I will paypal $100 to the first person who can tell me how to fix my car.

[veget8]

Here's what I got today:

"Stone Cold" temperature sensor data:

Actual ambient temperature outside: 7.5 C
Fuel temp sensor: 10.8-11.7 C (toggling back and forth)
Coolant temp sensor: 10.8-11.7 C "
Intake air temp sensor: 6.3-6.5 C "

Unloaded WOT RPMs (redline is located at 4600)
-----------------------------------------------
Bosch TDI MAF : 4600, then immediately fall to 4250 and quiver
Pierburg MAF: 4600, then immediately fall to 4250 and quiver
Bosch 2.0 MAF: 4600, then fall to 4500 and quiver
Disconnected MAF: 4700 and holds steady. Noise, backfiring and lots of light grey smoke also noted, not present with MAFs connected

That's all I had time to get today. In all the cases I had the pedal to the floor until the car stopped accelerating. The missing plot is the boost with MAF disconnect. I will have to redo the run, but the RPMs maxed out at 3990 - definitely slightly higher than with any of the MAFs. Overall it had less power (low end and top end) as one might expect.

Also, note the interesting last plot- it was done on the interstate with the pedal held to the floor in 4th gear. Note the oscillation in the MAP actual, while the MAP request stays steady. Towards the end I started to go up a hill, so that's why RPM drops (not enough power to hold speed)

suggestion: If you want to compare any of these plots side by side, you can open them up in separate browsers. right click and go to "view image" or copy the link location and paste it into the new browser. If you have Firefox, you can use the tabbed browsing to rapidly switch between frames for an almost laid-on-top comparison.

Gotta run... I will post more later. Thanks as usual, lots of good stuff coming out here I think.
-Scott

 

[Fortuna Wolf]

Could it be possible that one or more of his valves are messed up? I'm hesitant to suggest that since his compression is good, but ...

Have you ever used any starter fluid?

 

[veget8]

Never used starter fluid. I have run lubrimoly diesel purge through it several times though, but I haven't heard anything bad about that stuff yet.

 

[Fortuna Wolf]

hm, Diesel purge is good stuff. I asked about the starter fluid because it can damage the valves.

 

[oldpoopie]

One more thing.... I know it sounds stupid, but get yourself a new fuel filter T. I think Dieselgeek sells them, so you could get a new filter too and just do it all at once.
Oh, or you could just bypass the return temporarily, or if you know someone with a tdi, borrow their "T" to test. I've seen a bad T or two cause funny issues.

 

[chromeBuddha]

While I believe your statement below is correct, I don't think it impacts my Wild Arse collapsing vacuum tube theory(more of a late night joke than theory). At higher RPM more vacuum is produced. The default, vacuum failure position for the VNT is such that the lowest boost will be produced. When there is a request for more air, it needs to be accompanied by more vacuum to actuate the N75 and move the veins toward their max boost position.

At higher RPMs it requires less vacuum on the turbo to produce the same amount of boost... I still think he should get a mechanical boost gauge.

 

[Fortuna Wolf]

chrome. Say that the vacuum hose collapses at 50% vacuum (so 50% actuation). At 2000 RPM it might produce 5 psi, but at 3000 rpm that might translate to 10 psi. It still wouldn't be flat.

Ok, lesse, more late night crackpot theories... Have you tried mainlining a can of diesel - completely bypass the fuel tank and filter?
THat would immediately rule out the filter, the T, the fuel lines, the tank, the tank sender, etc.

 

[veget8]

I have already changed the fuel filter in an effort to solve this problem, as mentioned in my first post, but I will try the can of diesel thing tonight or tommorrow night after work.

Also, I'll get a plot with MAF disconnected, that should be an interesting one. The car definitely revs higher with no MAF connected. Question: is there any other reason why the car would receive an improper reading from the MAF sensor besides a bad MAF sensor itself? I know the connector could be responsible, but I have packed it with dielectric. Harness? A sub assembly board seperate the ECU?

 

[bam_bam_dip]

Question: is there any other reason why the car would receive an improper reading from the MAF sensor besides a bad MAF sensor itself? I know the connector could be responsible, but I have packed it with dielectric. Harness? A sub assembly board seperate the ECU?

