Mechanics

SOMETIMES MISFIRES BADLY, OTHER TIMES

1991 Pontiac Trans Am

Engine Performance problem
1991 Pontiac Trans Am V8 Two Wheel Drive Manual 60,000 miles

I have a 1991 Firebird with 60K original miles, manual 5 speed. I make a daily commute of about 35 miles one way. It drives fine for about the first 2 ~ 5 minutes, but after then it SOMETIMES misfires and jerks under load (acceleration or uphill). Sometimes badly enough to buck strongly at low speed in higher gears under light load. It also might be the same symptoms, but not as bad.

No backfiring. Constant highway speed on level ground is ok. If I rev it in lower gears, sometimes at least one or two cylinders quit only at high rpm (or some similar feeling power loss), but sometimes this will remove the problem. Also, after about 20 minutes of normal freeway running, it usually will clear up on it's own. Most of the time, it just works fine.

The fuel filter might be original, I plan to change it soon. I reason that it might be passing small cruds, causing one or more injector(s) to act up sometimes. But wouldn't this cause problems at idle and constant speed too?

Some other sensor might be causing it, but not sure which one has a capability to " fix itself", work fine for a few days, then get bad enough to make me wonder if I'll make it to my destination.

How about any connections that are known to go intermittant, wires that are known to break or ground, brain box gets forgetful, then remembers, or?

Vacuum leak?

Another possibly related point - the cruise control acted up by not holding constant speed, but this is now gone (I hope) for a long time after lubing the cable and making sure the floor mat was out of the way - maybe it thought it was a Toyota?

Thanks!
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The Real Roger Davis
February 10, 2010.



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