Backfiring
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Backfiring
I just replaced the plugs and wires on my truck and now when I start it it runs for 15 seconds or so then starts to backfire real bad then dies even if I try to keep it running with the gas pedal. Then if I try to start it again it takes awhile to get it started again.
I have checked the wires many times and they are all in the correct place. None of them are crossed.
oh its a 1977 400
Ill bet Mil1ion has an answer for me
I have checked the wires many times and they are all in the correct place. None of them are crossed.
oh its a 1977 400
Ill bet Mil1ion has an answer for me
Last edited by 77F250Custom4spd; Oct 11, 2007 at 09:12 PM.
Elder User
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From: Sin City, USA
Originally Posted by danlee
How did you replace the wires?
Did you replace them one at a time, or did you remove all of them and replace the whole set?
Did you replace them one at a time, or did you remove all of them and replace the whole set?
Postmaster
Joined: Aug 2001
Posts: 4,270
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From: Delaware
Originally Posted by 73XAFalcon
Just what I was thinking. You have 2 wires crossed. Trace your plug wires back and see which 2 you swapped.
Did you also replace the cap and rotor?
MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
I have been told that on a 400, you can't let the #5 and #6 plug wires run parallel. That means you can't clip them down next to each other on the valve cover. Instead of clipping them as 5, 6, 7, 8 you should do something like 5, 7, 6, 8. This is said to be because cylinders 5 and 6 fire right after each other per the 400 firing order which causes inductive coupling problems if the wires run parallel too much. This will cause crossfiring issues.
I can't readily say that I believe it, but I've seen it in enough places, including my 400 build book, that I think it's at least worth looking at.
I can't readily say that I believe it, but I've seen it in enough places, including my 400 build book, that I think it's at least worth looking at.
Last edited by fmc400; Oct 12, 2007 at 10:33 AM.
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Originally Posted by danlee
How did you replace the wires?
Did you replace them one at a time, or did you remove all of them and replace the whole set?
Did you replace them one at a time, or did you remove all of them and replace the whole set?
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Originally Posted by danlee
Or he started the firing order one terminal off of #1. The #1 mark on the cap may not truly be #1.
Did you also replace the cap and rotor?
Did you also replace the cap and rotor?
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Originally Posted by fmc400
I have been told that on a 400, you can't let the #5 and #6 plug wires run parallel. That means you can't clip them down next to each other on the valve cover. Instead of clipping them as 5, 6, 7, 8 you should do something like 5, 7, 6, 8. This is said to be because cylinders 5 and 6 fire right after each other per the 400 firing order which causes inductive coupling problems if the wires run parallel too much. This will cause crossfiring issues.
I can't readily say that I believe it, but I've seen it in enough places, including my 400 build book, that I think it's at least worth looking at.
I can't readily say that I believe it, but I've seen it in enough places, including my 400 build book, that I think it's at least worth looking at.
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A backfire is pretty much always caused by the wrong timing, either ignition or cam.
If all you did was replace the plugs and wires, and it ran ok before, then you know something is wrong with the wire routing. A bad wire or plug will make it run rough, but i dont think it'll cause a back fire.
Check the wires again... firing order should be 13726548 counter clockwise. I'd remove the number 1 spark plug, and turn the engine over until number one piston is tdc on it's compression stroke, then take the cap off and make sure the rotor is pointed at number one, then check the firing order from there.
If all you did was replace the plugs and wires, and it ran ok before, then you know something is wrong with the wire routing. A bad wire or plug will make it run rough, but i dont think it'll cause a back fire.
Check the wires again... firing order should be 13726548 counter clockwise. I'd remove the number 1 spark plug, and turn the engine over until number one piston is tdc on it's compression stroke, then take the cap off and make sure the rotor is pointed at number one, then check the firing order from there.
Last edited by RJR99SS; Oct 12, 2007 at 03:23 PM.