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'99 F-250 5.4L cylinder not firing

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Old 07-02-2006, 06:48 PM
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Exclamation '99 F-250 5.4L cylinder not firing

I'm hoping someone out there has had a problem with their 5.4 "p.o.s." engine as I am having.

My #3 cylinder will not fire. It has spark, a new coil pack, new spark plug that is gapped correctly, the injector is working and it is delivering fuel. The fuel pressure in the system is perfect, there is no vaccuum leak, there are no computer codes. It has had a compression test done and compression is fine

However, this cylinder 3.5 years ago had that famous blow-out problem. It was fixed with a heli-coil and has worked great ever since.

So, there is spark, fuel, and compression, but still the cylinder will not fire. There are no bad sounds coming from the engine - no rapping, ticking, pinging, valve noise or otherwise. In fact, the engine sits there and idles great and the only thing that tells you that it is missing a cylinder is you can hear the exhaust sound is rough.

Any ideas?
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Old 07-02-2006, 07:36 PM
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Vehicle: 1998 Ford F150
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How do you know if it's #3 cylinder if there aren't any codes? Several things will cause the same symptoms as a misfire, most notably plugged EGR ports. Remove the throttle body and check the ports that go to the EGR valve. More than likely clogged with carbon...
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Old 07-02-2006, 07:47 PM
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it is cylinder #3 because i brought it to ford and they put it on their computer and you could see the diagnostics of all 8 and #3 was dead.

also, as i should have mentioned, the egr was checked and is functioning properly
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Old 07-04-2006, 08:40 PM
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Based on your description of the tests performed and that this cylinder has a heli-coil, I can only come up with one idea.

I suspect that the heli-coil has lost its electrical integrity to the head. Probably corrosion or the effects of fuel/exhaust at the junction of the heli-coil spring and the head. Perhaps a chemical reaction with the coil's material or coatings. If this has happened, the plug will not fire properly.

Did the Ford dealer offer a diagnosis or not?

Steve
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