So what did you do to your GMC today?

[LarryW]

Sailor, you might want to check the 5 and 7 plug wires, they should have a fair bit of separation but in the photo they look like they're very close or even touching in a couple of places.

View attachment 18543

Pretty engine!

Richard RV is right. 18436572 is firing order. 5&7 are adjacent in firing order and when close parallel install may get some induction from one wire to the other making it feel like a minor miss. Just say'n.

 

[Wally]

Richard RV is right. 18436572 is firing order. 5&7 are adjacent in firing order and when close parallel install may get some induction from one wire to the other making it feel like a minor miss. Just say'n.

Jasper engines has a tsb on 5-7 ignition crossfire. Attached file

 

[Richard RV]

Jasper engines has a tsb on 5-7 ignition crossfire. Attached file

Good find, Wally. Absolutely should be posted in Resources.