greaseman69

2000 ws6 m6 here, just went from my 25k mile TR55 copper plugs (.050 gap) to TR5 iridium (.038 gap) since allegedly GM put out a bulletin calling for these. They're NGK though, not GM. I now have a rough idle even when warm and misfire under load when cold for only a minute or 2. I have a small (?) exhaust leak from my headers at the y pipe, could the new plugs somehow be more sensitive to an off AF ratio? Checked narrowband O2 voltage and one side is consistently around .450-.550 and the other jumps anywhere from .015-.950. Any help is appreciated.

Kjduvall

im thinking you pulled a plug wire or cracked a porcelin by accident.

RPM WS6

iTrader: (3)

Me too. Cracked plug (perhaps one got dropped during the swap?) or a plug wire that either isn't fully seated or became slightly damaged during removal.

FWIW, on my '02 Z28 I went from factory platinum tipped plugs gapped at .060" to the (then) GM updated/recommended service replacement iridium plug gapped at .040" and didn't have any issues at all.

greaseman69

You're likely correct, forgot to add I actually had to replace a wire afterwards because I literally ripped the innards out of one due to how stuck it was on the plug...probably didn't do any favors to the others either.

greaseman69

Update: Installed new wires and now it runs fine. Not sure if any were damaged or if one or two weren't seated all the way. The driver side rear wire was suspiciously easy to pull off. Thanks fellas

greaseman69

Spoke too soon, cold morning today and it was acting up again. Guess I'm gonna pull the plugs and see if anything's chipped, check the gap, etc

greaseman69

Okay- pulled all plugs and wires. Closely inspected every plug, no cracks in the porcelain. Two of them on the driver side had oil on the threads, probably valve cover gasket? The problem still exists, unfortunately no code so I don't have much to go off of. Check oxygen sensors next?

Full Power

.Sounds like intake "vacuum" leak may have developed, just happened to coincide with your tugging on plug wires, hanging over the engine, etc.............. Whats your MAF trace look like at idle ? SMOOOOOTH is good .
Still, possible that you have a defective spark plug, or wire.

Y2K_Frenzy

If the problem happens when the motor is warm & cold I don’t believe I’d suspect the O2 sensors.

greaseman69

I'll check for vacuum leaks. I forgot to mention I had a Frost tune done a few years ago (LTs, air lid, egr and air pump delete) would a tune for TR55s have any issues with these plugs?

Y2K_Frenzy

No. The plugs won’t affect the tune.

greaseman69

Arrgh I'm losing my mind a little bit. Went and dropped 40 bucks on a set of TR55s just to see what would happen since those were in it before and it feels exactly the same. My new plug wires may even be a little wonky now since I've taken them off a few times already. Didn't see any possible vacuum leaks but I haven't smoke tested. What vacuum lines are even around the plugs? PCV is there but thats all I could think of bumping. Gonna be pissed if it does end up being a total coincidence like a coil pack

wannafbody

iTrader: (2)

Try misting some water from a squirt bottle on the wires and look for arcing.

greaseman69

I'll give this a try, already popped the hood in the dark a while ago and couldn't see anything but that might do it.

Also, good news, slapped some dialectric grease on the plugs and it definitely runs better. Still just a LITTLE hesitation when cold and the idle isn't perfect, but 80% better. Must still be the connection on one or two wires. Third plug wire back on the passenger side could be wiggled more easily than the others. Gonna try to swap an old wire and see if it stays tight. These are MSD by the way, never had any issues the first time I did plugs.

greaseman69

Dropped even more money on a second set of msd wires and same issue. Made positively sure they're on tight...two clicks on the coil and one on the plug every wire. One of the wires was fault and wouldn't click at all onto the coil so I have one older wire but I left it on a plug I was 90% sure was tight. Same issue!!! Pulling my hair out. Unless it's that last plug. Gonna switch another older good condition wire with that and see how it goes. Other than that, I don't have a clue. 2 sets of new plugs and 2 sets of new wires. Are there scan tools out there that will detect misfires on specific cylinders even without a code? If i know what cylinders are the issue I'll be golden.

RPM WS6

iTrader: (3)

My old AutoTap scanner will show cylinder specific misfire data like you're asking for, but this is an ancient program running on my 1997 IBM laptop with Windows 95, and it requires a serial port connection for the cable. I'm sure there are modern tuning suites that will give this same data.

Getting back to basics here; did this issue ever exist before you did the plug swap? You mentioned something about an exhaust leak at the header - if it's near an O2 sensor then I would probably fix this before digging any deeper with cylinder specific diagnosis. It does seem coincidental, but maybe this problem just happened to get worse during the plug swap (maybe something was touched/shifted/bumped that worsened the leak)?

Y2K_Frenzy

If it is giving him problems when it’s not up to operating temp then I don’t think I’d be looking at the O2 sensors. If you were to remove the sensor from the exhaust and start that car (cold) it won’t make any difference how it idles. I’ve
removed one while it was running before (cold)
and there wasn’t even a stumble.

RPM WS6

iTrader: (3)

But how are we defining "cold"? Is the OP certain that the issue occurs even when the engine is in (confirmed) open loop? Or are we just assuming 'cold' based on run time? OL will not last nearly as long if the engine had been run semi-previously (vs. true overnight cold start). Also, if the car has headers (which was mentioned early on) then it's likely been tuned at some point. Has CL (closed loop) enable temp been changed in the tune?

It's best to get answers to all of these questions before dismissing the possibility, especially since the OP has had no luck fixing this thus far.

Y2K_Frenzy

You’re correct that I am making an assumption that it was running bad when he fired it up on the cold morning that he spoke of in a previous post. I suppose it might have been running well and then it started acting up once it got up to operating temp. However, on another post he said it still has a little hesitation when cold, but it’s 80% better. I assumed he was talking about the motor being cold and not the weather. However, I could be mistaken.

99Silverado5.3

iTrader: (7)

If its misfiring you can run the car for 30 seconds, turn it off, touch the headers and see which cylinder isn't hot.