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-   -   Mass Air or Turbo issue? (http://forums.tdiclub.com/showthread.php?t=494963)

montanajetta December 15th, 2018 21:39

Mass Air or Turbo issue?
 
New to TDI's and the forum. I have been searching the forums for an answer, with no luck. I have a 2002 Jetta Wagon have had a reduction in mpg and no power above 3400 rpm. I logged my Mass Air on my VCDS (as stated on ross tech) and noticed the graph was surging. I assumed I needed to replace my mass air sensor, until I noticed my boost followed the same wave. Does this still lead to a bad mass air sensor or another problem? Thanks for the help!
https://www.dropbox.com/s/gu9u4g2spp...graph.jpg?dl=0
https://www.dropbox.com/s/snafusgd50...graph.jpg?dl=0

2000alhVW December 15th, 2018 22:01

Seems VERY similar to my situation before I got it mostly fixed. My car had the exact same "MAF waves". Step on the pedal, MAF briefly gives a proper value, then falls, then comes back up a bit, falls, comes back up, falls. Each time the bounce gets lower and lower.

My car ran so poorly with the MAF plugged in, I drove with it unplugged just to be able to achieve high way speeds. The car was just plain gutless, and would slow to a stop up hills.

I would recommend a few easy, free tests:
First, unplug the MAF and see what changes.
Then unplug the vacuum line that goes down to the turbo vane actuator.

When I unplugged the vacuum line, it was like this weird...'calming of the storm'. Where my car had low power, but it...worked. I step on the pedal, it went faster. All my MAF graphs immediately whipped into shape, and it worked perfectly, just without the boost.

I eventually narrowed my issue down to my turbo vane actuator rod being out of adjustment and over boosting immediately, so my car would actually trip into limp mode at the very first throttle demand. It would literally go into limp mode on flat ground within .5 seconds of being started up.
When the computer trips limp mode, it cuts fuel heavily (among other things). So you've got low power on top of low power conditions.

When I disconnected the vacuum line (effectively removing the turbo from the equation), the turbo could no longer overboost and trip limp mode, so the computer spit proper fuel into the car based on proper MAF values.

But it could be other things too

montanajetta December 15th, 2018 22:14

Quote:

Originally Posted by 2000alhVW (Post 5465474)
Seems VERY similar to my situation before I got it mostly fixed. My car had the exact same "MAF waves". Step on the pedal, MAF briefly gives a proper value, then falls, then comes back up a bit, falls, comes back up, falls. Each time the bounce gets lower and lower.

My car ran so poorly with the MAF plugged in, I drove with it unplugged just to be able to achieve high way speeds. The car was just plain gutless, and would slow to a stop up hills.

I would recommend a few easy, free tests:
First, unplug the MAF and see what changes.
Then unplug the vacuum line that goes down to the turbo vane actuator.

When I unplugged the vacuum line, it was like this weird...'calming of the storm'. Where my car had low power, but it...worked. I step on the pedal,
it went faster. All my MAF graphs immediately whipped into shape, and it worked perfectly, just without the boost.

I eventually narrowed my issue down to my turbo vane actuator rod being out of adjustment and over boosting immediately, so my car would actually trip into limp mode at the very first throttle demand. It would literally go into limp mode on flat ground within .5 seconds of being started up.
When the computer trips limp mode, it cuts fuel heavily (among other things).
So you've got low power on top of low power conditions.

When I disconnected the vacuum line (effectively removing the turbo from the equation), the turbo could no longer overboost and trip limp mode, so the computer spit proper fuel into the car based on proper MAF values.

But it could be other things too


Interesting, I will try unplugging the mass air sensor tomorrow. Will the car go into limp mode without throwing a code? I donít seem to have any codes, and can still get up to speed and hold speed up hills, but after 33-3400 rpm itís like the can loses almost all power....

2000alhVW December 15th, 2018 22:27

Quote:

Originally Posted by montanajetta (Post 5465478)
Interesting, I will try unplugging the mass air sensor tomorrow. Will the car go into limp mode without throwing a code? I don’t seem to have any codes, and can still get up to speed and hold speed up hills, but after 33-3400 rpm it’s like the can loses almost all power....


"Can car go into limp mode without throwing a code?"

Short answer: Yes. My car NEVER threw a CEL (dash light illuminated) for ANYTHING, despite having pending and current codes logged. Additionally, I could drive my car for hundreds of miles in "limp mode" before ANY codes would show up when checking via VCDS. This sent me into somewhat of a fury that these ECMs are quite stupid.

Long answer:
I'm not really sure the answer of this. For a couple of reasons...
I've found this particular question/topic/point to be seldom directly talked about. The relationship between limp mode and CEL has gotten mixed answers when I've read.
The ambiguous part, for me, is the "limp mode" itself. Like, what is it really? I've poked around quite a bit with VCDS and haven't found any sort of data box or anything to indicate whether limp mode has been tripped or not. Maybe this is the fact that my car is an early version (2000) and not as intelligent as later models, but I'm almost convinced that the computer itself might not even know it's operating in limp mode.
It might just dumbly be bumped over to an alternate fuel map, similar to, say, open loop fueling during cold starts on a gas car.

