Intermittent fire on #3 cyl
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Cargo Master
Joined: Jul 2000
Posts: 2,281
Likes: 18
From: Northern California
Intermittent fire on #3 cyl
The truck wasn't running right and I pulled all the plugs. they were all light tan except #3, it had a wet black film on it and it wipped off and looked new.
I did a compression check and it came out at 190. I cleaned gapped and replaced all the plugs. Cleaned the cap and rotor and hooked the timming light to each wire to see if it was getting fire.
#3 was getting intermittent fire whereas all the others were good. I replaced the cap and rotor and nothing changed. I swapped the #1 & #3 wire and nothing changed.
I thought the Pertronix was bad so I moved the mag pickup below the rotor to see if it was bad and still # 3 was the only one with a problem.
I'm running the Pertronix unit with coil and bypassed the resistor wire. I'm using the big cap upgrade and MSD wires. All these have < 100 miles on them.
I just don't understand how the pertronix can miss on just one cyl. I thought the mag pickup could be too far on one part but when I moved it, the same thing happened. They use a seperate mag for each cyl on the pickup and that's the only thing I can think of.
Any ideas?
73 F250 4x4 428 HEI cap MSD wires Pertronix unit Pertronix coil no resistor wire.
I did a compression check and it came out at 190. I cleaned gapped and replaced all the plugs. Cleaned the cap and rotor and hooked the timming light to each wire to see if it was getting fire.
#3 was getting intermittent fire whereas all the others were good. I replaced the cap and rotor and nothing changed. I swapped the #1 & #3 wire and nothing changed.
I thought the Pertronix was bad so I moved the mag pickup below the rotor to see if it was bad and still # 3 was the only one with a problem.
I'm running the Pertronix unit with coil and bypassed the resistor wire. I'm using the big cap upgrade and MSD wires. All these have < 100 miles on them.
I just don't understand how the pertronix can miss on just one cyl. I thought the mag pickup could be too far on one part but when I moved it, the same thing happened. They use a seperate mag for each cyl on the pickup and that's the only thing I can think of.
Any ideas?
73 F250 4x4 428 HEI cap MSD wires Pertronix unit Pertronix coil no resistor wire.
New User
Joined: Jun 2002
Posts: 5
Likes: 0
From: medical lake USA
Intermittent fire on #3 cyl
[updated:LAST EDITED ON 13-Aug-02 AT 07:24 AM (EST)]if plugs don't fix it. rotate the plug wires 1 post over on the distributor, rotate the distributor back and retime it. if the problem stays in the same cylinder it mechanical, if it move one over its in your distributor.
Posting Legend
Joined: Sep 2001
Posts: 30,255
Likes: 37
Intermittent fire on #3 cyl
I got 3 bad plugs in a set of AC-Delco's I installed on an old Mopar. I swapped back to Champion. I would be inclined to return the entire set since the others in that lot may be marginal also.
Intermittent fire on #3 cyl
