Erratic timing light
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Joined: Sep 2004
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Erratic timing light
I have a 1976 F150, 390, auto, w/4bbl. When I put my timing light on the #1 wire I get erratic firing. Two to three flashes, then nothing. Maybe nothing for a few seconds, then a flash, nothing, several flashes, nothing, etc, etc.... When I put the light on another wire I get a constant flashing. What, if anything, does this mean? I have had trouble lately with the motor running rough.
Cargo Master
Joined: Apr 2004
Posts: 2,574
Likes: 4
From: Golden, CO
Ahhh, the scientific method! Did you check against all the other plug wires?
You've isolated the problem, it's most likely from the cap and rotor to the plugs. Check these components first, look for corrosion, oxidation, fouling. If everything is clean, replace the affected secondary wires.
Another less likely problem would be wear in the distributer. If the shaft has too much lateral play, it would affect spark gap. It would also make a godawful noise as the rotor hits the inside of the cap.
Good luck, Mike
You've isolated the problem, it's most likely from the cap and rotor to the plugs. Check these components first, look for corrosion, oxidation, fouling. If everything is clean, replace the affected secondary wires.
Another less likely problem would be wear in the distributer. If the shaft has too much lateral play, it would affect spark gap. It would also make a godawful noise as the rotor hits the inside of the cap.
Good luck, Mike
Posting Guru
Joined: Jul 2003
Posts: 2,232
Likes: 1
From: Colville, Washington
It sounds like you have isolated the problem! It is likely the plug, plug wire or the #1 contact in the distributor cap. As Mike mentioned it could also be caused by a worn shaft, but that would likely cause intermittent probs in all cylinder firing not just 1.
Easy check for the wire is to switch two plug wires and see if the problem follows the wire.
Easy check for the wire is to switch two plug wires and see if the problem follows the wire.
Laughing Gas
Joined: Jan 2002
Posts: 1,008
Likes: 1
From: Tucson
Oops, must be the wrong group; I thought that said "erotic timing light." Anyhow, so what did you find out? If you can afford it, buy a new all (points, rotor, condensor, plugs and wires). You may not need all that but having them will make you feel better and likely fix your problem.
jor
jor
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
Have you actually checked to see if you have a strong spark from the coil. Most times when I have seen this problem it has either been a bad pick up on the timing lite (don't bang the inductive pickups around) or the spark is weak. The first only requires putting the lite on a good ignition system of the same type and the second requires checking to see if the spark is able the jump the gap spec for that ignition system.
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