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

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

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).

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??

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.

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.

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.

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