Should I Increase the Gap of my Spark Plugs?

[streetxj]

Hello everyone. My current ignition setup is jegs performance ignition coil, accel cap and rotor, taylor 8.2mm ThunderVolt ignition wires and champion RC12LYC spark plugs .035 gap. Should I increase the gap to .040?

It's a 1996 jeep cherokee 4.0 with lots of bolt-ons.

 

[souske]

Bolt ons dont do much for an otherwise stock big stupid tractor motor.

 

[streetxj]

Bolt ons dont do much for an otherwise stock big stupid tractor motor.

And how does this answer my question on whether I should keep the stock .035 spark plug gap or increase the gap to .040?

 

[souske]

You can play with it, but I doubt you will sen any improvements.
You might throw a code, or have other issues

 

[ehall]

I tried a larger gap several years ago, jeep ran awful until I closed it down again. My guess is you would need to buff the rest of the ignition system to get away with it.

 

[streetxj]

Thanks guys. I'll just take them out to make sure they are still in good shape and make sure that the gap is still the same.

 

[Dr. Dyno]

Hello everyone. My current ignition setup is jegs performance ignition coil, accel cap and rotor, taylor 8.2mm ThunderVolt ignition wires and champion RC12LYC spark plugs .035 gap. Should I increase the gap to .040?

It's a 1996 jeep cherokee 4.0 with lots of bolt-ons.

If the coil puts out a higher voltage than stock, it might just deliver a fat enough spark for you to increase the plug gap to 0.040" or even 0.045".
The only way to find out will be through trial and error.

 

[hayhaulerleradoxj]

Yea, if your ignition coil runs hotter spark than stock you can play with the gap a little, otherwise keep them 0.35........

 

[yossarian19]

The underlying assumption in the parts list & question being asked is that the factory must have left power on the table when they spec'ed the ignition system.
To the best of my knowledge, they didn't.
Supporting my thinking is that all the stroker engine builders say "Cold air intake & exhaust needed to get the most out of these engines" and not "CAI, exhaust & ignition upgrades".
Further - to get more power out of the engine from an ignition upgrade is more or less requiring that there is unburnt gas (unrealized potential) in the exhaust stream. With emissions regulations / OBD II you can be pretty sure this isn't the case or if it is, it's a negligible amount. Catalytic converters don't like to be fuel soaked and the EFI is minimizing fuel consumption.
Basically - the EFI is designed to run WOT on the factory injectors and not destroy the cat. Unless you are running (much) bigger injectors, I doubt the ignition needs to be upgraded (unless worn out to begin with) or the plug gap opened.

 

[cruiser54]

Bolt ons dont do much for an otherwise stock big stupid tractor motor.

Ha Ha. Car engine.

OP, I think it would be a neat deal if you increased your plug gap to .040 and report back.

If the report is favorable, go to .045 and let us know those results.

 

[streetxj]

I removed the distributor cap and there was very little build up. I cleaned the terminals and the rotor. It runs very good and always did as a matter of fact. I decided not to mess with the spark plugs. Thanks for the advice guys. For future reference I've read recommendations of running Autolite AP985 spark plugs. Should I just stick to the factory champion RC12LYC spark plug recommendation or go with that other spark plug next time I do a tune-up?

 

[streetxj]

Bolt ons dont do much for an otherwise stock big stupid tractor motor.

Before I forget again to respond to that statement, my 96' tractor motor has been more responsive to bolt-ons than my old 93' 5.0 mustang gt automatic (AOD) convertible. The biggest improvement I felt was when I got rid of the log intake and swapped in the newer style 4.0 intake manifold. I'm currently using that, plus 62mm throttlebody, bosch 703 fuel injectors, gibson stainless header, factory dented pipe underneath the header collector replaced with a smooth pipe, 2.5 inch I-cannot-mention-in-any-jeep-forum :shhh:, 2.5 inch aero turbine, 2.25 inch dynomax tail pipe with 2.5 inch stainless exhaust tip. It's a 96' 2 door, 2-wheel drive, XJ automatic that weighs 3217 pounds according to the title of the vehicle. That about the same weight as an 87-93 mustang 5.0 hatchback, but with aerodynamics of a garden shed. lol I'm pretty sure it can troll lots of ricers and be a good challenge for stockish 5.0 mustangs (foxbodies and sn95's) up to 80-85mph. I don't street race, just in case anyone is wondering.

 

[Dr. Dyno]

Should I just stick to the factory champion RC12LYC spark plug recommendation

Yes. I'm running the same plugs as they came out of the box pre-gapped.

 

[streetxj]

Cool. Thanks
Even if they come pre-gapped, I always check them to make sure they are all .035 cause they can come with gap imperfections.

 

[00BlackClassic]

I don't think I've EVER come across a set of plugs that was "pregapped" I think they're assembled and its just where they end up once their built. But ALWAYS, ALWAYS check your gap before putting in plugs. It only takes a minute and I've never had a set have a consistent gap.

 

[Fred]

My experience with my 90 is that ignition mods make no difference. I will say that it "seat of pants" seems to run a little better when everything is new. In regards to gap, when we bought a 99 WJ with the coil on plug 4.0, it ran fine. It had 50k miles. I pulled the plugs, the gaps were .050 or more. New plugs at .035 made no measurable difference in MPG.

 

[Ewenm]

I have a scream demon ignition oil in my xj and run 0.45 gap, have done for a couple of years and it seems to run well for me

 

[Dr. Dyno]

I have a screamin' demon ignition oil in my xj and run 0.45 gap, have done for a couple of years and it seems to run well for me

In my XJ, the screaming demon is usually the person sitting in the driver's seat.

 

[UncleSarge58]

FWIW My 96 2 door XJ 4.0 HO w/ Mallory Coil & 8.5mm Plug Wires, Runs best w/ Stock Number Champion Copper Core Plugs @ 0.36 Gap.
Been Runnin Them this way for the last 5 Years.
Tried Up to 0.40 & backed off in 0.02 Increments over a period of days.
0.40 Ran Really Crappy w/ Lots of Misfires.
0.38 Ran Great under Heavy Acceleration @ WOT Pedal to the Metal.
But, 0.36 Has turned out to be the Best for All around Performance & Gas Mileage.
Just my 2 cents,
UncleSarge58

 

[cruiser54]

FWIW My 96 2 door XJ 4.0 HO w/ Mallory Coil & 8.5mm Plug Wires, Runs best w/ Stock Number Champion Copper Core Plugs @ 0.36 Gap.
Been Runnin Them this way for the last 5 Years.
Tried Up to 0.40 & backed off in 0.02 Increments over a period of days.
0.40 Ran Really Crappy w/ Lots of Misfires.
0.38 Ran Great under Heavy Acceleration @ WOT Pedal to the Metal.
But, 0.36 Has turned out to be the Best for All around Performance & Gas Mileage.
Just my 2 cents,
UncleSarge58

You're missing some zeroes I'm thinking..

So, all that to gap your plugs one thousandth of an inch larger than stock?

I'm confused.