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Topic: Replacing An In-tank Fuel Pump With An In-line Pump (Read 574 times) previous topic - next topic

Replacing An In-tank Fuel Pump With An In-line Pump

As a follow-up to my earlier query re. the fuel pump relay, all the electrics checked out and I am now blaming the fuel pump for my starting problem.  I have managed to start the engine but the fuel pressure maxed out at only 3.5 psi on the pressure regulator gauge.
 The fuel lines are clear and she ticks over nicely.  However, whenever I disconnect a fuel line (engine off) there is no fuel in there so it must be draining back into the tank.  I am assuming that the pump cannot produce sufficient pressure and I wasn't cranking long enough to get fuel to the engine.

I have dropped the fuel tank (if you have never tried this at home then I thoroughly recommend it to all masochists) and removed the pump.  However, I am considering installing an in-line pump instead of replacing the in-tank one.  I intend talking to a Holley tech when I can get through but wondered if anyone else has done this and how they got on.

My engine is a carbureted Ford 460 7.5 litres.  I believe the H.P. is between 212/220 but have been unable to confirm this.
Marty Day
1986 GV 36'

Re: Replacing An In-tank Fuel Pump With An In-line Pump

Reply #1
I had one on my Cat. It was located near the primary filter and worked for the 9 years I owned it. They are relatively cheap and worth the try. It has to be rated for fuel injection.
1994 U280, Build 4490
Deming, NM.

Re: Replacing An In-tank Fuel Pump With An In-line Pump

Reply #2
 I use Facet pumps. Best source is Aircraft Spruce.  They make a 3 or 7PSI, mounted at the back use the 7 .  I always use the little pre filter and an extra pre filter  into the pump. If you have  metal fuel lines, use an additional filter as close to the carb as you can .
 When you fit  the new pump, make sure the inlet line is clear into the tank and reaches near the bottom .  Often the inlet screen will plug up , allowing to start and run for a few minutes and then stops.
 7psi at the pump is not 7 psi at the engine ; http://pressureconnections.jhmservices.net/site/Downloads/Hose_Pressure_Drop_Chart.pdf

Re: Replacing An In-tank Fuel Pump With An In-line Pump

Reply #3
The pump was located in the tank to eliminating vapor locking when it is hot out.

If you have more then 3.5 psi you might run the risk of overpowering your carb floats and putting excess fuel into the motor our out the vent tubes.

Unless engine has not been used for an long time and the fuel evaporated out of the bowls you should have enough fuel in the bowls to start the motor. 

It is also possible that your accelerator pump is leaking and not having any fuel in them when you go and start the engine.

My 2 cents is,  if you have not done it yet a carb rebuild needs to be done first before making other changes.
2014 ih45  (4th Foretravel owned)
 1997 36' U295 Sold in 2020, owned for 19 years
  U240 36' Sold to insurance company after melting in garage fire
    33' Foretravel on Dodge Chassis  Sold very long time ago

Re: Replacing An In-tank Fuel Pump With An In-line Pump

Reply #4
Had a lot of fuel pump problems with our Ford 460's in the 80's, finally found the cure was a Rotary Fuel Pump made by Carter.
1988  40' Grand Villa Cat 3208t

Re: Replacing An In-tank Fuel Pump With An In-line Pump

Reply #5
Thanks to all for responding.

Holley recommends 6 to 7 psi (ideally 6.5) for the carb.  Amongst other things, low pressure lowers the boiling point of gasoline which can lead to vapour lock.  I was told that as long as the fuel lines are airtight then vapour lock is unlikely to occur except under extreme circumstances.

I too was surprised that the engine would not start from residual fuel in the float chambers but that was some months ago and I cannot remember if it fired up at all.  My companion Mr. Alzheimer is no help either.  However, I am pretty sure that my pump needs replacing and I think I shall try an in-line pump for ease of access in the future.  I shall probably buy a Holley 12-430 which provides 33 GPH at 9 - 11.5 psi which will be regulated down to approximately 6.5 psi.  This pump can be situated up to 10 feet from the fuel intake but I shall position it much closer.  It also has a replaceable filter in a clear bowl which should be useful.  I already have another filter positioned before the pressure regulator.

Fingers crossed!
Marty Day
1986 GV 36'

Re: Replacing An In-tank Fuel Pump With An In-line Pump

Reply #6
Aircraft Spruce is a good source but you pay list price for the Facet pumps. I replaced the Facet on our plane last year from either Chief or Aircraft Spruce.

This ebay site has lots of Facets as well as clones. For a motorhome, a clone will do the job nicely and at about $30 delivered, is about one third the price. facet fuel pumps | eBay

I like the longer cylinder shaped pumps. I've had the square type start leaking so I can't recommend them. Our Foretravel's diesel generator has the cylinder shaped pump but I think the later models went to the square type.

With pumps that look the same, several pressures and GPMs are available so check the specs before ordering. Check the recommended pressure for your carb because too much pressure will cause fuel to go past the needle and seat on the float. Don't think I would go over 7 psi. It is a long run from the back to the front of the coach but with no fuel flowing but the key on, the static fuel pressure at the carb will quickly build to the rated pressure for the pump. A new needle and seat for the carb is never a bad idea.

