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1987 - 1996 F150 & Larger F-Series Trucks 1987 - 1996 Ford F-150, F-250, F-350 and larger pickups - including the 1997 heavy-duty F250/F350+ trucks

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Old 04-05-2011, 10:08 AM
Bob Fletcher Bob Fletcher is offline
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F150, 5L rough idle, low vac, no power

1988, approx 150,000 mi. Rarely leaves the yard. Seldom driven. Starts instantly but barely idles when cold. Somewhat better when hot. No power. No codes. Good ignition on all 8 but sounds as if it is running on less than 8. Vac about 9 in. at idle. By carefully pumping throttle will increase to 2000 rpm with severe back fire. Will some times get to 3000 rpm. Vac drops to zero above 2000 rpm. and, momentarily, jumps to over 20 in. at deceleration.

Have used two cans carb cleaner searching for vac. leak. Could find none. Because of little use, treated both oil and gas with no effect. Have not yet checked compression. Cat was removed years ago. EGR was sealed off years ago. Ran very well until recently.

Other than checking compression, I have no clue.

Thanks for any help.
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Old 04-05-2011, 03:38 PM
duckhunter 51 duckhunter 51 is offline
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WRONG FORUM !!!
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Old 04-06-2011, 07:39 PM
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Moved to correct forum.
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88 5.0 LX Mustang
63 F100 351W/C6

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Old 04-06-2011, 08:29 PM
bent-1 bent-1 is offline
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I wonder if the motor jumped time. Do you have a timing light?
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Old 04-06-2011, 09:00 PM
Bob Fletcher Bob Fletcher is offline
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F150, rough idle, low vac,no power

Thanks Jimmy. Don't know how that happened.

Thanks bent-1. Good thought. Did not know that could happen. Of course, the old girl is a lot like me. After 80 years, my timing is a little off too. Yes I have a light and will check it out. Puzzled why I get no codes.

later
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Old 04-06-2011, 09:38 PM
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Define no codes.... KOEO System pass code is 11 pause 11.

That low of vacuum reading with no "flickering" of the gauge usually means late timing, plugged exhaust or perhaps a HUGE vacuum leak.
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Old 04-06-2011, 09:38 PM
 
 
 
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