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Old 02-11-2009, 16:43   #1 (permalink)
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2002 5.4L Bad Low RPM miss

Hello. I just want to say thanks in advance for any help, I'm eternally grateful. So, I have a 2002 F150 5.4L with 130,000 that is missing bad. It started slightly, only over 80-85MPH, then it got worse. I got it home, and then it flashed the check engine light at me. The codes are (5) of them: P0171 P0174 P0301 P0303 & P0316

Odd thing being I have O2 sensor cheaters in all 3 locations, due to the fact that my Catalytic converter is missing. :D not sure what those codes are about. Currently this setup has been running perfect for 5 yrs.

So, here's what I did. I checked out the 2 misfiring cylinders. 1 and 3 one looked like the injector plug came loose? Not sure how, but ok. Then cyl 3 had the worst plug I've ever seen in it. The ground was completely gone, looked burned. The plugs are all less than 5,000 miles old, autolite double platinum. The electrode was pretty bad too. Replacing the plug, and verifying spark, now installed, it's running worse. I now have a HUGE shake with the miss. and new codes. The miss is now all over the speed and RPM range, however, it's slightly better without load. They are, P0308 P0352 P0351

The cyl 8 misfire i think is a symptom, as the coil, and plug look great. I had a small vacuum leak at the PCV, i got a new valve and routed same diameter new hose for it. air tight now.

I'm kinda lost where to even begin. I've been 2 days on this and now I'm frustrated. I work for my church, so money is kind of an issue, which is why I'm doing the work, and posting here.

Thank you everyone,

Jeff

Last edited by guy_over_here; 02-11-2009 at 16:45. Reason: clarify...
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Old 02-16-2009, 07:03   #2 (permalink)
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Re: 2002 5.4L Bad Low RPM miss

More info. I've removed the TPS, and it looked dark, but not gummed up or blocked with carbon or anything. I've looked also at the wiring from the PCM to the COPs, pulled a diagram from Chiltons. All the wires have good integrity. I checked them to the grounds and they all show the same voltage at the plug receptacle to the COPs.

This is even more frustrating now, as I can't find anything more wrong. I've heard PCMs get bad? How do I check this? I'm totally stumped now.

Thanks everyone. Also, please feel free to shoot ideas, no matter how silly or simple you think. I see people looking, but no one replying. Thanks again.

Jeff
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Old 02-19-2009, 11:41   #3 (permalink)
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Re: 2002 5.4L Bad Low RPM miss

PCMs do go out. It's not entirely a rare problem, but it's a mechanical part just like anything else. It's not cheap to replace. Generally a dealer can diagnose the PCM - for a price. It can be a pricey item to replace as well. Some salvage yards carry PCMs, but they have to be programmed correctly with your VIN or it won't function making it a dealer only install item....or a high end specialty shop. Again, not a cheap fix no matter you try to go about it.

I would run standard copper core plugs. They're $2-3 each and work just as good as a platinum tipped plug. If one does foul a bit it's no high expense to replace it. Perhaps a full tune up is what you need and the PCM is fine....
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