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Discussion Starter · #1 ·
Hi everyone. It been a year and half almost that I decided to swap a 3.9 ISB in a 69 Tbird. Recently started driving it more and more this year. I never think I have the fuel system plumed properly, or always think I didnt get the right electric supply pump for it. Every so often I would be able to drive it daily, sometimes next day after lettting the ing on the key letting the pump prime (I am deaf, but the pump is loud enough and vibrate enough to feel the difference when it building pressure) when it feels solid and steady. It often just starts right up, or cranks forever, or if waited long enough for pump to prime, itll start. It will start up if I unhook the FCA (fuel control actuator on the cp3 pump). It always had a bad leak from the old tank with modified ports that feeds from the bottom of the tank, then leaks from the old water seprator unit with, I had more problem starting it up those times.

This time I have a 20 gal boat tank, with 10 an fitting welded to the bottom to feed a tall fleetguard water/fuel separator using 10an line from tank after the filter another 10an line to a 3/8npt to a fuel pump (the one I have is very close to this one Speedway Electric Fuel Pump, 115 GPH, 14 PSI) to a 6 an to a 3/8 hardline into this gear pump thing on the cp3 then out to the oem filter housing then out to the cp3. The Injector rails has a welded cap on the relief. The return line back of the head has a tee to the cp3 and to the tank.

Sometimes I think maybe I need to replumb my system, or get another fuel pump ( wanted get something like a airdog/fass, just cant afford that). I also wondered if I need to put a one way check valve after the fuel pump to maintain its prime after running and sitting for a moment? I also wanted to know more about the gear pump on the cp3, it has two allen heads on the ports, I have no idea if I really need this thing, because I looked up on google just for a cp3 pump it mostly never shows these kind of gear pump, just looks like a cap or cover the ones i been seeing online. I even tried adjusting the gear pump allen heads to see any difference made. I cant really tell sometimes but the filter on the engine area does seem empty at times when I undo one of the feed line with pump running. Should I get get a gear pump cover and remove the the I have on the cp3, should I replumb the system differently? I had a few Ideas maybe adding a surge tank, act as an revivor to make sure the water fuel separator filter is always full when there's fuel in the tank. I also noticed when the tank is low enough going at different angles on the road the fuel wasn't going into the water fuel separator at all. Maybe the water fuel separator is too high up (the unit inlet and outlet fittings is on the top of the fuel tank level, while the bottom of the filter is at the bottom of the tank level). Id imagine it work better by feeding the system if I placed the pump before the filter, or even flipping the water filter unit upside down when the inlet and outlet lines are at the lowest point (but I feel like doing these two things greatly affect the performance of the water and fuel separation performance.

Thanks in advance those who replies, I been having this issue forever. Its the one thing preventing calling this thing my reliable daily driver.
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1964 Chevy C10, Cummins ISB170, Allison 1000 5 speed, full float 9”, ECU Tune, 5/7” static drop
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If you go to quickserve you can see factory layout. First question is are you using the factory quick connect fittings? Do you have the factory check valve on the fuel exit on the back of cylinder head? This valve is need as cp3 can push fuel into the head. I would recommend putting a line on the rail to let the pressure relief valve work. The gear pump on the CP3 is required as it takes your 15 psi lift pump pressure and turns it into 73-189 psi at idle into the CP3. You should have a maximum of 29psi pressure drop across fuel filter. The FCA should ohm at 0.1-5 ohms, if not replace it. A check valve from your lift pump to your engine should be used directly after lift pump to keep prime, let lift pump run 30 seconds before starting.
I will need to make a fuel line diagram later and send to you. Hope this helps. Where is your ecm mounted? These are cooled by a fuel plate and you never mentioned it in the routing.
 

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1964 Chevy C10, Cummins ISB170, Allison 1000 5 speed, full float 9”, ECU Tune, 5/7” static drop
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211 Posts
Line route
Fuel tank
Water fuel separator
In top port of ecm fuel plate
Out bottom of ecm fuel plate
In top port of CP3 gear pump
Out bottom port cp3 gear pump
In fuel filter
Out fuel filter
In cp3 port near FCA
Out cp3 port above inlet port
In fuel filter head return line port.

From back of cylinder head
Come out with a check valve
T from outlet side a check valve to fuel rail return
Then take this to return on the factory filter head

factory filter head has one fuel inlet port, one fuel outlet, 2 inlet return ports and one outlet return port.
 

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Discussion Starter · #4 ·
If you go to quickserve you can see factory layout. First question is are you using the factory quick connect fittings? Do you have the factory check valve on the fuel exit on the back of cylinder head? This valve is need as cp3 can push fuel into the head. I would recommend putting a line on the rail to let the pressure relief valve work. The gear pump on the CP3 is required as it takes your 15 psi lift pump pressure and turns it into 73-189 psi at idle into the CP3. You should have a maximum of 29psi pressure drop across fuel filter. The FCA should ohm at 0.1-5 ohms, if not replace it. A check valve from your lift pump to your engine should be used directly after lift pump to keep prime, let lift pump run 30 seconds before starting.
I will need to make a fuel line diagram later and send to you. Hope this helps. Where is your ecm mounted? These are cooled by a fuel plate and you never mentioned it in the routing.
Line route
Fuel tank
Water fuel separator
In top port of ecm fuel plate
Out bottom of ecm fuel plate
In top port of CP3 gear pump
Out bottom port cp3 gear pump
In fuel filter
Out fuel filter
In cp3 port near FCA
Out cp3 port above inlet port
In fuel filter head return line port.

From back of cylinder head
Come out with a check valve
T from outlet side a check valve to fuel rail return
Then take this to return on the factory filter head

factory filter head has one fuel inlet port, one fuel outlet, 2 inlet return ports and one outlet return port.
It has been some times since you replied. I wanted thank you for your response. I bought a 10 an check valve, I was going to plumb it to the return system, but I put it after the lift pump to the cp3. I saw it doesnt loose pressure immediately "I bought a electric 0-100 fuel pressure unit with gauges. I discovered a few things with this set up, when the motor runs, I could actually turn off the eletric fuel pump while its running. The pump when before it run, it goes to 20 psi to 14-16 psi ( I wait at least 15-30 sec) before starting it up. It has been super reliable ever since placing a check valve after electric pump. I was going to place one on the back of the head line but i havent not done that yet. its all basilly open from cp3 back to he head and to the tank as it is now, also my rail pressure relief return is blocked off too.
 

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1964 Chevy C10, Cummins ISB170, Allison 1000 5 speed, full float 9”, ECU Tune, 5/7” static drop
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211 Posts
Glad to hear it’s running good. The rail pressure return is to save your cp3 and injectors, they are pricey. They are fun little engines. Anything else just post or PM. Thanks
 
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