Join Date: Sep 2019
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'85 6.9 with air in fuel MYSTERY.
I'm seriously stuck with a mystical problem with my '85 6.9 F250 diesel. You guys are the last attempt to save it, before I push it off a cliff. And, if you help me, you will have the ego-stroking pleasure of being able to solve what all the mechanics in Moscow, Idaho can't. That may not be saying much, but we are in some of the richest farm country in the world, here, The Palouse, so a F250 diesel is hardly a rare vehicle around here-- but, nobody can seem to fix my truck.
It used to be a rather intermittent problem that is steadily getting worse, to the point that the truck is almost un-driveable. I will be driving down the road, at 55mph, and it will start running rough, and then slowly die, exactly as if it is running out of gas. I coast to a stop, restart it and go down the road again, where it may or may not do the same thing. Then, it might run perfectly for 6mos, towing my boat, everything. Then, mystically one day, it will become so gutless that it can't haul a bag of potato chips, and it will die like that every drive for a few weeks... until it starts running well for another few months.
I finally determined that maybe there was air in the fuel. So, I patched in a piece of clear tubing in the fuel line just before the fuel filter (brand new fuel filter, of course, I had tried that... oh, and brand new fuel pump). Sure enough, there are a ton of air bubbles and random chunks of solid air coming through the hose. I thought perhaps the ends of the fuel hoses throughout the engine had gotten brittle and cracked. So, I replaced three of them with new hose, and throughly inspected every inch of the rest of the hose and metal pipe all the way back to the gas tank. Every connection looked perfect-- no leaking fuel. The hoses that I replace looked perfect, too, no apparent cracking. After putting in the new hose, it seemed there was a lot less air in the line.... but, not completely gone. I started the truck, and it seemed to run WAY smoother. I got out on the highway, and was shocked that it was running incredibly smoothly-- it went 55-60mph perfectly for 8mi., I turned it off, did an errand, and started it up to drive back home. I got on the highway again, and it did the EXACT SAME SHUT-DOWN that it has always done. Every couple of miles, it would strand me, and I'd have to wait and restart. Took me an hour to get home. It seems that perhaps this problem happens more often when the engine is hot.
So, here I am. No idea what to do. The mechanics in town can't figure it out. I can't sell it when it does that. I have no idea what to do. ARE ANY OF YOU SMARTER THAN MY MECHANICS??