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HELP Touble bleeding fuel system

Old 02-13-2019, 10:47 AM
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HELP Touble bleeding fuel system

I have an 89 cummins, lift pump went bad and I replaced it with a new one fairly simple replacement. Been bleeding the fuel system by popping the banjo bolt on top and running the manual paddle on LP. Close the banjo bolt. Crack 2 injectors crank motor and bubbles are coming out. Close injectors open 2 more repeat process. Go thru all six truck wants to start. Fires up eureka. Runs for 30-40 seconds than dies out. Repeated the injector crack numerous times. Have gotten truck started a dozen times never runs for more than a minute. Now I am thinking I'm sucking air from somewhere or my ve pump is **** the bed. Need my pl low truck running just got a foot of snow and more coming.
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Old 02-13-2019, 04:47 PM
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What made you think that the lit pump went bad? Do you have a fuel pressure gauge to show that it wasn't producing pressure? I ask because maybe the pump wasn't bad and there is another leak, or maybe both. Suction side leaks can be a pain to find, what I do is put a few psi'sof pressure into the fuel tank and wait a few minutes to see if something starts dripping...Mark
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Old 02-13-2019, 04:54 PM
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Originally Posted by maybe368 View Post
What made you think that the lit pump went bad? Do you have a fuel pressure gauge to show that it wasn't producing pressure? I ask because maybe the pump wasn't bad and there is another leak, or maybe both. Suction side leaks can be a pain to find, what I do is put a few psi'sof pressure into the fuel tank and wait a few minutes to see if something starts dripping...Mark
when I tried to start the truck last she would turnover fine but sounded like she wasnt getting fuel. Cracked the injectors and cranked engine snuggled injector and she came to life and evened out. 2 days later same thing wont start try injectors again no luck. Why was truck losing prime. Did some research online found the lift pump and she was slack when trying to manually prime things took it off and u can here it weeping. That's how I figured out to change the lift pump. But there could be other leaks. Tomorrow I'm buying rubber hosing and taking the feed side off the lift pump and feeding from a gallon jug of diesel taking off return line and feeding that back to the jug. If she still pulls air i have narrowed the problem to the injector pump. Shrug open to other suggestions. I'm no mechanic so please steer me in the correct direction of I'm wrong
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Old 02-13-2019, 05:01 PM
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If you got it running fine, then two days later is was full of air again.
I am with Mark 100%.
You have an air leak in your fuel system somewhere.

You will find your issue is old dry cracked fuel lines, cracked nipple on fuel sending unit, missing clamps on the fuel system, ETC.

I would also bet your old lift pump was not the issue.
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Old 02-13-2019, 05:12 PM
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Well unfortunately this truck has a pto driven dump body. Cant get to the sending unit untill truck is running. Hence my idea to fuel out of a jug at the lift pump.
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Old 02-13-2019, 05:47 PM
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You can get to the sending unit out by either dropping the tank, or jacking up the dump bed. Both of which I have done.

Using a jerry can adds variables into the equation. If the air leak is at the sending unit, the jerry can method will show all is cool, while you still have a problem.

Do as you please, I am just offering FREE advise and trying to help. I have been in the same spot as you many times before.
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Old 02-13-2019, 08:54 PM
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Originally Posted by Greenmtncloud View Post
when I tried to start the truck last she would turnover fine but sounded like she wasnt getting fuel. Cracked the injectors and cranked engine snuggled injector and she came to life and evened out. 2 days later same thing wont start try injectors again no luck. Why was truck losing prime. Did some research online found the lift pump and she was slack when trying to manually prime things took it off and u can here it weeping. That's how I figured out to change the lift pump. But there could be other leaks. Tomorrow I'm buying rubber hosing and taking the feed side off the lift pump and feeding from a gallon jug of diesel taking off return line and feeding that back to the jug. If she still pulls air i have narrowed the problem to the injector pump. Shrug open to other suggestions. I'm no mechanic so please steer me in the correct direction of I'm wrong
Ok, you are probably wrong. You are right that the test you want to do will implicate the pump, but that is a rare source of air leaks when compared to the things listed by Oliver. I like to use the KISS method and start easy and common and work towards the more rare and complicated. I think that if you were to replace the ve today, you would have the same problem tomorrow. It is very easy to stick a compressed airline into the fuel tank, stick a few rags around it as a seal and give less than 10 psi and less than 10 minutes, your leak may show itself. If not, then you look at the fuel tank components, sender...etc. Good luck...Mark
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Old 02-14-2019, 08:16 AM
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Man this is a hot topic, air leaks on a first gen. Well Oliver and Mark are spot on, you'll go the jerry can method and still have an underlying issue as I did. What i've noticed from my trials and tribulations are of this,
I ended up with air being pulled in the first place and replaced my lp guess what my old lp was old but still functional, next the situation wasn't the sender or the pickup it was at the filter the rubber seal shrank from the temperature changes and i'm sure my own fault but ill leave that one alone. Pressurize the tank and start looking for leaks, check the hard lines to the IP check if you don't have leaks from where if you still have the heater in place between those seals they do leak.
then there's the sender if you have an 89 i'm assuming you may be like me and have the metal lines and rubber connections not the push locks, those little connection hoses get super brittle and old and do pull air found that out myself too.
the other thing I did which I know isn't the normal is I ditched the hard lines between the filter LP filter and IP deleted the heater and went to positive lock fitting and heavy duty hoses made for oils and fuel.
just some of my experience and busted knuckle rant. Id totally take the advice oliver and mark just gave its spot on. ZAR
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