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Fuel pressure overwhelming carb...

35Remmy

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Hey fellas, i did get my 363 stroker running (88 that was a 2.9L)....new in tank (low pressure unit), new rail mounted high psi pump....that all comes to a head at a Holley 12-845 fuel pressure regulator. Unfortunately, it will only bring the pressure down to around 10ish PSI...the Quick Fuel carb i am running calls for 5.5 psi...so, as a result, she runs, but i am getting SERIOUS fuel dilution in the oil. Serious as in i drained the oil and WAY more was in the drain pan than is supposed to be. (I am using Duff heavy duty mounts...they are bloc¹king the bung my engine builder welded into the pan for a dipstick....my luck)...in any case i believe I have 2 options...1) increase return line size...i believe it may be deadheading at this point and constricting flow, increasing fuel pressure....but...what do i do when i get to the tank, the quick-connect fittings on the fuel tank are a specific size...so increasing line size wont matter because once the fuel gets to the tank fittings, there is another restriction
.....2) Delete the high pressure frame mounted pump and just rely on the in-tank low pressure pump...but i dont know if it pushes enough to supply my engine/carb....carb is a 680CFM and HP is 500.
Any ideas would be greatly appreciated!!! Without this site and all of you guys over the last couple decades, i would not have been able to figure out a LOT of things.
 


85_Ranger4x4

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If the in tank can feed it now it should be able to feed it without the high pressure pump.
 

alwaysFlOoReD

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Delete the high pressure. Either the low pressure will keep up or it won't. At least you will know and it's fairly easy to do.
 

35Remmy

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Thanks for the replies...if it doesnt keep up, would you recommend replacing the in-tank pump with something rated with a higher flow or get rid of it altogether and mount an aftermarket pump in place of the high pressure pump along the frame rail?
 

35Remmy

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85 that does make sense since the low preasure is feeding the high pressure, besides the canister/reservoir in between the 2...would that be deleted as well?
 

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Put a return line in before the regulator. Than you can lower the regulator.

I had the same issue on my 79 bmw 320i when i put a weber on it
 

4x4prepper

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> that all comes to a head at a Holley 12-845 fuel pressure regulator.

I have a Holley regulator and I thought you picked the wrong one, right from Summit: " Thank you for your question. The Holley 12-845 will only work with low pressure fuel systems. They offer a 12-846 for high pressure fuel injection, but the top is different and the rebuild components are not interchangeable." This is for the <14 psi systems and drops it to 4.5-9.5 ish. You might have already destroyed this regulator.


Holley HP Billet Fuel Pressure Regulators 12-846

"Fuel Pressure Regulator, Inline, 15-65 psi Pressure Range, -8 AN O-ring Female Threads Inlet/Outlet, Each"

From having dealt with electric fuel pumps and from seeing others deal with them for reliability stand points, I would go with a mechanical fuel pump, but, you can always use the in tank pump to feed the mechanical pump, if the pump will be sitting higher then the gas tank in your conversion. I did that once on an Alfa Romeo 2.8L conversion. BUT, note that I shut the electric pump off once the engine was primed and running.
 

35Remmy

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Well, that would be my luck....i originally purchased it BASED on a customer review on Summit that said they were told they 845 is what he needed for the high pressure system after initially purchasing the wrong regulator.
Its also interesting that the IN/OUT connections are -8AN but the return is SMALLER, at -6AN....makes no sense to me...return line should never be smaller!!!
So now im at 3 options? Delete high pressure frame mounted pump and rely on low pressure in-tank pump, replace in- tank lower pressure pump with a higher pressure unit, or buy another regulator.
Just a thought, if I got back all of the money I have thrown away on this project in the last 10 years, I could have probably bought another project truck. Insanity. In any case, thank you for the response and the heads up I appreciate it!
 

35Remmy

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Oh, i forgot...I need to check on a mechanical as you recommended
 

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Oh, i forgot...I need to check on a mechanical as you recommended
98.3% chance it won't fit with the factory steering box if your belt drive even allows it.

No way I could get either style pump to fit my '85 even before I went with the Explorer belt drive.

I would just get the right regulator.
 

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Need to ask a couple questions....

is this truck a daily driver on roads and highways?

or is it a race only truck?

Why not eliminate the in tank pump all together and use a low pressure high volume electric pump mounted on the frame?

something like this?

 

rusty ol ranger

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Just curious....did you get one with a return line? I see holley offers both. I had a similar regulator on a 89 F250 with a 460 some dumped a 79 lincoln 460 in with a 650 edelbrock. The regulator was returnless and was taking fuel from the factory high pressure pump...any kind of low speed or extended idling would let it load up as the regulator wouldnt handle the pump.
 

35Remmy

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Angie, i am liking this idea, thanks for sending that link. Plenty affordable too....truck will only be used for fun, i.e.cruising and blasting around town.

Rusty...yes it has a return that is 1 size smaller than the supply (-8AN to 6-AN)....

85 Ranger...I am running an AGR Superpump (old GM/Ford style "ham can" shaped pump that turns the 35s with ZERO noise and zero effort...just had to have a new line made as the pump end is different threads than the Ford steering gear end....Im running March aluminum brackets...

Also, the 12-846 Holley says it is good down to 15 psi? My Quick Fuel carb has a 5.5psi recommendation...

As for going mechanical, MAN....id have to change the whole front dress from the heads forward...change waterpump, timing cover, fan, etc.
 

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that is the exact pump I am using on my truck. works great. a bit of noise, but no issues. it is wired direct from a cab switch, into an enertia switch. and if i want to kill it i have a ground on off switch also.

As for going mechanical, MAN....id have to change the whole front dress from the heads forward...change water pump, timing cover, fan, etc.


My guess is the off block mechanical pump would NOT fit .... unless you have chopped the frame to pieces and remodeled the steer box into an under frame or some type of magical steering by remote control. lol

cheers
 

alwaysFlOoReD

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I thought the return line is smaller because the engine uses some fuel...
 

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