i have a 1991 Volvo 740 turbo, And when i drove it today, i noticed that the slightest bit of gas to accelerate caused the boost gauge to go really high. Even under hard acceleration ive never seen it go that far to the right, really high, towards the end of the stock gauge. I did a little searching and saw i may have a vacuum leak, or the wastegate maybe stuck open? I just wanted to know if these seem like feasible answers to my problem? How can i go about solving my problem? Thanks for your help

 

overboost is a fast track to totalling your pistons.

the wastegate actuator is that thing on the lower side of the turdblo that looks like a cylinder with a vacuum line coming off it and a pushrod that goes under the turbo.

I'd check/replace that vacuum line, along with the one to the upper cylinder, which is also part of the wastegate system

 

Like pierce says check those hoses. But usually a vacuum leak would cause you to lose boost development because there is no vacuum to open and close the CBV and likewise the actuator... But I'm not an expert just throwing info out there.

Also, a problem I had on my turbo was that the pin that holds the actuator arm to the wastegate lever was totally rusted out and wasn't even attached. Unfortunately you can't see it unless you are under the car. You should still be able to feel around to see if that arm is attached or not, while the turbo is cold of course.

Also, if you feel comfortable disconnecting that arm from the wastegate you can try moving the wastegate manually with your fingers to see if it moves.

And while your at it you can also take the three bolts that hold the CBV to the turbo off and inspect the membrane inside and make sure its not cracked or full of holes.

Pics

 

Overboost? Overboost? No such thing!! Just add more fuel and you'll be fine!! Bigger injectors, bigger intercooler, bigger turbo and a wide band O2 setup!! Seriously, obviously something has changed; the wimpy non-numeric, take-a-guess stock boost gauges leave a bit to be desired. Your car has an overboost switch that should shut it down if your car goes over ~10 p.s.i. Unless someone has bypassed it by blocking off the inlet boost line with a golf tee. My point being, while the car is obviously showing more boost than before, it's doubtful piston met down is imminent (unless you dog it a lot and run regular). Check the vac hose leading from the snail of the compressor...a leak there will act like a bleeder style boost control and allow boost to run higher than stock.

 

Thank you everyone for the help, im going to check, and or replace these vacuum lines. Ill keep ya posted.