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Old 01-07-2009, 08:22 AM   #1
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Coil bar for 4.0L

I have a 2006 Unlimited with around 65,000 miles. I have a vibration under load that has been traced to the engine but is not the mounts. I believe that I have a bad coil.

From one source that I met that was a service adviser with a Jeep dealer he said it was the ignition coil.

Is this a common issue? Is it recommended to stay with the OEM setup? Dealer has it for $230.00 local auto parts store for $120.00

Any thoughts?

Thanks

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Old 01-07-2009, 08:27 AM   #2
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If you really do have a bad coil then you could just buy a msd or accel coil and you should be fine.

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flowmaster40,hpd30 with aussie locker,currie upper joints,4.88's, lca skids,chromo shafts,vanco brakes,d35 with super 35 and arb locker,re 4.5" springs,currie arms,re front uppers,Re shocks in back,walkerevens shocks up front, Re track bars with currie jj joints,anti rock,ss brake lines,re rear sway bar links,jks 1.25" bl and mml,bfg 35x12.5 km2's,craiger soft 8's,ome steering stabilizer,currie hd steering,rockmen front bumper,emp tank skid,lots more too.
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Old 01-07-2009, 08:30 AM   #3
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Maybe I am not too smart, but they don't appear to replace the integrated coil bar that is in my engine. I am guessing that I can replace the 3 individual coils on the top of the rail, but not easily.

Is this easy to do? I am relatively mechanically inclined, but not an expert by any means.

Thanks
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Old 01-07-2009, 10:03 AM   #4
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Not real hard at all!!! The bolts you see on top of the coil rail hold it down once you remove those the rail has to be lifted off of the spark plugs.Does it have a really rough idle???Is it a misfire that is causing the vibration?Is this what you are saying?If it is then I would unplug the injector wires one at a time to see which cylinder is not firing,that will narrow down witch coil it is before removing the coil rail.
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Old 01-07-2009, 11:42 AM   #5
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Accel, MSD and the others haven't made anything for them. It's entirely different than older ones.

I'm told a replacement rail from a "quality" parts house is made by the same MFGR that MoPaR uses. They look identical, even to the little coding marks.
I've already gone through 2 of them. Same thing, lower price.

Easy way to tell if it's been misfiring under load. Drive it hard around the block. Quick - Use a laser thermometer (HF $30?) - measure the temps of the inlets to the cats - they should be almost the same temp. Hard to see, do it from underneath. Hit right on the intake pipes on the cats.

On those I've seen the coil rail fail, the temp on one cat goes way low, like 190-200 degrees. The other cat goes to 700+! Reason is each coil fires on both banks - waste spark doesn't fire like it should.
Average cat inlet after running with a load is about 450-500.

Bad injector, bad plug, gap etc - one cat will read low, the other normal temps.
When the coil fails, it affects both banks.
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Old 01-07-2009, 02:04 PM   #6
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The coil bar is no problem getting off. I was wondering if it was possible to replace the 3 individual coils on the bar. I have not looked too close, but I did not see any connectors.

I don't have any misfire, just really rough when under load. I will check the temps.

Thanks
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Old 01-07-2009, 02:47 PM   #7
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""""I was wondering if it was possible to replace the 3 individual coils on the bar. """"

It would be nice if it was, but NO. It's all potted together.

Before spending the $160 or so, try the temp measurement trick.

Rough feeling under load is one of the symptoms. Under load the plugs require more voltage to fire, if the coil rail's internal insulation is breaking down at that voltage it'll feel rough, even though it runs fine the rest of the time.

So far, in this big world of technology or ours, the only real way is to swap in a known good one. What happened to the days when things were simple?
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Old 01-07-2009, 05:01 PM   #8
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opps didnt see it was a 06
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4.0/np231/ax15/d30/d35
flowmaster40,hpd30 with aussie locker,currie upper joints,4.88's, lca skids,chromo shafts,vanco brakes,d35 with super 35 and arb locker,re 4.5" springs,currie arms,re front uppers,Re shocks in back,walkerevens shocks up front, Re track bars with currie jj joints,anti rock,ss brake lines,re rear sway bar links,jks 1.25" bl and mml,bfg 35x12.5 km2's,craiger soft 8's,ome steering stabilizer,currie hd steering,rockmen front bumper,emp tank skid,lots more too.
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Old 01-07-2009, 05:52 PM   #9
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Yeah I don't really guess it matters which coil it is that is not firing since they are all molded together huh!!I had never tried with the Jeep before but I was figuring they would be individually replaceable or they should have been anyway.

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