over boost and missfire

hi ive been getting a bad periodic missfire, mostly happens when at crusing speed and slowely accerate, or come to a hill, i went to a shop to get them to look for engine codes, andcame up with a missfire and overboost, any help would be good, and the miss fire is so bad ity shakes the whole car,. but goes away if i stomp on it and get the rpms up

how old are your plug wires?

Albertj

Yep...check the plug wires and plugs for any carbon tracking. This means a wire is sliced, broken, etc. Also if a plug is cracked it can do this. The overboost code is odd though....punching it "solves" the problem?! Possibly the boost bypass valve is stuck, which could explain it running fine under WOT.

3rd for plug wires. Check your plugs too, but most likely it's the wires. Get a good set like AC Delco.

ok thanks for yhe advice, id did the plugs in the summer, but the wires avent been done in the 3 years ive had the car so ill try that. where can i get a new boost bypass valve, and is there any way 2 test the old 1

The boost bypass valve is located on the driver side on the front left of the intake manifold. There should be a vacuum line going to it, and it works sorta like an IAC valve. It mainly is there for when the car is in reverse, but you can disconnect it and see if the "output" rod moves or not. I see you have a '95 series I. If I'm not mistaken that engine also has an actuator in-line with the solenoid. This can be checked using a vacuum pump. These may not be your problem, but the overboost code along with misfires bothers me......

Agree. Normally I'd say wires, but punching the throttle should make the condition worse, not better. Wires may be bad, but I think there's another problem.

might want to disassemble the coil pack (its a nut-driver job, not hard) and check to see that the ground plane, and the ground line underneath, are clean.

Albertj

peev0021 wrote:

...mostly happens when at cruising speed and slowly accelerate, or come to a hill... but goes away if i stomp on it and get the rpms up

[u]

I agree that plugs/wires should be checked first... What he's describing is gradually lugging the engine, then driving through it by most likely releasing the TCC and/or dropping a gear, both of which would lessen the load.

broke down and took the car to a garage today, it turns out it was the egr valve, and of corse my left ball joint was gone(luckly under ac delco life time warinty) and my right rear break was seased

So the valve stuck open, but didn't throw any codes/light the SES light?

im not shure if it stuck open or was just sometimes sticking, i did have an ses light but thats been peridocly off and on for the past 2 years so i just normally ignore it because i brought it in a few timew and now morrable codes. ill hopefully e picking up the car tonight or tomorrow and find out what happened with the valve

Ahh yes, love when a hard part FA!Ls and sets other codes other than any for itself. Hard to diagnose that over the internet . EGR valves have a pintle inside of them that sticks from time to time....carbon builds up in there and, well, you have your scenario. It usually sets a code for EGR circuit low/high voltage depending if it's stuck open or shut. Glad to hear it's fixed though!

just got the car back and drives so much better, amazing difference in throtel response, plus not stuck rear breaks and new ball joint wake it ride like new, only 600 dollars later

the car started to do the same thing agian yesterday so i took it back 2 the garage, and it needs plug wire now, whitch i would normally do my self but unable to do so due to a broken wrist, picking up the car today and hopefully will be running beter

albertj wrote:

how old are your plug wires?

Albertj

Too bad about your wrist.

Might want to replace the set of plug wires not jsut one. Might want to get Magnecor wires.

Albertj

ya i went wires, i got them to change the plugs also,and it turs out the was a crack spark plug as well (on the porslen), so im shure that was the main culpurate, but the egr valve was defective, and when the mechanic spraid water on the pulg wires it was missing (so they werent taking me 2 the clearners). what a differnce in how it run, feels like a new car