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Old 08-09-2010, 05:00 PM   #31
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Originally Posted by Wrangler97-EEK View Post
You say nothin more than 87 octane? My 97 is not adjustable on timing and idles at 17 degrees btdc. You can tell the difference between 87 and 92.
The TJ's engine will not run any differently with 87 vs. 92. Really, aside from a possible Placebo Effect.

There is no knock sensor in the 4.0L engine so there is nothing in the computer that could advance the timing to take advantage of a higher octane, even if the engine's compression warranted use of a higher octane which it does not.

Trust me, your engine isn't running any differently with 92 octane. In fact, in an engine without a knock sensor to help with the engine timing, running a higher octane than the engine was designed for can even leave deposits in the combustion chambers behind. That is because higher octane gasolines are not as easily ignited and they are slower burning than a lower octane gasoline.

By itself and without an engine designed to run a higher octane, an engine will run no differently and have no more power or run more cleanly than a similar engine running the standard level of octane it was designed for.

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Old 08-09-2010, 06:34 PM   #32
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I always recommend to use the OE plugs at my shop. Always had problems when varying too much in plugs.

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Old 08-09-2010, 06:40 PM   #33
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stopped in several places today and couldnt find a single Autolite APP985. NAPA ordered them and said they would be in 7am tomorrow. They tried and tried to sell me something else but I told them I would just wait.
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Old 08-10-2010, 09:00 AM   #34
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Spark plugs

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Originally Posted by sbregister34 View Post
I always recommend to use the OE plugs at my shop. Always had problems when varying too much in plugs.
The reason for that is some maunfacturers do a great job matching heat ranges, some do not. I work for Autolite so I am not going to name the names of those who do not! We make OE plugs under several brand names. That said, an engine doesnt have any idea what brand of plug is in it, it only knows if its good or not. We work very hard to match OE heat ranges and never have a problem. If any of you would like to learn more about spark plug metalurgy, heat ranges, DIS and other ignition systems, go to Autolite Challenge Professional Technician Program: Home Page. Register and watch the videos #1 and #5. If you watch all six and answer the questions by august 31st, you will win a free Carhart jacket.

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Old 08-15-2010, 04:50 PM   #35
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Did you do the plain jane AP985?
No I just went with plain 985's The AP985 will be the wrong plug, the APP985 would however work. Jerry gave me the info and I can't believe how much better it runs. This site is great, especially if you're a first time Jeep owner like myself.
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Old 08-15-2010, 06:19 PM   #36
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Under the hood, top of the firewall, driver's side - a white label - it tells what plugs that particular engine was designed to use. Not all 4.0's are the same, some are different, due to small head changes etc.

Bosch and many of the others - especially many of the "trick performance plugs" go by "one size fits all." If it fits the hole, they say to use it. Just because a plug that's designed for a Yugo fits the hole it doesn't mean it's the right one. Ask your wife how "one size fits all" fits her.
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Old 08-15-2010, 06:58 PM   #37
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Take that spark plug and ignition course Motorking provided above Rich, you will be surprised at some of the information contained within it. Especially what plugs DIS engines require which of course includes the newer distributorless 4.0L engine. Especially in the #1 module that is only about 15 minutes long. I completed all six modules, it was worth the just over an hour it took.
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Old 08-15-2010, 09:40 PM   #38
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Interesting - so far I've only had time to do module 6 - but I will do them all.

As both of us speculated a year ago, the misfire code for a particular cylinder is detected by that cylinder not contributing to the rotation. They showed a square wave pattern from the CPS - with a missing pulse. That's what the PCM is monitoring. I've seen that CPS pattern many times with my software, but I guess never with a misfire.

They said people expect more than 30K miles on a set of plugs, that's why the plats. My '03 Rubi new didn't come with Plats. It had what the label said.

I haven't worked on it for a while, but I'm still trying to make an adapter so a conventional scope pattern can be seen with the coil rail. It would be nice to see the scope pattern - it can tell lots of things at a glance.
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Old 08-15-2010, 10:25 PM   #39
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My automotive teacher once told me when it comes to spark plugs, stick with OEM, all the high dollar stuff is just snake oil.
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Old 08-15-2010, 11:16 PM   #40
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Originally Posted by Jerry Bransford View Post
Take that spark plug and ignition course Motorking provided above Rich, you will be surprised at some of the information contained within it. Especially what plugs DIS engines require which of course includes the newer distributorless 4.0L engine. Especially in the #1 module that is only about 15 minutes long. I completed all six modules, it was worth the just over an hour it took.
Hey Jerry, was there any great revelation in that course ? I went to register but it seemed Autolite only wanted professional mechanics to take the course. The required fields included employers and managers names etc.
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Old 08-16-2010, 12:43 PM   #41
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Originally Posted by rrich View Post
Interesting - so far I've only had time to do module 6 - but I will do them all.

