New lml engine build, no fuel rail pressure

Toxic

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Dec 30, 2015
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Mansfield, OH
Finally got around to putting my built engine and trans back in the truck. Has a 10mm cp3 and stock injectors. Been trying for 3 days to get it started. Won’t build more than like 65 psi of fuel rail pressure. Only codes it has is for the ac pressure switch cause I don’t have the core support in or any Freon in it yet.

Things I’ve done:
Pinched injector return line with vice grips, also tried air pressure from air compressor.

Verified cam and crank signal seems to be good.

It’s getting fuel to the rails and injectors, just not pressurized.

Has 8psi of lift pump pressure and good solid flow direct to cp3.

Will hit on a very minimal shot of ether.

Pulled the driver side rail pressure relief regulator out, doesn’t seem like its stuck open or gummed up.

Made sure I have the right plugs in the right places, and also swapped the regulator plugs around . Have the plug with yellow and black wires on the pump, yellow and purple on the rail.

I’m not sure where to go from here. Did notice when I put air pressure on the injector return line I had atleast one injector that was leaking air from the return fitting thing. Kinda got it sealed up better but I think it still leaks a little. Thinking I may get a new injector return assembly and new o rings. New O rings were just put on when the engine was assembled though.

Not letting me post the videos but I have a couple short clips showing live data while cranking if that helps anyone.
 

Chevy1925

don't know sh!t about IFS
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Oct 21, 2009
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Im trying to remember but im pretty sure that does not pinch off the fuel rail return IF the fuel pressure regulator on the rail is stuck and returning fuel

I know you said you oulled it and checked it but it doesnt take much for the pump to not build pressure. Pinching that line off and seeing if it starts would be an easy test
 

Toxic

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Dec 30, 2015
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Mansfield, OH
Im trying to remember but im pretty sure that does not pinch off the fuel rail return IF the fuel pressure regulator on the rail is stuck and returning fuel

I know you said you oulled it and checked it but it doesnt take much for the pump to not build pressure. Pinching that line off and seeing if it starts would be an easy test
You are correct in that pinching off the injector return line, doesn’t do anything for that rail relief valve return. I had thought about pinching off the main return line going back to the tank and that would cover both the injector and rail return. Just wasn’t sure if it would cause any issues blocking it off so I didn’t try it. But I will try that.
 

Chevy1925

don't know sh!t about IFS
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Oct 21, 2009
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You are correct in that pinching off the injector return line, doesn’t do anything for that rail relief valve return. I had thought about pinching off the main return line going back to the tank and that would cover both the injector and rail return. Just wasn’t sure if it would cause any issues blocking it off so I didn’t try it. But I will try that.

If it fires up, just shut it down quick. Shouldnt be an issue.
 

Toxic

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Dec 30, 2015
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Mansfield, OH
So with the cp3 return, rail return and injector return all pinched off. Still won’t make any decent amount of fuel rail pressure. Also noticed it’s not showing any oil pressure anymore. It did before, when I first tried starting it, not sure why it’s not now.
 

Jakezed22

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Dec 2, 2016
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Can you try pull the lines of each bank of injectors at the regulator and put shop air to them, then also shop air to the regulator it self. Make sure you are blowing the air backwards towards the injector return.
 

Toxic

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Dec 30, 2015
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Mansfield, OH
Can you try pull the lines of each bank of injectors at the regulator and put shop air to them, then also shop air to the regulator it self. Make sure you are blowing the air backwards towards the injector return.
Yes but concern now is the lack of oil pressure, confirmed by taking the turbo oil feed off and cranking. Not sure what it could be other than that o ring on the front cover blew out or something. Have a very minimal drip from the oil cooler area, in a weeks time made a 4” spot on the ground.
 

Jakezed22

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Dec 2, 2016
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Yes but concern now is the lack of oil pressure, confirmed by taking the turbo oil feed off and cranking. Not sure what it could be other than that o ring on the front cover blew out or something. Have a very minimal drip from the oil cooler area, in a weeks time made a 4” spot on the ground.
Usually it’s takes some running for the crank pin to fail, but perhaps yours is forgotten? I think a front cover pull is in order
 

Chevy1925

don't know sh!t about IFS
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Oct 21, 2009
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All the oil galley plugs in place on the block?

As for fuel, seems like a supply issue now or a failed hard part.
 

Bdsankey

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I would be hesitant to doubt an Exergy CP3 but it is possible. How many miles are on it?


Does the rail pressure sensor ever go above 65psi? If not, I would look at possibly a failed sensor IF the pump is moving fuel like you claim to the rail/lines.