Real dis explanation

[tca7291]

Ok, 1991 Mustang 2.3l 8-plug. I am having misfire issues and I am trying to diagnose the issues, but through my research only brings up more questions. First of all, I've heard that one coil pack works as primary, and the other for secondary for the waste spark, but that really doesn't make much sense. I would think that the one post on one pack would be primary and the opposing post would be for the waste spark on the same pack. Secondly, which side is primary, if any, because I would think that the plugs on the intake side would be the primary plugs, to be able to burn the air/fuel faster. And on that note, my mustang has all 4 intake plugs on one coil pack, and the exaust plugs on the other pack. If each pack has 2 primary and 2 waste sparks, then this would not be right (two firing on intake and two firing on exaust side of head). Is my car miswired? Or is my idea of one pack producing waste and primary sparks at the same time wrong? Any insight would be great. All the info that I've read on the internet is very contridicting to the same stuff I've read on other sites. If anyone knows the real answers about this dis system, please reply. I wish I had bought a '90 with a regular distributor, it's so much simpler. Thanks y'all!!!

 

[Delray Dude]

Each coil pack is a seperate system. I believe the front coil pack is the primary coil pack and fires 1st and the coil pack behind it is the secondary coil pack and fires almost immdiately after the 1st.

Think of each coil pack as a stand alone distributor. Each of the coils on the front pack need to go to the correct cylinder on the engine and the same for back coil pack. If the coil packs are correct in wiring, you will have one from each coil pack going to each cylinder. I think the original configuration is that the front coil pack has all the wires going to the drivers side plugs and the back pack for the passenger side. If wired correctly, you can unplug one of the coil packs and the engine will run fine and not misfire.

 

[Delray Dude]

It appears from what I am reading, your car is wired correctly as far as one pack to one side of the engine.

It is common after time for the coil packs to have one or more go bad. If one coil pack is 100% fine and the other has one or two coils go bad, you wont notice a misfire. If you have a bad coil complete and then the other coil pack has a coil drop - you will get a misfire.

On my mustang - I had one coil pack have a dead coil and the other had another one. when both systems were plugged in it ran fine - and then i had another coil go out - resulting in a misfire. replaced both packs and ran great.

 

[KhanTyranitar]

Yeah basically the plugs on the exhaust side I'm pretty sure are primary. Both packs fire waste spark, but only one pack comes online during startup. Each individual coil within the packs fires a primary spark to one cylinder and a waste spark to a different cylinder. There are two coils in each pack. So each pack services all 4 cylinders. The second pack fires the second set of plugs on the opposite side of the engine.

 

[tca7291]

Thanks for the insight fellas, I'm not sure whats going on with this sparratic misfire, had a bad coil pack and icm a while back, replaced the one pack and the icm at that time. More recently, started having the tach drop issue again (dropping to 1/2 rpms with misfire) and was thinking the icm was going out again. But on a hunch, I swapped the two coil packs (newer one up front and oem in back to newer one in back and oem up front) and it cleared the tach issue but made the misfire more often. I have a strong feeling that the old pack is bad, but when it was in the up front position, I unplugged it and the car sounded like it dropped all but one cylinder and stalled within one second. Does this sound like the newer pack that I put in the rear position is bad also? Or do you think my icm is going bad again? I'm planning on replacing the oem pack and doing plugs & wires this coming weekend, but just trying to make sense of this weird system. But thanks alot for the replies!!!

 

[tca7291]

Oh yeah, how much resistance should each post on the coil pack have normally?

 

[tca7291]

Oh boy, y'all are gonna laugh at me now. Whats that old rule? Check the simple stuff first? How bout a bad plug wire? Haha. Broke out my dmm and was checking resistance in the wires and #4 on the passenger side was open. DUHH. Thanks for the help and am still figuring how all this ***** works but you guys have been a great help and I am sincerly thankful that you guys are willing to help. Thanks again!!!

 

[KhanTyranitar]

Out of curiosity, what kind of wires are you running?

 

[tca7291]

The wires that were on the car, I'm not too sure, the previous owner had put them on, no brand name, just gray and said 8mm. I replaced them with a set of napa belkin wires, 8mm. I know they are not the greatest, but its not exactly a performance setup either. I've always had pretty good luck with napa products in the past. But while removing the old generic wires several terminals on the plugs pulled right out of the wires so I know there was probably more than just the one wire having alot more resistance than they should of. Engine runs so much smoother and idles so much better now. (more power too!)

 

[KhanTyranitar]

The Belkin wires are ok, but some cheaper wires can cause seeming unrelated issues. Also lots of performance wires, namely Taylor, Ford Racing, Accel, and MSD can cause seemingly unrelated issues. You would think such wires would be better than OE or standard wires, but basically all such wires are is standard wires with the carbon resistors disabled. This causes excessive EMI and feedback issues. That is why they are usually cheaper than OE wires, its because they are cheaper.

The Belkin wires are descent, but won't last as long as the genuine Motorcraft.