I think your beginning to see just how "touchy" these MAF's are.

Answer: I'm not convinced it is the MAF. Your MAF is just reading the air as it flows by. If, for some reason, there is a restriction in the airway, only so much air can get by, and thus the lower than requested actual MAF readings. Now, it is still possible that all the MAF's you have are not operating properly, but it is highly doubtful.

capiche??

 

[turbosc20]

almost sounds like a boostleak.

I remember when my pipe blew off... I gave it too much throttle: BOG. SPUTTER. SMOKE Damn cars with MAF sensors... Sees all that airflow but really the engine is not seeing it.

 

[golfstream]

Several have mentioned replacing the N75 valve... has this been done?

Sorry if I missed it.

Mel

 

[veget8]

BugBug- I've hooked up a vacuum gauge so I could watch the vacuum between the n75 and the turbo actuator, at the same time as the boost. I couldn't really figure out what I was seeing, so I will try to take some video and post it. There definitely seemed like there was vacuum when the ecu wanted there to be. Also, with the engine idling, there was something like 30 inches of vacuum.. so I guess there's no problem creating and holding vacuum.

Have you checked the applied vacuum from the vacuum pump while driving i.e. under load at full throtle?
I read somewhere that if the engine is cold, the ECU limits boost. If the coolant temp sensor is defective (I believe this is a dual element sensor (one for the ECU the other for the guage)), then the ECU is cutting your boost.
Let us know what you find.

 

[veget8]

I may have neglected to mention it, but yes, we did try replacing the N75 when I was at Herm's and it didn't make a difference.

Several have mentioned replacing the N75 valve... has this been done?

Sorry if I missed it.

Mel

 

[weedeater]

To me, it is noteworthy to see that the boost says up fairly well but the airflow drops off. Also, it drops off pretty consistently across all the MAFs you used.

So the pressure is staying up, but the flow is not.

If it were easy to do, I would remove the cat and everything behind it and try another run.

and I would look for that rat's nest in the intake...

 

[veget8]

Good observation weedeater, but that's probably an indication that the ECU is limiting the fueling based on the amount of airflow it sees. Less fuel means less air is required to maintain requested boost pressure, so if it is a restriction, it still could be on either side of the turbo.

So we're down to the following possibilities if it's air related:
1. Restriction in the intake path (but where? intercooler; intake ports on head)
2. Problem within the engine (i.e. valves not opening all the way)
3. Restriction in the downpipe (i didn't replace it, although I like to think it would have been obvious when the turbo and cat were replaced)
4. Problem with the air metering (MAF sensor voltages are being dampened or altered somehow)

Can anyone else verify that these have/haven't been ruled out, and what I can do to test for more specifics?

Thanks!

 

[Fortuna Wolf]

veget8, have you measured boost with a boost gauge, or is this all from vag-com?

 

[Galactic_Warrior]

Good observation weedeater, but that's probably an indication that the ECU is limiting the fueling based on the amount of airflow it sees. Less fuel means less air is required to maintain requested boost pressure, so if it is a restriction, it still could be on either side of the turbo.

So we're down to the following possibilities if it's air related:
1. Restriction in the intake path (but where? intercooler; intake ports on head)
2. Problem within the engine (i.e. valves not opening all the way)
3. Restriction in the downpipe (i didn't replace it, although I like to think it would have been obvious when the turbo and cat were replaced)
4. Problem with the air metering (MAF sensor voltages are being dampened or altered somehow)

Can anyone else verify that these have/haven't been ruled out, and what I can do to test for more specifics?

Thanks!

Based on the data and previous posts, I have to concurr with your listed possibilities. You have boost, but no flow and that leads me to believe there is either an intake flow resitriction or an electrical harness issue. The MAF's seem good (or at least consistant with each other)

I doubt that you have any exhaust restrictions since you have replaced the cat back and you are making boost. If you were not making boost, I would consider the exhaust a possibility, but without exhaust flow into and out of the turbo, there would be no boost. Confirming the MAP readings with a boost gage can only further confim this (still a good idea).

