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Discussion Starter #1
I have a 2006 Jetta that seems to have "flat" spots during acceleration. There are a couple of spots during acceleration where the car seems to have less power and when you get past them - it seems to have a rush of power - almost to the point of breaking the tires lose. The most noticeable one is around 2K RPMs. It is very consistent behavior which will hopefully help figure out the cause. It also seems to smoke more when we start the car.

This first started happening during a trip to Colorado (from Minnesota) when we were just getting into the mountains. At the time, I thought it may be been from some bad fuel - since we had just refueled. But it has continued for the rest of the trip and has done so for many months since.

I just ordered the Ross Tech VAG to help with the diagnosis. Any ideas?
 

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If it's almost to the point of breaking the tires loose there's a pretty big problem. Is the flat spot always there? Normally, flat spots or bucking is a boost leak but your description of the rush of power is unusual.
 

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Discussion Starter #3
The flat spots are pretty consistently in the same places. Depending on how hard you are accelerating, the feeling is less or more. I exaggerated a bit with the breaking loose of the tires but when it gets past the one at 2K rpm's, it feels likes a pretty strong surge. I have listened for differences in the turbo sounds but it seems to sound as expected - not a huge difference after the flat spot.

As I mentioned, this happened last year when we were just about to the mountains in CO. We had just re-fueled and got stuck behind a slow truck. I had to really step it down to pass and after that it seemed to run differently with this problem. I don't recall hearing a "bang" or any other noises but it sure seemed like it all started at that time. I should also say that occasionally, I used to hear what sounded like "fluttering" when accelerating. Not knowing that much about how the turbo functions, I thought it sounded like a waste gate valve chattering. I took it to the dealer (since it was still under warranty back then) and they didn't find anything. I don't hear that sound much anymore so I don't know if that is related or not.
 

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Overall miles on the car?

Look through the FAQ for an article on low power. After you get the VCDS, log the MAF readings, EGR readings, and MAP (turbo boost) readings. Also check for boost leaks or broken vacuum lines.

While I haven't heard of this happening on a BRM engine, I've heard of earlier TDI engine turbo wheels grinding away on the housings. It rubs and then gives way which could cause lack of power and then a surge. This is just a total guess because of the conditions which you said it first appeared. It could be something else.

Because you said it happened after you were in the mountains and heard fluttering, it's possible the thin air combined with low RPM - high power request cause the turbo wheel to surge to the point of failure. Basically, the turbine can't work right under the conditions and is shaken/slowed by buffeting air. It's possible that this causes turbine-housing contact which either breaks the wheel or shaft. I'm not saying this is what happened, but it's a guess based on the fact that you said it happened when you were in the mountains (thin air), were stuck behind a slow truck (probably low engine rpm), sudden power request, and it didn't sound right after that. Especially at high altitudes, shift and rev the engine higher. It's also possible the bearing happened to go out or go out because of surging and a damaged turbo wheel.

If this is the case (just a guess) I would go back to the dealer and tell them to check the turbo wheels and that it was under warranty when you first had this problem which they didn't fix at the time. And of course, it was caused by a manufacturer defect that would be covered by the warranty which the dealer should have fixed at the time.

If the turbo bearings start pouring engine oil you can get a smoky exhaust or oil into the intake which causes a runaway engine: http://www.myturbodiesel.com/1000q/stop-runaway-diesel-engine-how-to.htm
 

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Discussion Starter #5
Thanks for the suggestions chittychittybangbang!

The car has 118K miles on it. I received the Ross Tech Vag last night and was testing it out today. It is quite an amazing tool for diagnosis! Initially, I focused on the MAF and the turbo boost. Based on the values (up to over 1000) on the MAF, I think it is ok. I did see something in the turbo boost graph that might explain what I am feeling when we accelerate. In the attached images from VC-Scope, the red line is the RPM, the green line is the MAF (actual), the yellow line is the boost (specified) and the light gray is the boost (actual). When I feel the car surge around 2K RPM's is when the boost (actual) spikes above the specified boost. It just seems to last a short time and then it drops back to where it should be. I can easily reproduce this condition when accelerating in 2nd or 3rd gear from around 1500 RPM - once it gets close to 2000 RPM, this spike occurs and I feel the surge of power.

Is this normal to see this spike or does it point us to the cause of the problem?

Also, I am planning to replace the timing belt this weekend and therefore will have part of the engine disassembled so it would be a good time to check out components around the turbo, etc...
 

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I think boost spikes are normal because of turbo lag. Is there a way to check fuel delivery through VCDS? Maybe the lift pump is dying?
 

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pic#1 first few spikes are abnormal because it looks like you were rapidly moving the engine rpm up and down. This can cause lagging. The next few look normal. It's normal to have a small spike before turbo boost levels off. pic #2 last few spike look abnormal to me because engine rpm goes up but turbo boost doesn't. The question is why, if the car was not revving in neutral. Was that one of the power lags you feel?

