Intermittent P0304 (cylinder 4 misfire)

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Feb 6, 2010
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My '02 Ford Escort is throwing a P0304. Thus far I've changed the spark plugs even though the old ones were still in pretty good condition, alternated the plug wires between cylinders 3 and 4 to see if the misfire would move to cylinder 3 which it didn't, put a different coil pack on from another car that uses the same coil pack and I'm still getting an intermittent P0304. Only other thing I can think of that could be causing the problem now is a bad fuel injector. Does anyone have other ideas? 9+ times out of 10 the misfire happens on start up and lasts less than 30 seconds. Sometimes it will go for several days without acting up then misfire on every start up for a day or two. I've also noticed that since the weather has cooled down in this area that it's not happening quite as often. P0304 is the only code I have. The engine is the 2.0L SOHC. I had a cam position sensor code about a year ago so the cam sensor was replaced at that time.
 
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yeah id try swapping a fuel injector and if that doesn't change anything then its sadly gonna turn into an electrical issue like wiring. the effects of temp changes is odd.
 
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Pull the plug first thing in the morning before you start it and see if there’s any coolant or moisture in that cylinder.
 
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Pull the plug first thing in the morning before you start it and see if there’s any coolant or moisture in that cylinder.
^ thats one but i think hedve noticed low coolant and the plug he changed wouldve looked bad unless he didnt catch them.
 
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These 2.0 SPI engines are notorious for dropping the #4 exhaust valve seat, and this is exactly how it acts. If everything goes exactly wrong eventually it will get stuck down far enough on the valve that the exhaust valve will hit the piston and ruin the engine. I drove our 99 for awhile like this, but it went bang before I figured our what was going on.
 

FordMan59

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yeah id try swapping a fuel injector and if that doesn't change anything then its sadly gonna turn into an electrical issue like wiring. the effects of temp changes is odd.
I agree the temperature effects are odd. Usually misfires are more noticeable in the cooler weather and this one is just the opposite. At the end of last week is when I changed the coil and I thought that was the problem because it didn't act up for a couple days then at the first of this week the temperatures rebound to around 80* and it started acting up again. For the last 2 or 3 days now it's been cool again and it's not acting up. You're also right about the spark plugs they looked normal when I removed them and replaced them with a new set of platinum plugs.
 

FordMan59

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These 2.0 SPI engines are notorious for dropping the #4 exhaust valve seat, and this is exactly how it acts. If everything goes exactly wrong eventually it will get stuck down far enough on the valve that the exhaust valve will hit the piston and ruin the engine. I drove our 99 for awhile like this, but it went bang before I figured our what was going on.
Yeah, I'm aware of the valve seat issue. Overheating is also often a contributor to the valve seat issues. I've owned the car since 2008 and it's never been overheated. If that does turn out to be the problem I'll drive it till it turns loose. The body is in poor condition where a lady hit my son in it several years ago plus it's got in access of 215K miles. There was more damage to the body than I'd paid for the car so I just put the money back to use toward the purchase of another car and continued to use it as a daily driver. I've got chronic back pain and don't feel like pulling the head myself and the car isn't worth paying someone what it would cost to have a mechanic replace it.
 
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FordMan59

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Yeah, I'm aware of the valve seat issue. Overheating is also often a contributor to the valve seat issues. I've owned the car since 2008 and it's never been overheated. If that does turn out to be the problem I'll drive it till it turns loose. The body is in poor condition where a lady hit my son in it several years ago plus it's got in access of 215K miles. There was more damage to the body than I'd paid for the car so I just put the money back to use toward the purchase of another car and continued to use it as a daily driver. I've got chronic back pain and don't feel like pulling the head myself and the car isn't worth paying someone what it would cost to have a mechanic replace it. As it is now with having done most of the previous work on it myself other than the cost of gas/tires/insurance I'm probably ahead on this car and have been using it for 13 years. I've got other cars fit for use as daily drivers if necessary.
 
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