Hello, I have a question.


Let me start off by telling you that I am new here and I am a GM tech by trade...Not a Diesel tech though, rather a very good gas engine tech.


I have been "forced" to work on a Duramax because the usuall diesel guy is backed up to his ears with diesels.


OK, this thing has been in before and the usual diesel guy installed a fuel pump and a FICM. It did not fix the problem.


The customers complaint is a "crank, no start" and a "long crank, hard start". I have so far checked for codes, there are no codes. I have checked for desired vs. actual fuel rail pressure and it looks to be good. I can get the truck to run easily and command the regulator to full pressure and it will achive 23,000 psi rail pressure @ 2000 RPM, so I know the pump is good.


I started out with the shop manual checking the supply side for air intrution. I plugged the supply tube at the back of the engine and applied 25 inches of vaccum to the return line...6 times with a pause to allow for stabilization, on Friday!


Monday morning the guage showed 22 inches of vaccum. So I don't see any leaks at the engine side of the system.


I then continued on to the supply from the tank as per manual procedures. Still no leak found.


Next step is to loop a transparent hose between the FICM outlet and the filter intet and watch for air bubbles.


If bubbles are pressent, suspect an air leak at the fuel tank pick-up. If air bubbles are not pressent, move on to the high pressure side.


Well here is my question:


I get little to no bubbles at idle, but if I command fuel pressure to max @ 2,000 rpm (about 23,000 psi) I then get a steady stream of air bubbles.


Is this normal, or do I have an air leak in the fuel pick-up in the tank?


Or is it something else? I'm not normally a diesel guy.


Please let me know if you need more info.


Thank you, Scott








Edited by: 1fatcat

Scott


My truck is at the dealer now for a similar problem I am getting air in the fuel system some how becouse sometimes it want start and I have to prime it manualy then it starts. The tech called GM and they were no help so they are still working on it I will let you know what they find or if yop find something let me know.


Thanks


Shaydog

Could also be one of the Quick disconnects (http://community.webshots.com/photo/67970835/72256238bjrjGJ) and/or hose crimps between the tank and FICM... The QD's are not a good design (IMHO)for a vacuum system.

1fatcat, I would agree with jbplock. It would seem that you have too much air in the system. When the engine does not start, can you bleed air out of the fuel filter with the primer pump?

Here is an update of what has been done, and what is being done to this truck.


So far, I have replaced the pick-up unit in the fuel tank and the two foot supply line that runs from the tank to the chassis/frame line.


This did not help at all, so I am thinking that the air I was seeing in the transparent hose is normal when the engine is running at 2000 rpm and the pump is commanded to full pressure.


I am in the process of replacing all eight fuel injectors (wow, what a job that is!), so we'll see what happens. I sure wish I was not the guy working on this thing. I realy don't understand anything about diesles.


Before anyone jumps to conclutions, this truck is still under factory warranty and GM is paying the bill. I realize my story sounds very unprofessional for a GM technition, but as I had mentioned earlier, I am not normally a diesel technition.


If anyone has any suggestions/ideas, please let me know. I will let everyone know what finaly fixes this problem.


Thanks for reading

Unfortunatly alot of the d-max's do this.


I am a gm tech also but I am the diesel guy.


It sounds like you have an injector leaking. disconnect the return lines at the back of the motor, hook hoses to them and run them into seperate containers. Crank the motor for a least 120 seconds straight the one bottle that has alot of fuel in it indictes the side the problem injector is on ( it tells one that an injector is letting fuel bypass straight into the return system causing hard or long starts) when you get that far replace all the injectors on that side. that will eiminate any come backs at least for that side of the motor anyway.


I have one of these in my stall right now doing the same thing. this test has not failed me yet.


let me know if you have anymore questions

Thanks for the info mahotas! So did issuzu fix the problem with the injectors, or are they the same POS injector that was originally installed?


I noticed that the replacement units are remanufactered by issuzu, I thought I would be getting new but I guess not.

Well folks, just to let you know, I had finished replacing all eight injectors on this truck about 1 week ago and haven't heard anything bad from the customer yet? So I'm assuming that this did fix his problem.


I hear alot of concern about bad injectors on this site, and just wanted to say that this is the first Duramax that our shop has had to put any injectors in. I also will tell you that when the parts department of our dealership had to order the injectors, they said it would take almost a week for them to get here because they were on national back order.http://www.dieselplace.com/forum/smileys/Confused.gif

Fatcat
How many miles on his truck?
Did he follow fuel filter replacement guidelines?
Did he run additives or extra fuel filter?

Just want to know.........

The truck had 20,000 miles.


His first and only filter replacement so far was the last time the truck was in for the injectors.....20,000 miles.


No extra filter, he did use one bottle of additive to try to correct for a hard start condition that he had been having on and off since 16,000 miles......This lead to a big mess with his warranty. It's a long story, but you can read all about it here...........http://dieselplace.com/forum/forum_posts.asp?TID=2401&PN=2