340 runs on only 4 or 5 cylinders after backfiring

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Dochal71

Dochal71

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Last weekend I was racing my 69 GTS 340. The engine has about 1000 miles on it. After I beat as 66 Charger with a 440. I was coming back and I believe I over revved the engine. It backfired and died. It would not restart. Checked and I was getting fuel. Then popped dizzy cap off. Rotor turned. Discovered the points were welded together. Popped them loose. One of the contacts fell off so reset the gap to get it to run. Limped it home (50 miles away) It didn't seem to be running on all 8. Got it home. I changed the plugs, dizzy cap & rotor. Put a Pertronix electronic conversion in. Changed the coil. Did a compression check. Around 150 PSI/cylinder. I felt the exhaust manifolds. Number 1, 2, 8 and possibly number 4 are cold. I even changed the distributor out today. No difference. The timing chain is basically new (1000 miles on it) I have the Mopar Performance tensioner on it. I even pulled the rocker covers off. All the rocker are articulating as they should. I also checked the spark plug wires. I am getting spark on the dead cylinders. Any Ideas?
 
Seems obvious but, are you sure the firing order is correct at this point with all the changes?
 
I'd be looking for bent push rods. Pop the valve covers off and make sure everything is moving correctly. Then go to the ignition.
 
I was having a problem close to that . I had bad 87 octane gas with ethanol that had sat for a month and a half. The fuel inside my edelbrock separated and what was left is the fuel and the ethanol turned to a clear wet chunky gelatinous stuff floating around in the bowels and clogged up the jets and passage ways in the carb . Made it seem like it was running on 3 cylinder on my 360 had to clean out tank and flush fuel line and clean out carb with carb cleaner and a air nozzle . It also smelled like it was running rich also? Now it runs great . I run 91 no ethanol. Try dribbling some gas in the cylinders and put plugs and wires back on and try starting see what it does? let me and the others know on any of the tests you do then we can try to figure some thing else out?
 
AJ/FormS said:
Wouldn't bent pushrods affect this?
Are you using a Holley? Check the PV cavity for fuel in it. If it's there, install a new PV.... a 10.5
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No as they would keep the valves from opening as far as they should. Would probably increase compression if anything.
 
AJ/FormS said:
Wouldn't bent pushrods affect this?
Are you using a Holley? Check the PV cavity for fuel in it. If it's there, install a new PV.... a 10.5
Click to expand...

Not if the valves are closed.
 
I wouldn't be pushing a fresh rebuild that hard with only 1000 miles on it, may have sheared a cam lobe or hopefully bent a pushrod. I'd also check fuel pressure because you may have pushed the mechanical fuel pump too hard
 
you said this problem happened on the way back after race / compression is fine so if that many cylinders are miss firing I would agree with a fuel or electrical issue not the engine itself
 
Dochal71 said:
Last weekend I was racing my 69 GTS 340. The engine has about 1000 miles on it. After I beat as 66 Charger with a 440. I was coming back and I believe I over revved the engine. It backfired and died. It would not restart. Checked and I was getting fuel. Then popped dizzy cap off. Rotor turned. Discovered the points were welded together. Popped them loose. One of the contacts fell off so reset the gap to get it to run. Limped it home (50 miles away) It didn't seem to be running on all 8. Got it home. I changed the plugs, dizzy cap & rotor. Put a Pertronix electronic conversion in. Changed the coil. Did a compression check. Around 150 PSI/cylinder. I felt the exhaust manifolds. Number 1, 2, 8 and possibly number 4 are cold. I even changed the distributor out today. No difference. The timing chain is basically new (1000 miles on it) I have the Mopar Performance tensioner on it. I even pulled the rocker covers off. All the rocker are articulating as they should. I also checked the spark plug wires. I am getting spark on the dead cylinders. Any Ideas?
Click to expand...

Dana67Dart said:
How about an update!
Click to expand...
I agree; Update???
 
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