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Discussion Starter #1
I have a 2001 Jetta TDI 5spd with 146K miles. I have been slowly loosing poser over the last 2 years. I cleaned the injectors, intercooler and intake (was about 50% restricted). I then disconnected the MAF (original 461 which had not changed in the recall by the previous owner). It had a dramatic increase in power, so I ordered what I thought was the ...461C. It was actually a ...461A. It ran great for a week and then had a sudden failure. The car went into limp mode. I pulled over and disconnected putting the car into the default mode. When I reconnected, it ran the same as the old bad 461. I got my money back and installed a new Bosch 0281002757/038906461C from MJM Autohaus. It was underpowered just like the original with the exception of when I get the revs up to 3,000 rpm, it kicks into the default mode. Everytime I turn the car off. I have to get back to 3,000 rpms to kick in the default settings.
I have cleaned the MAF connection, both ends of the cable and the ECU connection and chassis ground. I get battery voltage (12.5V) on pin#2, 20 ohms on #3 pin and 5V on Pin #4 on the MAF connector.
I get an open circuit between all of the MAF pins (2 to 3 & 4 and 3 to 4), Seems like there should be some ohm reading when checking the others the #3 ground pin.
Bottom line. I notified MJM Autohaus and they suggested that I take my car to a VW dealer to have it checked. This would probably cost more than the $90 for another 461C. The VAG-COM printout show2 90 mg/str at Idle when 260 mg/str is specified. After the default kicks in, It is a continuous 550 mg/str reguardless of rpm. Also the check engine light does not come on with the MAF connected. Shouldn't this be enough to convence MJM to exchange my MAF for another. What should the resistance reading be between MAF pins, so MJM can test if need be?
 

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Stock ECU

Fluid,

The car is 100% stock except for the 100,000 mile timing belt. The turbo works perfectly.
the first MAF that I installed less than a month ago made the car run like new until it failed after 7 days.
If one unplugs the MAF, the ECU goes into the default mode and sets the mg/str at 550.
The ECU is sensing the current MAF because it is underpowered (calling for a too low mg/str) until I get to 3,000 rpm and then it goes into default mode (not limp mode) and stays in the default mode until I restart.
All indications are that the MAF is bad, but it seems strange that I would get a new Bosch that is bad right out of the box.
I am driving and using the VAG-COM so I didn't do anything other than block 3. I will do the IQ in a bit and get back with you, but i don't think that it will tell anythiing new.

Update, Drove the car a little and the Check Engine came on (probably MAF). Need to do a couple of chores, but will check DTC and IQ in a bit.
2nd update, The DTC was for improbable MAF signal. Which I reset.
I checked the IQ at Idle and at first it was 2.8 to 3.0. After I drove it around a bit, it dropped to 2.4. I will try raising it up to 6. The battery on the old laptop is weak and pooped out, so it is charging up now. I called the VW dealer to ask for the cost of a diagnosis check and he said $110. This is unfeasible since another MAF from MJM only costs $90 total and if I can convince him that it is bad, all it will cost is my return shipping.
 

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Discussion Starter #4
IQ misprint or what

OK, Fluid,

I tried adjustion the IQ and it responded backwards to the IQ link you provided.
"A lower adaptation number entered in the blank will reduce fueling and increase the "x.x" m/R value. A higher adaptation number entered will increase fueling and lower the "x.x" mg/R value."

I raised the number to the max and it lowered the mg/R to 2.0. I then lowered it to the minimum and it raised the mg/r to 4.8 to 5.0.

I then drove the car around and it performed the same. Default settings kicked in around 3,000 rpm.
Is anyone else reading this? shure woulf sppreciate some kind of comment.
 

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A lower mg/R IQ number means more fueling.

Maybe there's a problem with the EGR - it's possible that EGR gasses are displacing the intake air and causing some problem but that doesn't explain why the MAF worked for a bit. But because of the repeat dead MAFs, this almost sounds like a bad wiring problem.
 

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Discussion Starter #6 (Edited by Moderator)
There does not seem to be a problem with the EGR, but it is simple enough to disconnect the vacuum line to the EGR (and plug it) to see if it makes a difference.
Maybe I am confusing people with my long discriptions, but the current MAF (the new Bosch 461C) never has worked. The 1st replacement (the 461A) worked great for a week.
Nothing was changed to the car from the time (6 days) the 461A was taken out and returned until the 461C was installed. Since the 461C was installed, I have sprayed Deoxit on both ends of the MAF cable, ECU plug and ground. This reduced the #3 ground pin resistance from 150 Ohms to 20 Ohms, but it did not change anything with the MAF.
There are a lot of vendors still selling the 461A. I don't know why since it was recalled and replaced years ago by the 461C. I am almost tempted to try another 461A. Any thoughts on that?
BTW, the wording needs to be changes on that IQ link (see Fluid's Post above).
 

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I don't have any advice at the moment but I'm thrilled to find someone on here who is actually being scientific about their MAF values, so many people tend to just say "change it" without knowing why.

