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Discussion Starter #1 (Edited)
Hi,

I just got new head gaskets on my truck, I started it after install, of course hard starting for a long time but it fired up and ran and idled very well. But this morning I went to start it again, activated the glow plugs for about 10 seconds, and it hesitated a little bit like the last few seconds of cranking last night (after having the system completely open). It didn't start as hard, maybe 4 seconds of cranking (usually starts instantly).

I am also observing some small bubbles in the return line that connects the low pressure side back to the injector Pump, I installed a clear line for it so I can see. Where might the bubbles be coming from?

I should add that I installed all new return fuel lines so the system should be sealed.
 

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You have an air leak some where IP and back.

Yes new return line seal weepy leaks but won’t cause air into the fuel system pre IP as it’s a pretty much gravity return to the tank.

We can walk you through finding this leak many ways but step one is go over every line and connection, clamp and tighten them, looks for any wet spots of fuel as fuel out, is air in pre IP.
 

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Discussion Starter #3
You have an air leak some where IP and back.

Yes new return line seal weepy leaks but won’t cause air into the fuel system pre IP as it’s a pretty much gravity return to the tank.

We can walk you through finding this leak many ways but step one is go over every line and connection, clamp and tighten them, looks for any wet spots of fuel as fuel out, is air in pre IP.
Okay, I checked all the connections, I didn't see any fuel. But when I went to start it again, it started hard and there was zero fuel in the return line going into the IP. Someone suggested a leaky injector draining into the cylinder, because this was going on when I was driving it last, are the injectors hard to rebuild or at least re seal? I can't afford 200 dollars right now for a new set...
 

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Thank you so much!

Is there any way I can pinpoint the specific Injector that is leaking?
Pull the injectors and pop test them to find any issues.
You can build a pop tester with a bottle jack if you are handy enough.
There are videos on Youtube on how to build one
 

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Discussion Starter #7
Thank you so much!

Is there any way I can pinpoint the specific Injector that is leaking?
Pull the injectors and pop test them to find any issues.
You can build a pop tester with a bottle jack if you are handy enough.
There are videos on Youtube on how to build one

I might do that. Thank you. What are the threads on the injectors where the high pressure line connects to it?

Also, hear me out. Could I discover the leaky one by attaching clear tubing and filling it with diesel fuel on a barbed adapter screwed to the injectors, and elevate the tubing, with a sort of "U" so dust doesn't get in, like a p trap? And when the diesel drains overnight, I will know which injector is leaking? But for like $10?
 

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Discussion Starter #8
https://mrotools.com/tu-15-13a-lang-diesel-adapter---motometer.aspx

I need something like this that I can connect clear vinyl tubing to to see which one is leaking. I am on a pretty tight budget and trying to keep my business going right now... Need this truck to work and stay reliable. My theory is that I can fill the tubing with diesel from a turkey injector, and mark the level, and by the next morning or even over the course of a few hours, I can see if any of the injectors are "leaking", and then I can address that injector specifically. I read you could use crocus cloth or fine sand paper to help the injector "seal" internally, that way I am not buying 8 rebuilt injectors for $200, i can get the truck back on the road for like $20.
 

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I would think you would be able to find the bad injector if when you pull it, it is wet with Diesel.
 
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Discussion Starter #12
Hey, so I pulled every single injector and not a single one looked wet like it was leaking... And it was running yesterday...

I took my inspection mirror and looked under the IP... No leaks there, either...

What else could it be? What is causing air to enter into the return hose on the top of thew IP?
 

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Discussion Starter #13
Yesterday I also pulled one of the injectors apart to learn how they work, and rebuilding them is actually pretty easy, as far as nozzle replacement and wave washer replacement, there is a company that sells all of those things on line, I will buy the kit and replace those things. My question is, because of the super high compression, could combustion be forcing air into the injectors, and the bubble eventually making its way into the IP? Because it doesn't seem like the injectors are leaking, though maybe 5 showed a little wetness, it appeared from oil being burned rather than fuel? I could be wrong. I want to seal up the injectors and go from there.
 

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Dang, I didn’t answer back fast enough, won’t be an injector.

It’s IP and back air leak.

A leaky injector will only bleed off the fuel in it’s line and the truck start and run away a bit cause of all the extra fuel in that cylinder if it was hydro locked.
 

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Discussion Starter #15 (Edited)
Dang, I didn’t answer back fast enough, won’t be an injector.

It’s IP and back air leak.

A leaky injector will only bleed off the fuel in it’s line and the truck start and run away a bit cause of all the extra fuel in that cylinder if it was hydro locked.

For the injector check I disconnected the output from the fuel pump and pumped about a quart of fuel into a clear jar... No bubbles

Will rebuild Injectors and get back to you.

Oh, also I notice more and more bubbles coming into the low pressure return line as it runs, and no bubbles when it's off, it seems to come from the injectors.

As I said new return lines, noticed zero fuel on or around Injectors.

Will advise as soon as injectors have been rebuilt.
 

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You have to check from the injection pump back, every connection, every fuel line.
You won't see leaks because fuel is under suction and not pressure from the tanks to the injection pump.


That's why Bigboy's method of finding leaks is key, it actually pressurizes the system from the tank to the injection pump.


Fuel lines that look ok along the frame could actually be sucking air. They won''t show as leaks because they are not under pressure.


I would run one line from one tank to the inlet on the fuel pump and see what happens. If your clear line stays pretty full of fuel over night then you have narrowed down where the air leak is.
 

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Also I wouldn't bother with trying to rebuild the injectors.
Without a pop tester or specialized equipment you won't really know if the injector is good.
We are talking about pressures measuring between 1500 and 2000 lbs.

These things
• Nozzle Opening Pressure
• Chatter
• Leakage
• Spray Pattern

Need to be checked to rule an injector good or bad.
I would start saving and just get a set of rebuilts when funds allow.
 

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Ya exit out of enhanced view, top left button, then in my sig line is ways of finding air leaks. I have a slick lil modified fuel cap that is very quick to use and make if you have a few things around. At worst it’s 35-40$ in parts.

The other option is to pressurize by the return system... also in my sig line
 

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Another option is a patch, not a fix, it’s check valves.

Yup, go hit eBay and find fuel check valves. I think I paid 45c each, put 1 before the pump, 1 after and 1 after the filter.... this stops the fuel from flowing backwards from the air leaking in.

Now this is not a fix in anyway cause you still have an air leak, but the valve stops it from getting shiet tons of air in the fuel line.
 

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Discussion Starter #20
Okay I got flexible fuel line for replacing all the soft lines between the hard lines, and bypassing the mechanical fuel pump. How often do the soft lines directly from the tank go bad?
 
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