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Jerry Newton
Jerry Newton, GMC Technician
Category: GM
Satisfied Customers: 4412
Experience:  ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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Truck runs bad misses and backfires, even after plug

Customer Question

Truck runs bad misses and backfires, even after plug exchange and wires, and new distributor, and oxygen sensor
Submitted: 9 months ago.
Category: GM
Expert:  Jerry Newton replied 9 months ago.

Does it idle well, but misfire while driving? When do you get symptoms?

Customer: replied 9 months ago.
No problem at idle while driving at speeds of 45mph and higher misses and backfires
Customer: replied 9 months ago.
Engine will not go over 2000 rpm
Expert:  Jerry Newton replied 9 months ago.

OK. I assume that you used AC Delco plugs, wires, cap and rotor. You didn't go cheap on these components, correct?

Any check engine light on while driving?

Is it only when you lean into the throttle, like passing someone or accelerating up a hill? Or any time you're above 45mph, even if you're just cruising at 45?

Expert:  Jerry Newton replied 9 months ago.

Ah, I see you added the bit about 2000 rpm while I was responding.

Even in park, you can't rev the engine over 2000?

Customer: replied 9 months ago.
I can in park over 2000 rpm
Expert:  Jerry Newton replied 9 months ago.

I suspect a plugged catalytic converter. You can test this one of two ways: get an exhaust backpressure tester, attach it to the oxygen sensor port, and measure the back pressure; or remove the converter and just see if the truck runs better.

Customer: replied 9 months ago.
Will give this a try
Customer: replied 9 months ago.
Check engine light comes on while driving
Expert:  Jerry Newton replied 9 months ago.

You can borrow a backpressure tester at places like Advance and Autozone. It might be a challenge getting the converter off in such a way that you can still run the engine, my recollection on 1995 models is that it's part of the Y pipe, but I'm not positive on that.

Do you happen to know what the trouble codes are?

Customer: replied 9 months ago.
No I don'the know
Expert:  Jerry Newton replied 9 months ago.

OK, we won't worry about that right now. Let's check that cat and see where it goes from there.

Customer: replied 9 months ago.
O'Kay we will try this
Expert:  Jerry Newton replied 9 months ago.

.