Follow up
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Follow up
Starting a new thread on my 1986 F150 5.0 auto EFI: Been chasing the extremely rough idle.Ran codes, no luck.
When check the timing with timing light, put clamp on no.1 wire, No light flickered. Tried on no.2, and flicker so I know timing light works. Pulled wire of no.1 plug and nothing. Checked the others and all gave a good spark except no.4. So 1 and 4 no spark. Same thing at distributor cap terminals nos. 1 and 4. What would cause only 2 out of 8 not firing. ?
Does the computer have anything to do with which plugs fire.
When check the timing with timing light, put clamp on no.1 wire, No light flickered. Tried on no.2, and flicker so I know timing light works. Pulled wire of no.1 plug and nothing. Checked the others and all gave a good spark except no.4. So 1 and 4 no spark. Same thing at distributor cap terminals nos. 1 and 4. What would cause only 2 out of 8 not firing. ?
Does the computer have anything to do with which plugs fire.
Last edited by saemetric; Dec 21, 2025 at 09:37 AM.
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Joined: Oct 2016
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From: Parts Unknown
A carboned tracked distributor cap.Maybe a worn distributor with a lot of sideway slop of the dist. shaft.
You need to correct the year (1086) and engine type (3.0) in your post. I am assuming the year is 1986 and the engine is 5.0. The computer is not capable of detecting which exact cylinder is not firing.
You need to correct the year (1086) and engine type (3.0) in your post. I am assuming the year is 1986 and the engine is 5.0. The computer is not capable of detecting which exact cylinder is not firing.
Last edited by raski; Dec 20, 2025 at 05:52 AM.