Random miss fire 5.4
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Tuned
Joined: Aug 2007
Posts: 492
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From: Louisville
Random miss fire 5.4
I am getting random miss fires when in 4th grear at about 2k rpm under light acceleration or sometimes just cruising. I do not have any codes popping up. The only time I had a engine light was when i floored it on the hwy and it blinked to indicate miss firing. The truck has 155k on it and has had the plugs and the cops changed once. The cops were changed early this year, and yhe plugs were changed with motorcraft plugs in 2017 at about 110k. What do you all think?
Fleet Owner
Joined: Jan 2004
Posts: 26,007
Likes: 575
From: Brentwood,CA
I think you are due for plugs and boots again. Your problem is carbon tracking or insulator cracking on the plugs.
Unless all the COP'S were changed with aftermarket then all bets are off...
Unless all the COP'S were changed with aftermarket then all bets are off...
Fleet Mechanic
Joined: Jul 2008
Posts: 1,937
Likes: 1,221
From: Southern Crescent
Also this engine has a problem with moisture getting into the plugs, especially the rear most (of course) and creating a corrosion problem. Getting in there and cleaning all the connection points real good might fix it.
Fleet Mechanic
Joined: Apr 2016
Posts: 1,653
Likes: 193
Do a hospital clean plug job
Failure to clean spark hole out with carb cleaner is a big mistake . That recess gets full of carbon Its very hard to burn out,carbon is tough stuff . Look how long it takes to burn a charcoal briquette in the open air with lighter fluid.
But it can dissolve with carb cleaner directly on it ,its up to you to get a swab in there to treat it . It was a stupid design but you have to get it back to factory clean like it was for the first 60k ,don't let plugs get more than 60k on them . 600 to 1200 bucks for plug change -you gotta be kidding .
Do you really want to put that new plug in that super filled in recess full of carbon .Do you think a shop will go to the trouble of cleaning it out .Failure to put new boots on ,failure to replace connectors that won't lock on , all this is not that hard.Take the time do a good job . Bad plugs will cause other serious problems .
But it can dissolve with carb cleaner directly on it ,its up to you to get a swab in there to treat it . It was a stupid design but you have to get it back to factory clean like it was for the first 60k ,don't let plugs get more than 60k on them . 600 to 1200 bucks for plug change -you gotta be kidding .
Do you really want to put that new plug in that super filled in recess full of carbon .Do you think a shop will go to the trouble of cleaning it out .Failure to put new boots on ,failure to replace connectors that won't lock on , all this is not that hard.Take the time do a good job . Bad plugs will cause other serious problems .
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Tuned
Joined: Aug 2007
Posts: 492
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From: Louisville
The coil packs were replaced with motorcraft cops in the spring of this year. It maybe time for plugs again, it has been about about 45k ish since the original set was replaced. They were changed by a ford dealer with the updated Motorcraft plugs.
Fleet Mechanic
Joined: Apr 2016
Posts: 1,653
Likes: 193
shops do not have the time to do it like an owner would. I wouldn't doubt you have a loose plug or two. torque them in 25 to 29 foot pounds . Torque pro can pin down your problem cly . Just need an old android $5 app ,cheap bluetooth reader from amazon .
Do you think they are going to put new boots in for the same money --noooooo. You should run some techron every now and then . But its getting time to consider new injectors. They are not hard to change Yes new plugs /boots would be good at this point.
Do you think they are going to put new boots in for the same money --noooooo. You should run some techron every now and then . But its getting time to consider new injectors. They are not hard to change Yes new plugs /boots would be good at this point.
Lead Driver
Joined: Sep 2006
Posts: 7,907
Likes: 143
You can see which cylinder is the offender with a Scanner looking at mode 6, and the misfire counts in the test ID s for misfire counts..
All 8 cylinders will be shown, one at a time.
Coils are most often the problem.
Don't hang on the replacement time. Any coil can fail any time or right out of the box.
All 8 cylinders will be shown, one at a time.
Coils are most often the problem.
Don't hang on the replacement time. Any coil can fail any time or right out of the box.
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