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We have a 2004 c5500 6.6 lly with a no start condition.

Cranks ok, appears to be fuel related. fuel rail pressure reads approx 230 lbs. checked for suction on inlet lines and found none at rear of engine where lines come in from tank. Checked filter inlet and outlet also none. traced lines all the way to the pump checking at connections along the way. removed inlet line from pump to also find no suction. PS pump is brand new along with regulator and relief valve.

Any Suggestions, did I possibly miss something?

On that system, the fuel injection pump is used to bring fuel from the tank and supply it under high pressure to the injectors. The inherent weakness on this system is the loss of suction ability after some miles on the pump to be able to suck the fuel from the tank. What we do is to install an aftermarket pump (Raptor or Air Dog) along the left frame rail and use that pump as a pusher pump between the tank and the injection pump. At the same time we lower the tank and install a larger drop tube. Often the life of the injection pump can be lengthened by doing this. However in some cases, the injection pump may also have to be replaced due to wear. One thing I will say: some shops will not advise the installation of an aftermarket pump and advise replacement of injector pump. I respect them for that. Injection pump replacement is certainly an option but by no means the only one.

Replaced cp3 pump along with regulator still unable to build enough pressure. according to our modis pressure is 6940kpa = 1046psi. Cust got pump from gm, cranking speed is 150 .

My guess would be that there is air in the system yet. Those engine can be real bears to get all the air out after pump replacement. You could unhook the glow plugs and give it a shot of ether an see if it will get to running. I am careful who I recommend doing that but it would be an option. The cranking speed should be ok at 150 rpms. As i mentioned, it takes quite a bit to get the air out of this system.

You could also crack the lines at the injectors to help let the air out, I have done this on these and it helped to get them going,

Tim Martin wrote:My guess would be that there is air in the system yet. Those engine can be real bears to get all the air out after pump replacement. You could unhook the glow plugs and give it a shot of ether an see if it will get to running. I am careful who I recommend doing that but it would be an option. The cranking speed should be ok at 150 rpms. As i mentioned, it takes quite a bit to get the air out of this system.

I thought ether was unsafe for deisals. I was told to use WD40. I dont do a lot of deisal so dont go by me.

Pauls Automotive wrote:

Tim Martin wrote:My guess would be that there is air in the system yet. Those engine can be real bears to get all the air out after pump replacement. You could unhook the glow plugs and give it a shot of ether an see if it will get to running. I am careful who I recommend doing that but it would be an option. The cranking speed should be ok at 150 rpms. As i mentioned, it takes quite a bit to get the air out of this system.

I thought ether was unsafe for deisals. I was told to use WD40. I dont do a lot of deisal so dont go by me.

With glow plugs , it is, can blow them to kingdom come, but unhook plugs and is OK, WD40 don't seemt to work for me to start them.......

Agreed! Use ether (starting fluid) very sparingly. And, always disable the glow plug or intake heater system prior to spraying starting fluid into the intake system.

Gave it a little snort of either to get it going, runs, but if you shut it off you will need ether again to start. Even if you try immediately

erlesauto wrote:Gave it a little snort of either to get it going, runs, but if you shut it off you will need ether again to start. Even if you try immediately

Get it going again and run it for a while, do a drive cycle if you can and that will help to get the air out of the system. They can be a bear to get all of it out.

OK so we addressed the drive cycle issue here but not the issue of not restarting after shutting down. Shut down the return line and see if you build up pressure enough to fire it off.

Found to much fuel returning to tank, did cylinder balance test found 4 injectors not contributing. Cust took truck claiming no money for inj.

Well now, that is a find.

Hopefully it doesn't have an injector stick open and melt a piston. That is the next step.