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Thread: Fuel pressure

Forum to discuss Austin Healey Sports Cars

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    Jedi Trainee aero3113's Avatar
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    Fuel pressure

    My engine is set up with a fuel pressure regulator, but it didn't have a pressure gauge. I wanted to see what my fuel pressure is so I bought a gauge and installed it on the regulator. With the key in the on position the fuel pump turns on but I'm not seeing any pressure at the gauge?? How can this be?(engine runs fine) Shouldn't I see pressure at the gauge with the key on? I didn't start the engine today to see if there was any difference, raining today. This is on a Chevy 350.

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    Jedi Warrior roscoe's Avatar
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    Re: Fuel pressure

    I'm assuming your gage has a range of something like 0 to 10 psi and you are not using a 500 psi gage that might not be sensitive enough.
    Does your regulator have more than one port that can take a gage? Be sure your gage is on the down stream side of the regulator. Other than that I have nothing. It is possible that your fuel pressure is low but high enough to keep the float bowls full when running.
    Jon Robbins
    1956BN-2 (do it all yourself, you'll be glad you did)

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    Jedi Trainee aero3113's Avatar
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    Re: Fuel pressure

    Here’s a pic of how it’s installed. It’s possible it’s set too low to read.

    A2E16E59-7D13-4E65-8EA7-8504D08011F0.jpeg

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    Yoda Michael Oritt's Avatar
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    Re: Fuel pressure

    Aero--

    If the regulator is cranked all the way closed your fuel pump may still run continuously depending upon what kind it is as some of the Facets hammer on regardless of whether or not the engine is running. In any case you should set your fuel pressure regulator up with the engine running and at different rpm's. If at that point you have no indicated pressure you might have a bad gauge.
    Last edited by Michael Oritt; 12-16-2018 at 08:22 AM.

    Best--Michael Oritt
    1954 Austin-Healey 100 Le Mans
    1959 Elva MK IV Sports Racer
    1961 Ginetta G4

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    Re: Fuel pressure

    See the previous thread from 10 days ago:
    https://www.britishcarforum.com/bcf/...ator-questions

    I have a similar regulator setup with a Facet gold box pump. When the float bowls are full, the pump keeps running, but zero pressure shows on the gauge.

    I was loosening the 4 screws to bleed the pressure out, then starting the pump again to display the approximately 2 psi the regulator is set at. I could then take the car for a drive, during which no fuel problems, then observe the gauge displaying zero pressure like the picture above.

    I then timed 60 sec of flow into a gallon can and observed 27 gph (18 gph needed for BJ8).

    Gave up worrying about it as everything seems to be working properly and I've driven it 30 miles since then.
    Steve Gerow
    Altadena, CA, USA
    Maker of most complete Big Healey rear disc kit
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    Re: Fuel pressure

    Most float needle valves can only hold back up to about 7 lbs. Anything more than that is a good chance of pushing past the needle valves. That includes and American down draft carb or an English SU. Typical early, old school carbs operate on about 4 lbs.
    If fuel is weeping past the needle valves you might not see any pressure on a gauge.
    About TV Shows-
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    Obi Wan RAC68's Avatar
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    Re: Fuel pressure

    Hi All,

    I have noticed that modern (fuel injected) cars typically use high pressure pumps that continuously flow fuel to and from the engine. Pressure is maintained to supply a sufficient flow for engine combustion with excess flowing back to the tank. This seems to allow the pump to maintain a constant pressure without the generated resistance inherent in a stop and go operation. Although non-continuous running pumps, like our Healey's SUs, were designed for low pressure and stop and go operation. However, replacements this type of unit with a pump designed to operate continuously would require a bypass valve built within the single path pump to allow excess fuel from building pressure or have a fuel backup cause problems within the pump.

    I replaced the original pump in my TR7 with a continuous running electric pump a while back and this thread started me wondering what would happen if the bypass valve in it or a continuous running Facet pump installed on a Healey gets plugged or fails?

    Just a thought,
    Ray(64BJ8P1)

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    Re: Fuel pressure

    Quote Originally Posted by RAC68 View Post

    ...this thread started me wondering what would happen if the bypass valve in it or a continuous running Facet pump installed on a Healey gets plugged or fails?
    That's probably why the Facets specify a filter on the input side.
    Steve Gerow
    Altadena, CA, USA
    Maker of most complete Big Healey rear disc kit
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    Re: Fuel pressure

    Hi All,

    Good point Steve. That is probably why AC Delco also provided an input filter on my TR7's continuously running pump. I wonder if installing a return tank line on a more powerful continuously running pump supplying the correct fuel pressure and volume to the carburetors via a regulator would provide even greater reliability and performance? But then again, why go to all that trouble when the SU has been quite reliable and has satisfied my Healey's fuel requirement for the past 54 years.

