Zero Rail Pressure when cranking

[Longrange65]

New to this forum, but not to diesels. If this post is in the wrong place I apologize and will repost if necessary.
My problem: I installed an Airdog 2 165gph lift pump and race plug this week, now I can’t get it to start nor does it have any rail pressure at all- literally zero.
I did the lift pump and race plug because three separate times while pulling (between 15k-28k lbs) I would get a ‘dead pedal’ and my rail pressure and flow would drop to 0 for about ten or fifteen seconds then come back normal. I found the cause to be collapsing fuel lines and replaced them. I have always been able to push 26kpsi+ no problem when WOT. No surging or idle fluctuations previously.
I have tested fuel pressure sensor and it tests okay. I have replaced the line before and after the factory filter with clear tube to verify no air bubbles are present going into CP3 feed. I am not getting any fuel passing the race plug. If I crack an injector line and crank the truck I get a little bit of fuel but not much. Lift pump is putting out steady 8 psi as measured immediately after Factory fuel filter before CP3 inlet. I do have fuel coming out of return line when cranking, that’s with the ‘u’ shaped hose by the race plug pulled off and capped. It is not much but I suspect if the injectors were passing fuel by I would still see at least some rail pressure? Or is this assumption wrong? My question is, what would cause me to have zero rail pressure? Sorry for the long post, I just wanted to give as much info as possible.

 

[2004LB7]

You didn't happen to accidentally swap the input and return hoses on the cp3 did you?

 

[Longrange65]

I just double checked, but they are on correctly.

 

[Longrange65]

Also, with the clear fuel hose I can see the the fuel is not even hardly moving while cranking. Shouldn’t it be moving a fair amount of fuel upon cranking, especially with the lift pump pushing as well?

 

[2004LB7]

Should be. You should check right at the CP3 that you are getting fuel. If so you may have a bad CP3

 

[Longrange65]

I am getting it at the fuel line going into the CP3... I haven’t had any symptoms of a weak pump though? The truck has ran great always (aside from the dead pedal). No idling issues, rail pressure keeps up great, follows desired pressure nearly perfect even weighing in at 34k lbs pulling a 6% grade. Would a CP3 go out with no signs?
I’m wondering if my monitor (bullydog GT) simply wont read rail pressure until running and maybe that’s why it’s showing zero. I’ve never paid attention to it before now. Also, thank you guys for helping me troubleshoot, I really appreciate it!

 

[2004LB7]

It could be difficult to read anything while cranking, especially if you have weak batteries. There is a lot going on while cranking and it is very easy to drop the connection to your reader. To test it you can unplug the pressure sensor and see it you get max pressure. If it stays at zero the bullydog isn't reading correctly

 

[Longrange65]

I have kept the battery charger on the truck and turned it up to 225 amps when cranking it.
With pressure sensor unplugged it is showing 29kpsi when off and during cranking, so I guess it’s safe to say the monitor is reading correctly.

 

[2004LB7]

Can you get any fuel with one of the high pressure lines disconnected?

 

[Longrange65]

When cranking I get a bit out of the injector lines when I crack them. I haven’t tried unhooking the line directly after the CP3 however. I guess I will try that next

 

[TheBac]

Didnt we just have another person ask about this very thing? The CP3 died?

 

[2004LB7]

Yep, I remember. It did end up being the CP3

 

[JoshH]

I know you checked pressure, but are you 100% sure you got the AirDog primed and it is flowing fuel to the CP3? Did you disconnect a hose and let it pump fuel through the system? I would be very surprised if an LBZ CP3 just all of a sudden quit building pressure like that.

 

[Ron Nielson]

I am not getting any fuel passing the race plug. If I crack an injector line and crank the truck I get a little bit of fuel but not much.

Is is possible that the race plug is blocking the fuel coming into the fuel rail? Do race plugs come in different lengths? or use different thickness gaskets? You have your old plug to install and see if there is a difference?

Cranking you should have about 4K - 5K pressure.

 

[Chevy1925]

Race plug wont affect this issue.

injectors wont fire unless rail pressure sensor sees 2500+psi, you may need to crack a couple injector lines and crank it for a bit if its air locked in the rail.

 

[Longrange65]

Thanks for all the responses!
I have bypassed the stock filter housing and ran clear hose from the lift pump directly to CP3 to verify fuel is free of air pockets. When cranking the fuel doesn’t flow at all, however if I undo the hose at the CP3 inlet then it flows like a fire hose, so lift pump is working great. I think the notion that it is air locked is spot on, I just can’t see the CP3 randomly going out with no previous issues. I won’t get a chance to work on it tonight, but tomorrow I will crack the injector lines and purge whatever air I can out, if that doesn’t work I will pull the line coming directly off the CP3 to see if it is even trying!

 

[Longrange65]

Update:
After cracking injector lines and then CP3 output lines, I realized the CP3 was not putting out anything more than a drizzle. I unhooked the glow plug module and sprayed a touch of starting fluid in her (bad,bad,bad) just to see if she could build pressure at all. It would fire for a split second and then die out without holding any meaningful rail pressure.
Determined that it couldn’t possibly be the CP3 when I had no previous signs of it going out, I started checking anything and everything.
After going over everything with a fine tooth comb, I decided to pull the feed hose directly off the CP3 and stick a length of hose on that was attached to my shop vac to try and suck out any contaminants that may have got in there. When I went to push the feed hose back on, I noticed it was very soft and had tiny pieces on the end. I pulled it out and inspected it, found the inner and outer plies of rubber were separating and the inner ply was rolling back into the hose blocking passage! I had previously specifically watched that hose while trying to crank it, and with the lift pump on and off to see if was collapsing and it was NOT, so I had eliminated that as a culprit.
I replaced all the rubber hoses in the valley, and she fired right up! She grabs 29k psi of rail pressure no problem when the skinny pedal meets the carpet!
Hope this helps someone in the future. Thanks to all of you that helped me bounce ideas around, I really appreciate it!

 

[2004LB7]

Thanks for the update. Always nice when it is something simple and cheap