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CUCV loses fuel prime

S

Stein

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If my CUCV sits more than a day it loses fuel prime. It starts instantly, runs for a few seconds then dies and is a bear to get re-started.

Recently I started immediately cranking for 2-3 revolutions before the glow plugs cycle (so it won't start), stopping and then cracking the drain on the top of the CUCV-type square fuel filter. The pressure from the quick crank pushes a bunch of airy fuel. After that I close the valve and start the truck and it no longer dies.

So, it's losing prime in or around the fuel filter area. I don't see any sign that it is leaking anywhere. The fuel filter is less than a year old so I'm hoping it's not leaking around the rubber grommets where the lines go into the filter but I suppose it is possible, or the is a pinhole in the feed line from the tank. It's under suction, not pressure so that might explain why I don't see anything wet. It would also explain getting air in but not fuel out.

What would you do? Pull, lube seals and reinstall fuel filter? Replace filter even though it doesn't have 3000 miles and one year on it? Replace fuel line from tank? If so is it just regular fuel line or something specific? What is the most common failure point?
 
I'm fairly new to the 6.2 diesel scene but if you have an 86 and would assume you have the "brick" fuel filter, is the air bleed valve on the filter tightened up? :dunno:
 
If it looses prime sitting overnight you have a pretty hole in a fuel line. It's a pain but start checking all of the fuel lines, from the tank on up. It's most likely a soft line between the filter and the injection pump. But it doesn't hurt to check them all.

Has the truck seen much use in the year the filter has been on it? Could be something stupid like the seals on the filter box have gone bad. Since you have to pull it off to check I'd just get a new one.
 
There is a shaft in the IP that has rubber orings that wear out over time and will leak diesel when it sits over night, I replaced these and my truck ran like night and day difference
 
Thanks for the suggestions. Yes the filter was new less than a year ago. It does see regular - at least once a week - use. If nothing else a run to take the trash to town.

I suppose it's just as easy to start from the tank and just replace everything. Is the spin-on filter available as a "kit" that replaces the square filter setup?
 
OK, doing some googling it looks pretty straight forward.
 
prm-81794_m.jpg


One like this setup works well and is much like the OEM ones GM had on the '82 diesel trucks...you can get the base and filter from WIX too,but it'll probably cost more,and is about the same thing...
Places like Summit Racing carry the Perma-Cool setup for about 35 bucks..

I would look closely at all the metal & rubber fuel lines leading to the filter from the tank--any pinholes can get it suck air or lose prime,and it may not even drip,it may appear wet...up here steel lines develop rust holes pretty rapidly--I replaced my main fuel line with 3/8" copper tubing...using as little rubber hose to connect it to the tank and filter as possible,and used new rubber hose rated for diesel..

My truck had been starving out on hard acceleration and would stall unless you pulled over,and feathered the gas pedal until I did that--more than once I had to let it sit,and let the electric fuel pump build pressure back up,to get it restarted....thought it was the filter clogging up,but I swapped another new filter on it and it did the same thing (a see through one I had kicking around)--next time it threatened to stall,I got out and looked at the filter--it was mostly air,not fuel,and foamy,you could see air bubbles being brought up from the tank..

Once I replaced the fuel line,that filter stayed full with no air,so I put the hoses back on the stock GM filter,and its been OK since..
 
If you're redoing the lines, it may be worth adding an electric pump somewhere along the line. Makes it MUCH easier to prime in the future.
 
Cucvnut said:
I would lose the lift pump all together
Click to expand...

I did just install a brand new one last year. Old was leaking from the weep hole.

Special fuel line for diesel or is all rubber fuel line the same? I'll probably just start at the tank and replace it all. Cheap and I only want to do it once. It is 30 years old.
 
Its low pressure fuel line. If you run Bio Diesel you need better lines so they dont degrade.
 
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