512 #7 cylinder not firing head scratcher
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512 #7 cylinder not firing head scratcher
Engine 400 based 512 -11 to 1 compression about 5k miles since built 600hp 700tq at flywheel
Prosystems venom vx 850 carb
phantom 340 fuel pump
comp cams hydraulic roller
trick flow heads
msd 6al
mopar distributor no vacuum advance 8* initial 36* total
Engine has developed a miss on number 7 only by plug inspection. Miss is at idle all the way through RPM range. I've had a few odd misses over the 5k miles but mostly above 4500RPM where it would kind of fall on its face. A few of those times were due to the headers scorching a random wire. I've got the headers wrapped up now so hopefully that is behind me.
What I've done so far:
Electrical:
checked for spark on #7 looks good visually
Swapped plug and wire with number 5 wire and plug- #7 goes dirty again same miss.
Cap and rotor swap
pickup coil and reluctor swapped
Wire resistance check
swapped coils
Gonna see if my machinist has a spare distributor laying around I can try on Monday to rule out all electrical.
Mechanical:
Compression check all cylinders look good within 5psi of each other
Leak down 100psi input- all cylinders between 95-97 number 7 cylinder leaked to 97
valve lash looks good, all rockers tight, springs look good, cant collapse a lifter by hand. No interference or visual geometry issues.
I'm running out of ideas besides a distributor issue or a weak lifter.
I did have a spring clip come off the cap one day and the rotor whacked the cap hard. When I had the distributor out I ran it up with a drill and couldn't see a wobble by eye. Just seems weird one cylinder is just dead missing.
Any thoughts?
Prosystems venom vx 850 carb
phantom 340 fuel pump
comp cams hydraulic roller
trick flow heads
msd 6al
mopar distributor no vacuum advance 8* initial 36* total
Engine has developed a miss on number 7 only by plug inspection. Miss is at idle all the way through RPM range. I've had a few odd misses over the 5k miles but mostly above 4500RPM where it would kind of fall on its face. A few of those times were due to the headers scorching a random wire. I've got the headers wrapped up now so hopefully that is behind me.
What I've done so far:
Electrical:
checked for spark on #7 looks good visually
Swapped plug and wire with number 5 wire and plug- #7 goes dirty again same miss.
Cap and rotor swap
pickup coil and reluctor swapped
Wire resistance check
swapped coils
Gonna see if my machinist has a spare distributor laying around I can try on Monday to rule out all electrical.
Mechanical:
Compression check all cylinders look good within 5psi of each other
Leak down 100psi input- all cylinders between 95-97 number 7 cylinder leaked to 97
valve lash looks good, all rockers tight, springs look good, cant collapse a lifter by hand. No interference or visual geometry issues.
I'm running out of ideas besides a distributor issue or a weak lifter.
I did have a spring clip come off the cap one day and the rotor whacked the cap hard. When I had the distributor out I ran it up with a drill and couldn't see a wobble by eye. Just seems weird one cylinder is just dead missing.
Any thoughts?
Mopar Lover
Joined: Apr 2010
Posts: 1,889
Likes: 170
From: Long Island, NY
75 -
Sounds like you checked everything.
Agree with replacing the distributor AND ALL WIRES. (Reroute #7)
Just for giggles, observe the engine running at night with all lights out and look for arcing.
Run the engine with the valve cover off and check rocker action.
Archer
Sounds like you checked everything.
Agree with replacing the distributor AND ALL WIRES. (Reroute #7)
Just for giggles, observe the engine running at night with all lights out and look for arcing.
Run the engine with the valve cover off and check rocker action.
Archer
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