Misfire caused by coil?

[Al 96 Ram Air T/A]

I'm wrapping up the interior upgrades...had surgery a couple of weeks ago, so the project stopped for awhile.

Anyway, I've got an ignition mis that only shows after the vehicle is fully warmed up. It runs and starts fine, but after 15 minutes or so, the misfire counts begin to rise.

Using my Aeromotive gauge, I can see the misfires on cylinders 5 and 6, which just so happen to be next to each other (in the firing order) on the Opti. The coil primary is between the two.

I've been avoiding the possibility that it's the Opti, as it has less than 200 miles on it, and I can't see why it would only act up when it's hot.

I'm wondering...can a bad coil do this? Specifically, if the coil is heat-soaked, will it cause these conditions? The wires are all new, as are the plugs, and they are run OTVC so I know there not the issue. (at least I highly doubt it).

What do you guys think/ Obviously, I want to avoid at all costs having to pull the Opti again.

[formula_gramps]

I wouldn't immediately leap to the conclusion that the problem is with the Opti distributor either. Sure, it's always a possibility, but I would hope, less so, since it's a new unit.

I was thinking about your question about the coil. We are talking about a single coil ignition system...correct? Assuming yes, if you had a coil problem like the type you were thinking of, it seems unlikely to only pop up consistently in just those two cylinders. I would think that if you had a flakey coil causing misfirings, it would be pretty random insofar as cylinders are concerned.

You don't have any of those infernal "cans" as I call 'em, on any of the plug boots by any chance do you? I'm thinking that it was only standard to have them on plug 5 and 7 and 8, but I don't remember for sure. Those things are known to cause misfire problems especially after you change s/p cables from the original equipment.

Apart from that I'm puzzled that you'd have consistent misfiring from two cables on opposite sides of the block (no induction problems etc.), and therefore opposite sides of the opti.

Try swapping the plugs from 5 & 6 into two other spots. I know that sounds silly, but then retest it, and see if the problem moves to a different cylinder. I once changed plugs in a V8 and discovered I had two bad plugs right out of the box. Naturally, you'd never expect that, but that's just what it turned out to be.

I'm sure there are others who will have some additional ideas to try.
Good luck!

[Al 96 Ram Air T/A]

To be honest, I'm not sure if it's a single wire or not...it's the latest design as found on the 96 - 97 LT1.

Actually, cylinders 5 and 6 are next to each other inside the Opti. The firing order is 1-8-4-3-6-5-7-2. The posts are on either side of the primary input tower. If the coil was not putting out the correct spark, I'm thinking, this could cause those two cylinders to act erratically.

I haven't ruled out the primary wire, but the resistance is right in line with the other 8 wires. There all Taylor Spiro Pro, that I made myself. I converted the wires to Over the Valve Covers (OTVC), so are contacting the headers. They do not have the metal boot on either. The electrical system is brand new, except for the coil.

BTW - the Opti comes from a trusted source. I looked at buying from the PartsLadi, but even he/she admitted all of the OEM Opti's were out of circulation. So I went with this outfit (out if Florida) that has contracted with a Canadian supplier to make their own with the upgraded components (brass contacts, improved bearings, etc.) I was skeptical, but they've sold thousands and have a lifetime warranty to boot. The supplier has stated if the Opti is bad, he will replace it. But the issue is getting the old off and new one on. It's a PITA of a job as you know.

[formula_gramps]

"Al",

I'm stumped.....

Maybe I'm missing something, but I don't understand if the misfire is always occuring in 5 & 6, why that would indicate a problem with the coil--- or for that matter the primary wiring. It would seem that either of those would result in intermittment spark in any plug.

Yes, I imagine that swapping the opti is a pita. About the only service function that isn't in that engine compartment is putting in winshield washer fluid...

Who is the Canadian source for the Opti's? I'm sure some of the readers here would like to consider them as an option when faced with replacement.

[Al 96 Ram Air T/A]

My primary reason for thinking the coil has something to do with it is because the problem only appears after the vehicle has been idling for 15 minutes or longer. Even then, the misfire counts are low. As the vehicle's temps rise, so do the miscounts.

If the Opti was the issue, I can't comprehend why it would malfunction when the engine is warm....more to follow. In a meeting now..

[Al 96 Ram Air T/A]

Well, decided to take a chance with the coil. I ordered a new AC Delco (OEM) coil. I will also use the recommendation to space the ICM and coil assembly off of the head.

I'm hoping the problem is the coil, but if not, I can always replace the ICM next.

If all else fails, I'll have to look closer at the Opti or at least the wire harness to/from the Opti. Here's keeping my fingers crossed...

[BrdWAtti2d]

Most likely if you have a problem in the harness to the opti you would be seeing some codes. On the other hand a spark issue, coil, icm, cap or rotor, etc, won't throw anything but a random misfire code. A new coil seems to me like a cheap solution if it fixes the problem, if not, worse case is you got a new coil. I'm going through the same thing right now and have a new coil on the way. If that doesn't fix it, i'll throw an ICM at it. The wires and opti are new for the most part. One other thing you might consider, I've heard of more than one person having issues with Taylor wires. If you have any of the old ones laying around you might try swapping out 5 & 6 just to see if the problem goes away.

[Al 96 Ram Air T/A]

Just an update...

Changing the coil had no effect. I also used the ICM cooling Mod (spacing away from the block)...also no change. Will have to check the spark plug wires again. Can't see that they are the issue, but I'll look again.


The computer is showing P0300, random misfires.


Also, I contacted TPI Parts (maker of the Opti). They will honor the warranty if the Opti is the problem, but they want me to rule out everything else first. Fair enough...

[Trash man]

could the ends on the wires you made, be a little loose? when the car warms up, they expand away from the plug and/or the internal wire? just something to thing about

[sneitzel]

could the ends on the wires you made, be a little loose? when the car warms up, they expand away from the plug and/or the internal wire? just something to thing about

I was thinking about something along these lines before Al 96 Ram Air T/A mentioned replacing the coil made no difference.

What if it was a combo of things. The coil is marginal. When it's cool it is up to the task and is putting out enough power but when it heats up it can just barely cut it. Combine that with 2 spark plug wires that may be just barely in spec (resistance wise) when cool. When they heat up their resistance goes above what they they should be but not by much. The coil can barely keep up anyway so the increased resistance of those wires when hot is causing the problem.

Could still be happening even with a new coil if the wires are really changing resistance as they heat up or are not making good contact as Trash man suggests.

Just a theory....