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Good bye coil rail.

Dedicated forum for all things electrical... Sometimes Electrical issues can really get you stumped! Not Stroker related.
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SilverXJ
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Good bye coil rail.

Post by SilverXJ » October 7th, 2011, 6:40 pm

For the past 9 years I have absolutely despised the stock coil rail BS/PIA. I had been researching a way to replace it for a while, but was unsuccessful in finding a solution. If the wrong coil was selected, best case the engine wouldn't start or run correctly. Worst case I would fry the PCM coil drivers. With NAJXA member offroadordnance's help I installed a Dodge Viper coil two weeks ago. He suggested using the Viper coil and he may be offering a kit for this in the future.

Why I wanted to get rid of the coil rail :
1) Its a real pain in the ass to remove that damn rail from under the cruise control cable, throttle cable, TV cable, heater hoses and AC compressor.
2) As I have an earlier head, it doesn't have the bosses to mount the coil rail to as the 0331 head had. I previously had some stainless steel straps securing the rail to the head.
3) It makes diagnosing a cylinder misfire difficult. You can't simply unplug a single plug and see what happens to the engine RPM/Sound.
4) Anything that involved removing a single plug is a PIA because of #1.
5) If I wanted to pull the valve cover I had to remove the coil rail due to #2
6) Perhaps a more powerful coil.
7) God I hate that thing

From what I have found the coil rail is an idea that came over from Mercedes when they acquired Chrysler, as their V12 engines have 4 of these things.

Anyhow. I mounted the coil near the coolant recovery tank using mount fabricated out of 1/8" aluminum. Its secured on the top on the coolant recovery tank bracket and on the bottom on the body side engine bracket. The engine bracket had two free holes which I used.

I used a Summit Racing V8 wire kit which I cut to length. Initially I had a wing style mount coming off the coil pack to mount the wires too, but once I had the Taylor wire clamps installed I found that to be unnecessary. Besides, it looked really odd.

As for plugging the coil into the stock harness, I spent about a hour going over the wiring diagrams and testing the stock coil to see which pin on the connector fired which plugs(the FSM only lists coil #s for the connector diagram). All I needed to do was run the patch cable in a straight through configuration. With a plug I got from offroadordnance I made a patch harness.

I have been running the coil with out a problem for two weeks. Hot idle quality has definitely improved a bit. And WOT seems to have a bit of improvement, but I am unsure... could just be the placebo effect. It was a pretty much uneventful install aside from making the bracket.

Some pics:
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Image

Image

Image

shawnxj
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Re: Good bye coil rail.

Post by shawnxj » October 8th, 2011, 4:49 pm

why did you go with a v10 coil over say a v6 coil?

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Re: Good bye coil rail.

Post by SilverXJ » October 8th, 2011, 5:17 pm

The Viper coil is a 6 post, 3 coil pack. The Viper has two coil packs. One for 4 cylinders, one for 6 cylinders.

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Re: Good bye coil rail.

Post by shawnxj » October 9th, 2011, 1:34 pm

did not know that

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Re: Good bye coil rail.

Post by 92tank » October 9th, 2011, 2:11 pm

i did not know that either. but that could be useful info in case you wanted to put one on a 4 cyl jeep motor. not that thats what this cite is about. but good to know anyways

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Re: Good bye coil rail.

Post by amcinstaller » October 9th, 2011, 2:15 pm

the 4 cyl one is likely the one that was already used on neons, pt cruisers, etc. (the 2.whatever it is engine) so its entirely possible it would work.
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Re: Good bye coil rail.

Post by SilverXJ » October 9th, 2011, 4:11 pm

92tank wrote: but that could be useful info in case you wanted to put one on a 4 cyl jeep motor.
I don't think the 4 cylinders in the TJ or XJ ever had a distributor less ignition.
amcinstaller wrote:the 4 cyl one is likely the one that was already used on neons, pt cruisers, etc.
According to rock auto the 4 post coil is used on the Neon, PT Cruiser, Avenger, Sebring, Stratus, Talon, Eclipse, Caravan, Ram, Stratus, Liberty and Wangler. The 6 post one is used on the Ram and Viper.