I would pull the cam cover and see what your cam lobes look like, since this is easier than pulling the intake. If you do not see appreciable wear and the lobes are normally shaped then it is not lileky the cam. Does anybody know the valve lift spec?

Next, I would pull the harness off the MAF sensor and the harness off the ECU and start checking for electrical gremlins. Check the resistance of each MAF lead to the ECU. Use your Bently for reference. I also suggest a digital VOM over an analog unit. Your resistances should be near zero. While you are checking each of the leads, wiggle the wires in the connectors, this could point out a poor or intermittant connection.

Finally, either find an industrial boroscope and look down the intake, or pull the intake and check the intake ports. It seems like you have covered all the rest. I also do not think you have an intercooler issue since the MAP sensor is at the exit of the intercooler. A clogged intercooler would indicate less boost.

My bet is either cam or intake ports. Why...all is well until the pressure builds near 1800 RPM. Then you have pressure and low flow (according to the MAF). Thsi indicates a downstream flow limitation.

Best of Luck!

 

[BugBug]

Veget8,

You mentioned that you have a race pipe installed. this would give you more air flow. along with the mufflerectomy reducing back pressure. Even more unresricted air flow.
Have you noticed any weak spots in any of the rubber air ducting? The MAF is set up for the stock air flow. with the race pipe and mufflerectomy the turbo might be pulling hard and causing a hole or rip to open in one of the rubber hoses. The MAF would indicate less and less flow as boost increases. Have you checked that none of the air hoses have rips or holes? There may be a rip in one of the hoses that may not be visible until you try to pull enough air through that hose, causing the rip to open.
If the problem is ever solved. I think this thread should be a sticky.
Good work with posting all the test results........

 

[jettajim]

Another thought.

I put a little dielectric grease around the GPs to keep out dirt & moisture--I did this just once about 2.5 yrs ago. When the grease gets hot, it migrates somehow between the boot and the GP thus preventing the signal between the boot and the GP. This throws a CEL and I have to remove the boots and wipe the inside off. I did this about 2.5 yrs ago and about twice a year, I still have to clean the connections. And this was just from a very very small amount of dielectric grease.

I don't know how sensitive the MAF connection is but you said you have it packed with dielectric grease. Maybe it's to much.

 

[mike944]

....... Finally, either find an industrial boroscope and look down the intake, or pull the intake and check the intake ports. It seems like you have covered all the rest. I also do not think you have an intercooler issue since the MAP sensor is at the exit of the intercooler. A clogged intercooler would indicate less boost.

My bet is either cam or intake ports. Why...all is well until the pressure builds near 1800 RPM. Then you have pressure and low flow (according to the MAF). Thsi indicates a downstream flow limitation.

Best of Luck!

I've got an industrial borescope, i can check the ports for clogging without dissasembling anything if you want, BUT.....I'm in central connecticut. Might be easier to just take the manifold off, and use a mirror and flashlight.

 

[veget8]

JettaJim- I was having this problem before I put the grease in, but good thought. I will try to extract some of the grease and see if that makes a difference.

BugBug- I have checked all the hoses and ducting several times and I haven't found anything so far. And thanks- I think I owe it to everyone who is trying to help me out to post good results in a prompt fashion.

Fortuna Wolf - I do have a boost gauge. The gauge drops as low as 10psi, and goes up to around 17-18psi, while doing these WOT acceleration tests. Does that concur with the VAG-Com plots I posted? i.e.:

GW- Thanks, I will check the camshaft this weekend, and if that looks good I will probably consider taking the IM off.

 

[Fortuna Wolf]

Hmmm, if those MAFs are telling the truth, then as the RPMs are increasing the air mass per stroke is decreasing, and then the relative pressure would also decrease. The only reason that I can imagine with a simple restriction that there would be a linear response is if there was a vacuum at the valves and the pressure differential was staying the same - but then I'd also expect to see boost having an effect. Unless, the restriction is before the air compressor.

It might be worth taking the hard plastic tube from the air compressor to the MAF off and checking for obstructions, but it just seems very very... weird.

