As some of you may know I aquired my 1991 Sport sedan in the summer when I found it abandoned in some brush next to a house. I took it home to fix it up (body wise), which I still am doing now as things progress slowly. So while I fix the car I somtimes take it out for the occasional spin. I always marvelled at the acceleration and it had some pinning, only a full open throttle though. Today I installed a boost guage and found out why it pulls so hard. In third gear I topped the boost out at 16 pounds !!! But I had no common fuel cut or boost cut. The thing just ran at that boost level. Only sometimes I would get the sudden jerking. Anyone know which one it may be? Boost cut or fuel cut? I'll check it out it's either a seized wastegate actuator or a bad boost solenoid thats keeping the boost that high.
Mark
1991 Turbo Sedan, Aspen White 5MT, Sold RIP
1994 Turbo Sedan, Crimson Pearl 5MT, from British Columbia-no rust!
I know this is an old post, so maybe you've found more out since then, but anyway...
As far as I know, the ECU cuts fuel if boost pressure exceeds its threshold of safety. The ECU also operates the wastegate control solenoid to bleed pressure away from the wastegate in an attempt to achieve its desired level of boost.
For both functions, it relies on input from the pressure sensor. This sensor acts both as a barometric pressure sensor and as a MAP sensor, because there is a three-way solenoid allowing the ECU to choose which pressure to read.
If the line to your MAP sensor had a leak in it, the ECU would allow boost to build up higher, and at the same time wouldn't know to cut the fuel. This is kind of what some manual boost controllers do (the bleeder-type ones, not the ball-and-spring ones).
!!! But I had no common fuel cut or boost cut. The thing just ran at that boost level. Only sometimes I would get the sudden jerking. Anyone know which one it may be? Boost cut or fuel cut? I'll check it out it's either a seized wastegate actuator or a bad boost solenoid thats keeping the boost that high.