When the engine is coasting down the turbo is relaxed which is why you see turbo boost drop down to a base level.
 

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Low power 1.9 TDI 115

Low power: Simultaneous Factors?

First of all, thank you very much for the information. I learnt in some days more than by assisting my father to tinker his Peugeot

The problem

I noticed some months ago a whistling just after stopping the engine. It seems that it came from the catalyst. My garage owner found nothing of abnormal. Then, this noise disappeared.
There was also a sort of smell of exhaust gas.

At the same time, the engine switched to limp mode (rough low power). My garage owner cleaned the EGR, but the problem persisted. He suggested then cleaning the turbo.

I then made move the VNT stalk. This operation doesn’t resolve the problem.

During the time of reflection, the Low power and the switches to limp mode become more frequent, even from the first meters of the first hill… The Low power became permanent.

At the same time, appeared a consumption of cooling water and a light smell. My garage owner put the cooling circuit under pressure and found no leak. I am nevertheless going to change the thermostat.

Concerning the Low power, he suspected the MAF sensor by saying I could by lucky.
To verify, I disconnected this sensor. I noticed an increase of power. The car better took up hills.

I thus changed the MAF sensor but it doesn’t resolve the problem.

The tests

I learnt the existence of the cable VAG-COM as well as a heap of information about turbo-compressors and engines TDI. Thanks again. I became better equipped than my garage owner. In fact, I live in the country side and the nearest VW and Ford garages are 30 km far.

The tool of diagnosis VAG-COM finds this, which directs to N75 fail:

17964 / P1556 - Load(Charge) Pressure Control: Negative Deviation.

I noticed visually that the VNT stalk doesn’t move.
To verify it by driving on road, I placed a scrap of paper in the abutment of the stalk near the depression valve and drove the car by hills. The paper did not move in this experience.
In a second experience I reset many times the management unit of the engine, switching off/on
the ignition. Suddenly, the car accelerated with a little of delay with regard to gaz pedal. It pushed me… then… the limp mode again. The scrap of paper had disappeared.

I made measures with cable. The following tables recapitulate the results:

MAF /EGR duty
EngineSpeed/MAFSpecified/Actual MAF/EGR duty cycle/ Coolant temp.
903/Mn 260.0 Mg / R 396.9 Mg / R 84,5 % 27.9°C
903/Mn 250.0 Mg / R 377.3 Mg / R 84,5 % 63.0°C
2331/Mn 260.0 Mg / R 362.6 Mg / R 84,5 % 71.1°C
3066/Mn 350.0 Mg / R 372.4 Mg / R 84,5 % 70.2°C

Pressure
EnginSpeed/SpecIntakePress/ActualIntakePress/D.CycleMAP/Coolant temp.
903/Mn 999.6 Mbar 999.6 Mbar 19.9 % 72.0°C
1743/Mn 1050.6 Mbar 999.6 Mbar 59.0 % 72.0°C
2898/Mn 1173.0 Mg / R 1020.0 Mg / R 50.2 % 52.2°C
2982/Mn 1183.2 Mg / R 1020.0 Mg / R 50.6 % 72.9°C

I noticed that, by accelerating between 903 and 1100 / mm, the actual pressure less is than the atmospheric pressure and the specified pressure.

I did not make measures by driving, because it is dangerous.

What diagnoses?

Actually, I do not know. That is why I raise the problem.
I think however that the problem comes from one of following devices: N75, MAF sensor or G71...

By hoping that the problem and the tests which I made shall help, I ask you to help me to find out the exact cause. D’avance, merci beaucoup.

Anne-Marie
 

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Discussion Starter #9
pic#1 first few spikes are abnormal because it looks like you were rapidly moving the engine rpm up and down. This can cause lagging. The next few look normal. It's normal to have a small spike before turbo boost levels off. pic #2 last few spike look abnormal to me because engine rpm goes up but turbo boost doesn't. The question is why, if the car was not revving in neutral. Was that one of the power lags you feel?

When the engine is coasting down the turbo is relaxed which is why you see turbo boost drop down to a base level.
In pic #1, I was accelerating hard and the up and down you see is the shifting through gears (2nd, 3rd, and 4th - if I recall). In each gear, as it passed the 2K RPM mark, I would feel the surge and I believe that corresponds with the boost spikes we see. In that test, I didn't let off of the accelerator pedal and I am not sure what drops the boost back down to "normal". Whatever does that - perhaps it is sticking or moving too slow so it doesn't release quickly enough. I am wondering if maybe the accelerator pedal or throttle position sensor is telling the wrong info. Also, it seems like in neutral, it is hard to keep the engine running at just under 2K RPM. It always wants to run above 2K. And when accelerating, as previously stated, it seems "flat" from say 1800 - 2000 and then has this power surge. I saw the test of the accelerator pedal in the VAG but didn't see anything for the TPS - is there a way to test it?

Thanks for the ideas...
 

