opinions wanted about misfiring.

[pointer80]

Hello all. I have a 97 ext. cab 4x4 z71 that I just picked up. It has a constant misfire on number 4 cylinder. Also a occasional miss on number 6 cylinder. I have changed plugs and checked wires. I have put in cap and rotor. Did compression check and it came out great. What is the next step. My mechanic says maybe timing (which he is thinking of computer being bad throwing the timing off or maybe a injector? What do you guys think? Thank you in advance.

[franken]

Put a light on each wire as it misses and see if the plug is firing, or if another cylinder is firing when it shouldn't?
An easy check is open the hood after dark w/ lights off and see if you see blue sparks, particularly when it misses. This is so basic its a forehead slapper when you find a problem.
My guess is a bad wire on number 4 and crossfire on 6...

[speedygonzales]

There is no timing issues in the traditional sense. If the the distributor were installed wrong, the check engine light would be lit.

Looking at plug wires means nothing.

How did the plugs you took out look? What was the gap you used on the new ones? Should be .060

For experiment try switching plug wires with a known good cylinder to the bad one. See if the misfire moves to the other cylinder.

Have the cam sensor retard checked when you have time . A good scanner like those from Snap-on are needed to check the placement of the distributor.

[pointer80]

When I took it in the service engine soon light was flashing. The plug on no. 4 cylinder looked bad and so did the cap and rotor. I believe my mechanic already checked the wires and they were good. The vehicle ran good and then I started it up one day after setting and it had the miss and ran rough.

[Kudzupatch]

Originally Posted by speedygonzales

Looking at plug wires means nothing.

For experiment try switching plug wires with a known good cylinder to the bad one. See if the misfire moves to the other cylinder.

I searched for a random misfire for months. Turned out to be my NEW plug wires. And they were not the cheap wires either. It finally got to bad I could hear it arcing and the idle would get rough at the same time. Never assume new parts are good parts!