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Old 07-23-2012, 07:36 PM   #1
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Red face 5.4 misfire low RPM's on freeway

This is what has been happening lately, and im not sure what exactly is wrong with it. I just dont want to keep throwing money at a bunch of different parts when it doesnt fix the problem. Once my truck warms up and I am either on the freeway or a back road (anything above 45 mph) my truck will start to shake and stutter (misfire). It will continue to shake and shutter until I step on the gas a little bit and get the RPM's up. I have replaced the fuel filter a few times, and the plugs too many times too count. Everytime that ive replaced the plugs, it'll run fine for a little while then it'll go right back to what it was doing just after a couple months. The last couple times Ive done the plugs i noticed that the tips were a little white, which means its running lean if im not mistaken. My trucks got 165k on it, and as far as i know the O2 sensors have never been replaced. Also my friend told me that the "cats" are known to go bad on my truck, and those are also stock. And I do have an upgraded exhaust on my truck. PLEASE any help or comments would be GREATLY appreciated, I am so frustrated.
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Old 07-23-2012, 07:37 PM   #2
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Oh and i just remembered that i didnt say that my truck is an 2003 F-150 Lariat with the 5.4L.
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Old 07-23-2012, 09:08 PM   #3
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Are you getting any codes? Autozone/similar places will pull the codes for free. Mine would do the shudder until I slammed the pedal. It was showing 2 misfire codes. I decided to replace all my COP's and haven't had a problem since.
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Old 07-24-2012, 12:47 AM   #4
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Are you getting any codes? Autozone/similar places will pull the codes for free. Mine would do the shudder until I slammed the pedal. It was showing 2 misfire codes. I decided to replace all my COP's and haven't had a problem since.
I haven't had them scanned in quite awhile and don't remember EXACTLY what they were, but if I do remember right they were lean on like bank one and then a misfire on one of the cylinders on that same side. I will go try to have them ran agian tomorrow, but my check engine light ain't on (it used to come on) but the second to last time I replaced the plugs I had the codes cleared
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Old 07-24-2012, 12:51 AM   #5
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Are you getting any codes? Autozone/similar places will pull the codes for free. Mine would do the shudder until I slammed the pedal. It was showing 2 misfire codes. I decided to replace all my COP's and haven't had a problem since.
Also were ur plug tips somewhat white as if its running lean?
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Old 07-31-2012, 08:37 AM   #6
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I am pretty sure I know what is going on because I chased the same problem for a while. If you go out an floor it and hold it on the floor does it have the same misfire? If so you have a coil that is failing on the secondary side. It will run smoothly durring normal operation but under heavy load like flooring it or at lower rpms at normal speeds when you try to accelerate or go up hills. Most scanners will not identify which cylinder is misfireing even if you go out and drive with the scanner on live monitering. You will have to check each coil one at a time with a spark checker that forces it to use the secondary side. The other problem could be a crack in the porcaline on the plug or a small split in the coli boot that is arking out under heavy load. I am going to order a spark checker today to test mine I can let you know how the one I order works next week.
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Old 07-31-2012, 11:58 AM   #7
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I think I'm having the same problem. When I floor it, it misfires badly. When I'm doing about 50+ on the highway and push the gas just little more to pick up speed, my truck starts to jerk and shake horribly.
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Old 08-03-2012, 09:40 AM   #8
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sdurosko5 do you have an k&n style air filter on your truck? With those oiled filters on the truck some of the oil gets pulled through the intake while the engine is running and gets on the mass air flow sensor. The oil on the sensor will cause it to read that its running lean. On my truck after I clean and oil my filter a week or so later I will clean the MAF sensor. It only takes 5 min to do but that stopped the lean running code.
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Old 08-03-2012, 09:40 AM
 
 
 
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5.4l. lariat., hesitates in high gears, misfire, stutters

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