Proper Spark Plug gap?

The Adam Blaster · Jul 1, 2007

So i was out driving around yesterday and heard this completely brutal sound from the 'ole XJ...
Turns out that the 1 cylinder spark plug was no longer screwed into the block. I took them out a few weeks back while checking to see if there was any water in the engine and it must have gotten cross threaded when it was put back in.
I was planning on buying new plugs anyways, it's just going to heppen a bit sooner than i thought.

So what's the proper gap for these boys?
'98 w/4.0
auto (if that matters)

aparke4 · Jul 2, 2007

The gap spec is 0.035 for the 4.0L engine, and 0.040 for the 4.7L engine.

these are for stock or slightly modified engines - any more is not needed for the 4.0 and will result in a poor running engine - oh and simple champion plugs will work best - most here agree the oem spec plugs will yield the best results

Murph

darjevon · Jul 2, 2007

The Adam Blaster said:
So i was out driving around yesterday and heard this completely brutal sound from the 'ole XJ...
Turns out that the 1 cylinder spark plug was no longer screwed into the block. I took them out a few weeks back while checking to see if there was any water in the engine and it must have gotten cross threaded when it was put back in.
I was planning on buying new plugs anyways, it's just going to heppen a bit sooner than i thought.

So what's the proper gap for these boys?
'98 w/4.0
auto (if that matters)

If I can't find NGKs, I use champion "copper plus" plugs gapped to .035 in my 99. Any more without an ignition system upgrade and the car will likely misfire... And to avoid crossthreading, use a lot of anti-seize on the threads and screw it in with a piece of radiator hose over the insulator. Kinda old school but it's very useful, as the hose will slip before it crossthreads.

The Adam Blaster · Jul 2, 2007

My uncle-in-law thought that a piece of garden hose works the same.
Plus the first cylinder is kind of tricky to get to becaus of the rad hoses and stuff almost right on top of your access point.

Thanks for the gap info!

sharq · Jul 2, 2007

if you gap too much with an upgraded ignition system you need to start thinking about addressing fuel delivery. i was running with a performance distributors firepower ignition kit w/ plugs gapped to .055. everything was great for a while. the it would run rough after starting the motor. eventually i burned a hole in the number one piston. i dont believe the stock fuel system was delivering enough gas.

Blaine B. · Jul 2, 2007

I think the #6 plug is the worst to reach.

Proper Spark Plug gap?

The Adam Blaster

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aparke4

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darjevon

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The Adam Blaster

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sharq

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Blaine B.

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