Low rpm power struggles

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poorboy1964

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Alright gang I have been having an issue with this since I bought my expy about a year ago, I have searched very similar threads from 2008 and on of people with the same complaint but no solutions.

2000 5.4 4x4 3.55 gears 140k miles
This thing is a gutless wonder there is no power at 50-60 mph it can't maintain it's on speed in overdrive on a small incline it downshifts. Pulling away from a stop light there is no power like it's starving for fuel until it gets to around 2700 rpm that it takes off like a turbo has kicked in.

What I've done
searched for codes none found.
New plugs Motercraft
New boots on coils
Ohm tested coils all within spec (looked like 2 have been replaced)
New throttle position sensor Spring was very weak
new DPFE sensor (old one had been broken and epoxied back together.
new fuel filter Fuel pressure within spec at idle I can't remember what it was???
cleaned MAFS and Throttle body
Checked temperature on exhaust before and after cats seamed reasonable to me so I don't think cats are plugged.

I will pull throttle body off and make sure egr passages are clean
I have an old compression tester but will need and adapter for this motor but I don't think it has low compression for the same reason I don't think fuel pump at high rpms it runs good.

I tried to tow my 12' trailer with a side x side on it last weekend and it was in second gear most of my trip trying to nurse myself home.

any ideas or help appreciated
 

ChrisOIFdoc

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I would have suspected most of what you listed, but have you checked for a vacuum leak? All this computerized crap we have to deal with now days makes us overlook the things we would have checked in the past.
 
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poorboy1964

poorboy1964

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Just a visual check, loaned my vacuum gauge out and it didn't make it back. I saw a video of someone checking it with carb cleaner or something I'll give that a try.
 
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poorboy1964

poorboy1964

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Last night I sprayed starting fluid around all the vacuum lines ans fittings I did not hear any change in rpms so for now i'll rule out vacuum leak. After i took it on a test drive and it popped a p401 code so I think I start looking for carbon buildup.
 
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poorboy1964

poorboy1964

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Maybe I'll try to test it first looks like I can bypass a vacuum line straight to it should bog down from idle if it's working.

was reading about the throttle body it has 2 ports from the egr that plug up often but you have to pull it off to clean them out and I guess this could be casing my problem. out if town this weekend so it will have to wait

download.jpg
 
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poorboy1964

poorboy1964

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Solution
I found an old post on another forum talking about a TSB 02-12-j reduced timing when temperature exceeds 95 deg. sucked up my pride and got a re flash at the dealership ( disclaimer I don't have a problem with techs just dealerships) to the most updated flash and problems seams solved wanted to add a final answer here
 

1955moose

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Huh, I've got exact same SUV. Mine runs great in town, strong power, but climbing grades or just be bopping down the freeway no pep. Weird thing with mine is sometimes I hear the exaust more, and have better pull on Freeway, when theirs a loss of power, exaust is muffled. I got to go by dealer today, I'm going to ask about reflash.

Sent from my N9131 using Tapatalk
 
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poorboy1964

poorboy1964

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It's been since I've owned it about 2 years and under 80 degrees run fine but when the temperature outside gets hotter I couldn't pull away from a stop light without making people behind me angry and on the slightest hill it would lug and ship down, I'm in Utah which is a mountain desert very hot and very dry climate
 
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