"Vapor lock" 82 chev 6.2 diesel
 

Hi All,
I have had three of these trucks (82 GM/Chev diesel 6.2 engine)--driven them a total of over a million miles -never ran into this problem before--hope someone else has, and has an answer.
After sitting overnight, or a number of hours, truck cranks right up, and will run for a minute or so, then dies, as if it has vapor lock, or no fuel. I had it towed to a known good diesel shop, and they "primed it", found some air leaks, after which I took it home and it did the same thing a day or two later--took it back, they supposedly "found the problem", and fixed it--claimed the fuel filter was leaking ( it was --fuel all over engine, and ground). Well got it home, again, yesterday, went to drive it this AM, -same problem--Once restarted, several times--Long cranking time required, it will run, but "lope" for a few minutes--after that, it's OK ?
Anyone have any thoughts ??
TIA, Ron Rich

Your fuel system should maintain a curtain amount of fuel pressure even after the truck is turned off.
As soon as the key is turned on, the fuel pump should immediately bring the fuel system back up to normal full operating pressure.

It sound as though your fuel pump is allowing your pressure to bleed off after the truck has been turned off for some time and in capable to bring the system back up to full pressure for cold starts.

I would say your fuel pump is on it's way out.

Hi Glen,
Thank-you--I thought the same, however the "shop said" that they checked the pump and it has plenty of pressure. My thought was to just add an electric pump that I could switch on, in the mornings--any thoughts on that ?
Ron Rich

Adding an electric pump that you would turn on yourself is possibly leaving yourself open to an accident. Like possibly inadvertently leaving it on when it's not needed.

Back to your existing fuel pump.
A tech could bench test it and if it runs, he could easily call it GOOD.
I would be curios to know how much pressure the pump is producing

Hi Glenn,
Thanks for the warning--I understand that, and would power it only when the ignition key is in the "on" position--plus, it would need to be manually held on with a "push and hold" type switch.
I don't know if they removed the pump to test it or not--If I get a chance, I will run by the shop and ask--gotta tell them that it's coming back, anyway--
Ron Rich

Hi Glenn,
Your thoughts on the following ??
Is it possible that the fuel caps on the tanks are "plugged up", thus causing a vacuum, or "reverse pressure", that when I shut it down, sucks the fuel from the line(s) ?
I recall that the "old gent" that used to service our trucks, insisted on washing (in safety solvent) the caps at every oil change--just can not recall his reasoning --
Thanks again, Ron Rich

Does the truck have a seperate pressure regulator?

Hi Danny,
Not to my knowledge--
Ron Rich

Does anyone know if the fuel pump has some kind of check valve that holds pressure in the line when shut down like gasoline cars do ?? If the valve goes bad the system leaks down and it causes excessive cranking.

I don't think it could be your fuel cap. You say your problem is starting after a lengthy shut down period. If your fuel cap was creating a vacuum in your tank you would probably have stalling issues after running for a certain amount of time