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4.0 Spark Plugs


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I’m trying to decide which spark plug to try in my ‘89 comanche. It has a ‘97 4.0 tj motor/head in it with the ’89 renix stuff, intake, exhaust, dist, etc.

 

I bought the jeep with the motor already swapped in. It has bosch super r6 plugs in it. I could go 3 ways on this. What do you think? tipshades.gif

 

Use the recommended champion rc9yc or equivalent for an ’89 comanche 4.0.

Use the recommended champion rc12ecc or equivalent for a ’97 tj 4.0.

Use the recommended champion rc12lyc or equivalent I already use in my ’91 cherokee 4.0.

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I read that same thing about the rc12ecc while I was surfing around. I’m wondering why the ’89 mj uses a cold plug like the rc9yc and my ’91 xj doesn’t. The only real difference is renix, right?

 

I actually plan on using bosch super equivalent at some point.tipshades.gif

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The only real difference is renix, right?

 

 

The ignition system works way different. Which is probably part of the reason?

 

 

I'm not a spark plug guy. I ran champions since I bought the truck. The same champions that is. I bought some NGKs for this 'rebuild' because the store didn't stock champions. And I wanted to set the gap for propane (which I didn't actually do in the end, I just threw them in. I will regap after I talk to the propane guy)

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I’m trying to decide which spark plug to try in my ‘89 comanche. It has a ‘97 4.0 tj motor/head in it with the ’89 renix stuff, intake, exhaust, dist, etc.

 

I bought the jeep with the motor already swapped in. It has bosch super r6 plugs in it. I could go 3 ways on this. What do you think? tipshades.gif

 

Use the recommended champion rc9yc or equivalent for an ’89 comanche 4.0.

Use the recommended champion rc12ecc or equivalent for a ’97 tj 4.0.

Use the recommended champion rc12lyc or equivalent I already use in my ’91 cherokee 4.0.

 

haha, let me get this straight... you bought a red 1989 MJ with a 4.0 from a 1997 TJ swapped in before you bought the truck.

 

this world is pretty small.. (check my sig. line) :D :yes:

 

i run the recommended 89 cheapo- champions for the record.

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haha, let me get this straight... you bought a red 1989 MJ with a 4.0 from a 1997 TJ swapped in before you bought the truck.

 

this world is pretty small.. (check my sig. line) :D :yes:

 

i run the recommended 89 cheapo- champions for the record.

 

Hmm, I think you’re my new best buddy here, lol. I have all kinds of questions about this setup coming up.

 

I’ll try the stock cold plugs for now.tipshades.gif

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I think the major difference is going to be the EGR system that the renix motor has. If you've got the 97+ intake and no EGR, I'd run the hotter plug, as the camshaft has different timing/overlaps and was designed for the hotter plug to pass emmissions and the like.

 

anyway, my junk get's champions, because the bosch made it run like @$$. besides, it's not a race car, am I really missing that extra 5 horse?

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I think the major difference is going to be the EGR system that the renix motor has. If you've got the 97+ intake and no EGR, I'd run the hotter plug, as the camshaft has different timing/overlaps and was designed for the hotter plug to pass emmissions and the like.

 

anyway, my junk get's champions, because the bosch made it run like @$$. besides, it's not a race car, am I really missing that extra 5 horse?

 

good point, and speaking of... i did fail emissions. (and havent passed yet)

 

shoot away man, my junk has treated me GREAT the year and a half ive had it, and passed emissions with flying colors the first year. (ill have to check with the newer plugs... hm)

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That’s my problem, too. It runs great but failed co2 badly according to the po. I have the egr and everything looks good but something is wrong. Looks like a few new sensors were put in with the engine swap or after it failed emissions and it has a brand new cat that was put in after it failed emissions. It barely passed hydrocarbons according to the po.

 

The engine swap was done a year before the po registered the truck with a city address and then needed emission testing so as far as I know it’s never passed emissions since the swap as it didn’t need to. Then it started running bad right before he sold it to me but it runs great to me.

 

I can only get two more temp registrations for a year so I have to get this truck to pass first time I try. You can only get three a year and I got one to drive it home when I bought it. The vehicle plates stay with the owner in this county. tipshades.gif

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yeah, vehicle plates stay with owner here too, i 'sold' it to my bro and he registered it out of the city to avoid emissions but i gotta pass by october.

 

i failed CO, and my truck actually does NOT have the EGR system.

 

since the passed test and before the failed test i have

1) durin first test it was running at 240ish degrees, fixed that problem, 210ish now.

2) new fuel injectors from 5-0 ford. (Same #/hr rate)

3) new fuel pressure regulator.

 

and i think thats it that would have to do with emissions. my guess for my truck is o2 sensor but idk. cat looks newish

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