In your cased, Holly recommends 7 psi max with around 4 psi available to the carb at full throttle. Here is a PDF of a Holly and the adjustments, etc: https://documents.holley.com/199r7923-2rev2.pdf . Lots of online info on Holly carbs.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Replacing An In-tank Fuel Pump With An In-line Pump

Reply #7
The power valve in your Ford holly carb could be bad which will let the fuel to drain out of the bowl creating a hard start condition.
previous 1984 35 ft ORED 250 HP 3208 Cat       
previous 1998 40 ft U295 CAI 325 hp Cummins
previous 2003 40 Ft u320 build #6140 450 Cummins M11.                                                         
1999 Mazda Miata
Ron, Nancy, Tipper the cat, Max The dog
1997 U 270 36 ft build number 5174 8.3 Cummins

Re: Replacing An In-tank Fuel Pump With An In-line Pump

Reply #8
Thanks to all for responding.

Holley recommends 6 to 7 psi (ideally 6.5) for the carb.  Amongst other things, low pressure lowers the boiling point of gasoline which can lead to vapour lock.  I was told that as long as the fuel lines are airtight then vapour lock is unlikely to occur except under extreme circumstances.


Fingers crossed!

I suggest trying another in-tank fuel pump.  You already have the tank out, and you have your choice of pumps to install if you're leery of using an OEM style pump.  I have a lot of experience with a 1941 Mercury with the pump located on the top of the engine, and we finally had to stop participating in parades altogether due to vapor lock problems.  I know you'll install your new external pump near the tank but in the tank, at the bottom of all that fuel is the best practice.

My previous motorhome was built on the Chevy P30 chassis with the 7.4L/454 Cu.In. engine and it had both the engine driven pump and an in-tank electric pump.
1992 Foretravel Grand Villa
U225 SBID Build No. 4134
1986 Rockwood Driftwood
1968 S.I.A.T.A. Spring
1962 Studebaker Lark
1986 Honda VF700C
1983 Honda VF750C
Charlie, the Dog was broken out of jail 24 Oct 2023
N1RPN
AA1OH (H)e who must be obeyed.

Re: Replacing An In-tank Fuel Pump With An In-line Pump

Reply #9
Thank you all so much for your suggestions. There are so many different routes to choose from.

I just do not fancy having to drop the tank again for any reason so I shall probably proceed with an in-line pump and offer regular sacrifices to the god of vapour locks.  Although that may change.......

I have received a pump from Holley after talking to a tech there.  He said the pump - p/n 12-430 - should be suitable for my needs.  In the description it states that the pump has a dry-lift capacity of 120".  More than adequate.  However, in the installation instructions, it states that the pump must be positioned between 60-120 vertical inches above the tank bottom i.e. somewhere between the top of the microwave and a pole on the roof!  I am awaiting a written response from Holley.

Mike: this pump has both Holley and Facet written on the box.

They say that ignorance is bliss but I am not so sure.
Marty Day
1986 GV 36'

Re: Replacing An In-tank Fuel Pump With An In-line Pump

Reply #10
Marty, I think you are missing an opportunity to save yourself a lot of grief in the future.  When your coach was built, gasoline did not have ethanol added to it.  The term "vapor lock" is as old as the internal combustion engine and had to do more with gasoline vaporizing in the fuel lines due to proximity to exhaust and engine heat. 

Today the real problem is not "vapor lock" but technically it's "pump cavitation", due to the much lower vaporization point of alcohol.  Once fuel was exclusively mixed with 10% alcohol, the conventional carbureted engine became practically doomed, as atomization at the carb jets is drastically reduced as well.  Unless you can get the pump into the tank liquid level, you must be pulling vacuum on the fuel coming out of lines coming out of the tank, and it will drop the vaporization relative pressure to the point it will literally boil in the lines, and cavitate the pump, regardless of whether it's engine driven or electric.  Add high ambient temperatures and hot road surfaces, and you'll eventually be on the side of the road.  BTDT a lot with my old GMCMH, even after I added a booster pump and converted it to throttle body FI.  Adding in tank pumps eradicated any vapor lock issues for 10 years. 

Today's fuels are almost exclusively laden with alcohol (or "corn" as I like to call it), and it's becoming increasingly more difficult to find alcohol free gas, although if you want to spend the extra bucks for hard to find premium unleaded alcohol free for the foreseeable future, you will probably be okay.

Here's a link to the chemistry:  Bioethanol: Bioethanol VS Gasoline

I'd definitely replace the in-tank pump and add a facet booster for a backup if you want.  Woody.
2001 4010 U320 build #5865 "Bluto-d-Bus" since 09/18
2006 Honda Element ESP Toad
Full timing since 2016 in Western MT
Copilot: Sitka
1975 GMC 260 Avion: sold

Re: Replacing An In-tank Fuel Pump With An In-line Pump

Reply #11
The power valve in your Ford holly carb could be bad which will let the fuel to drain out of the bowl creating a hard start condition.
I forgot about the power valve.  Easy to tell if bad after removing it.
2014 ih45  (4th Foretravel owned)
 1997 36' U295 Sold in 2020, owned for 19 years
  U240 36' Sold to insurance company after melting in garage fire
    33' Foretravel on Dodge Chassis  Sold very long time ago

Re: Replacing An In-tank Fuel Pump With An In-line Pump

Reply #12
The bad thing about the power valve is if the engine backfires it will blow the power valve again. I used to have a list of what gaskets were needed and the power valve part number. That was over 20 years ago so don't know what happened to the list of course Ford probably don't have those parts anymore.
previous 1984 35 ft ORED 250 HP 3208 Cat       
previous 1998 40 ft U295 CAI 325 hp Cummins
previous 2003 40 Ft u320 build #6140 450 Cummins M11.                                                         
1999 Mazda Miata
Ron, Nancy, Tipper the cat, Max The dog
1997 U 270 36 ft build number 5174 8.3 Cummins