OBDII scan showing multiple misfires NEEP HELP!

[jabsTJ]

Ok new 4.6L stroker ran great for first 400 miles after being installed. On my way home last week on a long up hill grade I shifted down into 4th and ran this grade accelerating to over 4k rpms and let off and the check engine light came on then I had a low rpm misfire and misfire while at constant speed not accelerating or decelerating. OBDII scanner is showing "random misfire" and misfires on all cylinders but 1 and 5. Any ideas on where I should start? Its a comp cam 68-231-4 and the head was completely redone with hesco springs and all I am hoping its not a burnt valve(s).

[IH 392]

Every time I've seen misfires setting codes it's been the plugs, WIRES, or the cap and rotor, make sure you're not running lean or rich, how are you ignition parts???

[Biggrnjeep97]

Every time I've seen misfires setting codes it's been the plugs, WIRES, or the cap and rotor, make sure you're not running lean or rich, how are you ignition parts???

I agree. Use a good quality replacement part. The factory parts, imo, arent the greatest ever, but they are leaps and bounds better than aftermarket. The SOP at the jeep dealer i worked at was to always replace the secondary ignition parts first with a P030x code(s). This does depend on what year 4.0 you have; the 0331 heads have coil on plug setup, so there are no secondary ignition parts, just plugs. BTW was it wet outside when the misfire started?
Cheers,
Will

[jabsTJ]

plugs (champion 412 coppers), wires (autolite), and cap and rotor (napa brass terminals) were all new on this build. My concern is possibly a burnt valve from running under load at about 4k rpms for 20-30 seconds. Is this a possibility too you guys think? I guess I need to start by pulling the plugs and see what they look like. It was dry when this happened not wet at all...

[jabsTJ]

its an 0630 ported head by the way, stock valve sizes

[4.whoa]

When you pull the plugs, double check the gaps. I i've had a plug slip when installing it and the gap changed

[IH 392]

I stopped using Champions 20 years ago, CRAP!, all my 4 stoke engines get AUTOLITE's, my 2 strokes get NGK's, I also don't use carbon core wires, all my engines get spiral cores for RF issues or solid wire if RF isn't an issue, the ECLIN cap and rotor are good components.

[SilverXJ]

x2. Not a fan of champion either. I tried them twice. Once was in my 2000 with the heat soak/cold start issue. Made it worse. I now use NGK for everything.

[amcinstaller]

i grew up using NGK. my dad used to get them for our dirt bikes, and i just grab them now for all my cars when i buy them, never know how long ago the PO did them

[jabsTJ]

pulled all plugs and they look good and all cylinders were right at 175psi on compression test......maybe I'll pick up some autolite plugs to give them a go....

[Biggrnjeep97]

were all new on this build.

With my personal experiences in the past, just cause theyre new, doesnt mean theyre good. Many a part store has sold me a new bad part.

[amcinstaller]

i just pulled a reverse light switch out of the wifes cavvy that tests fine on the bench with my meter, but doesnt work in the car. like bigger said, if it looks good, might not be.

[jabsTJ]

OK put in new autolite 985's and still doing the same thing. Cylinder #1 plug was not in great shape though I was actually under decent light this time and the electrode looked burnt/melted a bit. A mechanic heard what I thought was just an exhaust rattle today and he seems to think my catalytic converter fell apart inside. So I am getting that taken care of tomorrow hoping that does something...

[SkylinesSuck]

Maybe I missed it but did you replace the wires?

[jabsTJ]

Yeah wires were replaced....found out whoever owned the jeep before me welded three pieces of pipe over the inlets/outlets of the cat that was on there. The inside diameter was literally about an 1-3/4". That woke the stroker up putting true 2-1/2 inch exhaust the whole way back with a high flo cat. Still got a very minor almost unnoticeable pop at idle but I can live with that. I think the cat was most of my problem, undersized and coming apart....