95 cav bucking

calhoontunaMarch 24, 2007

95 Chevy Cavalier. 170,000.

The thing bucks -- either hesitates for a millisecond or surges -- when you put the needle at a steady 40 miles per hour. Does the same thing as you ramp up speed, but the thing is it seems to go away momentarily when you shift to the next gear.

Replaced: fuel filter, fuel pressure regulator, plugs, wires, crankshaft position sensor, and most recently the EGR valve.

Thought the EGR valve was the culprit because I discovered that if you plugged up the vacuum hose going to the EGR valve the car ran perfectly fine, albeit with an ever so slight drop in performance. Nope. Put the new EGR in and still with the bucking.

Tried cleaning the EGR passages -- thought that perhaps they were clogged. Stuck a wire brush down there and tried navigating the corners but hard to tell how far the passage goes.

Anyway, anyone have any ideas?

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Do you have an automatic transmission? If so, could it be the lock-up clutch cycling on and off? Also, check out the engine mount/arm that counteracts torque. Some torque reaction 'thunks' can be felt when the bushings are beat out.

However, if this is a case of engine cut-out, its a good case for taking it to a qualified shop for diagnostics. You may be replacing parts at random while missing the true problem.

    Bookmark   March 24, 2007 at 4:14PM
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Actually it's a manual.

Many of the parts, but not all, I was able to get for free from another Cavalier, which is why I was throwing parts at the car.

Thought I had the problem cornered here to somehow related to the EGR but perhaps that was only a symptom of a much larger problem.

    Bookmark   March 24, 2007 at 4:35PM
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