Engine Performance problem
2001 Chevy Silverado V8 Two Wheel Drive Automatic 94000 miles
This problem only happens at speeds past 65mph. Got the Code p300 Random misfire. Replaced plugs and wires no help. Then replaced fuel filter no help. Then had the injectors cleaned no help. Replaced all 4 o2 sensors no help. Scoped eng. Found #1 #5 #6 and #8 cyls. Misfiring swapped #1 coil pack with #3 to see if misfiring would follow it stayed on #1 all Vacuum lines look good. No other codes show up.
A P0300 Random Misfires normally caused by vacuum leak and bad fuel.
Engine misfiring can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel.
October, 8, 2009 AT 12:03 PM
Did all that. Don't believe it the EGR valve because at low power settings runs good.
November, 3, 2009 AT 9:14 PM
Kidblue, I am currently working on a 02 Silverado with the exact same symptoms. Mine only sets the code on decel. I can drive uphill without a problem, coast downhill above 65mph, and the check engine light starts flashing. Have it on my schedule for Wed morning. If I find the answer, I will get back to you!
November, 4, 2009 AT 7:20 PM
Kidblue, I spent several hours today following up on the Code p0300 on the Silverado. My syptoms were identical to yours. Cyl 1, 5, 6 and 8 showed a misfire even though the engine ran smoothly. I won't go into the amount of work that went into eliminating possibilities. At the end of the day, I replaced the crank sensor, which only made the problem more pronounced. At the recommendation of a friend in the business, I did a CKP variation relearn and it instantly fixed the problem. Can't believe this problem boils down to a calibration problem in the PCM, good luck.
April, 1, 2013 AT 9:13 PM
I have a 2001 Chevy Silerrado 5.3l with 81000 miles on it doing the exact same thing. I was just talking to a co-worker about it and we decided the same concussion the crank sensor or doing a variation relearn. I am also going to check on software updates. I also wont go through what I have been doing but nothing helped. The truck has always ran great and it is hard to pin point issues like. I glad I ran across this post thanks for the insight.
April, 23, 2013 AT 7:05 PM
The first thing the diagnostic chart P0300 has you do is a crank senor variation relearn. I don't remember seeing this before but in took care of the problem. Something must get off with time and needs to be relearned.