I'd be happy to check the values on my 2002 MAF tonight and let you know what resistance I have between pins and the model number as well, since mine seems to be working well. My in-laws 2000 TDI has low power output above 2500 RPM and I.Q. really drops at that point, so I've been trying to diagnose that one as well (installing my MAF on their car changed nothing unfortunately).

One more thing, how do you tell when it is in default mode? I am familiar with what default mode is and why it would enter that mode when the MAF fails or is disconnected, but when I unplugged the MAF on my in-law's 2000 Jetta it never seemed to change any I.Q. values, even once the CEL came on. Does your CEL turn on immediately after unplugging the MAF, or only after a specific time period?
 

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Discussion Starter #9
Sematics I guess

Chitty,

I guess it is sematics. When I read "increase fueling" I took it to mean the amount of fuel per stroke of the distributor. The VAG-COM screen says mg/str. I do not know what mg/R stands for.
A lower adaptation number entered in the blank will reduce fueling and increase the "x.x" m/R value. A higher adaptation number entered will increase fueling and lower the "x.x" mg/R value..
I have contacted MJM and they say that they do not accept returns on electronic items, but they will get back with me. If I can't get them to exchange mine for another, I will go with a Pierburg...which I wish I had done to start with.
 

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I don't have any advice at the moment but I'm thrilled to find someone on here who is actually being scientific about their MAF values, so many people tend to just say "change it" without knowing why.

I'd be happy to check the values on my 2002 MAF tonight and let you know what resistance I have between pins and the model number as well, since mine seems to be working well. My in-laws 2000 TDI has low power output above 2500 RPM and I.Q. really drops at that point, so I've been trying to diagnose that one as well (installing my MAF on their car changed nothing unfortunately).

One more thing, how do you tell when it is in default mode? I am familiar with what default mode is and why it would enter that mode when the MAF fails or is disconnected, but when I unplugged the MAF on my in-law's 2000 Jetta it never seemed to change any I.Q. values, even once the CEL came on. Does your CEL turn on immediately after unplugging the MAF, or only after a specific time period?
kd7wp
Thanks for the resistance offer. I had to take mine out of the car to check the ohms since the pins are so small and close together. If I had an old MAF cable or some female plug that I could connect to pins 2,3,4 &5, I could do a bench test by supplying 12v to pin 2, grounding pin 3, supplying 5V to pin 4 and reading the voltage at pin 5 after duct taping the exaust from my shopvac to the MAF inlet (while it is off the car). I could very the airflow by restricting the shopvac suction. The voltage should vary between 0 and 5V and mA output should be less than 100 ma.
ALH's go in to the default mode when the MAF is disconnected. The ECU sets a constant 550 mg/str (must be scaled cause it seems high) MAF actual reguardless of RPM. My current MAF is strange because with it connected, the default mode kicks in when the engine reached 2,600 to 3,000 rpm and stays in that mode until I restart the car. BTW, my car runs adaquately in the default mode, doesn't smoke, still gets around 50 mpg, etc.
I would think that a the 2000 tdi might have a clogged intake. This is easy to check by disconnecting the inlet tube going into the ECU. Peer into it and see what it looks like, but do not try to remove any of the gunk. The EGR valve stem goes thru the center of the inlet housing. It is a big job removing and replacing the intake because you have to do it by feel. If this looks clean, I would suggest cleaning the injectors with Lube Molly.
Don't look at IQ values, Engine Grp 3 vs Grp2 (MAF specified vs actual). It seems like I saw a way to attach a file to a post, but will try to email you my log.
 

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Thanks for the reply. I am familiar with the intake clogging issue since I removed my manifold on my Golf a few weeks ago to clean it, and then created a catch can for the CCV system. I haven't checked the manifold on that 2000 Jetta yet. Cleaning didn't seem to make any performance difference on my Golf even though the buildup was close to an inch thick (though the Golf's performance hasn't been poor).

I have contemplated the idea of using a shop-vac as well to measure a MAF's performance, though I don't think I would know what the actual airflow is from the shop vac, but at least you would get some type of readings from the MAF by varying the suction.

That sure is odd behavior how your ECU would go to default settings after reaching a certain RPM, but without triggering a CEL immediately. Now that I think about it, I never tried logging with Vag-Com while the MAF was disconnected, to see that my car was showing me the default values.
 

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Discussion Starter #12
kd7pwp

You ask about the CEL time. I had no CEL and disconnected my MAF cable. Starting the car and letting it idle, the CEL came on in 27 seconds. If you had an inch buildup on your Golf and cleaning made no difference, I would think that your MAF needed replacing or your injectors needed cleaning. Inner-cooler cleaning is easy, and would not hurt, but I do not think that it is a big factor.

BTW, I think that if the MAF works at all, it should be fairly accurate, so the shopvac air flow should be an indicator. max air flow = minimum volts, minimum airflow = maximum volts - 5V
 

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Sunshine
Did you find the fix??? I am having the exact same problem & the same results, with 2002 Jetta TDI 167K. Any update would sure be helpfull
Thanks JC
 
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