Black Smoke?? Mass air flow? o2 sensor??

[tcorbeil]

hey I have a 92 jetta,

starts up fine and after a few mins black smoke start blowing out the tail pipe.
any ideas?

i got a differnt mass air flow sensor from the wreckers but it does not seem to change anything..
any ideas?

Another question. are there any engine codes for the A2s? how would i get them???

thanks
TIM

[boschmann]

I take it that you have the Digifant system, which has an air flow meter (officially it's not a MAF) rather than the CIS-E injection system, no braided steel fuel lines right? You can check codes. Is the engine light on, if so I can get you through how to read them. I suspect the coolant temp sensor, it's located in the cylinder head flange where the upper radiator hose enters. It has a brown/white & brown/green wire & checking it is fairly simple. Test with a multimeter set to Ohms. Between the two pins should read 800-1000 Ohms @ 50F (cold)and gradually decrease to 100-200 Ohms at operating temp (195F).

[tcorbeil]

Yeah thats night, no steel braided lines... I'll check check out the resistance of the sensor as soon as I can.


What do you mean by the engine light being on? you mean on the dash??

[boschmann]

Okay, since you don't seem to have the check engine light you have the Digifant II system. It was a long shot that you had Digifant I (with the check engine light) as they are mainly California models. You should have two small connectors under the shift boot, one balck & one white. Unfortunately the only way to connect to the ECM is with a VAG scanner or VAG-COM with the 2X2 adapter. The systemis pretty basic & usually doesn't provide much help anyway. Aside from possibly being the coolant temp sensor, I had one with the same symptoms that turned out to be a problem with the ECM. Once it warmed up it would run very rich & begin flooding out.

[tcorbeil]

Today I unplugged on of the temp sensor plugs... the blue one actually closest to the engine block.. the engin began to run properly..
So today I just drove the car with it unplugged...

Do you think it could be the sensor itself or the computer??

I measured the sensor and read about 2.5K Ohms cool, and 300 ohms once the engine was warm.

[boschmann]

The coolant temp sensor readings sound fine. Unplugging the sensor is just causing the computer to ignore all sensors & run in a default mode. Without a scanner the only other thing I can think of that would cause those symptoms is the oxygen sensor. There are special O2 sensor testers on the market, but they cost about the same as a new sensor. Again as last resort it could be the engine control module.

[tcorbeil]

I will check out the idea of the O2 sensor... do you know where it is located??