Enough information to determine a bad MAF?

[Sabadecade]

The problem started back in March. It appeared my 2002 Golf was going into "limp mode" It wouldn't happen all the time either. I checked the snow screen (found I had none) air filter and connection to the MAF. It seemed like the cold weather aggivated it as I noticed that the problem would go away after the engine had been running a while and cycled the engine off then on. Also if the car was still warm after getting home from work and going out shortly after it would be fine. Since it was spring and getting warmer, the problem kind of went away... (I suspected a vacuum leak due to this)

A couple months later... there's no question, it isn't "limp mode" as I get low power all the time, even when cycling the engine off and on again. I'm still asking myself Vacuum leak or did the MAF finally die? God forbid it's something as labour intensive as sticky turbo vanes.

I unplugged the MAF, as suggested on these forums, and ran with it disconnected for a couple of trips to and from work. It seemed to perform a little better.

I also scanned with VCDS and got the following codes:

17964 - Charge Pressure Control: Negative Deviation 
        P1556 - 35-10 -  -  - Intermittent
16486 - Mass Air Flow Sensor (G70): Signal too Low 
        P0102 - 35-00 -  -

Could the second code be because I disconnected the MAF?

I've gone through Canadian Grizzly's "Low Power Troubleshooting guide" - Fantastic by the way. I like pictures and diagrams.

Anyway, I guess what I'm asking is. Do I have enough evidence that it's the MAF and buy a new one or should I rule out a come more things first?

P.S. I found some MAFs for sale here http://www.autopartsway.ca/autoparts2/index.cfm?fetch=part~ID=2002~Volkswagen~Golf%20Turbo%20Diesel%20GL%201.9%20L4~240551
They seem to be the correct one and a little cheaper that other places. I'm just not 100% due to the difference in part numbers from other sites I've been. Opinions on these too are welcome.

Thanks for reading.

 

[puter]

try replacing your vac lines.

There is a ross-tech article on checking the maf with vag-com

I would start there.

 

[VOLKSWAGEN_JETTA_TDI]

Are MAF's a common problem with these cars? I know with benz c-class kompressors they are.

 

[2004STARWARSTDI]

Maf

MAFs are a common problem if you use an oiled air filter such as K&N. Make sure you have a clean paper air filter and you can buy some MAF spray cleaner at aut store.

 

[puter]

Mafs are a common problem regardless of filter

The reason I don't think it is his maf is because he did not see a marked improvement. I think the maf may be a problem as well, but I think there is something else lurking there.

 

[Sabadecade]

OK, I'll check the MAF using VCDS first, then look for vacuum leaks. I kind of do hear a faint hiss when the engine is idling, it hard to tell sine there is so many other noises what with then engine running and all.

Could a vacuum leak be so loud I could hear it?

I'm not using a K&N filter. However all this talk about air flow restrictions and vacuum make me want to double check the filter again. This also makes me wonder if the filter was not replaced properly, or not replaced with a genuine OEM one this could have caused my MAF to go bad. I'll keep a closer eye on that next time.

 

[puter]

You should not open the air box unless you are replacing the filter, that is a quick way to a bad maf.

You would not likely be able to hear the vacuum leak. I would recommend just replacing all the vac lines, you will have to pull most of them anyway to test them with a pump...and it's only like 10 bucks to replace them, and the same amount of work.

 

[Sabadecade]

OK I did a little poking arround and found this powerpoint presentation from the 2002 TDI Fest on Ross-Tech's website: http://www.ross-tech.com/vag-com/cars/tdispecial.ppt

I did the tests as per slides 6 and 7 "Checking the MAF":

1. Go into Engine measuring block 003
2. Start Logging data
3. In a high gear (4th/5th), give full throttle from 1500-2000 rpm up to 3500-4000rpm.
4. Find and Open the Log file in Windows Explorer
5. Graph MAF specified/actual/rpm -vs- time in Excel
6. The MAF is OK if the actual value is more than 850-900 mg/h at 3000 rpm.

