Mass Air Sensor

I have a '96 Passat Wagon TDI w/205,000 miles. I'm getting some white smoke when just easing back on the throttle at higher RPMs in 2nd and 3rd gears. Took to a local shop (limited options in Helena MT) and he says there are no codes showing. He couldn't diagnose anything so I thought I start considering replacing a few likely items.

I unplugged the MAS connection today....it made no difference in the smoke issue. This suggests to me that the MAS may not be functioning. If I can replace it for less than $100, I thought I'd give it a try. Is there an currently active source for the MAS other than a dealer?

Thanks

Hi, welcome to Fred's. Danix has new MAFS for all TDis.

It's not likely that is the issue. I'd like you to find out if the smoking recall work has been completed on this car. Do you know how long you have owned this car for?

I've owned the car for four years...have maintenance records since 1998....no recall work is noted. The problem started about a year and a half ago. It came on slowly. Does not otherwise impact performance other than a slight hesitation right when the smoking event occurs. It is more apparent when cold but it occurs anytime throttle, RPM, and load conditions are right.

I've cleaned the intercooler, removed and cleaned the intake mainfold, checked all vacuum lines, run diesel purge through it, and checked all the sensors that I could based on resistance specs in Bentley manual.

What did the smoke recall do or replace?

On the '96 passat, there is a 5th fuel injector just infront of the catalytic converter. The idea was to take the hot air in the exhaust system, fire in a bit of fuel, and get mini combustions going on. Why? Make the exhaust hotter, therefore reducing soot, etc.

All this 5th injector ended up doing is adding more smoke under certain conditions, and possibly ending up clogging the CAT. For some of the '96s, there is also a recall on the ECM. I think it had to do with changing the programming to get rid of that 5th injector or something. Not 100% sure.

If your dealer won't honour the recall for whatever reason, search for '5th injector' and there should be some posts on ways to block it off. Should get rid of your smoke problem.

I plugged the fifth injector today. Unfortunately, there is no difference in the white smoke when holding at relatively high RPM in 1st, 2nd, or 3rd gear under no load.

It feels like you lighten up on the throttle a little and it continues to give fuel that can't be burned so it pukes out smoke(vaporized fuel). I was thinking it is the MAS since it really seem to be a fuel-air problem....lmeaning, you back off the throttle slightly, less air is moving through but the fuel flow momentairly stays high.

Any other thoughts are appreciated.

Not ruling out the MAF, but to properly diagnose it, you really need a vag-com. I am guessing you don't have a boost guague. If you would, you could tell if you are getting proper boost, etc. White smoke usually isn't an overfueling issue. Black smoke is. In gassers, white is generally from water, but in diesel I believe it is something else. It couldn't hurt to drain your fuel filter and check if there is any water in your fuel, though.

Did this happen recently with a new source of fuel, or just after you filled up? It could be fuel related.

no, I don't have a Vag Com close by, though I do see from the list that someone has one in Montana. I may try to connect with him to see if we can come up with something definitive. No boost gauge either.

The problem didn't start suddenly, came on slow. So it didn't appear to be related to a specific tank of diesel. After it became apparent that something was up, I changed the filter and ran a can of diesel purge through it, but there was no change.