As both of us speculated a year ago, the misfire code for a particular cylinder is detected by that cylinder not contributing to the rotation. They showed a square wave pattern from the CPS - with a missing pulse. That's what the PCM is monitoring. I've seen that CPS pattern many times with my software, but I guess never with a misfire.

They said people expect more than 30K miles on a set of plugs, that's why the plats. My '03 Rubi new didn't come with Plats. It had what the label said.

I haven't worked on it for a while, but I'm still trying to make an adapter so a conventional scope pattern can be seen with the coil rail. It would be nice to see the scope pattern - it can tell lots of things at a glance.
It was module #1 that I especially wanted you in particular to see.
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Old 08-16-2010, 02:38 PM   #42
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I finished the rest of them this morning. I'd recommend everyone watch it - good information.

During one of the modules the guy said the 3 most important things are fuel, spark, and compression. My wife argued - "No! The 3 most important things are finding the keys, lipstick, and the cell phone."

I'm not so old and closed minded I can't try new things. I've had lots of bad experiences with plats - based on experience. Starting years ago when they first got popular I still had my dyno performance shops - sold the last one in '84. Every time, with no exceptions, plats always caused misfire and terrible running. We did not work on imported cars - they seemed to work OK in some of those. I would not stock plats, nor would I install them.
I tried them quite a few times using my dyno - even experimented with the heat ranges - all bad results.
But I don't remember what they were - possibly Bosch. I threw the Bosch rep out - I would not stock or use his junk.

My mainstay was Champions.

Champion was very good to me - when we'd build up a race engine I'd call the Champ Rep - he'd come out to my shop and use his equipment - pyrometers, internal cameras, etc to determine the right plug to use. Things like indexing, reach, and the heat ranges at low, med, and high speeds as well as heavy and light loads. He'd spend 2 or 3 hours on the dyno. In turn I let him use the dyno for some of his projects.

I'd think Jeep would understand the reasoning behind the double plats with waste spark ignitions. Why don't they call out plats on the underhood label?

Now in my limited business at home - (I thought I retired) - when it's been a misfiring problem and I found plats, trashcan time. Using the plugs called out on the label has always worked - when it was a plug issue.

But - after seeing the video - and years have passed since I became prejudiced - technology must have changed - I'll try a set in my Rubi.

You can teach old dogs new tricks - it's just more difficult.
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Old 10-10-2010, 01:57 PM   #43
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Champion Truck Plug 4412

Just thought I'd throw this link out there:

ChampionSparkplugs.com - Cross Reference Search Results

Looks like it is true that the Champion Truck Plug (4412) actually has been discontinued.

Just an FYI
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Old 10-10-2010, 02:42 PM   #44
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So with the stock plugs, what mileage should I start to think about replacing them? 2006 4.0L. Distributorless.
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Old 10-10-2010, 02:48 PM   #45
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25K miles is about as much as I'd trust conventional spark plugs, especially in a distributorless engine that will go through conventional plugs nearly twice as fast.
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Old 10-10-2010, 07:41 PM   #46
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Thanks, I got 23000, might explain why it occasionally idles slightly rough, looks like I got a(nother) project!
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Old 10-10-2010, 09:28 PM   #47
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Jerry is right. Higher octane in any low compression engine does nothing for performance. Keep using 87 octane. High octane is used to prevent detonation in higher compression engines. Using a higher grade fuel will just waste your money.
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Old 12-22-2013, 01:09 PM   #48
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Bosch plugs bad, High octane good.

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Originally Posted by drivebytruckerz View Post
Just like it's love of 87 octane (simple) gasoline.. the Chrysler 4.0, as stated by pokey, are simple engines and are made to be maintained simply with simple, common parts. Just stick with the basics.
I've also had bad experiences with Bosch plugs. On 4.0 and other engines. I think it's because of the tiny center electrode. Any blowby or stem seal leakage will foul them in no time. First experienced this on a '68 Ford 302. Maybe they're OK on BMW or whatever, but on US made pushrod engines, no dice. For me, it's NGK, Denso or Champion all the way.

On a side note, in my experience 4.0s and lightly modded 258s both really like 93 Octane. 87 is OK, but I get almost 10% better fuel mileage using high-test. I wonder if this is unique to my vehicles and/or climate. I advance the timing quite a bit on the distributor models, and usually use platinum plugs.
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Old 12-22-2013, 01:18 PM   #49
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Increasing the octane above what the engine was designed for will not affect its mpg in the least. In fact, the higher the octane, the harder it is to ignite and the slower it burns. If running a higher octane gasoline by itself improved fuel economy, you can bet Obama or the EPA would have long ago mandated its use.

I'm not making this up, even the EPA agrees with what I said here.

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