I just got back from a weekend round trip of 400 miles of highway
driving. I averaged about 80MPH, and the car got 27.3MPG average for
two fill ups. Overall, the car is performing great, BUT it occasionally
misses at 3700RPM.
I had to merge that required a WOT, and at 3700RPM the car bucked and
the check engine light was on. I drove the car for approx 100 miles,
and stopped at an AutoZone to pull the codes. The reader said "Misfire
detected number 4". He cleared the codes, and said it is probably a
spark plug wire????
I drove another 120 miles with no problem, then did a brief fast
acceleration to 3000 RPM, and no problems.
On the way home (approx 200 miles) the car performed well. I slowly
crept up the speed, and sure enought at 3700RPM the car bucked, and the
Check Engine Light came on (approx 110MPH!).
So, another stop at AutoZone and the same code is read; :Misfire
detected number 4".
The plugs were replaced about 19K miles ago with the same AC Delco
So, I really do not think it is plug wires. The car gets great gas
mileage, idles smoothly, and only misfires at 3700RPM.
The car has 59K miles, and is a 3.8 V6.
Thanks for any help, and have a nice day,