92 C2500 6.5 TD engine dies after starting, low power...

[Hiwaycruzer]

When restarting after a 10-20 minute hot soak, the engine often stalls right after starting. Before it dies, the idle starts rolling up and down. It restarts after a couple of attempts of extended cranking. Also, the truck doesn't seem to have much power, barely pulling an empty 20' v-nose trailer above 65 mph. The air and fuel filters were recently replaced, and the engine, exhaust, and intake have not been modified. Is it possible that the lift pump is going bad? Looks like is has the original pump. Does anyone recognize these symptoms?
Thanks in advance for any help/suggestions!

1992 C2500 Cheyenne 6.5L TD w/mechanical FI, NV4500 5-speed trans, 3.42 diff gear ratio, 78k miles on truck

[grancito]

Put some additive in your fuel, the type that takes water out, I use Bardal, if that's how it is spelt. The mechanical injector pump is very sensitive to damp fuel. The loss of power is probably wear, you can adjust the pump to compensate.
Remove the return line and wires from the top of the pump, undo the 4 screws and remove the top. Unsrew with Allen key at the back of the pump the shaft that supports the throttle mechanism inside the pump. Move the throttle to remove the rest of the mechanism. In the bottom around about center is a hole about 1/4 inch diameter, have someone turn the engine over slowly with a socket on the crankshaft bolt until you see a small Allen screw appear in the hole. Screw it in half a turn. Test drive to see that there is not too much black smoke with your boot down. I had to give mine 3/4 turn, it could hardly move off from stopped. Had to back it off from a full turn because of black smoke and bad fuel economy.

[Hiwaycruzer]

Thanks Grancito, for your analysis. Does a mechanical fuel injector pump with only 78,000 miles on it have enough wear to require a timing adjustment?
You didn't mention anything about the symptoms of a failing lift pump... does it not have anything to do with the engine's performance?

[grancito]

No the timing won't need adjusting unless you think that the timing chain has stretched, mine became noisy and so changed it and noticed easier starting, but not much increase in power. The surging is usually caused by air entering the injector pump, or the throttle valve sticking. It is at the back bottom right, inside the injector pump, and you could lift it out and polish it with some brasso if it does not turn real smooth. Try the fuel additive first.The other thing that reduces speed is a blocked fuel filter, but I see that it has been recently replaced. Test your lift pump for pressure also, or at least for flow. Open the air bleed after starting to also see if there is air in the system. There is a test for a sticking fuel valve, it sounds horrible but I've used it. With the engine at opperating temp, in park, put your boot to the floor. The governor will cut in at the apropriate revs, and if the revs cycle up and down, then the valve is sticking, and needs, additive or polishing.

[Hiwaycruzer]

Thanks once again, Grancito. I'll try your recommendations and let you know the results...

[grancito]

When I said the revs will cycle up and down, I mean really dramatic, and clouds of black smoke. If they cycle mildly then no problem.

[Hiwaycruzer]

Hello Grancito
I replaced the lift pump, and the accelleration is dramatically improved. Now the engine pulls smooth and strong, winding out to considerably higher RPM's before I need to upshift. The real test will be to see how the old diesel pulls my loaded 20-foot cargo trailer on the interstate. I'll be pulling it to Georgia this weekend.

[timlmiller]

well i have a 93 and i had the same problem i replaced the lift pump and it didn't help then i tryed fuel filters no go i tryed every thing then i found a bad fuel line sucking air it helped then the sending unit in the tank was bad once i replaced that the truck run great

[grancito]

Good luck HIWAYCRUSER, I hope your trip goes well.