Replacing the 00+ coil rail with aftermarket coils

[Talyn]

I've been thinking about replacing the coil rail for a while. I just hate it. Pain in the ass to get in and out and hard to diagnose a misfire with it. I'd probably go with something like this, 2 of them:http://www.msdignition.com/Products/...Coil_Pack.aspx or one of those coil packs off a 6 cylinder like this:http://easyautodiagnostics.com/img-h...-coil-pack.jpg

The only think I am concerned about is what the PCM is looking for and what would specs would be needed to keep the PCM safe. I asked MSD about retrofitting and they said that if the wrong coil is used PCM damage could result. However, I don't know if that is just their blanket response for something they don't offer a bolt in option for.

Any ideas?

[Tim_MN]

Coil rails pretty much work, or they don't. You are setting yourself up for some expenses and endless screwing around for something that may or may not improve anything and according to MSD has the potential to do some major damage.

You are using AutoLite APP 985 spark plugs like all the TJ coil rail owners recommend ?

If you are experiencing mis-fires, the coil rail is the least likely cause.

[wheeling365]

The factory coil on plug setup is pretty well built but I can also understand the desire to get rid of it.

I'd be trying to figure out the internal resistance of the primary side of the factory rail and then find a coil(s) that are as close to that as possible. That should protect the PCM since the resistance would be the same and I'd venture to bet the amperage draw would be similar.

I know that the ford coils like you are showing are also a waste spark setup in that they fire on the exhaust stroke also in that application. That may have an bearing on if you can or want to use them.

Are the factory coils fired individually or in batches of 2 or all plugs at once?

I've never looked at the factory rail connector but if it has 6 wires in the plug I'd bet it is going to be easy to do. It would just be a matter of mounting the new coils and grounding them and then wiring the ecm to them. Finding plug wires to fit might take a bit of hunting or possibly a cut to fit set?

EDIT* I would think something like this would be better suited so that if a coil died you could still limp the vehicle off the road vs just being dead in the water all at once.

http://www.msdignition.com/Products/...wer_Style.aspx

[RCP Phx]

Good luck with that,you do realize the coils fire the opposing cylinder at the same time?

[Talyn]

Originally Posted by Tim_MN

You are using AutoLite APP 985 spark plugs like all the TJ coil rail owners recommend ?

No, nor will I. Running a stroker I use a colder plug to begin with and I have found NGK works better with the coil rail.

If you are experiencing mis-fires, the coil rail is the least likely cause.

I am not experiencing misfires, but being that I have a higher compression engine I would like to see what a more powerful spark would do. Besides the fact that the factory design is just craptastic.

Originally Posted by wheeling365

I'd be trying to figure out the internal resistance of the primary side of the factory rail and then find a coil(s) that are as close to that as possible.

Primary resistance is 0.71 - 0.88 Ohms for the stock coil. Those MSD units I linked to are .53 OHMs. I am unsure of what the drivers can handle in respect to Ohm differences and if that is all it needs. According to kastein there are other considerations as well.

I know that the ford coils like you are showing are also a waste spark setup in that they fire on the exhaust stroke also in that application. That may have an bearing on if you can or want to use them.

The coil rail is a waste spark design. 3 coils, firing two cylinders at the same time. Also, the plug has 4 pins. One from + from the ASD relay, and 3 firing pins from the PCM.

Are the factory coils fired individually or in batches of 2 or all plugs at once?

sequentially in two plugs at a time.

EDIT* I would think something like this would be better suited so that if a coil died you could still limp the vehicle off the road vs just being dead in the water all at once.

Yes, Using those Ford MSD coils there would be a coil unused, which could be used in an emergency. The MSD coils have a e prong plug. One for hot and two from the PCM to fire. Both coils would get the + from the stock ASD. One pack would have two of the wires from the PCM going it to fire both of the coils on that pack and the third wire from the PCM would go to a single coil of the remaining coil pack.

http://www.msdignition.com/Products/...wer_Style.aspx

That would be another option, 3 of those. They have a primary resistance of .35 OHMs

Originally Posted by RCP Phx

Good luck with that,you do realize the coils fire the opposing cylinder at the same time?

Yes, I do. I know the wires wouldn't be as neat as it could if the coils fired cylinders next to each other.

[Milford Cubicle II]

I can offer you what I know.

I had a bad coil rail about a year ago and it was sending between 100 to 400 volts throughout the electrical system, including to the PCM. I drove it like this (before I knew what was going on) for weeks before I finally figured out that it was the coil rail. My PCM and all of my sensors have been working fine since, absolutely no failures since or throughout the bad coil rail.

It was producing a high enough voltage through the wiring that it was enough for my DVOM to pick up the inductance voltage if it was anywhere near the valve cover (that's how I finally figured out what was going on, lol). My point is, I think that the electrical system and PCM is MUCH more durable than people talk like they are.

That being said, I don't see how the resistance of the coils would affect the PCM. The coils produce their own voltage, the PCM simply fires them.

IIRC, the factory harness has 4 wires going into the coil rail. A power wire, and a signal wire for each pair of cylinders (3). I don't see why it wouldn't work. I would just get some individual coils (http://www.summitracing.com/parts/ACC-140032/), steal some Ford connectors, do some custom wiring, fab up some hold downs, and call it a day. You've now got a mustang ignition system.

