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Jumping spark #800214 03/25/07 08:45 PM
Joined: Apr 2000
Posts: 947
Berkeley Offline OP
Jeep Moderator
I noticed a sweet little bolt o' lightning jumping from the top of my #5 plug boot to the block today. Probably not a good thing. This could be *the* reason the XJ has been running so poorly, or it could be *one* of the reasons it's rough. Pre-HO Renix 4.0, btw. After restarting, the spark was not jumping anymore.

Time to buy new plug wires, or could there be something else wrong, too?

Re: Jumping spark [Re: Berkeley] #800215 03/25/07 08:51 PM
Joined: Oct 2003
Posts: 7,768
BigJim Offline
Web Wheeler
I see you live in a coastal area.. Lots of humidity? That is what kills wires. Unless the plugs are gapped at .60 or so I'd bet a new wire set will cure your ills.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />


professional bovine relocation specialist
Re: Jumping spark [Re: BigJim] #800216 03/26/07 08:26 AM
Joined: Apr 2000
Posts: 947
Berkeley Offline OP
Jeep Moderator
Not much humidity around here, cause we're protected by the coastal range.

Just had the plugs changed... you suppose the high school shop kids might not have adjusted the gaps exactly right? <img src="/forums/images/graemlins/smile.gif" alt="" /> I'll check! (then, buy new wires)

Re: Jumping spark [Re: Berkeley] #800217 03/26/07 02:20 PM
Joined: Oct 2003
Posts: 7,768
BigJim Offline
Web Wheeler
I'd bet the hischool guy broke the wire tugging it off of the last plug...that's what I have done anyway!
For that reason alone I always change wires with a plug change. Unless the wires are new and I am fooling around changing plug temps... But after a couple of years the conductors inside the wires break too easily when they are tugged on.
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />


professional bovine relocation specialist
Re: Jumping spark [Re: BigJim] #800218 03/29/07 03:26 AM
Joined: Apr 2000
Posts: 947
Berkeley Offline OP
Jeep Moderator
I pulled all the plugs, and they're perfect. Perfect meaning all identical... ~0.037". I couldn't find a direct reference to the '90 4.0L gap anywhere, and my underhood decal is covered up with my compressor.

The new wires worked wonders. My 16yo daughter even called me from school to tell me how much better it ran. Woot!

Thanks for the help! <img src="/forums/images/graemlins/kewl.gif" alt="" />


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