Re: 91 turbo pops and runs bad at about 5PSI of boost
Did you check the fuel pump relay? It might not be a problem with the fuel itself. It might be an electrical problem. Get a DVOM and do a resistance check on the relay. if you get a high resistance its just a bad relay. If it is a bad relay then the car will crank without turning on.
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There are a few possibilities that come to mind.
3K RPM is generally about the break-even point for when Turbo boost would kick in. There is a dump valve on the turbo system that opens up and vents the extra turbo pressure under high-rpm situations where the boost isn't needed - say high but steady speed on a freeway. If the dump valve system is malfunctioning, then that anticipated turbo run-up in power won't happen.
Revving fine when in neutral may not tell you much, other than that the engine can rev. The gating system will (or should) run differently under load - whether climbing a hill or accelerating, this is where you want the turbo boost to give you the extra power. THat's where the exhaust gate should stay shut, or mostly shut, to allow the turbo to force more air into the pistons.
You might want to check whether the APC (Automatic Performance Control) for the turbo has a separate fuse. (The name might be different on your model, I'm remembering from my 80s/90s era Saabs). If the fuse is blown, that could also lead to lame performance, especially as I'd imagine that the system would be built to fail or go to full open if the APC fails or loses power - that'd keep people from having run-away power that they can't manage.
Have you checked the PCV system?? If its stuck in the closed position then you will lack power and turbo boost. A vehicle needs 3 things to make it run proper; FUEL,FIRE and AIR. Try that and see if it helps.
you may be having problems with the turbine or it could have a heavy short in the system. check the tuning on the turbo it may be starting the boost to soon or to late causing problems also check your intake setup this includes your pcv valve