LB7: Fuel Rail Pressure Issues

WisconsinHick1

WisconsinHick1

New member
Mar 11, 2009
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Alright I am having problems holding Rail Pressure. I am attaching a log if anyone could take a look and let me know what you think.

I was thinking FRPRV is opening. Otherwise my worst nightmare the injectors are returning too much fuel. Its odd that it holds good rail pressure up until about 75% throttle and then it just dies off.

Any suggestions would be great. I know a bottle test would be best but just trying to get other suggestions.

View attachment Log_0009.zip
 

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WisconsinHick1

WisconsinHick1

New member
Mar 11, 2009
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Minnesota
I took a look at my tune compared to my log and its a little strange. At 75% throttle the tune is asking for 20000psi and the log shows that the Desired is 25000psi.

Is that normal?
 
Devon

Devon

broke my curse
May 2, 2010
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Hinsdale ma
Mine does the same thing. Full throttle position it will drain the rails, but even at 75% it will stay 22k desiring 24,500 on my big tune(stock turbo). I know I have at least 1 bad injector though.


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S

S Phinney

Active member
Aug 15, 2008
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Quncy, Fl
Have you dropped your tank to check for black algae growth? As bad as it was falling off the truck should have wanted to die on you. On a LB7 it is fairly unheard of for it to relief pressure through the relief bypass. I would check for restrictions then if that turns up fine then bottle test for return. If you are running the lift pump in your sig you could also have one of your fuel lines sucking shut on you. Check the fuel lines by the tranny where it goes from metal to flex and check by the hydroboost where it does the same. If you can squeeze those shut with your fingers change that out. Check the FICM lines also because they will do the same. Good luck with it.
 
blk smoke lb7

blk smoke lb7

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Nov 8, 2010
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belvidere,ill
whytry said:
Kinda hard to do the bottle test on an lb7
Click to expand...
Why? you can test the over all return at the return line by the hydro boost and you can test each bank of injectors where the banjo bolts to the head on the front of the head passenger side and the rear of the head on the drivers side.After that you need to get under the valve covers if you are only going to replace 1 injector which you can vaccum test each 1.Bullfrogjohnson has pics on a thread of how to do it.
 
WisconsinHick1

WisconsinHick1

New member
Mar 11, 2009
1,231
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Minnesota
S Phinney said:
Have you dropped your tank to check for black algae growth? As bad as it was falling off the truck should have wanted to die on you. On a LB7 it is fairly unheard of for it to relief pressure through the relief bypass. I would check for restrictions then if that turns up fine then bottle test for return. If you are running the lift pump in your sig you could also have one of your fuel lines sucking shut on you. Check the fuel lines by the tranny where it goes from metal to flex and check by the hydroboost where it does the same. If you can squeeze those shut with your fingers change that out. Check the FICM lines also because they will do the same. Good luck with it.
Click to expand...

I should update my sig. I have a FASS now and I ran the 1/2 line from the FASS all the way up to the metal light on the driver side of the motor. I'll check the rubber lines by the FICM tonight.

Scott do you have a fuel line laying around so I can check the return lines. From my understanding I would just pull the banjo bolt off and the ignition fuse hook up another fuel line and run a rubber line into a bottle crank for 15 seconds and see how much fuel I have in the bottle. Over 20ml its the injectors. Under 20ml its the CP3.
 
S

S Phinney

Active member
Aug 15, 2008
4,008
18
28
Quncy, Fl
WisconsinHick1 said:
I should update my sig. I have a FASS now and I ran the 1/2 line from the FASS all the way up to the metal light on the driver side of the motor. I'll check the rubber lines by the FICM tonight.

Scott do you have a fuel line laying around so I can check the return lines. From my understanding I would just pull the banjo bolt off and the ignition fuse hook up another fuel line and run a rubber line into a bottle crank for 15 seconds and see how much fuel I have in the bottle. Over 20ml its the injectors. Under 20ml its the CP3.
Click to expand...

You will have return from the CP3 there really shouldn't be much at from injectors. They should be done separate from the CP3 also. You would need a old line and connect to where it come out of the head. That will give you the return for that side. This is only telling you if that side is out of whack. The CP3 willl have plenty of return because what is not used is returned (extra from lift pump etc...).
 
blk smoke lb7

blk smoke lb7

<-----Lots of green $
Nov 8, 2010
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belvidere,ill
WisconsinHick1 said:
I should update my sig. I have a FASS now and I ran the 1/2 line from the FASS all the way up to the metal light on the driver side of the motor. I'll check the rubber lines by the FICM tonight.

Scott do you have a fuel line laying around so I can check the return lines. From my understanding I would just pull the banjo bolt off and the ignition fuse hook up another fuel line and run a rubber line into a bottle crank for 15 seconds and see how much fuel I have in the bottle. Over 20ml its the injectors. Under 20ml its the CP3.
Click to expand...
I have some short pieces like the line that goes from the cp3 outlet to the fprv and the piece that runs to the test port.I would get a piece of high presure fuel injection line or you can get a piece from a parker dealer.Ill send you what i have if you want i just dont thing the 4 inch ond 6 inch pieces are going to do you any good.Do you need a fuel return line?
 
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