fox128

I've been researching for some time but can't find someone that has the same problem I do.

I just picked up a 1990 XJ with a Renix 4.0 that runs awesome when its cold all the way through the rpm range. Once its warm it still idles and runs fine until I stomp on the throttle it will sputter and miss. If I slowly rev it up it won't miss a beat. Its the same under load, if I floor it, it misses, if I slowly accelerate no problem.

Is this some sensor or timing or what? I'm not sure where to start looking so I would appreciate any input!

ZINGGG

This happened to me. Replaced the spark plug wires with some 8 mm wire and all was fixed. When was the last time you did a tune up?

DFlintstone

X2 Have you done basic tune-up stuff/checked the plugs? Do you know if/when the 02 sensor has been changed?

cruiser54

X3. New plugs (Champion Copper), quality wires, cap and rotor with brass contacts. Clean the throttle body. That's what is due for a tune-up every 30,000 miles.

fox128

Actually I just bought it yesterday so.....no I have not done a tune-up recently. When i test drove it, the thing ran great, but I didn't get it fully warmed up. Once I got it home and got it hot it started to miss. The PO said he only drove it like once in the last year, maybe this is why.

I'll start with a tune-up and go from there I guess!

Here's what i got for $1200. Didn't think i could go wrong considering it has a year-old RC 6.5" long arm and a SYE with a tom woods driveshaft on 35" BFGs. just gotta get it to run right.....

ZINGGG

Sounds like a pretty sweet deal if you ask me! Good find

SneakyXj

I'm having issue with my wires arching across each other..at night you can see little blue archs jumping from 1 wire to the next..its weird, what causes this?

I have a stumble & miss in mine to..If I roll into the throttle no issue, if I floor it from a stop I'll get slight misfires from idle-2000 or so rpm..wonder why?
This is with a full tune up, new everything..Never buying autozone wires again lol thats for sure!

ZINGGG

Recheck that you have the firing order correct. You may have gotten a couple wires mixed up

SneakyXj

Nope all correct, and my jeep drives great..I daily drive it 48 miles a day. But I get get that weird issue and its only when going WOT. If I'm over 2000rpm and I floor it no issue..but taking off from a dead stop at wot it will stumble until your past 1800-2000rpm then go..its in no way super terrible or anything, but it does happen. Its a small hickup, and I jsut learned to roll into the throttle a little more vs smashing it down.
I honestly wrote it off as a Renix thing...
And the arch I think is because the shotty Duralast wires I have. If not then idk, all is correct and all in new in the jeep?

ZINGGG

Yeah I haven't had the best experience with autozone parts either... Try replacing them with a quality brand like Accel

SneakyXj

Today I let it idle, and heard a clicking, zapping sound..never heard before! Its the damn wires literally arch with a say fishing line size arch from wire to wire.
Loud enough to make a sound lol..so they are deffinetly getting replaced.
Any other reason the arch would jump other than shotty wires?

cruiser54

Crappy wires.........

DFlintstone

X2^...Even when I spaced it out and let my plug gap's go up over .45, I didn't have any arcing. Now if the electrodes where farther gone.......

cruiser54

Champion Copper plugs, new dizzy cap and rotor with brass, not aluminum contacts, quality wires like Napa/Belden every 30,000 miles.

fox128

I swapped plug wires with one of my parts jeeps and it helped. It acts up a little if I let it get too warm but it is bearable for now. If I decide to keep it in one piece I'll put all new ignition parts in it. Thanks for the help!