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Big line question

Lone Watie
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Lone Watie

Lone Watie

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When I install my big line kit from FF to VP, and if I keep my pressure gauge tapped at the fuel filter test port, will the increased fuel line size result in more pressure at the VP inlet that I won't be able to see on my gauge because it's mounted at the fuel filter test port. Just curious. Thanks.

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flman

flman

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Agree with M73M, the line will be too short in length to have any pressure drop only a foot away. I have the OE line going from my OE filter housing, and I am getting 20+ PSI at the VP44 inlet, I am sure it would be a little higher at the filter housing, but at that short of a distance, only a very little bit higher. I might pick up a couple of banjo fittings and put the left over hose to use later?

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Mopar1973Man

Mopar1973Man

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If the test port is on the outlet side of the filter then you will not be able to measure the differenc between the FF and VP. If its on the inlet side thats a different story.

If you had a electric fuel pressure gauge and 2 senders you could hook up a sender in both port (with needle valves to protect the senders). But then wire the senders to a toggle switch in the pod (or anywhere you wanted) then be able to toggle between the 2 sender and see how plugged up your filter was. If the fuel pressure drop was more than 5 PSI then its time for a filter. But remembering the minimum pressure... Just a crazy dumb idea... But goes along with AH64ID...
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Lone Watie

Lone Watie

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Good info - now for the next question: If my pressure valve on the return line doesn't open until 14 PSI, but I'm rolling down the road with 13 PSI, what happens to the fuel in the VP which isn't used by the injectors, but does not return back to the tank because the valve is not open? I'm still learning this system, so please bear with my questions. Thanks. In response to AH64, I thought the whole idea was to measure pressure on clean side to give you a clean pressure reading with a clean filter, and when you see a pressure drop (in my case, filter is clean - just changed it couple weeks ago), the first culprit to check would be the filter before suspecting the lift pump. All the recommendations I've read stated to tap the pressure on the clean side, maybe I didn't understand your response, so just seeking further clarification - thanks again.

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flman

flman

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Good info - now for the next question: If my pressure valve on the return line doesn't open until 14 PSI, but I'm rolling down the road with 13 PSI, what happens to the fuel in the VP which isn't used by the injectors, but does not return back to the tank because the valve is not open? I'm still learning this system, so please bear with my questions. Thanks. In response to AH64, I thought the whole idea was to measure pressure on clean side to give you a clean pressure reading with a clean filter, and when you see a pressure drop (in my case, filter is clean - just changed it couple weeks ago), the first culprit to check would be the filter before suspecting the lift pump. All the recommendations I've read stated to tap the pressure on the clean side, maybe I didn't understand your response, so just seeking further clarification - thanks again.

I would think you would be still getting fuel return through the injector return lines at 13 PSI? I would suspect you would still be getting good VP cooling at that pressure?
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Mopar1973Man

Mopar1973Man

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Good info - now for the next question: If my pressure valve on the return line doesn't open until 14 PSI, but I'm rolling down the road with 13 PSI, what happens to the fuel in the VP which isn't used by the injectors, but does not return back to the tank because the valve is not open? I'm still learning this system, so please bear with my questions.

Nothing... There would be technically no flow... The injectors are not firing so there is no return... And the Overflow valve is closed... So the only fuel that would be moving is what little fuel there is bleeding past the 0.016 size hole in the overflow valve. Maybe that why I opt for the 15-17 range of pressure most of the time... At least then I know the overlfow valve is open...
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Mopar1973Man

Mopar1973Man

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So, nothing returns from the injectors? When does fuel get returned from the injectors? I may be ignorant, but there is a return line from them right? At least I know there is a Tee in the return line. Refresh my memory please.

I think I mis understood the last post... I was assuming coasting/deceleration conditions with <14 PSI of fuel pressure... (re-posted to clarify). If you coasting down hill or decelerating... There is no fuel pumped to the injectors if there was you would be accelerating or maintaining road speed. The injection pump is literally turned off. So there would be zero return from the line at the back of the head. The only time fuel returns from the rail is when the injectors are fired (bleed off pressure) is drained to the return rail. This small bit fuel is the remain of fired injectors and bleeds off the line pressure and drain into the return line. So since coasting/deceleration tends to shutdown the VP44 from firing the injectors that means that return rail will be dry and if the fuel pressure is below 14 PSI so is the overflow return line. (except what will ooze out of the 0.16" inch bleed hole...)
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Mopar1973Man

Mopar1973Man

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I'm not sure... But there has been talk in the past that the VP44 has a small vane pump in it but how much pressure, suction, volume it capable of producing is totally unknown to me. But from what I've learned so far is if the truck is coasting then the injectors shutdown (VP44 doesn't produce line pressure). So this means that the overflow valve must be venting... But theat hard to measure return volume while cruising down the road... So maybe in your case the overflow valve is a bit weak opening at 13 PSI and venting back to the tank... Or that little vane pump is giving it that extra 1 PSI to open the overflow valve... (speculation)

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rburks

rburks

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Well' Give this a thought, If the overflow valve on the return side is stuck open or partially stuck open then the fuel pressure would only build up & hold as long as there was pressure comming in...When you are idling or deaccelerating very little pressure is flowing thru the VP Pump and with the stuck overflow valve there can't be any pressure because it is being released as quick as it comes in I mean i could be wrong so take for what its worth ...sound logical though

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rburks

rburks

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Good info - now for the next question: If my pressure valve on the return line doesn't open until 14 PSI, but I'm rolling down the road with 13 PSI, what happens to the fuel in the VP which isn't used by the injectors, but does not return back to the tank because the valve is not open? I'm still learning this system, so please bear with my questions. In response to AH64, I thought the whole idea was to measure pressure on clean side to give you a clean pressure reading with a clean filter, and when you see a pressure drop (in my case, filter is clean - just changed it couple weeks ago), the first culprit to check would be the filter before suspecting the lift pump. All the recommendations I've read stated to tap the pressure on the clean side, maybe I didn't understand your response, so just seeking further clarification - thanks again.

"I would think Nothing,.. it sets there until it builds 14psi and then opens & closes in a nano second, will be very hard to actually see on anolog gauge when only falling back 1-2psi.." with a lift pump thats shot it may not open at all which means 0 return... = wiped-out VP pump
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