Engine Misfire
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Joined: Feb 2011
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From: Utah
Engine Misfire
I own a 1997 F150 with a 4.6 V8 and got a check engine light with a code of P0303 cylinder 3 misfire, I changed Spark Plugs and Wires and Im still getting the same code. I can usually figure things out but right now Im at a loss as to what steps to take next, any suggestions would be appreciated. 140000 miles, original plugs and wires. Whats odd is sometimes the CEL goes off on its own, sometimes stays off for a week or two running smooth and then comes back on running rough again.
Last edited by Schlim; Feb 15, 2011 at 07:39 PM.
Member
Joined: Jul 2009
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From: Tennessee
Since you have the 4.6 with the two coils and independent wires, you can easily check the coil for this cylinder. Since you have already replaced the plugs and wires, try this: When it starts acting up again, pull the plug wire, stick a screwdriver in it and hold it close to some bare metal, start the engine and observe the spark. This sounds like an intermittent coil issue to me. I would check compression next and then consider the injector being bad.
Senior Member
Joined: Mar 2009
Posts: 2,072
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From: Bedford, TX
I JUST had that problem, computer said misfire but the truck was running smoother and better then the day I bought it
It ended up being the injector for that cylinder, replaced it with a injector from a 93 lincon towncar with a 4.6
Our injectors are the same as about any v8 that ford has built in the last 30 years because they match the 5.8, 5.0, 5.4, and the list goes on and on. Just go to the scrapyard and grab a few and start switching them out one by one until one works
It ended up being the injector for that cylinder, replaced it with a injector from a 93 lincon towncar with a 4.6
Our injectors are the same as about any v8 that ford has built in the last 30 years because they match the 5.8, 5.0, 5.4, and the list goes on and on. Just go to the scrapyard and grab a few and start switching them out one by one until one works
Senior Member
Joined: Jul 2007
Posts: 134
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From: White Lake, MI.
May sound stupid, my 4.6 had a bad miss fire, changed plugs . wires and changed the two coils around and one oxy sensor. finally changed the fuel filter and a can of sea foam and she started running back to normal at once
Senior Member
Joined: Mar 2009
Posts: 2,072
Likes: 31
From: Bedford, TX
Originally Posted by DaleD
May sound stupid, my 4.6 had a bad miss fire, changed plugs . wires and changed the two coils around and one oxy sensor. finally changed the fuel filter and a can of sea foam and she started running back to normal at once
Senior Member
Joined: Jul 2007
Posts: 134
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From: White Lake, MI.
Yes, put a scanner on it several times and got different plug misfires, never would believe that it could possibly be a fuel filter problem causing such a bad miss and rough idle. I'm ashamed to say I never changed the filter until I had 200,000 on it. Scanner also said I had a bad oxy. sensor so I changed that also with no results until the sea foam in the tank and a fuel filter.
