This issue is for a Turbo 2, 1992:

I was accelerating hard today and the boost pressure gauge reached maximum. I heard like a few backfires in the exhaust muffler, and then the power dropped dramatically. From the sound of the engine, I'm sure it's running on 1 rotor. I'm pretty sure that the boost cut-off hit in, but it didn't release. Does that make any sense? I can hardly drive the car now If I release the throttle, it dies. And it sounds like a SAAB V4... The boost gauge seems to read normal values.
Anyone have any suggestions? Should I get a new boost pressure sensor? They are very expensive... Or can it be something else?
Thank you for your time.

 

Uh-oh...Not GOOD News..you popped your rear rotor.(Rebuild time Buddy..)

What you describe is what I just went through.
A compression test will tell you what you need to know.

 

Thanks for your suggestion. I will try to do some checks but I don't have access to a proper compression tester. Another rebuild is out of the question... I have started the search for a new car...

 

try this,as it will give you an idea if the engine went,bye,bye.
LINK:Rotary Resurrection home of the budget rebuild.

 

just pull the plug and turn it over, if its pushing air you will hear it.

 

Thanks for the tip. I tried with a conventional compressiontester and I found out that there is close to no compression on the rear rotor.
I will put the car away for the winter and buy another. Will see later if I find the energy to open it up again...

Thanks again!

 

If the boost gauge went to maximum, it sounds as though you've opened up the exhaust or intake, or fitted a boost controller. And then to allow it to go maximum, fitted an FCD.

This is a disastrous combination when not combined with some way to add additional fuel, as you have unfortunately discovered.

It's certain the engine ran lean which is what caused the failure. That is indicated by the backfires. It must have gone very lean either due to high boost pressure or a failure somewhere else in the system.

Just remember that unless this is corrected, you're just going to blow another engine.

At the very least, reverse whatever you did to increase boost and remove the FCD. Then approach from the correct direction by first building up the fuel system (including some way to monitor AFRs and an ECU capable of supplying correct fuel/timing), then carefully increasing boost.

For the record, the boost cut feature in the stock ECU is not what killed the engine and because it is a software feature, cannot be "stuck on".

 

My car is 99% original. Only modification made is the Racingbeat exhaust system. The same backfire sound happend about 1 year ago. Than I was also accelerating hard as well. I assumed it was the cut off that made that sound. And since I heard the similar sound this time, I was thinking it was the cut off again, but this time it felt like it didn't go back. Just lost a lot of power. I was thinking the pressure sensor got stuck somehow and gave wrong signal to the ECU. But after checking the compression, I'm sure it's the rear rotor.

 

Just a RB exhaust is more than enough to raise boost to an uncontrollable point. It should have cut off at 8.6 PSI, but these cars are old, things malfunction. As you suggest, perhaps the pressure sensor is not reading correctly or has been hacked.