Gillespie1082

So i recently bought a 97 Z28 LT1 and it had a #2 mis fire. well i have replaced the opti (the whole thing) all plug wires and the plugs themselves. the cylinder also as perfect compression and i have even switched the fuel injectors to see if the miss would move to another cylinder. consistently through all of my troubles the car has maintained its #2 miss... any suggestions on what to go to next?

parkers Z28

Strange ?? clean the connection on the opit. ( the wiring harness ) swap the #2 plug wire with another plug wire.

slick1hunting

I would consider visually inspecting #2 with existing wire connected for weak or inconsistant spark(compare with another easy to get to plug). I also would look at it in the dark for any arcing(extra attention by headers or exhaust manifold as well as the plug boots. What opti did you replace with? Did you loctite the rotor? I would also inspect the opti harness for any corosion or open wires(and give a little dielectric grease).


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Injuneer

Might want to check for a problem with the crank position sensor..... loose reluctor, reluctor contacting timing cover or sensor.

Gillespie1082

I've done all of these things sadly.. dialectic grease on everything and have switched the whole #2wire to the #4 cylinder and still had the miss on #2 and have checked the spark on it, it looked a little weak before I switched the wires and plugs (also no arcing anywere not even down at the opti). I will re check the spark once home. I'm actually in highschool and am in a auto tech class my teacher is telling me to switch the injector lines and not the whole injector to see if its a computer issue. Can I do this? And if so would it throw timing off by switching the lines to a different cylinder causing it to try and spark at wrong times? If I confused anyone in all of those words I will be happy to re-word them

Gillespie1082

We actually started with a new plug first, then replaced them all, then a new wire, then replaced them all, We pulled the opti and found a lot of corrosion and the purge lines rotted (as well as reversed). replaced all that, cleaned the metal plate and base as well as the sensor with elec cleaner. air dried and blew it all clean and installed a new rotor and cap. Same problem. Next We did use a cheaper version of a new opti assy but wanted to try that first. Even if it went out in a week we'd know it fixed it then replace with a delco or equivalent (it's not too hard to remove, labor cheaper than the 450 for a delco). This new assy still gives a #2 misfire. The harness is the same (not replaced but we did clean the connector). and have not checked the crank sensor. This cyl isn't contributing by that I mean removing the inj harness makes no difference. I can pull #4 0r any other cyl and hear an immediate miss. Compression is 175-180lbs same as other cyls. and have not done a leak down test. Thanks

Vader

Perhaps an intake manifold gasket leak? Does the cylinder pick up as the throttle is opened? In other words does it only misfire at idle?

Gillespie1082

I haven't pulled it at an elevated RPM only idle. Looked for an rpm drop when removed (with my code reader). I can run it up to about 1500 or 2k and remove see what happens when the inj is disconnected. Will do. How would the crank sensor effect it as stated Injuneer states above. Could it not be picking up a crank position in that spot? Not sure if it detects all cyl locations or just rpm. Way I undertood it the CS looks for hesitation in crank speed in conjunction with high res opti signal to determine which cyl is missing.

ACE1252

Why haven't you guys put an ignition scope on it? Your high school program not have one?

You can also use an oscilloscope to look at the wave form of the injector. That alone can tell you if the injector is opening and closing(there is pintle bounce on the tail end of the waveform that shows it opened and closed). No pintle bounce, means dead injector.

You should find this Youtube channel very helpful. This guy knows his stuff....

www.youtube.com/user/ScannerDanner

There are several misfire case studies in his videos. He shows how to examine the ignition system for misfire issues. Check them out.

Z28Freak86

Check for power to the injector from battery, pluse from ecm, and check to make sure the harness on your injector ground correctly. Switching the Injector completely makes me think that there may be a frayed wire to the injector or may not be grounding correctly.

Gillespie1082

used a noid light and everything looks to be working properly. Consistent blink on the light not intermittent.