5.3L LM7 Misfire
Thread Starter
Teching In
Joined: Jun 2023
Posts: 6
Likes: 0
5.3L LM7 Misfire Hi all,
Surfed many threads on here and my issue still remains. Purchased a 5.3L swapped C-10 this weekend and upon getting home, P0307 code is showing (misfire #7). Also, had both O2 sensors showing rich. Identified the following, in the following order:
1. Cleared codes
2. Confirmed coil produces spark, wire produces spark, and replaced plug
3. Sprayed intake manifold with brake clean
4. Tested compression on 1-3-5-7 (135-150psi) (did not open throttle, numbers likely to bump up with throttle open)
5. Confirmed pulse on injectors (screwdriver to ear)
6. Verified valves moved smoothly and lifter was plenty firm
7. Swapped #5 and #7 injector (did not appear completely gunked)
8. Misfire continues
9. Swapped coil pack #7 with #1
P0300 code arrives, exhaust continues to sputter inconsistently
I have confirmed wiring does not appear damaged. I now notice that exhaust on 1-3-5-7 are all hot compared to my original #7 issue where #7 was colder.
The miss is enough to send a light vibration through the cab. Next plan is to take heat temp gun to each exhaust and see which is coldest, and swap #1 coil (previously #7) with new AC Delco.
If those don't work, leak down test.
Crank relearn? Burnt valve? Or simply a faulty coil that fires sometimes, but not all the time?
At this point I am stumped, as it seems to be an inconsistent miss rather than a complete dead cylinder. Any advice is helpful.
Surfed many threads on here and my issue still remains. Purchased a 5.3L swapped C-10 this weekend and upon getting home, P0307 code is showing (misfire #7). Also, had both O2 sensors showing rich. Identified the following, in the following order:
1. Cleared codes
2. Confirmed coil produces spark, wire produces spark, and replaced plug
3. Sprayed intake manifold with brake clean
4. Tested compression on 1-3-5-7 (135-150psi) (did not open throttle, numbers likely to bump up with throttle open)
5. Confirmed pulse on injectors (screwdriver to ear)
6. Verified valves moved smoothly and lifter was plenty firm
7. Swapped #5 and #7 injector (did not appear completely gunked)
8. Misfire continues
9. Swapped coil pack #7 with #1
P0300 code arrives, exhaust continues to sputter inconsistently
I have confirmed wiring does not appear damaged. I now notice that exhaust on 1-3-5-7 are all hot compared to my original #7 issue where #7 was colder.
The miss is enough to send a light vibration through the cab. Next plan is to take heat temp gun to each exhaust and see which is coldest, and swap #1 coil (previously #7) with new AC Delco.
If those don't work, leak down test.
Crank relearn? Burnt valve? Or simply a faulty coil that fires sometimes, but not all the time?
At this point I am stumped, as it seems to be an inconsistent miss rather than a complete dead cylinder. Any advice is helpful.
TECH Apprentice
Joined: Aug 2018
Posts: 383
Likes: 108
You got a P0300 after swapping the coil? I think that's a random misfire code, no?
Seems like the coil is the problem, intermittently? Can you swap a known good coil, maybe from another engine that runs good?
Seems like the coil is the problem, intermittently? Can you swap a known good coil, maybe from another engine that runs good?
