5 cylinders misfiring
Thread Starter
Melting Slicks
Joined: Apr 2000
Posts: 2,005
Likes: 0
From: Ridgecrest CA
5 cylinders misfiring
I have been having trouble getting the idle set on my 78; I have been fighting with the fuel injection for a couple weeks.
On a whim today, I hooked up my inductive timing light to each of the cylinders in turn, to see how they were each firing. It turns out that 5 of the cylinders are intermittantly not firing. My guess, from watching the light, is that they miss about every 10-12th revolution (1-2 sec @ ~700rpm).
I swapped those plugs and wires with cyliners that were firing fine, and they only have problems on those points. I pulled the cap and rotor, but they both appear fine. I don't see any cracks or streaks in them.
Could this be a coil problem? A chip problem (whatever you call the chip in the base of the distributor)? Something else?
Any suggestions?
On a whim today, I hooked up my inductive timing light to each of the cylinders in turn, to see how they were each firing. It turns out that 5 of the cylinders are intermittantly not firing. My guess, from watching the light, is that they miss about every 10-12th revolution (1-2 sec @ ~700rpm).
I swapped those plugs and wires with cyliners that were firing fine, and they only have problems on those points. I pulled the cap and rotor, but they both appear fine. I don't see any cracks or streaks in them.
Could this be a coil problem? A chip problem (whatever you call the chip in the base of the distributor)? Something else?
Any suggestions?
Last edited by Berserker78; Sep 17, 2006 at 02:51 AM.
Thread Starter
Melting Slicks
Joined: Apr 2000
Posts: 2,005
Likes: 0
From: Ridgecrest CA
Plugs are brand new, did the same thing with the old plugs. The wires were new about a month ago, but swapping those wires with cylinders that work has no effect on which cylinders misfire.
I just checked the firing order and it is correct as well.
I just checked the firing order and it is correct as well.
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
I have had great troubles with int ignition firing due to heat from headers, finally went the Jacobs ceramic boots route, that cured the problems.....this crap drives me crazy.....I find it tough to diagnose....which cylinder that is.....
Thread Starter
Melting Slicks
Joined: Apr 2000
Posts: 2,005
Likes: 0
From: Ridgecrest CA
I put a Holley FI system on. I replaced the coil this afternoon, and that helped quite a bit. I think I am going to try replacing the HEI module, but the local expert here thinks it sounds like an exhaust port isn't shutting right (89k miles).
As to which cylinders, it is 3,4,5,6,8.
As to which cylinders, it is 3,4,5,6,8.
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