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Old 10-28-2010, 06:35 AM   #1
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Question Coil Rail

Question. On a 04 4.0 the coill rail are cyl. 1&2, 3&4, 5,6 on the same section or coil. The reason Im asking is I'm having problem(another post) and I changed out my plugs after reading some very good info on this forum and spark plug for 1&2 had black carbon on them and I am getting a p0301 and p0302 also a p0300. the other plugs where fine. So I guess i am trying to decide to try a coil rail next to solve problems. Ive done IAC TPS new o2 sensors ran seafoam through engine yesterday

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Old 10-28-2010, 09:32 AM   #2
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Shortly after I bought mine, it threw a code and went into limp mode. I replaced the coil and plugs and no more problem. The funny thing is, the problem could have been caused by just dampness from washing the engine. Good luck.

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Old 10-28-2010, 12:09 PM   #3
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They look like they fire like you said, but they don't.

The 3 coils are in a line, but inside the potting they have straps or wires directing the spark to the appropriate cylinders.

The 4.0 firing order is 153624 (15 too young, 36 too old, 24 just right.)

They fire in pairs - each coil fires 2 cylinders at a time - in each firing one fires a cylinder under compression on the firing stroke, the other cylinder fires after the exhaust valve closed and before the intake opens. That's called the waste spark.

They fire complimentary or companion cylinders together:
1 and 6
5 and 2
3 and 4

A good way I've found to find a bad coil rail - LISTEN carefully. If you hear it sparking it's shorting inside.
Another good way - rev it for about one minute - go underneath while it's running - use a laser thermometer right on the exhaust outlets. If the rail is breaking down one cylinder will be colder than the others, and the complimentary (companion) cylinder will be too hot.

The last resort - swap it out.

Too bad there's no fixing them.

Be sure to get high quality coil rails. Autozone and the like sell a Chinese knock-off, it may last a few months. Dealers, NAPA, Car Quest sell better quality - made by Standard Ignition. They cost a little more but are well worth it!
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Old 10-28-2010, 05:13 PM   #4
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Quote:
Originally Posted by rrich View Post

The 4.0 firing order is 153624 (15 too young, 36 too old, 24 just right.)
Thats pretty good, never heard that one before!!!
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Old 10-28-2010, 07:38 PM   #5
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what is the average price on a quality coil rail?
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Old 10-28-2010, 08:38 PM   #6
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I picked up a coil rail on way home from work. I got it from autozone (before I read not to go there) It has a 2 year warranty so ill chance it. Any it was 129 and change out the door. Guess what it solved the problem (or at least so far)i will run it hard tomorrow and repost. Tell you what this site you guys have a world of information and I want to thank everyone who responded to my problems and helped me solve the problem. Jeep is like no other vehicle Ive owned and I'm loving it
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Old 08-03-2012, 04:20 PM   #7
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Quote:
Originally Posted by Mr Custom View Post
I picked up a coil rail on way home from work. I got it from autozone (before I read not to go there) It has a 2 year warranty so ill chance it. Any it was 129 and change out the door. Guess what it solved the problem (or at least so far)i will run it hard tomorrow and repost. Tell you what this site you guys have a world of information and I want to thank everyone who responded to my problems and helped me solve the problem. Jeep is like no other vehicle Ive owned and I'm loving it


what do you mean by "coil rail?" I'm not sure I know what that is, but I am having the same issues and want to look into my coil rail.
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Old 08-03-2012, 04:33 PM   #8
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Quote:
Originally Posted by Olive Beast

what do you mean by "coil rail?" I'm not sure I know what that is, but I am having the same issues and want to look into my coil rail.
All your coil packs are made as 1 unit, like a rail
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Old 09-25-2014, 05:34 PM   #9
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Coil Rail

I bought a new coil rail off of Amazon for about $129.00. It lasted about 7 months and then went bad without warning. Spend the extra $ and buy Jeep parts!! It cost about $229.00 at Jeep.

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