Ok, here's another hypothesis, The plate you used to block off your exhast manifold is loose. At low RPMs there is low backpressure in the exhast manifold. As RPMs increase there is more and more back pressure, until it starts to push the plate off and exhast escapes. This escaping of exhast prevents the turbo from working and limits boost. As RPMs increase, the turbo's ability to produce boost is lessened and that gives the flat MAF response.

Can you get a graph of the RPM, MAP, and turbocharger/N75 duty cycle? Requested MAP, MAF, and requested MAF would also be helpful.
If as the RPMs go up and the MAP stays the same or lowers while the N75 duty cycle shoots up to 100% and stays there then either the turbocharger can't spin fast enough, or the air compressor isn't working.

 

[WantingaTDI]

Scott? Clogged fuel filter; iust a thought based on the loss of power.

 

[nicklockard]

If you inspect the rear of the engine carefully, do you find any soot streaks or spots {just working with FortunaWolf's hypothesis here}...

Also, please clarify: is that vag-com plot of the car under full load (driving uphill for example?)

 

[Fortuna Wolf]

Just wanting a bit more here. In neutral what can you rev the engine up to? You could remove the intake and exhast manifolds and redline a healthy engine (not that I advocate doing that).

If you are unable to get it to go past the RPM limit, get someone to work the gas pedal while you stick your head into the engine bay and listen for sounds of escaping gas or the smell of uncatalyzed exhaust.

 

[veget8]

Scott? Clogged fuel filter; iust a thought based on the loss of power.

Thanks for the suggestion, but fuel filter was replaced as mentioned in first post.

If you inspect the rear of the engine carefully, do you find any soot streaks or spots {just working with FortunaWolf's hypothesis here}...

Also, please clarify: is that vag-com plot of the car under full load (driving uphill for example?)

No soot streaks or spots are visible. Yes, the plot is under full load- I was driving up a very slight hill.

Just wanting a bit more here. In neutral what can you rev the engine up to? You could remove the intake and exhast manifolds and redline a healthy engine (not that I advocate doing that).

Please see "Unloaded WOT RPMs" at the top of page 3 of this thread. The redline was able to be reached and slightly exceeded with the MAF disconnected, and fell slightly short of redline with any of the MAF sensors.

If you are unable to get it to go past the RPM limit, get someone to work the gas pedal while you stick your head into the engine bay and listen for sounds of escaping gas or the smell of uncatalyzed exhaust.

This sounds like something to try. Thanks for the suggestion! Simple, yet effective
-Scott

 

[chromeBuddha]

That has to be magic, redline with the intake manifold removed...maybe circus folk spitting the diesel/air mixture into the head... JK and no offense intended. Just lack of sleep and circus folk on the brain...

Just wanting a bit more here. In neutral what can you rev the engine up to? You could remove the intake and exhast manifolds and redline a healthy engine (not that I advocate doing that).

If you are unable to get it to go past the RPM limit, get someone to work the gas pedal while you stick your head into the engine bay and listen for sounds of escaping gas or the smell of uncatalyzed exhaust.

 

[weedeater]

Can you do a run with IAT showing as well? I'm thinking about the intercooler...

 

[Rickstah]

Greetings,

Been away for awhile, but this sounds a lot like how mine acted when I sealed up the weep hole for the egr, accidently of course...it doesn't sound like you did anything to do that, but if your boost is getting knocked out by limp mode kicking in, I'm sure you have cleared the code? Also, just for grins, on my model year you can reset the ecu back to factory defaults by turning on the ignition without starting, then holding the fuel pedal down for at least ten seconds, then letting up and starting the car...this cleared something in mine that was causing some bad running conditions. I'm just spent, now , hope it works out.

 

[nicklockard]

Rickstah mentions the key reset procedure, which I've used sucessfully to clear up smoke issues with Ups-I chips before...


Have you tried it (long shot here, but can't hurt anything.)

1. depress accelerator to floor and hold
2. turn key to 'on' but don't start car--hold 15 seconds
3. turn key off, release foot from pedal. Wait 1.0 minutes for TPS to reset zero
4. start car normally.