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Discussion Starter · #1 ·
I have a 2012 Chevy 3500HD with the LGH. This is a farm truck with no emissions requirements here in AZ so it is fully deleted legally. I just finished an engine swap because the crankshaft snapped on the original. I installed a fass lift pump to resolve a crank no start but it seems I have not isolated the issue. The engine cranks strong and fuel pressure builds in the high pressure rails. The only fault I can discern as a cause now is the "fuel pressure regulator 2 control circuit short to ground fault" shown in the obd2 scanner. However, the fuel regulators on the CP4 pump and fuel driver side fuel rail are new. Batteries are new with full charge. I thought I'd post here for some suggestions before paying an arm and leg for a diesel shop.
 

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What are the exact codes you are getting?
Have you checked all fuses?
 

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Discussion Starter · #3 · (Edited)
What are the exact codes you are getting?
Have you checked all fuses?
Truck is throwing no codes, except for a few glow plugs. all fuses are good. grounds are good. the only fault I can detect is displayed when exploring the live fuel data on my tech2 for the regulator.

I may have stumbled onto the problem. Desired fuel rail pressure while cranking is approx 6000 psi but the actual rail pressure from the sensor is only 500 psi. Is this the result of a bad cp4 pump or maybe a regulator stuck open and pressure can't built?

640271
 

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Truck is throwing no codes, except for a few glow plugs. all fuses are good. grounds are good. the only fault I can detect is displayed when exploring the live fuel data on my tech2 for the regulator.
The pics of your FASS setup that you posted show a wet line. You might want to go back through and check those lines again. if you have any wet spots/weeps then you have a good chance of air getting into the system..
Make sure none of the lines are kinked
 

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Discussion Starter · #5 ·
Truck is throwing no codes, except for a few glow plugs. all fuses are good. grounds are good. the only fault I can detect is displayed when exploring the live fuel data on my tech2 for the regulator.
I may have stumbled onto the problem. Desired fuel rail pressure while cranking is approx 6000 psi but the actual rail pressure from the sensor is only 500 psi. Is this the result of a bad cp4 pump or maybe a regulator stuck open and pressure can't built?

View attachment 640271

640272
 

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Discussion Starter · #6 ·
The pics of your FASS setup that you posted show a wet line. You might want to go back through and check those lines again. if you have any wet spots/weeps then you have a good chance of air getting into the system..
Make sure none of the lines are kinked
the diesel is from draining the tank and immediately installing the pump, but I'll definitely check again for leaks. I'm reading 12psi at the low pressure fuel port under the hood. I bypassed the stock fuel filter with plans to just bypass it with a bit of hose.
 

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Have you checked for leakage from the fuel rail relief valve? If you have a standard relief valve not shimmed and not a race plug you can unplug the regulator and that will give you max pressure if the regulator is not stuck open. The regulator gives max pressure with no current to it. On your data display it shows 1223 ma that seems high to me. If the system is trying to make pressure that current should be low.
 

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So it sounds like the regulator 2 opens when the truck is off. So ecm powers it close it.
 

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Discussion Starter · #13 ·
I may also be full of **** on the regulator on a cp4 I was thinking you had a cp3.
it's a good thought. Not sure if cp3 vs cp4 makes a difference on regulator functionality. It's a new part but I'll try unplugging it to see if that raises fuel pressure. It's rather cheap so I'll order another and see if I just got a bad part. the pump should produce the desired rail pressure of 6000 psi while cranking, right? if not the ECM won't fire the injectors as I understand it. I installed a donor engine block that came complete with the cp4, injectors and turbo. salvage yard claimed it had only 50k miles. that could mean anything.
 

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I'm reading in service info you should see 1888 minimum of rail cranking. You need enough pressure to spray out of the injectors to start.
 

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Engine speed should be greater than 80 on a cold engine more than 125 on warm engine.
 

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I wish i could just copy and paste all the service info for ya. You should just get a subscription for your vehicle from all data or identifix. It will give you the service manuals that will take you step by step through diag of fuel system. If you have the info you can figure this out.
 

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Discussion Starter · #19 ·
it's a good thought. Not sure if cp3 vs cp4 makes a difference on regulator functionality. It's a new part but I'll try unplugging it to see if that raises fuel pressure. It's rather cheap so I'll order another and see if I just got a bad part. the pump should produce the desired rail pressure of 6000 psi while cranking, right? if not the ECM won't fire the injectors as I understand it. I installed a donor engine block that came complete with the cp4, injectors and turbo. salvage yard claimed it had only 50k miles. that could mean anything.
I got the truck to fire up. I unplugged the driver side fuel regulator and got the ECM to throw a code and report " reduced engine power" on the display. I deleted the code and tried starting the engine and it fired right up. WTF!? I plugged the regulator back in while the truck was running. truck now starts. YAY!

thanks for the responses.

now I have a few leaks to resolve. tranny fluid leaking from the radiator area. likely a loose fitting.

anyone know if there is suppose to be a washer for the upper hydraulic line connecting to the power steering pump? my just gushes fluid. worried about over tightening.
 

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Discussion Starter · #20 ·
I wish i could just copy and paste all the service info for ya. You should just get a subscription for your vehicle from all data or identifix. It will give you the service manuals that will take you step by step through diag of fuel system. If you have the info you can figure this out.
I have alldatadiy, haynes and identifix. :+)

I know. I'm effing retarded. lol
 
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