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I have a 1985 F250 6.9L 4x4. Recently purchased. First time I took it on the highway for a 3 hour trip. About 45 minutes in I noticed the cruise control was surging, trying to maintain the speed. About 5 minutes later the truck stalled. I pulled over to the side of the road and it started right back up with no problem. I revved the truck a bit and it would stall as soon as I let off the pedal. I started it back up and it seemed that if the pedal movements were smooth and steady, it would not stall. I drove it back home and did not use the cruise. The motor sounded like it was knocking a little louder then before and I had to push the pedal down more to keep up my speed. I had a look under the hood and there was some diesel dripping from the return lines on one side. It is my understanding that the dripping return lines should not affect the driveability. I drove it around town the next day and everything ran fine. Motor sounded normal and did not stall. I have been driving it around the city only for the past 2 months and everything is running normally.
I am concerned about taking it on a trip again due to the stalling issue. It only showed up after the 45 minutes of continuous highway driving. I thought it might be something due to temperature but it has gotten plenty hot in the city and no issues.
The previous owner changed the lift pump and I changed the fuel filter prior to the attempted trip.
Any thoughts on where to start looking?
 

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Air entering the drainback system only causes long cranking for an engine start after the pickup has sat for a period of time like overnight on the first morning start. Dying at idle after the engine has been running is most always a sticking metering valve in the injection pump. Leaking drainback lines won't cause surging. Matter of fact, once the engine is running you could pull a few drainback lines and run diesel all over the ground and the engine will run fine.


" It is my understanding that the dripping return lines should not affect the driveability. "
Correctamundo!
 
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