Some mis-firing input please....
 

Car is a '93 GT. It has heads, cam, intake, etc...5-speed car.


It starts, runs, idles fine and revs fine at a stop. Nothing wrong.

Start to take off and there's a bad bobble/misfiring under part-throttle like spark issues. Give it more gas (ie: roll into it hard) and it is not noticable...

Or, let it accelerate through the bobble to about 2400 RPM and it clears up. Otherwise no problems.

I've set timing, replaced TPS, tried another MAF, sensor and complete meter (19# injectors), and checked cap/rotor/wires, etc...). I also disconnected the MSD and ran stock ignition...no change. Still a bobble/sputter up to 2400...unless you're about 1/2 throttle or better.

My next step will be try another computer and/or distributor.

Any other suggestions? :shrug:

Re: Some mis-firing input please....
 

What's the results of a compression/leak-down test?

Re: Some mis-firing input please....
 

Pull codes.

Re: Some mis-firing input please....
 

No compression tester.
But no crankcase pressure problems. Fairly fresh motor.
Could a O2 sensor or both be causing this??? It's ONLY at very slight throttle up to 2400 RPM. Any hard throttle or past 2400 and it's fine. :think:

Re: Some mis-firing input please....
 

does it do it when cold or all the time?

Re: Some mis-firing input please....
 

any mods on the engine?

Re: Some mis-firing input please....
 

Vacuum leak possibly.

I have seen similar with O2 sensors. Even had a friend whose sensor coupler got burned on the exhaust such that he could plug it in wrong. He chased an intake backfire for weeks.

Re: Some mis-firing input please....
 

:jester:

Re: Some mis-firing input please....
 

now why didn't I think of that?!? :nono:

I bet that's it. Will let you know.

It does it cold AND warm.

(Oh I also removed the spout connector and ran straight 25º timing... it still did it so it's NOT the computer control of timing. Either vacuum or dist.)

Re: Some mis-firing input please....
 

Also try cleaning the MAF.