2002 F150 Misfire

wizdawg

TCG Elite Member
May 1, 2005
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My dad's 2002 F150 was running cold, about 1/4 or less reading on the temperature gauge. He bought a new thermostat and the gasket from Ford and replaced it. The truck now runs where it used to, about right in the middle of the gauge. But after driving it arouind for a little bit, after it had time to warm up, its starts missing real bad. I plugged my SCT tuner into it to read for codes and am getting a P0308 which is a Cylinder Number 8 Misfire Detected. It runs fine until it has warmed up, then the misfire starts.

We checked all the connections and everyhting seems to be in place. He didn't really even have to take much apart to replace the thermostat. I think just the intake was removed from the throtle body and pushed aside. And he cant think of anything that he did that would cause this, but it just seems more than a coincidence. A very little coolent spilled out by cyl #5, but nothing came close to #8.

Any ideas?

Thanks!
 

01bluesnake

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Jul 8, 2009
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It's more than likely a bad ignition coil. easy test is place number 8 coil to a different cyl, and see if it throws a code for the other cylinder with the suspected bad coil. if it now misfires in the other cylinder replace the coil. if it still misses in 8 with a different coil, we can go from there.
 

01bluesnake

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The coils do suck to change, but only way to find out without crazy ford diag. equipment. coils go whenever, issue i see daily at ford. If he got some coolant in the plug well, this would also cause the misfire, and may have caused the coil to die out.
 

01bluesnake

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The coolant is just one example that could cause a bad coil, but they go bad very often on their own without any outside damage or contamination. if you do need a new coil, let me know and i can get you a new ford one fairly cheap as i see you aren't too far from me.
 

wizdawg

TCG Elite Member
May 1, 2005
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You dont find it weird that this happened at the exact same time as changing the thermostat?

Thanks for the offer on the part, but I think my dad will probably just want to bring the car in and have them do the work. I think a coil replacement, especially back on cyl #8 is something he wont want to do himself.
 

01bluesnake

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You said the truck was operating at a lower temp range for a while, then when it actually ran at the correct temp is when it started to develop the concern. that could be an odd way but a way the coil now went bad. There all a couple other concern's on the 4.6 and 5.4 series to cause miss concern's but are more rare. Is it a miss only when warm, or is it almost all the time now, cause that could point to something else if only when at operating temp.
 

01bluesnake

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Ok, that does sound a little funky, do you want me to run a ford oasis on the vin and see if anything comes up. As far as i know there is nothing to specific for misfires on those, but i have seen bad heads cause this, possible bad injector, or a overheated coil after engine warm up. how many miles does the truck have?
 

01bluesnake

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ya, That's not a lot of miles. it would be more common for a coil to go at the lower mileage he has, but i have seen it all. I have access to the ford scan tool to bring and rule out any possible base engine, or injector issue. Let me know if you want me to swing by with a new coil and plug see if that fixes it and check it out, cheaper than the dealer for sure. trust me lol. On a regular dealer price, diag, coil and install is $350 plus, depending on dealer labor rate.
 

Dana

Bluesmobile
Mar 2, 2004
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Just tell him to go get a new plug and a new coil and swap them out. It isn't that diffucult. If he did the thermostat, he can do the plug/coil.

Now if it was an 04 5.4L that would be a little different. Now you have to worry about breaking plugs in the head.
 

aod92

Regular
Aug 26, 2008
229
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Just tell him to go get a new plug and a new coil and swap them out. It isn't that diffucult. If he did the thermostat, he can do the plug/coil.

Now if it was an 04 5.4L that would be a little different. Now you have to worry about breaking plugs in the head.
I think the 4.6 has the same problem with the spark plug issue? Also it probably is a coil that is causing the misfire. I've changed 6 out of the 8 on my expedition and there not that bad to change.
 
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