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Boost gauge showing maximum boost when not touching gas pedal

NotEnoughGPs

NotEnoughGPs

New member
Helping a neighbor with a SC Buick Regal.
There is 161,000 on the OD.
He has done a good bit of engine maintenance and other items over the years, but has NOT replaced everything.

Right now, the engine will start up normally, without any hesitation, when engine is completely cold
Engine idles smoothly. Upon driving it runs well, but there is slight fluctuation of tachometer, but not all the time.
But I am puzzled by the stock boost gauge. At very slight throttle, it reads boost at halfway on the gauge.
Then, once the car is driven on the open high at speeds over 50mph, the gauge is reading almost full boost even when slightly pressing the accelerator.
The engine seems to be chugging, surging.
The tach does not jump around.

Yesterday, when the car is brought to a stop and left in gear, the engine will just stall. Upon trying to restart, it would do so at the first try.
But now, this morning, after the engine is fully warmed up, the boost gauge continues showing boost at halfway to full boost even when barely touching the gas.
Then, when the engine is shut off, it will not easily restart. Only after 10 tries, it will eventually start again.
I have not yet tried to unplug the MAF sensor when I can will not start. I am aware that when a fully warmed up engine won't restart, it could be the MAF.

But what is causing the factory boost gauge to read 1/2 to full boost?
 


might be a bad map sensor, or maybe its vac line is busted off.

surging is likely a large vac leak if its 3 to 500 rpm.
 
Ok, located the MAP sensor, removed it and installed another known good MAP sensor from a L67.
I also checked the electrical plug for breakage and I checked the hoses going to the MAP sensor as well as all other vacuum hoses. Did not see anything bad.

Drove the car, and at speeds less than 50mph, the car ran well. Then once got on the open highway, the boost gauge on the DIC once again read halfway boost up to full boost. The boost gauge reads high boost even when not touching the gas pedal. The car seems to surge/chug. Upon returning to house, before placing the transmission in park, the engine stalled. I tried restarting the engine and it would not restart. At this point, I unplugged the MAF sensor. The engine still would not start.

Finally, after about 20 minutes, tried one last time to start the engine and it sputtered and finally started. Once started, it idled well. So, I took it for another drive and it seemed fine. Even when stopped with shifter in Drive, the engine idled ok. It's just after the engine is driven for any distance that the boost gauge is ready nearly full boost, and the engine sputters and stalls, and won't restart until allowed to cool down.

Doing a search on here, someone mentioned checking the Fuel Pressure Regulator. I removed the fuel line and no fuel squirted out. I think that means the FPR is ok.

The check engine light is not on.

What are some other items I can check?
The owner said the catalytic converter is original. If clogged, would the back pressure cause the boost gauge to read high, and cause stalling?
 
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