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Old 10-14-2010, 03:01 PM
woodoctor38 woodoctor38 is offline
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02 f150 rough idle and misses around 45to 50 mph

I bought an 02 f150 with 4.6. I've had about two months .It run really good an has just about 60,000 miles on it . I noticed it runs alittle rough at idle ,but it misses when I'm going 45 to 50 mph .If I go faster it's fine or slower it ok ..I don't have any engine codes or check engine light on . I had to replace the tranny internal wiring harness a week ago.Thats how I know there are no pending codes. Any help woud be great .
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Old 10-14-2010, 04:20 PM
joey_espo joey_espo is offline
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Originally Posted by woodoctor38 View Post
I bought an 02 f150 with 4.6. I've had about two months .It run really good an has just about 60,000 miles on it . I noticed it runs alittle rough at idle ,but it misses when I'm going 45 to 50 mph .If I go faster it's fine or slower it ok ..I don't have any engine codes or check engine light on . I had to replace the tranny internal wiring harness a week ago.Thats how I know there are no pending codes. Any help woud be great .
i have the identical problem.....Anyone have it and able to fix it?
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Old 10-14-2010, 08:11 PM
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Originally Posted by woodoctor38 View Post
I noticed it runs alittle rough at idle ,but it misses when I'm going 45 to 50 mph .If I go faster it's fine or slower it ok.
First guess, you have a C.O.P. going south.
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Old 10-16-2010, 12:54 PM
Bluegrass 7 Bluegrass 7 is offline
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Bluegrass 7 has a good reputation on FTE.Bluegrass 7 has a good reputation on FTE.
Added information about certain coil faults.
Coils can develope various degrees of winding shorts that may be temperature sensitive and act up under various other operating conditions and still not set a code because the fault is not "hard".
Missing under cruise conditions above about 45 mph is due to a very lean fuel condition that is totally normal by design.
EGR function by design leans out fuel delivery such that a coil with shorted turn has low output and will not be able to reliably fire the lean mixture in that cylinder that also has exhaust in it's mix.
A throttle off slow down also cuts off fuel such that when throttle is reapplied, the mixture is again lean and a low output coil will cause studder until the mix goes richer, the studder goes away. (no code will be set).
Coils are often a cause of these elusive missing events.
Finding which one is the most difficult.
Good luck.
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Old 10-17-2010, 11:04 AM
woodoctor38 woodoctor38 is offline
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Thanks for the info. I guess i will have to wait till the coil goes bad to find it .In my 99 f250 they just died it was alot easier to find .Thanks again !!

Last edited by woodoctor38; 10-17-2010 at 11:06 AM. Reason: missed words
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Old 10-17-2010, 02:15 PM
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Originally Posted by woodoctor38 View Post
Thanks for the info. I guess i will have to wait till the coil goes bad to find it .In my 99 f250 they just died it was alot easier to find .Thanks again !!
Start pulling injector power terminals and see if u find a cylinder that ain't up to snuff. I've done this several times to find a problem. Also look for any vacuum leaks and clean the MAF with MAF cleaner.
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Old 10-18-2010, 12:53 PM
Bluegrass 7 Bluegrass 7 is offline
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Bluegrass 7 has a good reputation on FTE.Bluegrass 7 has a good reputation on FTE.
Pulling injector plugs won't find much of anything but a dead cylinder that would set a code in any event. Sorry to disagree but it's not a very good way, on these computer controlled systerms, to totally cut off fuel or spark for anything but conferming a dead cylinder that should be backed up by a code.
If you wait for a coil to go fully bad, it may be a long time you have to put up with the drivability hassle.
A coil with shorted turns often never fully opens or shorts to the degree it disables a cylinder.
At least sub one cylinder at a time with a known good coil to get it a bit quicker.
Good luck.
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Old 10-18-2010, 12:58 PM
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Works 4 me. lol
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Old 10-18-2010, 08:51 PM
woodoctor38 woodoctor38 is offline
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I have new coils I bought for my 99.I got a good deal on them from e-bay so i bought extras. I was kicking that idea around myself putting a new set of plugs in it and start switching a coil and see what happens..Thanks for your help ....
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Old 10-20-2010, 07:21 PM
deljer55 deljer55 is offline
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is this a common school of thought even for the 4.2 (bluegrass 7)
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Old 10-20-2010, 07:51 PM
Bluegrass 7 Bluegrass 7 is offline
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In my experience, the 4.2 does not very often get into the 'same' coil fault situation compaired to the COP, but is possible.
The coil design is totally different and the location is different.
The 4.2 ignition system was discontinued as not as good as COP for emission performance.
The COP system has very little dwell time lag compaied to any coil that has to service mutiple cylinders.
Another way to say this is each cylinder's ignition timing point can be instantly changed by the PCM as it runs with no delay or poor coil saturation from lack of time to saturate the coils core.
Problem with the COP is that they sit in the heads plug wells and are subject to hight heat cycles and exhaust heat. Design and manufactring is a prime item in making them live.
Thing is most people cannot get over the cost of a single coil, there being 8 to deal with instead of one or two.
It's really no different than replacing tires when they wear out at 50 to 60,000 mile and cost more to boot for less total life.
Coils are considered a service item like brakes, tires, fuel pump, DPFE etc..
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Old 10-20-2010, 07:51 PM
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