Some questions about my 6.5

[76k5blazerr]

So I recently got a 95 k3500 from my uncle, its got the 6.5 TD with only 88k on the clock. He bought it from a friend of his' elderly father. It runs great and drives great but sometimes it has an attitude when you go to start it. So I guess ill start the story here, the day after my uncle got it, he went out to drive it and it wouldnt start, so he ordered a new pmd, the new style that mounts to the top of the intake, I put it on for him. Then he took it to his mechanic and had him go through it and replace what needed replacing. Im not excatly sure all that he did but I know he put 2 new batteries in it, changed the belt, I think he may have done fuel filters as well. So about a month later I got it from him and Ive been letting it share DD duties with my 72, here are the issues I am having.
If it sits for several days, I go to start it and it cranks right up, runs for 30 seconds or so and then dies, then I have to crank, crank, crank and it will fire up and run good. Sometimes, on hot starts, it will not want to start and take alot of cranking to get it to run. And lastly, usually almost every cold start after sitting overnight it will crank up and stay running but its like it is cutting in and out on me, it runs jerky for like the 1st minute that its running. And one last thing. The fuel gauge doesnt work, usually it stays pegged out past the full mark, but sometimes it will go down to F or to 3/4 tank at random. Would you guys be checking the sending unit ground or replacing the sending unit. Or is it possibly the gauge? Sorry for the newb questions but this is only my second diesel vehicle, used to have a 6.2 jimmy but sold it because I never could get it running. Just trying to see if I need to start replacing some parts that might be causing these problems. Thanks guys.

 

[campfire]

Sounds like air is getting into the fuel system when it's sitting (a pin-hole somewhere). That explains the cutting out and the choppy running, especially if it clears itself after a bit of cranking or running.

That rig should have a fuel pump pin in the OBD1 connector, try running the fuel pump for 30 seconds before starting it (to pump the air bubble back to the tank via the overflow line) and see if that clears the problem. I will confess that this has worked well enough on my K10 that I still haven't gotten around to fixing the pinhole, I just start an electric pump before I wanna go anywhere.

The PMD should be located as far away from the engine as possible. Firewall is a better option than the intake. But you do have fins on it now, right? That's a big step in the right direction, the original setup has a very high failure rate.

As for the fuel gauge, going high is what it does under open circuit conditions. You could have a break in a wire, a loose connector, or a failed potentiometer in the sending unit. A failure anywhere can cause that, check the connections and get an ohmmeter reading of the sending unit (ask if you need instructions on how to do this).

 

[76k5blazerr]

Sounds like air is getting into the fuel system when it's sitting (a pin-hole somewhere). That explains the cutting out and the choppy running, especially if it clears itself after a bit of cranking or running.

That rig should have a fuel pump pin in the OBD1 connector, try running the fuel pump for 30 seconds before starting it (to pump the air bubble back to the tank via the overflow line) and see if that clears the problem. I will confess that this has worked well enough on my K10 that I still haven't gotten around to fixing the pinhole, I just start an electric pump before I wanna go anywhere.

The PMD should be located as far away from the engine as possible. Firewall is a better option than the intake. But you do have fins on it now, right? That's a big step in the right direction, the original setup has a very high failure rate.

As for the fuel gauge, going high is what it does under open circuit conditions. You could have a break in a wire, a loose connector, or a failed potentiometer in the sending unit. A failure anywhere can cause that, check the connections and get an ohmmeter reading of the sending unit (ask if you need instructions on how to do this).

I replaced the PMD with the FSD Heat SYnc kit from some diesel company on the web. Apperently thats what everyone does when their PMD fails. Explain how I go about running the fuel pump before I start it? You got any idea on the hot start problem where it just takes forever to start? I kinda think all this stuff is because its a tempermental old diesel but I want to fix it if I can. Thanks for the reply.

 

[campfire]

I replaced the PMD with the FSD Heat SYnc kit from some diesel company on the web. Apperently thats what everyone does when their PMD fails. Explain how I go about running the fuel pump before I start it? You got any idea on the hot start problem where it just takes forever to start? I kinda think all this stuff is because its a tempermental old diesel but I want to fix it if I can. Thanks for the reply.

Find the ALDL (OBD1) connector, and apply 12V to pin G.

Pictures/film here:
http://67-72chevytrucks.com/vboard/showthread.php?t=368785

The hot starting issue sounds a lot like the cold start issue. If I understand it correctly, it sounds like the same air bubble issue. Either way, if there's an air issue, purging the lines *BEFORE* cranking will keep the air out of the IP, and the truck should fire up without difficulty. Once air gets to the IP, it's a lot less fun to deal with (can't feasibly spin the IP without cranking your starter into oblivion like you are already doing).

Try running the pump for 30 seconds before cranking and let us know how it turns out. If you're feeling ambitious, do a hot-start test, too, to see if the issues are connected.

 

[campfire]

Also, if the engine is temperamental, something is wrong with it. There's no reason that it hasta be hard to start simply due to age. When things are working properly these engines start promptly (unless it's bitterly cold and you didn't use your block heater).

 

[76k5blazerr]

Alright, I'll try that and post back.

 

[76k5blazerr]

Also, if the engine is temperamental, something is wrong with it. There's no reason that it hasta be hard to start simply due to age. When things are working properly these engines start promptly (unless it's bitterly cold and you didn't use your block heater).

Ok, so the truck has been sitting for since Wednesday. Been driving my 72. I go down to start it today and it fires right up, 30 seconds dies. Then it would not restart like usual. I cranked and cranked and cranked, wouldn't fire up. Then I tried the fuel pump thing, ran it for like 30 seconds, it still wouldn't start. What should I start checking. I need this thing running. Buddy is coming over in a bit to work on it with me.

