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Air in Fuel Line problems

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My 2000 Dodge 24v (with 540k mi) started to run rough then stopped.  Thought it was the VP44.  Installed clear tubing between fuel filter canister and VP44, purged air and got running.  Like someone flipped a switch, LOTS of air showed up in clear tubing, engine faltered and I shut it down.  Put clear line between Raptor RP-100 and tank: purged air, got running, no air, then engine shut down on its own.  Put clear tubing on pressure side of RP-100 with additional clear tubing back between filter canister and VP44: tiny, tiny bubbles by RP-100 and then, like someone flipped a switch, aquarium aerator bubbles after fuel filter canister.  Replaced canister top, put new "O" rings on water/fuel separator with no change.  Not seeing evidence of leaking between RP-100 and fuel canister.  Fuel supply fitting to the fuel filter canister was pretty snug.

 

Any suggestions other places air may be getting in?  Is there a replaceable seal at the fuel heater?

 

Thanks!

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Mopar1973Man

Mopar1973Man

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Then the Raptor series is known for the issues of the quick connectors that they use. The seal will not prevent air from being sucked in on the suction side of the pump. So a quick test is to disconnect the suction line using clean thick axle grease then coat the the nipple with grease on the pump and side the connector back on and it should seal for a temporary time. If it does you need to convert over to the old school JIC fittings and push lock fittings that are all steel fittings. This would stop this issue. The other rare one is the pick up tube in the sender has cracked and sucking air when the fuel level drops below the crack in the plastic tubing. 

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The fittings on the RP-100 pump look like the female fitting on the rear (inlet) side of the fuel filter canister...which to me look like the pics of JIC fittings on McMaster-Carr's web site - but I'm not fitting savy.  The canister fitting has a thread pitch of 1.50 but didn't measure the fittings on the pump (yet). 

 

Since I had clear tubing in two locations: between the VP44 and fuel filter canister showing lots of air in the line and between the RP-100 and fuel filter canister (with tiny bubbles) are there other likely entry points?  Is running new fuel line between the fuel filter canister and RP-100 worth it?  Maybe a little crack in the steel tubing fuel line?

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So I put in new fuel line between the RP-100 and fuel filter canister...glad I did it but no improvement.

 

After chatting with a mechanic buddy, and thinking more it's the lift pump (but "...probably more than one nail in the tire" as said by Doug at Blue Chip Diesel) called for warranty support on the lift pump.  They wanted to see a fuel pressure gauge on the outflow of the lift pump and direct 12v and ground wired to the pump.  So that was this weekend. 

 

Saturday, for a short period of time, the pump was delivering 18-20 PSI, drawing 5.7 amps (Fluke 325) and no air in the clear tubing between the fuel filter canister and VP44.  Then pressure dropped along with current to where no pressure was being delivered, current measured 0.5 amps concurrent with lots of air in the clear tubing.

 

My original RP-100 was put into service in 2009.  Current pump I replaced on warranty in January 2014.  So here is hoping the new lift pump gets me going.

Fuel pressure gauge T & line volt to lift pump_2023-10-01.pdf

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JAG1

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On 9/13/2023 at 10:52 AM, Mopar1973Man said:

Then the Raptor series is known for the issues of the quick connectors that they use. The seal will not prevent air from being sucked in on the suction side of the pump. So a quick test is to disconnect the suction line using clean thick axle grease then coat the the nipple with grease on the pump and side the connector back on and it should seal for a temporary time. If it does you need to convert over to the old school JIC fittings and push lock fittings that are all steel fittings. This would stop this issue. The other rare one is the pick up tube in the sender has cracked and sucking air when the fuel level drops below the crack in the plastic tubing. 

I cut those quick connects off and used barbed fittings and clamps. It works great.

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Warranty replacement RP-100 is installed and the Cummins is back to life!  No issues through test drives.  Presently, I have the lift pump pressure set at 19 PSI during idle (as measured at the VP44 inlet fuel banjo bolt); full throttle under load (accelerating to freeway speed) pressure drops to 11 PSI...such hard throttle is almost never used.

 

I'm still curious about the air in the clear tubing I saw.  Maybe the lift pump was the significant contributor after all - in addition to failing to pump fuel?

 

So for now, the not-running-problem and associated air-in-fuel-line is solved. 

 

Getting into the weeds a bit: apparently, the original lift pump supplied by PureFlow Technologies was done through their heavy duty (and medium duty?) truck business.  Some time later (probably after my 2014 warranty replacement) the light duty side split off.  So there was a bit of back and forth where the heavy duty folks (the phone number on my 2014 warranty replacement invoice) sent me to the light duty folks who couldn't find my paperwork in their system...because they never had it.  Light duty folks sent me back to the heavy duty side where my warranty claim (transaction was found in their system - but my saving the paperwork was very helpful) was processed quickly.

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Mopar1973Man

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Will admit that the 3rd Gen Pumps had issues with the shaft seals and bearing. Once fuel starts to seep out of the seal a little bit, the fuel will wash out the bearing eventually. Now the 4th Gen pumps have been upgraded with dual bearings and upgraded seals. I'm currently running a 4G AirDog 165 pump on my 150 GPH base with no issues. 

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