acer99

I have a 2000 Cherokee, and a bit of a theoretical question - and I don't actually have any plans to do this:

Is it possible to replace the coil bar with individual coil on plugs?

The reason I ask is because I see MSD and JEGS sell individual coil on plugs for Hemis that come in both the dual and single plug versions. I think these are also available for Fords, but I didn't look too closely as I don't know how specific the coils are for each engine/make/model (or if one size fits all).

I'm just wondering if it's possible to rewire the coil bar to work. I know the coil bar has 3 coils that feed 2 plugs each (one spark is wasted).

I got this idea of one coil per plug because I read a thread where a guy hated the coil bar so he took a Dodge Viper coil (there are two, one feeds six plugs and the other feeds 4). The part number for the six appears across Dodge platforms for a bunch of V6 engines and such. So I was thinking why not take it a step further and do one coil per plug using something like the MSD system to produce a very hot spark.

Anyhow - I need to replace my coil bar so I'm just going to go the easy route and get one from AutoZone.

200sportxj

anything is possible with money and knowledge... lol

offroadordnance

The Viper coil is plently hot enough for the 4.0L and compatable with the OBD2 computer. Individual COP's (coil on plug) don't have more energy than the Viper coil does, cost is much more, and they would be difficult to mount. In a water crossing situation, it's easier to pull wires off the Viper coil and blow them out than unbolt 6 COP's to dry off the ignition.

tjwalker

I have never heard of it being done. Could it be done? Possibly. But I'm a big fan in choosing my battles. And that is one that I wouldn't want to take on. Some things are better off left to the Jeep engineers! The coil rail on the 00-01 is actually pretty efficient. I recommend using NGK plugs in the 00-01 XJ, as they hold up a little better than Champions do over time with the waste spark ignition. Not a big deal, but the gap on the Champions open up a little quicker than the NGK. Either way, change them 30k and there will be absolutely no issues.

rrich

The coil rails from Autochina are cheap Chinese knock-offs - good for only 6 months to a year. The internal insulation fails - often you can hear it "snapping" inside.

Best place is the dealer to get a real one. They are not much more expensive - if at all - but will last much longer.
Dealerships are assumed to be expensive, but that's not always true.
Get to know your parts guy at the dealer - often they are cheaper than a parts house. No, I'm not associated with a dealer, I just buy quite a bit from them - price, quality, and reliability.

NAPA sells coil rails made by Standard Ignition - supposedly OEM - plus they sell the China knock-offs. Price difference isn't much.
When you consider longevity - the cheapies are much more expensive and you have the pleasure of replacing it often.

You could adapt something else, but as designed it's a good system. The plugs fire twice - on the compression stroke like normal and on the backside (called the waste spark) - helps ignite any fuel that didn't burn and lets the cats do the rest.

Notice 3 plugs wear different than the other three - center electrode vs ground electrode. The polarity is reversed on 3 (coils are double ended.) That's why if you use Platinum plugs you have to use DOUBLE PLATS, not single. Also why E3's and multi-electrodes don't work well.

The PCM also uses the signal to check the RPM increase on each firing - that's how it can determine WHICH cylinder is misfiring or weak and give a code for THAT particular cylinder - amazing when you think about it.

Plus getting the PCM to adjust the timing properly would be unreal.

I talked to MSD about making a coil rail for the jeeps with a hotter spark and better internal insulation - they said the market is too limited and the Jeep system doesn't leave much room for improvement.
The comment the engineer said was "like trying to make the wheel rounder!" I'd take that as a compliment!

rrich

Water crossing? I'd use lots of silicone dielectric grade on the plug boots, and waterproof/insulate the connector on the end.

But I'd be afraid of the rail's plastic insulation cracking from hot to cold so fast.
Water really creates a big "bag o worms."

Maybe water experts could chime in?

LOL - we don't have water in So Calif - but we do have plenty of dust!.

acer99

Thanks for all the info! I recently rebuilt my engine into a 4.6 stroker.

I've had an ongoing problem that I thought would be remedied with the engine rebuild, but its still there. Sometimes when cranking the engine - either cold or hot - there is a series of mis-fires. I'm not sure which cylinder or what is specifically causing it.

The mis-fires continue for a while, and then eventually go away. If I press the gas, the engine tries to rev but doesn't really succeed. After about 20 or 30 seconds, sometimes a bit longer, the rough idle and misfires start to go away and the engine runs smooth.

I thought this was happening due to a bad fuel injector, but I've got all new injectors and the problem is still there. All my groundings are good, vacuum lines are good, sensors have been replaced... the only thing left is the coil bar. When I saw the price tag, about $100+, I cringed. Especially since having just dropped a load into getting everything rebuilt. I'm just getting nickel and dimed broke.

After seeing the costs, in addition to other things I gotta fix on the Jeep, I started seeing if there were alternatives that might be cheaper. Doesn't look like it - better just to get it all done right so I don't have to spend the money again.

I presume the coil bar is a pretty good setup and can handle the 24# injectors and stroked out engine.

Has anyone ever done the Viper coil swap? If there isn't much to it beyond wiring and splicing, maybe I could save myself some money getting a coil and wires off eBay.

offroadordnance

He is on the Jeep Stroker forum as well

http://naxja.org/forum/showthread.php?t=1066869