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Re: Good bye coil rail.

Post by 92tank » October 11th, 2011, 6:15 pm

i was meaning if you ever wanted to get away from the dizzy.

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Re: Good bye coil rail.

Post by amcinstaller » October 11th, 2011, 6:23 pm

though i do like that idea (for the 4 cyl) i think it would be alot of screwing around seeing as the the ecu wouldnt have drivers for the multiple coils. but if someone were to attempt to swap an entire computer system, or an aftermarket one that did have the drivers, could get interesting. or you could just put in a 4.0 for half the fuck around :lol:
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Re: Good bye coil rail.

Post by 604rail_king » January 25th, 2012, 5:08 pm

updates ?

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Re: Good bye coil rail.

Post by SilverXJ » January 25th, 2012, 6:27 pm

Not much other than it is working fine!

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Re: Good bye coil rail.

Post by Jim K in PA » April 10th, 2012, 4:35 am

Thanks for pointing me to this thread Chris. In addition to the reasons you list for wanting to rid yourself of the stock "donkey dick" coil rail on my LJ is that I hate the fact that the design forces replacement of all three coils if a single one fails. What I was looking at replacing my coil rail with was a trio of twin-post GM coils commonly used in the 80s and 90s. There are several aftermarket versions of these coils from Accel and MSD, as well as Jegs own brand. Carrying a single spare coil takes up a lot less space too.

Do you have a diagram for the pin-out from the stock harness and a link to that connector you found?

Thanks again.

Jim

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Re: Good bye coil rail.

Post by SilverXJ » April 10th, 2012, 7:12 am

There is a whole lot more that goes into picking a coil that will meet the needs of the PCM and of the ignition system. Resistance, inductance, number of windings and charge time just to name a few. Just picking one of the shelf because it looks like it might work could prove to be a bad idea, especially for the PCM. I originally was looking at some Ford MSD coils, but I was persuaded not to use them because they were not a good match at all. I understand the desire to use the GM coil though, it makes sense.

The small harness I used was one end of an old coil rail and the other was Dorman 902-303. For the Viper coil the plug is straight through, basically just extend the harness. I'll try to remember to check my notes later on the exact pin out.

-Chris

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Re: Good bye coil rail.

Post by Jim K in PA » April 10th, 2012, 10:12 am

SilverXJ wrote:There is a whole lot more that goes into picking a coil that will meet the needs of the PCM and of the ignition system. Resistance, inductance, number of windings and charge time just to name a few. Just picking one of the shelf because it looks like it might work could prove to be a bad idea, especially for the PCM. I originally was looking at some Ford MSD coils, but I was persuaded not to use them because they were not a good match at all. I understand the desire to use the GM coil though, it makes sense.
Oh, I am aware and understand fully. Do you know the specs for the stock coil? The GM coil has a primary resisitance of .35 ohm, secondary resistance of 7.8k ohm, 80:1 turn ratio, and 4.2mH inductance. What is the specification of the Viper coil you used? I also looked at the Ford COP as well as the GM LS COP, and neither seemed appropriate due as much to size and geometry as electrical compatibility. MSD does not list the specs for their stock Ford COP coils.
SilverXJ wrote:The small harness I used was one end of an old coil rail and the other was Dorman 902-303. For the Viper coil the plug is straight through, basically just extend the harness. I'll try to remember to check my notes later on the exact pin out.
Thanks - I was mostly concerned about the Jeep harness end, and had planned to cup up a donor coil rail to harvest the connector. From there I planned to just make up an adapter using weatherpak connectors.

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Re: Good bye coil rail.

Post by Jim K in PA » April 11th, 2012, 4:54 am

Nevermind - found my answers here: http://naxja.org/forum/showthread.php?t=1066869

So the Viper coil will work and seems to be the only option, but it only solves the installation/removal problem. If one coil fails, the whole unit must still be replaced. I'm not sure if there is enough justification to make this swap. Did you see any improvement in efficiency (power/mpg) with the Viper coil?

Jim K

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