Need Chrysler Ignition 101

[RIP]

Ok. I'm putting my ignorance on my sleve. Be kind.

My question concerns the coil driver circuits from the PCM to the coil pack. The coil pack contains 3 coils. Each individual coil within the pack fires two spark plugs. Each individual coil is fired by a ground pulse over a single wire from the PCM and a common B+ power wire, common to all three coils. Here's the question. What determines which of the two spark plugs will be fired by it's coil? Both plugs can't fire at the same time right? I don't see it in schematics. I can't find a narrative on it. What am I missing? I appreciate any light you can shed on this.

I'm betting it must have something to do with the PCM grounding the driver circuit or is there something in the coil that lets the driver fire one plug or the other?

[Airjer_]

3-6 fire at the same time. 2-5 fire at the same time. 1-4 fire at the same time. so each individual coil fires 2 times to supply spark to its respective cylinders. I think its called a waste spark system. Its the same for the 4 cylinder Chryslers that use a coil pack. Its also the same with GM and Ford that have similar coils that fire two cylinders at the same time.

[RIP]

I need to read up on the DIS system. Be nice to find a good authoritive article on it somewhere. I know this is a distributorless system but I've always pictured a distributor firing one at a time on the rare occassion I've worked on them. Luckily I've never needed to know it fired two at a time.

So, what brought me to this question was a problem posted on that other forum. Misfire on #6, getting spark, fuel, compression check good, no oil fowling. I'm thinking he's missed something in the process. In any case, based on your info it couldn't be a coil pack or PCM and the wiring between. He doesn't mention plug wires. Hope it doesn't come down to something that simple. Thanks for the education Airjer.

Firing two at a time makes me think a lot of engineering has gone into these engines with a DIS system or similar to hold vibration at bay. Then again firing two on opposite banks at the same time may decrease the vibs. Have to think on it.

[wafrederick]

Plus DIS ignition systems are called heart attack machines due to the high voltage coming out.One advantage to the DIS system is it uses less moving parts.Only use Champion plugs in Chrysler ignition systems and avoid Bosch plugs.

[RIP]

Just to clarify... http://autorepair.about.com/library/...bl-fo-5204.htm

Three coils in the coil pack 1,2 & 3.

Coil #1 fires 3 & 6
Coil #2 fires 1 & 4
Coil #3 fires 2 & 5

According to the diagram firing order is 123456. Are you saying both #1 and #4 fire, but only the #1 cylinder fuel injector opens hence, "waste spark"? That's about the only way I can see it making any sense. So in reality the fuel injectors actually determine firing order.

[Airjer_]

The cylinder that is firing is on its compression stroke. Its paired cylinder is on the exhaust stroke. There no sense in firing fuel in the cylinder on the exhaust stroke. I would think that the valve train ultimately determines firing order.

[Spit]

I would agree with Airjer.. It's all inter-related... Spark, Compression and Fuel.
The 1-4 example given if the injector injected fuel on the 4 at the same time it did the 1 the fuel would just be wasted on an exhaust stroke in #4. That's what engine timing is all about. it might ignite but it wouldn't run very efficiently.

This happens in small single cylinder lawn mower engines when the flywheel key shears, and the flywheel rotates some degrees out of time. The engines can and do run in some instances...If you ever have a hard starting mower that snaps back the starter rope hard enough to hurt your arm...you're probably running out of time. Had a Buddy who's wife hit something a year earlier and ran it that way for over a year.

I don't know it for a fact but I bet if you reversed wired all 6 cylinders (4 to 1, 1 to 4 etc.) the engine would start & run..not run well but it would run.

Spit

[Alphabravo]

Originally Posted by Spit

I would agree with Airjer.. It's all inter-related... Spark, Compression and Fuel.
The 1-4 example given if the injector injected fuel on the 4 at the same time it did the 1 the fuel would just be wasted on an exhaust stroke in #4. That's what engine timing is all about. it might ignite but it wouldn't run very efficiently.

This happens in small single cylinder lawn mower engines when the flywheel key shears, and the flywheel rotates some degrees out of time. The engines can and do run in some instances...If you ever have a hard starting mower that snaps back the starter rope hard enough to hurt your arm...you're probably running out of time. Had a Buddy who's wife hit something a year earlier and ran it that way for over a year.

I don't know it for a fact but I bet if you reversed wired all 6 cylinders (4 to 1, 1 to 4 etc.) the engine would start & run..not run well but it would run.

Spit

Well, Spit, if AirJer is right, you in fact could reverse all wires like you mentioned and it should run just fine. Is anybody willing to try it? I may one day.

BTW, interesting thread, RIP.

[Airjer_]

If you think of bank fired injectors one bank would fire at the same time. Fuel would be sprayed onto the intake valves where it would either be sucked in or vaporized. and then sucked in shortly after I don't see a conflict with the paired plug wires being switched, I've never thought to try it. I also don't see any difference in when the injector is fired. If you switch the paired injectors it would mean that the would fire fuel onto the still closed intake valve. Much like a bank fired injector setup.

I agree that somebody needs to Mythbust this!

[Alphabravo]

OK The curiosity was killing me so I tried it!
I reversed the #3 with #6, #1 with #4 and #2 with #5.

Gave it a crank, and...... (drum roll, please....).....

....It RUNS! not only that, it runs so well I can't tell the difference from this and the normal wiring setup.

I never heard of the "waste spark" system. This forum taught me something new yet again! Thanks to RIP for posting it and Airjer for clarifying.

[RahX]

I don't think they fire the injectors in pairs, i'm pretty sure they only fire the injector when it's respective cylinder is going to suck in the fuel which is called sequential injection. They used to use port injection which was bank fired.

[Airjer_]

I realize that its sequential. The point I was making is that there where plenty of early fule injected vehicles that where bank fired that ran well. Obviousy sequential is a lot better but I would put money on the the vehicle running if the paired cylinders (I should have said that instead of paired injectors to make it more clear) injectors wiring where swapped.