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I have a 85 k5 6.2l diesel ex military truck with 39,xxx miles that I've been daily driving for about a year with no problems. Ive converted it to a 12 volt system and put new glow plug in it when i got it. The other day on my way home from work the truck had little power and it started to hesitate at higher rpm and wouldn't shift unless I lifted off the throttle. To me it felt like it was running out of fuel. I changed the fuel filter and lift pump already, made sure I had no contamination in the fuel, and made sure the air filter was clean. I'm hoping that its not the injection pump but I'm running out of options. Does anybody have any suggestions on other thinks it could be? I've been searching around this site and others for 3 hours now and can't find anything.
 

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Try installing a piece of clear fuel line on the return side of the Injection Pump to help look for any air in fuel gremlins
 

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I have a 85 k5 6.2l diesel ex military truck with 39,xxx miles that I've been daily driving for about a year with no problems. Ive converted it to a 12 volt system and put new glow plug in it when i got it. The other day on my way home from work the truck had little power and it started to hesitate at higher rpm and wouldn't shift unless I lifted off the throttle. To me it felt like it was running out of fuel. I changed the fuel filter and lift pump already, made sure I had no contamination in the fuel, and made sure the air filter was clean. I'm hoping that its not the injection pump but I'm running out of options. Does anybody have any suggestions on other thinks it could be? I've been searching around this site and others for 3 hours now and can't find anything.

It sounds like you have an automatic. If it hesitates to upshift, you may not have good vacuum. This is a problem with even a simple cracked hard hose.
 

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Discussion Starter #4
Sorry its take so long, had a bunch of crap hit me with the turbo on my daily blowing up and family rebellion happening that im just now able to get back to this.

Yes its a auto but the engine is the one hesitating/ losing power. I did find some bad vacuum lines on it so I fixed them and took it out but still no dice. By the time I got back home I was giving it 3/4 throttle just to back up my flat driveway.

I did put the clear hose on the return line off the pump and see no bubbles in the line at all.

Any ideas before I end up throwing a injection pump on it?
 

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Air, exhaust fuel timing. IP could influence this. Or injectors..... Given the mileage retime. My success has come from restarding mainly. FTB will add performance.
 

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That is the way mine ran when the filter was plugged up. You said that you changed it, is there way to check if you are getting fuel from the tank? I ran mine off a temporary jug in the engine bay just to confirm what was happening a while ago. Let us know if you make any progress.
 
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