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Faunsdale, AL | The problem with using the injection pump vane pump is on those old IDI diesels is it’s sucking on a fuel system that has an air bleed back to tank after the filter base.
I would have to go look at it to make sure, but I think you’ll see a return hose that starts at the filter base (high point in the fuel system on that truck) to allow air that bleeds through a small drilling in the filter base a way to bypass the injection pump. This fixed bleed gives a way to purge air and de-aerate the fuel……..as long as there’s a lift pump pushing fuel through the filter!
When the Stanadyne pump sucks on the supply line, especially after a filter change, it can pull air back through that bleed from the fuel return system. There’s probably a leaking injector return boot seal or two or an old section of hose somewhere in the system that lets air in while it’s sitting and can make the pump loose prime. If it is very hard to start after it sits overnight, you need to do the return line kit mentioned above. If it starts right up after sitting, don’t mess with it yet. Your current problem is a separate event from that one.
I think I remember adding an electric boost pump ahead of the mechanical pump, but if I remember correctly it didn’t last long before it quit. That was before I had ever heard of an airdog or any of the other aftermarket lift pumps that’s been available for decades now.
I know the last few years I ran that truck it had begun to suck air at ever increasing fuel gauge levels in the rear tank. I think it was up to a quarter tank when it would suck air and you had better have a lot of speed and a downhill ahead if you wanted it to prime back up after you switched tanks.
Ours was a 5 speed, so if you were lucky and paying attention, and you could keep the engine turning after it lost prime, it would catch back up. Or if I wound up stopped with a dead engine, I could get someone to pull it a little way to save melting down a starter trying to get it started again. Always amazed me how short of a distance it took to get it to start pulling vs how ineffective cranking with the starter was.
I managed to get that truck going after it lost prime using several different techniques over the years, but hands down, coasting down with the engine spinning or pulling it in gear worked the best. Got stranded on a long uphill grade with a load behind it one day coming up out of the Mississippi delta. Switched tanks immediately but it didn’t catch up. Cranked until batteries were flat and still no luck. Finally put it in reverse and let it start rolling back downhill and it skidded the tires on the pavement a few feet when I let out the clutch but then it started spinning over and fired up! I’ve done that with a medium duty gas truck, but never a pickup. If it hadn’t been such a steep grade, and a heavy hitch load I don’t think it would have done it.
Edited by ccjersey 1/8/2025 10:48
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Can this be it?
