Misfire #7 Cylinder
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Misfire #7 Cylinder
Hello all. I have a 98 F150 with the 4.6L. I see lots of posts around here about misfire being caused by plugs, wires, and coils. Here's my problem. I have the check engine light on. Hooked it up to the code reader, P0307. Misfire #7. The cylinder acts like it is dead! The problem is intermittent and only happens when the outside air temp is below 50 degrees. It happens more often when the truck has sat for more than two days without running. When it happens the cylinder will be dead for 15 minutes to a day or two. Then, as if by magic, it will kick back in and run fine for a week or whatever. Had this problem on the number three cylinder last year. A coil pack cured it. Not this time. I have tried swapping spark plugs. Miss didn't move. Swapped coil packs. No difference. Tried running a seperate spark plug that was located away from all other wires to the #7. No help. It NEVER does it in the summer, only in our mild Phoenix winters. ABout the only thing I haven't done is pull the EGR and check for carbon build up and swap injectors to see if the miss moves. Any suggestions?
THanks all, Curt
THanks all, Curt
Senior User
Joined: Nov 2003
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From: Royal Palm Beach, Fl
How Many miles are on it since the plugs and wires have been changed. I once had a wire that would only miss after it warmed up. That is the reverse of your problem but the cold maybe doing it too. I don't thing you can pull on those wires very much before they start to break down inside. If the wires are old enough I would change them. 98 4.6L F150
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Truck has 66K. Plugs have about 5K. Wires are Original, but I tried running a new sparkplug wire to the cylinder. It was located away from all the others. I have also swapped spark plugs. No help. I think it's fuel related.
Thanks
Thanks
Hotshot
Joined: Aug 2002
Posts: 12,679
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From: BC, Canada
Hi Curt and welcome to the forum 
Have you tried checking for vacuum leaks when the engine is cold? Sometimes they show up more when cold. You can spray some Carb-Medic spray carb cleaner or something similar around the intake manifold with the engine running and if the idle changes when you spray it you've found your leak. Concentrate on the vacuum hoses and where the intake meets up with the heads, especially at the #7 port.
After that I think I'd try having the injectors cleaned or maybe try moving a couple around and see if it makes any difference.
Let us know what you find.
Have you tried checking for vacuum leaks when the engine is cold? Sometimes they show up more when cold. You can spray some Carb-Medic spray carb cleaner or something similar around the intake manifold with the engine running and if the idle changes when you spray it you've found your leak. Concentrate on the vacuum hoses and where the intake meets up with the heads, especially at the #7 port.
After that I think I'd try having the injectors cleaned or maybe try moving a couple around and see if it makes any difference.
Let us know what you find.
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Thanks for the ideas Racerguy. I would suspect a vacuum leak if it happened everytime it was cold, but it is intermittent. It is gettring more frequent though. I came out of a store the other day and started the truck; it started missing on #7 even though the truck was warm. It has never done that before. I starting to think that the #7 injector has a leak that is allowing it to coke over, or it's just plain faulty. I'm going to try both of your suggestions. Hopefully one of them will shead some light on the problem.
Regards
Regards
