2000 LM7 dead miss cylinders 3, 4 and 8 help plz
03-31-2017, 12:39 AM
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2000 LM7 dead miss cylinders 3, 4 and 8 help plz Hello all. I have been a reader of the site for a long time and finally joined. I have a 2000 5.3 in a desert race truck that has me boggled. It is running the ECM that came with the motor as well as the factory harness. The motor did sit for 5 years while I built the truck. I kept oil in the cylinders and made sure it was spun by hand often. It was stored inside a climate controlled room.
The motor had a miss from the first start. Here are the things I have done to stop the miss. The only code was a P016 before I replaced the cam/crank sensors. There are no codes currently.
Tr-55 plugs gapped at .40 (3 sets)
Swapped coils, injectors and plug wires with cylinders that run well, the problem didn't follow.
Noid test on the dead cylinder injector wires with positive results.
Inline spark tester on dead cylinders with good strong lighting of the tester.
Sprayed brake fluid / carb cleaner around the intake, no leaks found.
Fuel pressure test, 52 psi while running.
Compression test on all cylinders. All were 141 - 150 psi
Cam position sensor replaced.
Crank position sensor replaced and crank relearn complete.
Replaced all ground wires and added another from the block to the roll cage. Ground wire directly from the battery to the passenger head, a ground wire from the passenger head to the drivers head, a ground from the alternator mount to the roll cage.
I had the truck Dyno tuned. I am not running a maf so I added a intake temp sensor to the intake and he tuned it for speed density. When it came off the dyno it ran perfect. Took it to the desert for a test day and it ran strong for 20 minutes or so. My co-driver said he thought he heard a miss and over the next 5 minutes the miss got much worse. We drove it back to make some shock adjustments and I turned the main battery switch off killing the power to everything. It sat for 30 minutes, we started it and once again there was no miss. For the next 40 minutes it ran perfect then slowly started missing again. Nothing stops the miss now. There is no difference in sound when pulling the fuel injector wires from those 3 cylinders while running but the other 5 cause the rpm to drop and add to the miss when removed.
Sorry this is so long, I just wanted to be sure I put all I did down. I'm very frustrated and and really need to figure this out so we can do final testing on this 5 year project!
Thanks I advance for any ideas!
The motor had a miss from the first start. Here are the things I have done to stop the miss. The only code was a P016 before I replaced the cam/crank sensors. There are no codes currently.
Tr-55 plugs gapped at .40 (3 sets)
Swapped coils, injectors and plug wires with cylinders that run well, the problem didn't follow.
Noid test on the dead cylinder injector wires with positive results.
Inline spark tester on dead cylinders with good strong lighting of the tester.
Sprayed brake fluid / carb cleaner around the intake, no leaks found.
Fuel pressure test, 52 psi while running.
Compression test on all cylinders. All were 141 - 150 psi
Cam position sensor replaced.
Crank position sensor replaced and crank relearn complete.
Replaced all ground wires and added another from the block to the roll cage. Ground wire directly from the battery to the passenger head, a ground wire from the passenger head to the drivers head, a ground from the alternator mount to the roll cage.
I had the truck Dyno tuned. I am not running a maf so I added a intake temp sensor to the intake and he tuned it for speed density. When it came off the dyno it ran perfect. Took it to the desert for a test day and it ran strong for 20 minutes or so. My co-driver said he thought he heard a miss and over the next 5 minutes the miss got much worse. We drove it back to make some shock adjustments and I turned the main battery switch off killing the power to everything. It sat for 30 minutes, we started it and once again there was no miss. For the next 40 minutes it ran perfect then slowly started missing again. Nothing stops the miss now. There is no difference in sound when pulling the fuel injector wires from those 3 cylinders while running but the other 5 cause the rpm to drop and add to the miss when removed.
Sorry this is so long, I just wanted to be sure I put all I did down. I'm very frustrated and and really need to figure this out so we can do final testing on this 5 year project!
Thanks I advance for any ideas!
Last edited by Kfalcon; 03-31-2017 at 12:46 AM. Reason: Wrong missing cylinders noted
04-01-2017, 04:39 AM
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Thanks for the idea. I will do a leak down on it to see. It was weird that the miss has come and gone a few times though. Is it possible to have a bad ecm that is sending the coil signal or injector signal at the wrong time to the 3 cylinders?