6.9 idi surging/stalling at around 45 mph

[mexicanfooddude]

Hello everyone, thanks in advance for the help.

I've got a 1983 F-250, 6.9 IDI, 4-speed manual, 40,000 miles. Just recently I noticed that when I get up to about 45, suddenly the truck starts surging (accelerating/decelerating on its own), and I can't get bring it up to any higher speeds. If I let my foot off the gas and coast, it will stall before it comes to a stop. The truck seems to drive normally at speeds below 45/50... I'm pretty confused as to what could be going on! Any thoughts would be much appreciated.

Thanks again.

 

[Thewespaul]

Change your fuel filter and fill the new one with atf when you install it. It sounds to me like you aren’t getting sufficient fuel or sucking air.

 

[DrCharles]

I agree, sucking air. If that doesn't fix it, check your lift pump...

 

[nostrokes]

X3 on the filter check. I'd check the oil and see if it smells/looks like it has fuel in it too

 

[gandalf]

Checking the fuel filter, or better, replacing it, is the best way to start. Remove to old filter, and fill the new one with ATF. Fill it through the center hole so that it gets filtered, just in case. Put the ATF filled filter on the filter head and start the engine. Let it run about half a minute, or until it sounds "different", but not much longer. Then you shut it down for the night. Start it the next morning and drive it like you stole it. This will, hopefully, clean the TPS/FIPL. It will do absolutely nothing for an air leak, though. If it still has symptoms, then start looking for the air leak.

Report back on results.

 

[frankenwrench]

Also check the fuel line that supplies the lift pump. Right where it makes that odd curl. Mine had similar issue and that looped hose was old and stiff and after removing it had a partial kink and was starving the engine of fuel. And was deteriorated so that the inside was breaking down. And as afore mentioned, change filter, check oil for diesel smell in case diaphragm in lift pump has a leak, use atf in filter, and check for air intrusion.

 

[mexicanfooddude]

Right on, thanks so much for the input everyone. I'll get to work on it this weekend and report back!