LB7 died today for no apparent reason

[cmwilga]

After sitting at an idle for about an hour I drove about a mile and when I came to a stop my engine started running rough and just died and would not start. I vented my fuel filter and pumped the primer and it started right up. Any of you guys have any clues as to what may have caused this? Thanks

[DmaxMaverick]

Long idle periods equals heated fuel. The lack of airflow under the truck means little to no fuel cooling via the free-air cooler. As you started driving, air was suddenly available for cooling, and there was a rapid fuel temp drop. This drop caused a rapid contraction of the fuel, creating a vacuum in the tank, as well as a quick rise in viscocity. This would take advantage of any air leak you may have, normally tollerable with slow temp/pressure swings. Add to that, the possibility of a fuel filler cap that may be of marginal performance (needs replacing). The fuel pump will tollerate some air, but once it gets a large enough slug, it will lose prime, and the engine will stall. As your fuel filter reaches its useful life, it will also exaggerate the situation, with additional restriction. Lower fuel tank levels will also add to this equation.

Well, that's my take on it. Mine will do it under the right (wrong) conditions. The fuel lift pump I can see in my future will cure it, though.

[Kennedy]

They all seem to run SO much better with just a little bit of fuel lift supply.

[cmwilga]

It was about 96 degrees outside and I was parked in the sun so thats probably what happened. I have a new filter that has about 1000 miles on it. Maybe the dealership didn't put it on good.

[almondfarmer]

Exact same problem here. 100 degrees outside, ran great, stopped for a bit, re-start, then stalled 30 sec later. Everything was VERY hot, though the engine temp was normal. I waited a while and primed the fuel. It started right up. However, I'm nervous about taking it anywhere. Any ideas on what to do now?

[JohnC]

Any ideas on what to do now?

Sounds like ordinary vapor lock to me. Not real common in Diesel applications, but still possible. any air leaks in the suction side of the fuel system will exacerbate the issue, but it could still do it with no leaks. the solution is either a cooler climate or a lift pump. The closer to the fuel tank, the better

[Kennedy]

Hot fuel, and reduced pressure (necessary to get fuel flow to pump) combine to make vapor in the lines. More of a fizz than anything. This fizz accumulates in the filter quite easily and reduces the effectiveness of the filter. This accumulated air tends to pass in gulps and can be hard on pump/injectors, and definitely could create the stalling issue.

Put a lift pump on it. The problem should go away and your fuel system will thank you.