I have a 91 740 Turbo wagon. Normally, it runs fine. Occasionally (maybe once a week) it has acceleration problems. The problem shows up on hills. Starting and level driving are ok but as soon as it downshifts (and the boost gauge hits the right side), the engine power drops (it's kind of like the gas flow cuts out). After parking and restarting the engine, it usually resumes normal performance. I suspect it is related to the turbo boost but have no idea where to start. Any ideas?

Thanks
Lee

 

Last tune up?
Intercooler hoses good?

 

Last tune-up less than 4k miles - hoses "look" good

I read somewhere that the turbos have some sort of knock sensor that when triggered causes a gate/pop-off valve/? to open. Could this be involved?

Lee

 

Not this car.
Was the throttle body cleaned?

Does the the guage go all the way to max?

 

Don't know about the throttle body. The boost gauge just goes a quarter inch or less past the midpoint (where the line changes).

The fact that the problem is cleared by stopping and restarting the car should point somewhere. Perhaps a loose wire that give the computer a bad signal that is only read at start-up? I just don't know enough theory about fuel injection systems to interpret the symptoms. Past experience with mechanics trying to find intermittent problems has NOT been fruitful! LOL

Lee

 

Any codes in the system?

 

none

As the turbo boost kicks in, there must be additional fuel added - How does the engine control system detect the boost? Or is it driven entirely by the oxygen sensor & MAF? (BTW - the MAF is new)

Lee