Here is a copy of the results I got: http://24.79.237.229/Misc/LOG-01-036-08F.htm

Run 1 Graph:

Run 2 Graph:

It looks to me that my MAF is bad as it only achieved 450 mg/h at 3000 rpm. Would I be correct in this deduction?

 

[puter]

are you certain you plugged your maf back in? The maf graph looks almost flat, and it's at the value that the computer chooses when it can't detect the maf.

If you do not have the maf unplugged, then I would say yes...you need to replace it.

 

[Sabadecade]

Interesting you should ask that, durring these test runs I had it plugged in. However, I had it unplugged a couple of trips to and from work. Perhaps the connection is bad.

I'll do a couple runs tomorrow with the MAF plugged in and a couple more with it not plugged in to see if there's any difference.

Thanks for responding puter. Without experienced people like you around I'd just be guessing.

 

[puter]

It could just be the zoom on it. I'm just noticing that the airflow doesn't really increase with the rpm

 

[Sabadecade]

OK I did a some more runs. Another with the MAF plugged in and another couple without.

Here is a copy of the results I got (including the first two I did yesterday with the MAF plugged in): http://24.79.237.229/Misc/LOG-01-036-08F.htm

Run 1 Graph:

Run 2 Graph:

If you notice on the second chart with the MAF unplugged I get a tiny bit more airflow than with the MAF plugged in. It's barely noticable when driving. But the data is alot more flat and consistent which looks alot more like the default setting is being applied. If you follow the link above I've posted the data table as well and it really looks obvious there. Not to mention I reached 3000rpm (100lm/h in 4th gear) 8 seconds faster with the MAF unplugged.

I'm convinced that my MAF is bad. I'm ordering one today.

Thanks for reading.

 

[KentSzabo]

I too am getting the 17964 code, after it heats up, searching aroung I have found:

"VWs offical text on it is :-

The solenoid valve for charge pressure control N75 applies pressure to the charge
pressure control valve on the exhaust gas turbocharger (waste gate).
Valve N75 receives electrical signals (pulse duty factor) from the EDC control unit.

Charge pressure is thus regulated according to a characteristic map.
Feedback on the actual pressure in the intake pipe is provided along a hose connection
routed from the intake pipe to a sensor in the control unit.
If a deviation from the setpoint occurs, the pressure is corrected accordingly.

The charge pressure is also corrected in the control unit by the intake pipe temperature
to make allowance for the effect of temperature on the density of the charge air.

To ensure that the air mass supplied to the engine stays almost constant, the
charge pressure specified map is corrected in dependence on the air pressure using
the information supplied by the altitude sender F96. The charge pressure is reduced
above an altitude of approx. 1500 m to prevent the turbocharger overspeeding in
excessively thin air.

Solenoid Valve for Charge Pressure Control N75

The EDC control unit sends output signals to the solenoid valve for charge pressure control N75 according to the charge pressure specified map. By changing the signal pulse duty factor, more or less intake manifold pressure is applied to the charge pressure control valve on the exhaust gas turbocharger.

The charge pressure can thus be varied between the minimum and maximum permissible values."

I will check out the intake air temperature sensor, and the F96 altitude sensor as I at 8600 feet, anyone has and then the N75 boost pressure control valve. If anyone knows how to check these devices I would appreciate your input.

 

[KentSzabo]

Limp Mode, 17964 Code, Hard Brake Pedal

After much reading and research under the hood, I discovered a bad vacuum line to the Brake Booster (splits at both ends). Causing loss of vacuum whch subsequently causes limp mode, code 17954 and hard brake pedal. Solution was not to buy the $39.95 new replacement but a $1 piece of 1/2 inch vacuum hose available at any of the CSK auto stores, ie. Checker. Additionally I discovered my vacuum pump nipple was loose and could be twirled, so before connecting the vacuum hose onto that side I applied JB Weld to where the nipple fits into the rest of the pump.
All is working fine now brakes are normal and no more intermittent limp mode.

 

[poor1]

Put a new MAF in they are not that expensive. If it's not that now you can guarantee you will need one sooner or later. If it is the MAF it will transform the performance of your car.

 

[KentSzabo]

Poor
The last line of my post says it is working fine now, I did clean the MAF temperature sensor with carb cleaner.