Okay, I'm getting some misfiring at idle. I have a spark plug question. Kinda confused. My owners manual gives 2 different gaps for the Champion spark plugs. One is smaller than the other, one PN ends in 5 and the other does not. So I "use the search no0b" and find people saying to gap at .38" and others saying to go .48"

Oy.

I checked mine and they are all sitting between .46-.48" From the one side of the tip to the other. (ie; one edge of the tip is at .46 and the other side is up against .48)

I got new plugs the day we started her up after the rebuild and AutoZone only had these Denso (?) K20PRU-11 plugs. Not the popular NGKs. :( So they are all gapped the same and look okay.

QUESTION 1: Are these the right plugs? They sound like a similar PN, but I don't know...

QUESTION 2: Should I still get the hotter range for mostly shorter distance driving in hotter climate even though I have 10.5:1 CR going on and want to avoid pre-det? Should I get normal range then?

THE SITUATION:
Idle with AC @ 800rpm. Intermittent misfire with tach dropping ~50rpm when stuttering.
Idle with no AC @ ~1000rpm. Misfire is almost non-existant. Steady idle.

AC on, some misfire during lower RPM gear changes, but otherwise runs great. Really.

Plug wires < 3000 mi old
Plugs < 3000 mi old
Coil, TPS, IAC > 143k (I have tested the TPS by reving and letting the TPS bring rpms back down, they don't go back up)
EDIT: the IAC had one bolt break off during P&P. I cut a slot in the housing from the outside and it's using one OEM bolt and another one with a nut on the back to hold it. I think it's pretty secure, but if this could be the problem, by all means...

I have CEL 31 and 25.

Should I look closer at one of the sensors or the vac lines? I'm not worried about the CEL as much as I am the misfiring/rough idle under load. Which route should I take? I know I'm looking at $20 for some silicone lines, but I don't want to pop for that if I need a new sensor.

Oy! Help a brother out?

Those codes you shot out seem to be the problem, well one anyway. Dont remember if you said you changed out the IAC but it sounds like thats a problem. Do you have your EGR hooked up? If you do make sure all the electrical/vacuum lines arnt grounding off or burning off of the hot pipe. Lots of times shit will just lay on there and burn through over time grounding out important sensors.

Changed out the fuel filter? Again i read your post but cant remember anything (alky) so im shooting in the dark. You can test your coil out with a multimeter, make sure its within spec. Your plugs seemed gapped right. I gapped mine on the short side assuming they'd widen themeselves out to the max spec by the time it's time to change the plugs again.

Check your plugs wires on the boot that goes into the head, make sure that there are no cracks where a spark could shoot out. Another way to check this is to have the car running and push each of the boots that attach to the spark plugs. You'll feel if there is a cross fire or something, it'll kidna twitch and you'll feel a sight jolt in your hand.

Other than that, I cant think of anything else right now other than sleep.

But im a noob, I just made all this up, right?:rolleyes

}(

What fuel injectors are you running? Stock, aftermarket? A faulty/dirty injector can cause a misfire code. I actually just workded on a 96 Pontiac Grand Prix with the 3.1 v6, and it was down a cylinder, missfire code. New plugs and wires no help, but traced it down to no fuel, or not enough fuel. A new injector fixed it, runs like a champ. To me, just sounds like a fuel issue...

Fuel injectors are his stock ones from 100k + miles.

Yes, Chris is right on the injectors. With the new CR, this would make me real nervous. :o I have no related codes though.

I've pretty much decided that my EVAP code is from teh roll over valve on the gas tank, but I really need to get some new vac lines going on in there.

My idle code is probably due to the fact that I used a Dremel and bored my TB and the runners in the inake manifold as much as I could, so I'm sure there are surface variations causing irregular airflow velocities in there. I've heard something like this can happen with ported vs bored TBs.

The only difference I noticed in the plugs (which would be a good indicator of fuel system performance if I'm right) would be that on the #3 and #4 plugs, the base of the plug (as in the flat surface on the bottom of the threaded body) was more black than the other two. Isn't grey or white deposits from running lean and black sootines from running rich? Left my Chiltons at the folks house.

I really need to find out what is most likely the culprit of the misfire at idle, since that's bugging me the most. I can handle a hunt at idle, as long as it's a smooth hunt. :P

Thanks for the help all! I appreciate it!

Anyway to get pics of the plugs up on here? Gives us something to look at..

I will pull them and get pics up hopefully by noon tomorrow sir. I just didn't take the camera with me when I went down to start changing sensors yesterday. :shryg

I'm going to go for the plugs.
I'm not exactly sure exactly if 10.5:1 compression is that much harder on a spark than stock, but I do know when you are boosting that it is hard for a spark to jump in that dense of air.
you might want to try gapping smaller (say .035).
I'm not that familiar with champions or their quality.
I would myself be looking into NGK's at the lower temp range with a smaller gap.

Okay. Here's the plugs. I just took these not 15 minutes ago.

Plugs are Denso K20PRU-11, gapped .46"-.48"
They are pictured in order 1-4. #1 looks maybe lean? While #4 looks to want to foul. Suggestions (other than get the NGKs today)?




TIA!

bump?

So my plugs say nothing to the experts? Bump? :o

Plugs 1-3 look great, but your #4 looks like its either too rich, or not perfect combustion. If it was an all around fuel issue, then all of your plugs would be very similar, but since its one plug, my guess is your problems lie in the #4 cylinder. I am still sticking with a fuel injector issue, that, or plug/wire issue.

I think I might swap my #1 and #4 plug wires. Leave that cleaner looking plug in cylinder 1. Then, after about a week or so(more/less time?), I can check them again. If that clean #1 plug is then fugly looking, then it would be safe to assume the injector is not the problem? If it is clean, then I guess I will have to get the injectors cleaned while I'm installing my new vac lines. :shrug...

Thanks! I'll update as I get info.