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Discussion Starter · #1 · (Edited)
Diesel fuel is not getting to the filter, I suspect the “pressure lift pump” is not working. Any thoughts on how to correct the problem?
 

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My lift Pump does not seem to be drowing any fuil. ...
I have no idea what you are trying to say. Please restate the question (and check the spelling before posting the reply)
 

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Discussion Starter · #3 ·
I have no idea what you are trying to say. Please restate the question (and check the spelling before posting the reply)
Diesel fuel is not getting to the filter, I suspect the “pressure lift pump” is not working. Any thoughts on how to correct the problem?
 

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What type of lift pump do you have?
By no fuel, is it not running or was the filter part empty when changing?
Cheers Steve
 

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Discussion Starter · #5 ·
The lift pump is for a P7100, first start in over 3yrs. Fuel filter is full of diesel and the P-pump is delivering diesel to the injectors. Engine runs using aerosol starting fluid. But if I stop spraying the aerosol the engine will stop running in short order. As near as I can determine the lift pump is not sucking diesel from the gas tank & or delivering fuel to the filter.
 

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If the fuel filter is full then the lift pump must be delivering it there. If by chance the lift pump was bad it is easy to replace. You could have air in the fuel lines. Have you bled the injectors to be sure of that. Is the fuel shut down solenoid on the injection pump working correctly. If not, no fuel can get into the injection pump. On the P7100, you can disconnect the solenoid and operate the arm manually. That is an item that would have high probability. There are a few other lesser possible causes. The overflow valve on the injection pump could be stuck open and venting all the fuel back to the tank. Having sat for 3 years there could be parts in the pump that are gummed up. My bet would be check the shut down solenoid.
 

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Those lift pumps have a filter screen in the suction.
This is another case of where a fuel pressure gauge comes in handy.
Disconnect the line after the lift pump and pump the lift pump and see what fuel comes out and/or hit it with the Ether and see if fuel is pumping.
Cheers Steve
 

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Plugged up fuel filter?
 

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Discussion Starter · #9 ·
If the fuel filter is full then the lift pump must be delivering it there. If by chance the lift pump was bad it is easy to replace. You could have air in the fuel lines. Have you bled the injectors to be sure of that. Is the fuel shut down solenoid on the injection pump working correctly. If not, no fuel can get into the injection pump. On the P7100, you can disconnect the solenoid and operate the arm manually. That is an item that would have high probability. There are a few other lesser possible causes. The overflow valve on the injection pump could be stuck open and venting all the fuel back to the tank. Having sat for 3 years there could be parts in the pump that are gummed up. My bet would be check the shut down solenoid.
Well I messed around with the in-line pump today; by disconnecting the "inline pump fuel line" to the filter I was able to get fuel past the pump and then after reconnecting the fuel line I was able to get fuel to the Injection pump, she then started right up. I guess there was proble air in the lines. I ran the motor for +/- 20 Seconds and the return line discharged perhaps 2 quarts of fuel in that 20 seconds; Does that seem to be normal? Or perhaps I should look at the overflow valve? The intake line from the gas tank is 1/2", maybe that's to big?
 

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The 1/2" feed line isn't too big. No problem there. 2 quarts of fuel in 20 seconds does seem a bit high. That would be circulating 90 gallons per hour back to the tank. The pump does send excess fuel to the injectors which is used to cool them. What fuel that comes to the pump and not used is routed back to the tank via the overflow valve. You have 2 return lines in the system, one from the injectors and one from the pump which join into a single line. The issue with the overflow valve is there is a spring that gets weak and sends too much fuel back to the tank. Those valves are not horribly expensive and very easy to replace. There are also adjustable aftermarket models which you hear mixed opinions about. Below is a drawing of the valve's location.
131168
 

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Discussion Starter · #11 ·
Thanks Charles, Is there a part # for the spring or for the overflow valve itself?
 

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Discussion Starter · #12 ·
The 1/2" feed line isn't too big. No problem there. 2 quarts of fuel in 20 seconds does seem a bit high. That would be circulating 90 gallons per hour back to the tank. The pump does send excess fuel to the injectors which is used to cool them. What fuel that comes to the pump and not used is routed back to the tank via the overflow valve. You have 2 return lines in the system, one from the injectors and one from the pump which join into a single line. The issue with the overflow valve is there is a spring that gets weak and sends too much fuel back to the tank. Those valves are not horribly expensive and very easy to replace. There are also adjustable aftermarket models which you hear mixed opinions about. Below is a drawing of the valve's location.
Charles, What is the proper amount of Fuel return per minute
 

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OK, I found some test numbers on the pump system for the P7100. The Carter lift pump on these engines is rated at 52.8 gallons/hour max so you number wouldn't be possible. Can't return 90 when the pump will only pump 52.8. Cummins shows a rate of 31 gallons/hour at idle. At idle speed of 800 RPM, actual tests the pump flowed .315 gallons/minute or 18.9 gallons/hour which is about 2.5 pints so in 20 seconds it would be .105 gallons or .84 pint. That is total flow so you'd have to take away what is burned in the injection process which isn't much. At idle the 4bt will burn roughly .22 gallons/hour or .0012 gallons in 20 seconds. That's a little under 1 teaspoon. Those numbers are a little rough but out of .84 pints circulated you would burn roughly a teaspoon in 20 seconds. Your 2 quart return is physically impossible and should have been closer to 1 pint or a bit less.
 
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