1999 Ford F-150 Loss of power

SULLIVANJO

MEMBER
1999 FORD F-150
V8
4WD
AUTOMATIC
216,000 MILES

I have a 99 F-150, 4.6L V8 with 216,000 miles on it. The truck reads no codes when hooked up to the computer and no check engine light is on. Several mechanics have ran diagnostics on my truck and can not find a single thing wrong with it. Driving it with the computer hooked up also found no problems, no misfires, MAF good, etc. I just replaced the fuel filter and have recently replaced the upper plentum gasket, spark plugs, plug wires, DPFE sensor, PCV valve, and my fuel pressure is at the top of the desired range. The truck runs excellent some times but then I can shut it off, start it back up, then drive away and its running sluggishly. When I reach hills, it slows down. If it is windy, that also slows me down drastically. If I am on the highway going 70, I can press the pedal down pretty far and get a very delayed response. The truck will slowly pick up speed after a few seconds and when I accelerate fast, I can let off the gas slowly and it will continue to rev the engine. Any clue as to why the truck has so little power when all engine tests come back good? My truck has 4 catalytic convertors but they can't all be plugged can they? Any help is appreciated.

7 Replies

DOCFIXIT

MECHANIC
18,828 POSTS

Hi
From stop good pickup? If you mat the pedal does trans down shift? Has anyone checked the trans for proper gear range to speed?
Let me know
Thanks fro donate

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Tuesday, May 19th, 2009 AT 2:55 PM

SULLIVANJO

MEMBER
3 POSTS

From stop, I have to really push the pedal down to get it to pick up good speed. But usually, it feels like the transmission is shifting out of gear before it should. When I mat the pedal, the tranny will downshift and the RPM's will jump but then it feels like it hits a wall becuase it picks up speed slowly. I just had a tranny flush and new filter put in last month. I do not believe it has been checked for proper gear range to speed.

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Wednesday, May 20th, 2009 AT 6:56 AM

DOCFIXIT

MECHANIC
18,828 POSTS

Have exhaust backpressure checked and has engine compression test been done? Also engine timing O.K? Has anyone checked to see if timing chain on marks?

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Wednesday, May 20th, 2009 AT 9:58 AM

SULLIVANJO

MEMBER
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The engine compression was checked a few times in the past couple months during diagnostics ran by Ford and they all came back with excellent readings according to them. I have been questioning the timing and I do not know if the marks are lined up. This morning was a prime example of my problem. I was on the highway going 70 and the wind started to pick up. The truck started losing speed and I starting pressing the pedal down further and further. I kept losing speed until it down shifted into 4th and eventually 3rd gear. When it shifts, tho, the RPM's jump but I can keep pushing the pedal down after it shifts and the RPM's will not increase until my speed increases. Which is very slowly. I really appreciate your help and I plan to make another donation. Thanks again.

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Wednesday, May 20th, 2009 AT 10:43 AM

DOCFIXIT

MECHANIC
18,828 POSTS

Hook up timing light disconnect IAC idle motor on throttle body. 8-10 deg BTDC. Then rev up to 3k does mark move? Also anyway you can rig up a fuel pressure gague route it out of hood see what happens when it tanks?