vagcom to check the MAF values as suggested by Chris.

Where is the best/cheapest place to get a new MAF sensor?

 

[rdkern]

You should have an error code stored. Since you have vagcom, let us know what it is.

 

[P2B]

Ross-Tech's instructions for logging MAF and MAP with VAG-COM are here

This should be the first step in diagnosing all limp mode and/or power loss problems.

Simon

 

[SilveR316]

So I went out and tested my MAF with vag com.

IDLE
Requested: about 370
Actual: about 420

FULL LOAD
Requested: 850
Actual: maxed out around 490 at 3.5k rpm at WOT going up a steep hill


So I unplugged my MAF sensor after that, and my Actual value stayed steady at 550, which leads me to believe the MAF is bad. My boost actually went up to about 5-6psi under hard acceleration with the MAF disconnected, whereas with it connected it got up to no more than 2psi or so.

Guess I will be driving around with the MAF disconnected until I get a new one.



I also checked the codes. I got this one, cleared it, and a few minutes later got the same one.

17964 - Charge Pressure Control: Negative Deviation
P1556 - 35-00

 

[alphaseinor]

Negative deviation is underboost... usually a clogged intake, collapsing vacuum line, or clogged turbo.

 

[P2B]

You definitely have a bad MAF if it won't go over 490. The ECU uses 550 when the MAF signal is missing - it should also have set a MAF code when you disconnected.

I would call Precisiontuning about a new MAF - he is cheaper and faster than the dealer.

Simon

 

[SilveR316]

Ill probably pick up the MAF from precisiontuning tomorrow on the way home from work.

I did some poking around under the hood just now, and hooked up a vacuum tester to the vacuum line that attaches to the black round ball in the middle of th engine (sorry the name of it escapes me at the moment). With the engine off, it did not hold a vacuum... at all.

I followed the vacuum lines all the way down to where the one vacuum line attaches to the turbo by the passengers feet, and pinched the line. It held vacuum rather well this time. This leads me to believe I dont have a leak anywhere in the vacuum lines. Correct me if Im wrong.

Now I watched the following video from the VNT repair procedure thread at the top of the forums.

http://pics.tdiclub.com/data/500/2006_0603_175432AB.AVI

Is the actuator rod supposed to move like that while the whole exhaust/turbo is in place and attached to the engine? I tried to move it and it wouldn't budge at all. Is this possibly the source of the problem?

 

[P2B]

Is the actuator rod supposed to move like that while the whole exhaust/turbo is in place and attached to the engine? I tried to move it and it wouldn't budge at all. Is this possibly the source of the problem?

Fire up your VAG-COM again and look for the ECU output tests. One of them exercises the actuator. The rod should move smoothly in both directions 2-3 times (until the vacuum reserve runs out). Total travel should be about 2cm.

Simon

 

[SilveR316]

I took a look for that earlier today but couldn't find it in vagcom. Any tips on where to go?

 

[P2B]

Open the Engine control module (01) then click on Output Tests - 03 under Advanced Functions.

http://www.ross-tech.com/vag-com/tour/open_screen.html
http://www.ross-tech.com/vag-com/tour/out_test.html

Simon

 

[SilveR316]

So I just did the output tests.

Some of tests activated certain valves near where the n75, and I could hear them clicking softly with the engine off.

I come to the test that is supposed to excersize the actuator/wastegate solenoid and it did absolutely nothing. No clicks, no movements, nothing, just dead silence.

Ideas?

 

[rdkern]

It's N75 time - unless you have a bad connection.

If it were mine, I'd buy the N75.

 

[P2B]

rdkern may well be right...

I don't remember the A4 output test sequence (I have an A3 - completely different boost control setup), but I believe you are supposed to have the engine running when you start the tests (builds vacuum), one of the tests is N109 which shuts the engine down, and the vacuum solenoid tests are after that. If the EGR solenoid test is before the N75 test, it's possible you have to click next quickly on the EGR test to avoid using up the vacuum reserve before you get to the N75 test.

On the A4 you can also swap the EGR and N75 solenoids as a test.

If you have a DMM, the solenoid coil resistance should be about 30 ohms. It runs on 12v, so you can also test it by disconnecting the harness and running wires from the battery.

Simon