I've been experiencing a missfire in 3 cylinders when raining heavy and as most here have dealt with, turn the ignition off to reset. However the other day when merging the hwy at almost full throttle, cylinders 1,4 and 5 missfired on a day with no rain. Took the vehicle to the dealer and the tech ran compression and leak tests. Checked the wires and coils then all normal and said he wanted to check the catylitic converters because of the aftermarket magnaflow exhaust and "back pressure" as he called it. I'm aware of backpressure from our exhaust but to cause a random missfire??
No oxygen sensor codes thrown just the missfireing cylinders.
Fuel pump maybe. CPS? Vacume leak possible. The valve covers were leaking and repaired 6 mnths previous at the dealer.
Anyone have or had the issue? At a loss. Charged $200 to diagnose with no real solution as yet.