5.7 Hemi coil madness! What the heck is going on?!?

I own a 2006 Chrysler 300C AWD that my son drives. It's all stock. I had an OEM Mopar coil sitting around and somehow that turned into "let's change the coils". OEM coils are ridiculously expensive so I ordered 7 Denso coils from RockAuto. I've always had good luck with Denso parts before. We installed the OEM Mopar and the 7 Denso coils and the car wouldn't idle. It was hard to start and if you held it at around 2500 rpm it would surge up and down by 300 rpm or so. We thought maybe we got a bad coil, so we started swapping them one at a time for an old coil. And just to be sure we tried 2 different old coils in each position. Each time the car wouldn't idle and was hard to start. After we had tried swapping out all eight coils, we put back 7 of the originals and the one new OEM Mopar coil and it ran and idled fine. Then, just to be sure, we grabbed 2 of the new Denso coils and tried swapping them into random positions on the motor. If we put ANY of the Denso coils in ANY position on the engine it would not idle. So after 4 hours we're back to the coils we started with except one new OEM Mopar coil. What the hell?? Is it possible we got SEVEN defective coils from RockAuto? Anybody have any thoughts or insight?

I have had a couple customers come in with similar problems from aftermarket coils but never seen any problem from a factory hemi coil. I usually put the original coils back in or one of my huge stash of stock coils then start all over with diagnostics and find the real problem, usually bosch spark plugs or something stupid like that.

If you got 7 defective coils it would have been from Denso, RA didn't make them.

I recall, vaguely, that mixing and matching different brand coils can cause issues. Seems you confirmed that. So all Denso or all MoPar.

Thanks for the input, and for confirming what I heard about spark plugs causing problems.

Someone else told me about different coils being incompatible. So the Denso coils aren't really REPLACEMENT parts, there more like alternate parts. I realize RA doesn't make the coils but if they are not true replacement parts I think they should say so on their website.

You need to dig into what the computer is doing to understand why you had issues. Do you know how the computer determines a misfire? By looking at the waveform occurring on the primary side of each coil. When you use different brands together you get different waveforms that confuse the computer. Sometimes a little research, on your part, helps prevent issues.

Ignition coils are transformers that step the voltage up from 12V to whatever voltage is needed to jump the gap in the sparkplugs.
When MSD first came out with their first Multi Spark Discharge race boxes, 404B,404C they had Mallory make special wound coils for those race ECU boxes.
I had done some drag race ignition testing in that era for Bill Hayes of Hayes ignition which later changed names to become Stinger Ignition, once I tried the MSD 404B box with the Mallory Pt # 28880 coil never went back
my message is maybe those aftermarket coils are not wound right for that ECU, if it ain't broke, don't fix it

Curious. How does the computer see waveforms? The computer controls primary on/off but I doubt it sees a waveform. He never stated the computer set a misfire code so unsure on that as well. Misfires are usually determined by the computer watching crank position sensor input(CKP) not primary coil control.

I have an OBD reader and we checked, there were no engine error codes. On another note, I contacted RockAuto, explained everything that occurred, and they authorized return of the coils. I am VERY pleased with the way they handled this issue!

Glad they took care of you. Possible the ECM didn't like the current flow through the coil primary but that should have triggered a PO3xx code associated with coil primary current flow. Strange it failed to do that. In order to set PO3xx misfire codes the ECM needs to see variations in crankshaft speeds via the CKP. Those are often 2 trip failures(i.e. need to see key cycles w/consecutive failures)

https://www.nyvip.org/PublicSite/OBDII/misfire-detection-monitor.html#:~:text=Continuous%20Monitors&text=The%20OBD%20II%20system%20detects,the%20speed%20of%20the%20crank.