6.7 extremely long crank

Tiha

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Yes, put the new set of injectors in and everything is perfect now.
Just wanted to say thank you for posting. I am finally going to dive into this in the next week or two and re reading everything, you answered every question I had so far without me having to ask.
 

ioang26

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I did, a simple way to do it is bypass the return line going into the upper filter, pull the return lines off of one bank at a time and put small clear hoses on the return fittings on the injectors. Run those into a container where you can watch them. Command your low pressure fuel pump on and watch for fuel to come out of the lines. Whichever line has fuel coming out is your issue.


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Hi, how did you bypass the return line ? Also, the size of the clear hose I need - is it 1/4" OD ? I have a long crank (2 sec)and believe an injector is returning too much fuel, just need to pin point it. I would appreciate any help and info !
 

Tiha

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You can pinch off the return line with a clamp tool, even a vise grips if you are super careful.

I am thinking I had like a 3/16" line. But really it doesn't matter, it will either flow fuel or not. You can run it without a hose and if fuel comes out it will make a mess but you will know that one is bad.

I did that test and I got no flow out of any of my injectors. Even with it running.
 

ioang26

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You can pinch off the return line with a clamp tool, even a vise grips if you are super careful.

I am thinking I had like a 3/16" line. But really it doesn't matter, it will either flow fuel or not. You can run it without a hose and if fuel comes out it will make a mess but you will know that one is bad.

I did that test and I got no flow out of any of my injectors. Even with it running.
Ok, so if you had no flow return of any of your 8 injectors , why did you replace them ? Which one was bad then and how did you test them ? I am a bit confused.
 

Tiha

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Ok, so if you had no flow return of any of your 8 injectors , why did you replace them ? Which one was bad then and how did you test them ? I am a bit confused.
The injectors are not supposed to have any return flow, or at least very little. Which was odd because since I had a no start I figured one would be dumping fuel like crazy. Or I was hoping one was.

On top of that, the injectors need back pressure to operate properly. So the test really is not accurate except to try and find a no start injector failure.

I pulled the injectors and took them to a diesel shop that ran them on their high dollar bosch machine. At the point where I was, it had to be injectors or pump causing my no start. I was not getting enough information or instruction on how to test the injectors any farther than I had. Honestly I could not find anyone else that had tried to do a return flow test so I had no idea if I did it right. But I did.
Same with the pump. Not enough information out there.
I think it is $25 or $50 an injector to run them on the stand and test them. Can't remember for sure.

On the high dollar bosch machine I had one injector that was not responding to computer control within limits. 3 others that were marginal. So even though they were not causing my no start 4 of them failed test and should be replaced. I have the test paperwork loaded up in my other thread.

I would imagine you take just about any 6.7 out there with over 100k miles and pull the injectors and run them on the test stand you will find a couple that are not working like they did when they were new.

In comparison the new injectors, I have one that has fuel trims twice what my original set was. I guess that doesn't mean it isn't working properly but still strange. That also means that fuel trims are not a great indicator of a bad injector either.

I don't know the science behind it. But I think the return line is more about purging air from the fuel system rather than an injector actually needing to return fuel.
 

lincolnlocker

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The injectors are not supposed to have any return flow, or at least very little. Which was odd because since I had a no start I figured one would be dumping fuel like crazy. Or I was hoping one was.

On top of that, the injectors need back pressure to operate properly. So the test really is not accurate except to try and find a no start injector failure.

I pulled the injectors and took them to a diesel shop that ran them on their high dollar bosch machine. At the point where I was, it had to be injectors or pump causing my no start. I was not getting enough information or instruction on how to test the injectors any farther than I had. Honestly I could not find anyone else that had tried to do a return flow test so I had no idea if I did it right. But I did.
Same with the pump. Not enough information out there.
I think it is $25 or $50 an injector to run them on the stand and test them. Can't remember for sure.

On the high dollar bosch machine I had one injector that was not responding to computer control within limits. 3 others that were marginal. So even though they were not causing my no start 4 of them failed test and should be replaced. I have the test paperwork loaded up in my other thread.

I would imagine you take just about any 6.7 out there with over 100k miles and pull the injectors and run them on the test stand you will find a couple that are not working like they did when they were new.

In comparison the new injectors, I have one that has fuel trims twice what my original set was. I guess that doesn't mean it isn't working properly but still strange. That also means that fuel trims are not a great indicator of a bad injector either.

I don't know the science behind it. But I think the return line is more about purging air from the fuel system rather than an injector actually needing to return fuel.
Makes sense. Still good info!
 
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