1995 940 Turbo that hasn't been run in a few years. Car starts and idles with no issue. Engine revs in park to high rpm without issue. Put the car in gear and once you accelerate to about 25-30 mph the car bogs down and starts to spew out black smoke.

History of what I have done:
1) Engine code orginally showed mass air flow unit bad. Replaced that, no codes, same problem persists.
2) Thought about plugged catalytic converter. Pulled it off the car and tried to run around the block. Now have same issue as well as a loud sounding car. I assume that means the catalytic converter is not the issue.

I am now at a loss of what to check next. Any thoughts?

 

Possibly a bad fuel pressure regulator. Check fuel pressure, it should be 30-35 psi. If the regulator is bad it will be well over 75 psi.

When you replaced the mass airflow sensor, did you pull the fuse for the enine module? (to reset the engine module settings) Try pulling fuse #1 I think, behind the ashtry, it's for the engine module.

3B

 

I didn't pull the fuse. I did, however, disconnect the battery while I was changing the MAF unit. Does this accomplish the same thing?

 

It does! Except you have to deal with the clock and rario codes.

Pull the vacuum hose of the fuel pressure regulator (FPR) and see if fuel is present. If so, replace the FPR. The FPR can still be bad if there is no fuel, but you need a fuel pressure gauge to know for sure.

Also, the main pump can be very noisy if the FPR is bad.

Is the new MAF the exact same part # as the old one?

3B

 

have you checked the torque conveter or clutch? These could be bad if the engine is running fine.

 

check the L shaped hose (Big) going into the intake manafold. Minehad a small hole in the bottom and would not allow the turbo to make boost under load. Changed that hose no other problems 2 years now.

 

check your wastegate my 88 740 turbo would loose power when it builds boost the wastegate was about to fall off