What’s in the cp3.......

[LBZ]

that makes the primer get hard? Is there a spring and a relief valve?
What stops the flow from just wailing through the pump when you prime it?
Buddy has an LB7 that won’t start. Only makes about 400psi RP cranking. When he primes it fuel just wails through and out the return.

 

[2004LB7]

Yes.

the two reasons it doesn't just spill out, is one - there is a gear pump right at the input of the CP3. this is a positive displacement pump and if everything is good, not much will get past this. so pressure will build here. two - the gear pump feeds the body of the pump providing it lubrication and cooling. there are now two paths for the fuel to go from here. up to the metering valve or (Fuel Pressure Regulator Valve) or out the pressure relief. this one is set to relieve the pressure around 75 psi or so. the volume of the gear pump is supposed to be high enough that it always keeps the inner body of the CP3 pressurized so fuel can be supplied to the FPRV. any pressure above the set point is bled off out the relief.

High volume pumps will often times mod this relief, amongst other things, to increase the pressure at which it opens. this will in effect put more pressure on the FPRV and into the pistons allowing more volume

 

[LBZ]

Thanks. That’s what I thought. Probably got a shit gear pump and/or relief valve then. Time for a new cp3.

 

[2004LB7]

before condemning the pump, check the cheaper stuff first. fuel line leaks or filter head can also contribute to the primer bulb not pumping up. sometimes a rebuild kit takes care of it but other times it requires a new head. do you have a lift pump installed?

 

[LBZ]

Filter head had a fresh rebuild. He rigged in a hand primer bulb right to the cp3. Its dicked. Also when he removed The turbo horn and some other pieces he noticed the turbo was seized solid and ate itself. Pieces right through the IC. So this engine is likely full of metal. He’s washing his hands of it now.

 

[JoshH]

I don't often see a bad CP3 cause a no start condition. More often than not it is bad injectors. Usually a bad CP3 just won't be able to build pressure.

 

[LBZ]

I don't often see a bad CP3 cause a no start condition. More often than not it is bad injectors. Usually a bad CP3 just won't be able to build pressure.

Which is exactly the case here. Only makes about 375psi.

 

[2004LB7]

when you get the pump out. can you take the gear pump off the back and inspect the shaft part that drives the gears? I would like to see if mine was the only one that failed there. you may also want to remove the fprv and inspect that too

 

[LBZ]

I feel like this truck might just get sold as is. I don’t think buddy wants to put any money into it as the truck isn’t worth it to him.

 

[JoshH]

What I mean is, the truck will crank and run with no problem but won't build more than 12k or so psi regardless of load. What you are seeing is usually a lack of flow (such as a restriction on the supply, a bad low pressure pump, or internal fuel leak in the CP3) or leak on the high pressure side which is more often a few bad injectors with high return rates. Hit it with some ether and see if it will run.