CDBiker220

Hey, a few weeks ago i decided to change the plugs on my 125K z28(stock other then cutout before axle) because i think they were the original plugs. i put in some NGK tr50's(gapped to .045) cause thats all advance auto had in stock. Took it for a test drive and it ran fine. later that night on the way home from a friends it started to miss randomly, at pretty much all rpm's when underload but was intermittent. After that for about 2 weeks it ran perfect. then i noticed it to start missing when it was idleing. since then it started missing at all rpms under load again and worse then before. I thought mabye a plug was bad or i damaged the original wires So i ordered MSD wires and tr55 plugs (.055 gap) and installed those yesterday. During a test drive i felt a miss twice but was way better then before, however on the way to work today it started missing worse then before, at around 2500rpm under load it goes into a constant miss untill you rev out of it, and still has an intermitent miss under load and will miss when sittin at idle randomly. I had a EGR code about 2 months ago that would come on for a day or so every few weeks then go away but it was doing that long before it started to misfire, i cleaned it and it seamed fine. It acctually came back today on the way to work, but can the EGR cause a misfire? I havent gotten any codes in the past two weeks except today, and i assume thats just the EGR code again. Im confused because it started right after i changed the plugs so i thought that had to be it but its still doin it on this second set. Mabye my car doesnt like NGK's? Any ideas?

camaroguy26

iTrader: (21)

you should be getting a code for the misfire and it should tell you which cylinder it is. I had this happen to me when I swapped plugs and I found out my buddy dropped the plug and cracked the ceramic around it. It ran fine at idle and light loads but under heavy loads it would miss. You might not have the wire fully seated either, same thing when I changed that cracked plug I didn't fully seat the boot and it would miss again under load.

CDBiker220

I made sure each plug wire is fully clicked onto both the plug and the coil, triple checked each one. I dont think its the plugs as this is the second new set, the plugs i pulled out with <500 miles on them looked great and were all gapped fine, no broken porcelin. Also NO misfire code. its misfiring like crazy why isnt the computer picking it up...i took it out during my lunch and if you get it to start misfiring bad at a certain rpm you can floor it and it will misfire the whole way through the rpm range, vibrates bad. but if you punch it when its not misfiring already it revs out fine. FUSTRATING....

samson_420

iTrader: (1)

Are coil packs all connected up?

Any vacuum leaks?

2001NBMZ28

See what the code is first and visit gearchatter.com and read the description/diagnostics, maybe it's not the EGR. I run NGK TR55's at .055 with no problems. Something else you can do is start the car in complete darkness and check for any arcing, like a plug wire against a header somewhere - especially if you have LT's.

CDBiker220

well i checked the code, only a 1404 egr code, could that honestly cause this? ive had that code on and off for months with no problems. Scan tool showed no misfires, even tho it almost feels like its running on 7 cylinders at this point, i checked all the wires and connection and their all perfect, im in the process of pulling a wire off one at a time, but it seams like it misses no matter what. i bought some cheap autolites i might throw in to see if it makes a difference, if not i guess i have to look into oxygen sensors or something, just feels like an electrical miss to me tho.

DSRCAM

iTrader: (3)

check your fuel injector clips that happened to me and it ended up being the fuel injector clip was loose!

CDBiker220

problem solved. Bought a set of cheapie autolites. car runs better then ever. put each plug wire on and off the NGK's again and still had the same problem before putting in the autolites. Two sets of NGK's (tr5 and tr55) gave my car serious misfire, guess it just doesnt like NGK plugs.