[offroadordnance]

The Ford coils have too short a charge time about 1.5mS compared to about 3.0 mS for the rail coil. This combined with lower primary resistance would tax the coil drivers within the PCM. Also, the Ford coil output isnt that great in single fire mode. The factory Ford PCM hits the coils with multi-spark like an MSD but inductive not capacitive discharge. THe Ford coil contains an internal magnet that helps it perform better in mutlispark mode. If you hook the Ford coil primary up reverse polarity, you will nuke the PCM due to short charge time and hardly any output. A better option is a Dodge Viper coil. Primary parameters are identical to the rail coil and output is an honest 33% higher. Primary connector will hook up to the OE harness with correct repinned adaptor so plug wires are loomed all side by side with no crossing over.

[O-Gauge Steamer]

Hey Talyn,
If I remember Ohm's Law, the stock coils should take in the neighborhood of 17 Amps to fire and the MSD look to be around 22 Amps. I would be concrned that the drivers in the PCM would overload and burn out. Numbers sound about right to you? 12 VDC/.71 Ohms vs 12 VDC/.53 Ohms. The .35 Ohm coils would draw a staggering 35 Amps. Say good bye to the PCM...

[Talyn]

Originally Posted by offroadordnance

The Ford coils have too short a charge time about 1.5mS compared to about 3.0 mS for the rail coil. This combined with lower primary resistance would tax the coil drivers within the PCM. Also, the Ford coil output isnt that great in single fire mode. The factory Ford PCM hits the coils with multi-spark like an MSD but inductive not capacitive discharge. THe Ford coil contains an internal magnet that helps it perform better in mutlispark mode. If you hook the Ford coil primary up reverse polarity, you will nuke the PCM due to short charge time and hardly any output.

Good to know. I guess fords are out of the equation

A better option is a Dodge Viper coil. Primary parameters are identical to the rail coil and output is an honest 33% higher.

I hadn't thought of the Viper coil, but I have considered other Chrysler/Dodge/Jeep vehicles. I will look into the Viper coil.. if I don't have to pay a Viper price tag for it.

Originally Posted by o-gauge-steamer

Hey Talyn,
If I remember Ohm's Law, the stock coils should take in the neighborhood of 17 Amps to fire and the MSD look to be around 22 Amps. I would be concrned that the drivers in the PCM would overload and burn out. Numbers sound about right to you? 12 VDC/.71 Ohms vs 12 VDC/.53 Ohms. The .35 Ohm coils would draw a staggering 35 Amps. Say good bye to the PCM...

Yeah, those numbers are correct.

Also, researching this last night i could that there should be a zener diode protecting the ignition driver from voltage spikes created by the collapsing magnetic field. However, I don't know if its in the PCM or the coil rail.

[Talyn]

The viper coil pack does look interesting. They have a 6 pack coil with a connector that looks similar to the XJ one.http://www.rockauto.com/catalog/moreinfo.php?pk=940061 However, the resistance doesn't match the stock coil exactly. The Viper coil is .6-1.4 Ohms (according to Airtex), and stock is .71-.88 ohms. However, that was just one I looked at from a 02 RT10 and I don't know if that difference would be an issue. I'll have to look into it more.

[offroadordnance]

The drivers in the PCM are darlingtons or IGBT's made for driving ignition coils. They clamp voltage at about 400 volts and current limit around 6.5 amps.

Ohms don't determine the operating amperage of the coil, the PCM drivers do by adjusting dwell or on time. The coil resistance increases with engine temp, the manual specs ohms at 25C. Coils operate @ 125C., hot cranking primary resistance is about 50% higher than published @ 25C. When you crank the engine the starter can load the battery down to 8 volts and the IGBT has a diode drop of about 1 volt = 7 volts to the coil, not to mention other voltage drops due to connector resistance and resistance in the wire harness.

Worst case of hot 1 ohm total series resistance and only 7 volts to the coil would still deliver 7 amps to the coil so 6.5 amps was chosen.

In the old days with points, resistance did limit current. Because of the reduction in available voltage during cranking, the starter solenoid bypassed the ballast resistor to deliver full amperage to the coil. Today the electronics do the work by limiting dwell or on time to deliver consistent amperage to the coil.

[Talyn]

With offroadordnance's help I installed a Doge Viper coil two weeks ago. He may be offering a kit for this in the future.

Why I wanted to get rid of the coil rail (again):
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:

[urban yan]

I really, really, REALLY hate you lol.

[tbburg]

Interesting concept. .

While I agree ignition diagnostics kind of suck with the rail, I haven't found any real problem with it. The biggest plus would be in cost of replacement. How much did the Viper coil pack cost? The other advantage (as mentioned ) is retrofit of the 0630 head.

Not really sure if higher voltage is going to make a huge difference on a street engine: the stock system has pretty high voltage to begin with

[Talyn]

Originally Posted by tbburg

The biggest plus would be in cost of replacement.

In my case it would be lack of despise upon seeing that coil rail attached to my engine.

How much did the Viper coil pack cost?

RockAuto has them for $60.

Not really sure if higher voltage is going to make a huge difference on a street engine: the stock system has pretty high voltage to begin with

Performance wise I am not sure of the benefit, but it did change the idle quality. Don't know what it would do for a stock engine, but it did make a difference on my stroker.