I just replaced a bad ICM into my 1990 C1500 5.7 liter pickup with a new Delco D1943A purchased from Rock Auto. The ICM is located inside the distributor cap. I marked the plug wires before removing and replacing the cap and rotor with new Delco parts. But after replacing the ICM and plugging in the wires onto the new cap, the firing order doesn't work. I'm thinking the ICM has a different firing order from the original. Any Ideas? Thanks!!

 

A new icm will not change firing order as that is controlled by the physical position of the rotor relative to the cap. Sounds like it's time to recheck wire position.

 

Thanks, Rednucleus. Yeah, I thought the same thing. So I went out and spent a couple of hours tracing the plug wires. This is gonna sound crazy, but my firing order appears to be non-standard. The published spec is: 1, 8, 4, 3, 6, 5. 7, 2. Mine is: 5, 8, 4, 3, 6, 1, 7, 2. The truck purrs like a kitten at idle and when revved, but I'm going for a test drive in a couple of days and see what happens under normal driving conditions.

Has anyone else experienced this?

 

Looks like you have the 1 and 5 reversed. Did you try 1, 8, 4, 3, 6, 5. 7, 2?

 

Yeah, it ran like crap and backfired until I swapped those two plug wire positions on the distributor. The rotor, and cap can only go on one way, and I doubled checked that the cylinder 1 wire is going to the 12 o'clock position on the cap and that the cylinder 5 wire is going to the 5 o'clock position, totally opposite of standard. Like I said, crazy.

I'll keep you posted in the days ahead. Thanks for your help, you guys!!

 

I checked this out in the light of day this morning and it turns out I traced the wires incorrectly. The firing order is factory after all.

Thanks for hanging with me, fellers, through all my late-night, bad lighting, too tired shenanigans!

 

It dosen't matter what is where on the cap, as long as you have the firing order, and plug wire to proper cylinder. In other words, instead of #1 being at the front, it can be anywhere , following the firing order.

 

Really?? I had no idea. I thought the distributor/rotor position dictated the contact on the cap that got the spark, or is that true only in the case of the old days before electronic ignition?

 

As I posted as long as you follow the firing order. #1 on tdc compresson with #1 plug wire whever on the cap with the rotor at the same location.