Chasing erratic misfire
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
With 3&5 only, being consistantly much leaner I would think
-vacuum leak in runners perhaps on bottom side?
-valve problems, not seating etc, leakdown compression tests?
-switch plug wires to test wires?
-hei pickup coil, test with other dist?
Doubt if it is a carb problem
-vacuum leak in runners perhaps on bottom side?
-valve problems, not seating etc, leakdown compression tests?
-switch plug wires to test wires?
-hei pickup coil, test with other dist?
Doubt if it is a carb problem
Thread Starter
Race Director
Joined: Sep 2002
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From: San Diego - Deep Within The State of CONFUSION!
Le Mans Master
Joined: Dec 2006
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Thread Starter
Race Director
Joined: Sep 2002
Posts: 10,362
Likes: 5
From: San Diego - Deep Within The State of CONFUSION!
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
Then my vote is with Noonie. I doubt it's valvetrain on adjacent cylinders. You've virtually eliminated ignition and fuel. I sure would like to hear more from the other motorheads first.
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Veteran
Joined: Oct 2005
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From: Nashville, TN
My 72 was doing misfire for a good time. I replaced the entire ignition system. Nothing. It turned out to be the timing chain. I replaced the chain and pulleys with a double roller chain and my problem was gone. The gears were worn on the original timing gear and was slipping in the same spots. Once I put in the new timing set & chain we were good to go. 6000+ Rpm today and not a single misfire. I have some oil problems but that is another story! If you already replaced this then I missed it in the posting. Hope it helps. 
Last edited by King Lear; Feb 11, 2007 at 11:59 PM.
Thread Starter
Race Director
Joined: Sep 2002
Posts: 10,362
Likes: 5
From: San Diego - Deep Within The State of CONFUSION!
My 72 was doing misfire for a good time. I replaced the entire ignition system. Nothing. It turned out to be the timing chain. I replaced the chain and pulleys with a double roller chain and my problem was gone. The gears were worn on the original timing gear and was slipping in the same spots. Once I put in the new timing set & chain we were good to go. 6000+ Rpm today and not a single misfire. I have some oil problems but that is another story! If you already replaced this then I missed it in the posting. Hope it helps.
Veteran
Joined: Oct 2005
Posts: 1,284
Likes: 81
From: Nashville, TN
Well by the sound of everything and its not the chain. I would say the only thing left would have to be the point of contact between the cam and the distributor. That is the only other thing I can think of that hasn't bee mentioned.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
Here's a long shot idea. You said that the stumble is when the car is stopped and idling in "drive". Have you checked the problem when it is in gear? The idle drops a few hundred RPM when in gear...maybe there is some voltage drop at low idle that is affecting the ignition (really grasping for straws here). If you have an induction pickup timing light, have your wife hold the brake while the car is in "drive" at idle; put the pickup on the cylinder wires you are concerned with and see if the flash is erratic. If it is, have her just give it a touch of throttle to see if it goes away. If so, test the system voltage at each condition.
Remember...I said it was a long shot. Good luck.
Remember...I said it was a long shot. Good luck.
Safety Car
Joined: Feb 2006
Posts: 4,855
Likes: 2
From: Columbia South Carolina
Have you adjusted the valves? I did one adjustment out of desperation on my old Chevelle and it fixed the miss fire I had. Just my .02
Last edited by 454_71Stingray; Feb 12, 2007 at 01:51 PM.
