im thinking my FPR may have stuck open and causing it not to build enough pressure to crank imgoing to take the large return line lose when i get a chance and and see if fuel comes out if it does my FPR is dead

 

while issues with the pressure relief valve on an LB7 are rare it is possible.

it is possible that by reversing the lines on the filter housing fuel was pulled backwards through the filter and junk got sent down the lines and jammed up the FPRV. also when priming the filter it would pull fuel backwards and may have pulled raw fuel from the return line in the tank.

fuel should come out of the return line while cranking the engine over and while running. there will be a small amount the will come from the CP3 as this is the fuel used to lubricate the internals of the pump. it shouldn't be that much but will be there if it is working properly. you would have to separate the individual return lines to see where the fuel is coming from.

 

ok maybe you can clear this up for me a diesel guy at the local gm dealer said that the small line on the driver side was the CP3/injectors excess fuel and the large one is the FPRV and fuel should only come out slightly when the trucks running as the FPRV opens and closes to keep correct pressure and if fuel comes out when cranking normally the FPRV is stuck open and not letting it build pressure to crank. is this true or just someone thinking they know how it works?

 

if you are referring to these lines:


the large one is the supply to the engine and the small one is the fuel return. on the right (drivers side) fuel rail there is a block that the pressure relief valve is located on that the returns all go to then run back to the engine via the smaller line in the photo. isolate the lines at this point and put them into a bottle and crank the engine over till fuel starts coming out. none should me coming out of the pressure relief valve, none from the injectors until the engine is running, and some will come out of the CP3 for lubrication.

 

ok thanks what would you do at this point if you were me you know more then me so maybe you can help me figure out whats gone wrong im just at a loss now. thanks for all the help youve been

 

the approximate sequence i would use

-replace fuel filter
-pull the line going into the CP3 pump and prime the filter to flush out dirty fuel
-reinstall the CP3 supply line. loosen the high pressure line on the fuel rail connecting to the CP3 pump at the "block"
-prime and crank engine to flush dirty fuel out of the CP3 pump. if no fuel comes out then suspect a clogged up pressure regulator.
-tighten the CP3 high pressure line
-remove the driver side fuel rail plug on the front of the rail and prime/crank engine to flush
-reinstall driver side rail plug and remove passenger side fuel rail plug on back side of rail, flush rail
-reinstall plug on rail, crack loose one of the injectors line on the driver side fuel rail, prime and crank to remove air and fill rail with fuel. tighten line and repeat with passenger side rail
-make sure all of the lines and fittings are tight. prime and crank engine till it starts.

for me it only takes several tries to get it to start. sometimes it will fire and die from air in the lines. just prime and start again. when i am in a hurry i put a cap full of gasoline in the maf sensor hole (maf sensor removed of curse) or in the intake heater hole.it will fire up on the first or second time like this. try it at your own risk.

i dont think any bad fuel made it into your injectors as the pressure never got high enough for them to open so there would be no flow going down the injector lines.

remember, the CP3 pumps rarely fail to the point that they can't build enough pressure to start the engine. typically symptoms are low rail pressure during hard throttle or high engine loads but will run fine otherwise. sometimes the pressure regulator starts to act up and causes surging during idle but would only stop the engine if the valve got stuck closed or particles plugged up the metering hole. if no fuel comes out of the high pressure CP3 line that feeds the rails (via the block) then i would replace the pressure regulator.

 

see attached

 

thanks I'll be doing this over the next few days after work I'll let you know my results

 

I got it primed to the "block" then was trying to remove the plug in the rail and broke off my snap on torqs bit. it had no fuel in the block till I done the priming to the CP3 it took about 4 secs of cranking to get fuel to come out then it blasted out pretty much so what should I do now

 

thats why i dont buy snap-on, over rated in my opinion.

did you get the plugs back in? if yes then crack one of the injector lines on each line rail one at a time starting with the driver side rail to bleed out the last bit of air.

make sure they are tightened back up and prime and start the engine.