To me, it would be super obvious computer logic. IF overboost, then throw into limp mode immediately (which it does) and then trip an overboost code which lights up CEL.
But no such thing happened for me. In my case, the ECM was utterly useless, and VCDS scanning/datalogging was only mildly helpful. I only solved my issues by getting down into nitty gritty old-fashioned mechanical diagnosis/logic.

indysoto December 15th, 2018 22:50

Clogged fuel filter? Or gunked up manifold?

montanajetta December 16th, 2018 05:53

Quote:

Originally Posted by 2000alhVW (Post 5465482)
"Can car go into limp mode without throwing a code?"

Short answer: Yes. My car NEVER threw a CEL (dash light illuminated) for ANYTHING, despite having pending and current codes logged. Additionally, I could drive my car for hundreds of miles in "limp mode" before ANY codes would show up when checking via VCDS. This sent me into somewhat of a fury that these ECMs are quite stupid.

Long answer:
I'm not really sure the answer of this. For a couple of reasons...
I've found this particular question/topic/point to be seldom directly talked about. The relationship between limp mode and CEL has gotten mixed answers when I've read.
The ambiguous part, for me, is the "limp mode" itself. Like, what is it really? I've poked around quite a bit with VCDS and haven't found any sort of data box or anything to indicate whether limp mode has been tripped or not. Maybe this is the fact that my car is an early version (2000) and not as intelligent as later models, but I'm almost convinced that the computer itself might not even know it's operating in limp mode.
It might just dumbly be bumped over to an alternate fuel map, similar to, say, open loop fueling during cold starts on a gas car.

To me, it would be super obvious computer logic. IF overboost, then throw into limp mode immediately (which it does) and then trip an overboost code which lights up CEL.
But no such thing happened for me. In my case, the ECM was utterly useless, and VCDS scanning/datalogging was only mildly helpful. I only solved my issues by getting down into nitty gritty old-fashioned mechanical diagnosis/logic.

Very interesting. I have been having this issue for a while. Good to see some possible answers.

montanajetta December 16th, 2018 05:58

Quote:

Originally Posted by indysoto (Post 5465487)
Clogged fuel filter? Or gunked up manifold?

I just replaced the fuel filter and ran a can of diesel purge. I also pulled the inter cooler and drained the oil at the same time.

I was leaning towards either the mass air sensor or a possible clogged intake manifold. I saw the tutorial on cleaning, is there a way to tell if it is clogged without pulling it all the way off?

eddieleephd December 16th, 2018 08:26

Look down the egr and see inside.

http://forums.tdiclub.com/showthread.php?t=179589

montanajetta December 16th, 2018 09:24

Quote:

Originally Posted by eddieleephd (Post 5465558)
Look down the egr and see inside.

http://forums.tdiclub.com/showthread.php?t=179589

I will check the EGR when I get home. Thanks for the link!

montanajetta December 16th, 2018 18:10

So I unplugged the Mass Air Sensor, No noticeable change. Not sure what that means. Any ideas? Pulled off the EGR and then the intake. It might be some of the problem.

https://www.dropbox.com/s/lfu771wcg1...%2008.jpg?dl=0

https://www.dropbox.com/s/bo9vudxbjs...%2039.jpg?dl=0

https://www.dropbox.com/s/924kel9gq3...%2047.jpg?dl=0

indysoto December 16th, 2018 21:00

Looks clogged!
It is the SUM = Your Problem
Merry Christmas!
You got a lump of Diesel coal ;)

mrfiat December 16th, 2018 22:16

I paid the NAPA machine shop $30 to clean my intake out. It's a messy job. People also burn out the gunk with a torch. (read up on the method here before trying it)

Nero Morg December 17th, 2018 00:07

Quote:

Originally Posted by mrfiat (Post 5465780)
I paid the NAPA machine shop $30 to clean my intake out. It's a messy job. People also burn out the gunk with a torch. (read up on the method here before trying it)

NAPA does that? So you mean the four days of soaking in Zep and scrubbing could have been avoided? I still have a flathead screwdriver covered in that sludge.

ToxicDoc December 17th, 2018 01:41

Quote:

Originally Posted by Nero Morg (Post 5465795)
NAPA does that? So you mean the four days of soaking in Zep and scrubbing could have been avoided? I still have a flathead screwdriver covered in that sludge.

Any general automotive machine shop can do it - some NAPA, Car Quest, locations have them. They just run parts like that through the hot tank (or whatever is currently in since many have gotten away from the chemicals and EPA requirements).

montanajetta December 17th, 2018 05:26

Awesome. Going to try and clean it today. I’m not sure anyone in town will touch it, so I have been reading up on the cleaning methods. What about the passages is the block? Should I clean those at this time?


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