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Jetta Fan, have you checked the camshaft?

azigui, why did the coolant temp drop from 72 to 52? I assume that was a typo but in the first data set you have it from 29 to to 63. Was the car still warming up? That error code is either a boost leak, boost too low, or sticking turbo. Does the turbo rod move like in the videos for fixing limp mode? It sounds like your rod is sticking since you said you did a test.
 

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Jetta Fan, have you checked the camshaft?

azigui, why did the coolant temp drop from 72 to 52? I assume that was a typo but in the first data set you have it from 29 to to 63. Was the car still warming up? That error code is either a boost leak, boost too low, or sticking turbo. Does the turbo rod move like in the videos for fixing limp mode? It sounds like your rod is sticking since you said you did a test.
Thank you grizzly,

Temperature:
The temperature was progressive from 29 to 72, but I classifyed the data by rpm values. On the other hand, the temperature shown on the dashboard indicates between 85 and 90°C when VAG indicates 72°C! Is it normal?

MAF and pressure:
The measures are made in neutral. For every measure, I let the sensors stabilize. The MAF sensor is new.
I think it’s normal that the measured MF is less than the values specified, because the turbo wasn’t active (the stalk didn’t move) and therefore, it didn’t suck up enough air.
This can also explain the measured pressure is less than the specified. But then, why the computer doesn’t move the stalk? Maybe it tries and that the N75 is out of order?

The stalk:
The stalk doesn’t move it self. It’s maintained by a spring against the abutment. I stopped the engine and moved the stalk using my finger, without any jerk. After that, I put my tests paper, and drove over hills.
- First, without switching ignition: --> permanent low power all the time. The stalk did not move (paper stayed in position).
- Second, with switching ignition several times: --> sudden Gush of the power (with delay on the pedal). The stalk moved! (the piece of paper has disappeared). After that...limp mode again.
How to explain this behaviour?

What would be then the good diagnosis?

Anne-Marie
 

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The dashboard always says the same coolant temperature unless it's too hot or too cold. They do this so it points straight up.

I don't think a piece of paper is a good indicator of if it's working. Get a vacuum pump and test the vacuum lines too. The lines are old and could be leaking. The N75 solenoid could be bad too. You can temporarily swap it with the EGR solenoid as a test.
 

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Thank you Vent5 for the suggestion. I'll switch câbles and vacuum lines of N75 and EGR. I hope that the connectores are compatibles.
Will this fill your suggestion ?
Anne-Marie
 

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Ok, Thank you CCBB.
I just can't find the N75 solenoïd! I followed the vacuum line from the turbo VNT, but it goes far to the fund. Where is it ?
I don't find any help on the net. My car is a VW Sharan 1,9TDI 115 (mk4 gen)..
Anne-Marie
 

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It should look like a little plastic tube with hoses and a wire coming out of it. Here is the diagram for an ALH engine, follow the hoses. They are normally mounted on a bracket or the firewall.
 

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It should look like a little plastic tube with hoses and a wire coming out of it. Here is the diagram for an ALH engine, follow the hoses. They are normally mounted on a bracket or the firewall.
Thanks again. I found the 2 solemoïds (EGR and N75) and I swop them. But the test failed for worse: Low power as before and no reaction to the reset. The vacuum system seems to work good (I tested it with my finger before connecting it to the last solenoïd).
Does it means that both the solenoïds are out of order?
However, I didn't notice any black smoke during the test.
What's your feeling ?
Regards.
 

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Not sure if both are working or both are not working. There are tests through VCDS that can let you know if the N75 is working. It's in the engine module. If the N75 is working the EGR solenoid is also probably working.
 

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bad actuator

I have the EXACT problem on my 2005.5 Jetta TDI, 120,000 miles. On acceleration under 2000rmp and especially under load as when going uphill, I get no power, black smoke.. take my foot off the gas and then put back on and car will run better and then take off like a rocket. My son works for Volkswagen. His research leads him to believe it is a bad actuator. They can be bought separately (but not from VW who will only sell you a new turbo for a grand). He is calling the company tomorrow to make sure their part will fit the stock turbo. If yes, he is ordering and I will have installed next weekend. Part goes for 139.00. I will keep you posted.
 

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I have the EXACT problem on my 2005.5 Jetta TDI, 120,000 miles. On acceleration under 2000rmp and especially under load as when going uphill, I get no power, black smoke.. take my foot off the gas and then put back on and car will run better and then take off like a rocket. My son works for Volkswagen. His research leads him to believe it is a bad actuator. They can be bought separately (but not from VW who will only sell you a new turbo for a grand). He is calling the company tomorrow to make sure their part will fit the stock turbo. If yes, he is ordering and I will have installed next weekend. Part goes for 139.00. I will keep you posted.
Have you read this article in the FAQ section?

www.myturbodiesel.com/1000q/a4/VNT-wastegate-adjust.htm

If you click on the links to vendors they sell it for even less.
 
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