 

[76k5blazerr]

Got it running, just took a whole lot of cranking.

 

[campfire]

Got it running, just took a whole lot of cranking.

Check for leaks in the supply line. Might look like weeping, might not be visible yet (mine took quite a while to become visible). Start replacing soft lines. If you wanna get all the possibilities hammered out at once, replace the hard lines, too.

Running the fuel pump won't help if the IP has already swallowed an air bubble. It is only helpful if it is able to push the air bubble back to the tank via the overflow line. Once the air gets past the IP you are stuck cranking. The test of the pump is whether it makes the problem go away when you run the pump before cranking.

 

[76k5blazerr]

Check for leaks in the supply line. Might look like weeping, might not be visible yet (mine took quite a while to become visible). Start replacing soft lines. If you wanna get all the possibilities hammered out at once, replace the hard lines, too.

Running the fuel pump won't help if the IP has already swallowed an air bubble. It is only helpful if it is able to push the air bubble back to the tank via the overflow line. Once the air gets past the IP you are stuck cranking. The test of the pump is whether it makes the problem go away when you run the pump before cranking.

Ok, will try the fuel pump prime before I start it next time.

 

[BadDog]

My little C10 has been doing that. Lights right off within 2 seconds, then does as described. Completely dry to the eye from tank to filter. I was convinced it was the complex Rube Goldberg square box filer base. After fiddling with it and checking/rebuilding/etc all the usual suspects, still had troubles. So I switched to a spin on filter. Same problem. The little truck often sits for a week or two between uses, but even 3 days is enough to cause it to crank, light, die, crank forever, light, caugh, die, crank, light, run like a top... When I got it it had been dead for some 7 years or so (IIRC), and I replaced all the lines from the filter to the injection pump and the return lines as well. At some point I'm going to replace the lines from the tank to the filter. Then it will be new end-to-end, and hopefully that will end the aggravation. I'm getting 2 new knees in the next 3 months, so it will be a while before I get around to doing anything more about it.

 

[campfire]

My little C10 has been doing that. Lights right off within 2 seconds, then does as described. Completely dry to the eye from tank to filter. I was convinced it was the complex Rube Goldberg square box filer base. After fiddling with it and checking/rebuilding/etc all the usual suspects, still had troubles. So I switched to a spin on filter. Same problem. The little truck often sits for a week or two between uses, but even 3 days is enough to cause it to crank, light, die, crank forever, light, caugh, die, crank, light, run like a top... When I got it it had been dead for some 7 years or so (IIRC), and I replaced all the lines from the filter to the injection pump and the return lines as well. At some point I'm going to replace the lines from the tank to the filter. Then it will be new end-to-end, and hopefully that will end the aggravation. I'm getting 2 new knees in the next 3 months, so it will be a while before I get around to doing anything more about it.

Take the time to install an electric pump while you're redoing the long line back to the tank. Really handy upgrade for priming.

 

[BadDog]

I've seriously considered it... EVERY time it does the caugh-light-die dance. But one of the best things about that little truck is it's brutal simplicity. Adding an electric pump is one more thing to go out, and has a much higher failure rate than the mechanical pump. Priming, starting with a tiny airy leak, changing the filter, so many things it would simplify; and if it was getting a lot of use then I would probably opt for the trade-off. But once I have this minor issue dealt with, it shouldn't make much difference in my over all satisfaction with the truck, and I keep the simplicity I love about it.

 

[campfire]

I've seriously considered it... EVERY time it does the caugh-light-die dance. But one of the best things about that little truck is it's brutal simplicity. Adding an electric pump is one more thing to go out, and has a much higher failure rate than the mechanical pump. Priming, starting with a tiny airy leak, changing the filter, so many things it would simplify; and if it was getting a lot of use then I would probably opt for the trade-off. But once I have this minor issue dealt with, it shouldn't make much difference in my over all satisfaction with the truck, and I keep the simplicity I love about it.

I added a pushing pump in series with the mechanical pump. It only runs when I want it to, it's not the primary fuel delivery pump. Running is still simple.

 

[diesel4me]

I have an electric pump about 18" away from the tank too,that feeds the stock lift pump...been on it 13+ years and still works fine,it runs constantly too...

If the fuel return line gets restricted or blocked,the engine will die out and stall....might be worth tracing where it goes and replacing it...hose is cheap compared to putting on a rebuilt injector pump that wont always cure weird symptoms..

I thought mine was junk till I put on the electric pump,new hoses,and a copper fuel line from the tank to the firewall filter...

I was scared to drive anywhere before,with it lurching and surging when it felt like it,or dying like it ran out of fuel...I still feel apprehensive,but so far its kept running "normally"...

 

[Big Ray]

Why copper? Copper crystalizes when subjected to vibration...

 

[diesel4me]

Well,I have used "soft" copper tubing for gas & fuel lines for years,after tiring of replacing rotted steel lines...never had one fail,crack,leak,they do turn that funky green color though pretty quickly...seeing my home furnace has a copper fuel line and has for nearly 40 years,I see no reason why diesel fuel would affect it--and furnace burners vibrate too..I realize copper can "work harden" and possibly crack,but it never has so far on things I have used it on...

I connected the copper at the fuel tank end with a short length of rubber fuel hose,the other end I flared and screwed right into the fuel filter on the firewall..that seems to work to avoid any vibration,and I did use zip ties to secure it along its run..(10+ years ago!)..

I have read in GM service manuals to NEVER use copper or aluminum tubing for tranny cooler lines too,but I have on some vehicles,and had no failures,but I used rubber transmission cooler hose at each end to join it at the fittings on the radiator and transmission...I trust copper a lot more than rusted steel lines,or old dried up rubber hoses..dont think I'd trust aluminum,even though some is sold for fuel delivery use...