problems when hot

Hi guys
I have a 1990 SC automatic. It runs fairly well when cold, no dash lights, pretty powerful, but when the car warms up after about 10-15 minutes of driving, I get stumbling and bucking under accel at low rpms and at high rpms the car accels erratically (the tach will jump instead of smoothly going higher) and is down on power. I also get check engine light. Sometimes my tachometer will cut out and read zero even though the car is running. Could it be a sensor thing? IC tubing leak partly to blame? I hear a hissing under the hood (when you shut the car off you can really hear the hiss until it loses pressure after about 3 seconds). The car never pushes more than 7-8 pounds of boost even under hard accel...is this normal? what explains the running poorly when hot?
Thank you SC gurus

i'm having the same thing happen you are. i replaced the crank sensor 2 weeks ago because it totally died. now i have the bucking with loss of tachometer and loss of power. this morning i replaced the dis module. we'll see if that was the cure. i'll let you know if that was the fix. only other thing i would suspect in the cam sensor.

sclovehater said:

Hi guys
The car never pushes more than 7-8 pounds of boost even under hard accel...is this normal?
Thank you SC gurus

Click to expand...

No, I dont think that is normal at all. I think stock boost maxes out around 12 psi. Even with an all stock engine, mine still pushed 10 - 11 psi with the entire exhaust opened up.

Loss of the tach signal or eratic tach is usually caused by a bad cam position sensor. It could also be caused by a bad DIS module, but try the cam sensor first.

David

UPDATE: went to drive the bird at lunch and was still bucking. i changed out the the cam sensor and now it runs great. hopefully the SC will be good for a while.