LB7: Fuel Pressure specification

[Harbin_22]

I thought on the lb7 is 23,000 psi or is that the maxs psi.

That is max

 

[nh_duramax]

Parts are indeed very expensive... The cheapest thing to do first is to see if you do have air getting into the system. You can try to methods to test for this.... One is to hook up an air line to the fuel tank and regulate it down to about 12-15 PSI. It should hold the pressure but if it doesn't what you will be looking for is fuel being pushed out somewhere on the fuel system from the tank to the CP3. Common places for these leaks are the fuel filter mounting housing and the pressure port shrader valve located at the front of the engine on the passenger side.
If this method is not available to you then I would suggest installing a clear hose from the filter housing that feeds the CP3 and then you can litterly see the air flowing to the CP3 if any. Make sure your tank is full otherwise you could get air into the fuel lines from sloshing.
If you determine that no air is getting in then next would be to do a return test on the injectors. It's a major pita but it will prevent you from buying parts you don't need. Do a search on the forum and you can find plenty of good info on to do this.
If your injectors test good then next is your CP3. Try running some 2-stroke first to see if maybe its just sticking, after that I would replace the regulator.
The fact that your actual pressure is tracking right along with commanded rules out a bad CP3 almost 100%. I think personally its air getting in.
Hope you get it nailed down though.

put pressure in the tank, about 15 psi. found a bad fuel line coming off the tank. i will replace and update this post with the results. before the stalling completely, i did put in 2 stroke to keep things lubed. many thx for all the good advice.

 

[nh_duramax]

I posted this on another thread I had going:...I worked on this for a day and a half this weekend. so here is the update. the leak was on the supply line at the quick disconnect joint between the supply line directly from the tank and the long supply line going to the top of the motor. I ended up having to puchase the Long fuel line and return line kit from the dealer and then the supply line coming directly off the tank because the rotted piece was corroded into the quick disconnect end of the line coming off the tank. Maybe I could have cut both ends at the leaky joint but puchased new OEM lines and spent about $600 for everything. And gues what it works great. Starts every time. Cranks for about 2 seconds and starts. I watch the FRP as it cranks and as soon as it gets above 1500 psi it starts right up. Performance is back to normal and it starts hot, cold, immediately after shutting off, or letting it set. Thank you everyone for the advice. It was a real bugger getting the OEM lines in but the key for the long run was to un-bolt the ABS unit from the frame and then I could thread the lines through to the back.

 

[TonOfDalt]

Glad to hear the suggestion kept you from spending on unnecessary parts, glad to hear tour back on the road too!

 

[nh_duramax]

Thank you for the advice. You were definitely correct with air getting in the line. Do you know how much vacumn is pulled on the supply line? I was thinking that I could have cut off the quick disconnect and made up a solid connection that would collapse under the vacumn. It would have been temporary but maybe save $600 for a while.

 

[TonOfDalt]

Not sure how much vacuum... I think its under 10 inches though. I know when I had put a clear line on mine from the filter housing to the CP3 it worked just fine for normal driving. The line I used had no braiding either. I did notice a lack of fuel delivery though at higher loads. But yes, you could have gotten by. In fact, you could have just used fuel injection hose as that's what's used pass the quick connect fittings anyways. When I did my injection pump I just replaced everything that was rubber just to be safe as my lines had over 240,000 on them.
Glad I could help though!