    Ray(64BJ8P1)

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    Re: Fuel pressure

    Quote Originally Posted by RAC68 View Post
    ...I wonder if installing a return tank line on a more powerful continuously running pump supplying the correct fuel pressure and volume to the carburetors via a regulator would provide even greater reliability and performance? But then again, why go to all that trouble when the SU has been quite reliable and has satisfied my Healey's fuel requirement for the past 54 years.

    Ray(64BJ8P1)
    According to Des Hammill, such return line setups have been used by racers when the SU float bowls weren't keeping up with power requirements.

    In my case, I never had an SU pump; my car came with a West German plastic SU-style pump IIRC from Beck Arnley. When I started having delivery problems, I tossed it and went with the Facet, which has worked flawlessly for probably 18 years.
    Steve Gerow
    Altadena, CA, USA
    Maker of most complete Big Healey rear disc kit
    Check out my galleries:
    http://www.pbase.com/stevegerow


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    Re: Fuel pressure

    [QUOTE=steveg;1101044]According to Des Hammill, such return line setups have been used by racers when the SU float bowls weren't keeping up with power requirements.

    Aside from racing applications, some production cars, like the Datsun 240Zs, had the return line. I always understood it was not to increase fuel delivery/flow but rather to help fight vapor lock by having a constant supply of cool fuel from the tank replacing the 'cooked' fuel in the lines in the engine bay.

    For the last 25 years I have used Carter constant flow rotary pumps in the 2 to 4 psi range and no regulator with good results.

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    Re: Fuel pressure

    [QUOTE=red57;1101061]
    Quote Originally Posted by steveg View Post
    According to Des Hammill, such return line setups have been used by racers when the SU float bowls weren't keeping up with power requirements.

    Aside from racing applications, some production cars, like the Datsun 240Zs, had the return line. I always understood it was not to increase fuel delivery/flow but rather to help fight vapor lock by having a constant supply of cool fuel from the tank replacing the 'cooked' fuel in the lines in the engine bay.

    For the last 25 years I have used Carter constant flow rotary pumps in the 2 to 4 psi range and no regulator with good results.
    Absolutely correct regarding the return, its a common set up on race cars and those with high under bonnet temps to mitigate for vapour lock. Its a simple enough mod and works best if the return goes back to the tank rather than the pump suction side ( the large tank volume helps with cooling). Its easy to set the carb delivery pressure with a regulator but does need a pump that will tolerate constant running as the system constantly circulates fuel. I've had my best success with the facet pumps doing this as the SU's tend to have a lower (3 to 4 psi delivery for a given volume) so the loss with the tank return flow is hard to compensate for and maintain proper delivery pressure. I run 3.5 PSI from a facet pump via a malpassi regulator, its not best practice to leave the gauge in place as its offers more leak paths if something fails.

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    Yoda Michael Oritt's Avatar
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    Re: Fuel pressure

    I am with Red here and use the Carter 2040 pump on both my Ginetta G4 (Ford pre-crossflow 1498 cc) and Elva MK IV (Coventry Climax FWB 1460 cc) both of which are fitted with two Weber 45DCOE's. On both engines I have the fuel pressure gauge and adjuster that have been the subject of this string. They are set to approximately 4.5 psi pressure which holds from low to high rpm's, at least with no load as I have not observed the setting during dyno sessions.

    At one time I was experiencing fuel delivery problems with the Elva Courier--MGA 1622 with twin 1-3/4 SU's supplied by a Holly Blue (higher pressure pump) also regulated by the Holly fuel pressure adjuster and gauge. I considered doing a fuel return set-up but finally solved the issue by increasing fuel pressure beyond the recommended 4 psi to about 5 or a little more which solved the problem and never resulted in flooding, etc. A return line might ensure delivery but requires more fittings, may lead to increased temperature/less density of fuel, etc. and is best avoided if possible.

    In any case I have had absolutely no fuel delivery problems with the Carter pump and if and when the double headed SU on my Healey or the Holly on the Courier should break (before I can sell it) I will go over to the Carter as it has proven to be trouble-free for several years of racing conditions.

    Best--Michael Oritt
    1954 Austin-Healey 100 Le Mans
    1959 Elva MK IV Sports Racer
    1961 Ginetta G4

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    Obi Wan RAC68's Avatar
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    Re: Fuel pressure

    Hi All,

    That's really interesting and something I hadn't thought of. In our cars, I can easily see the reasoning for countering vapor lock. However, since return lines are common on modern fuel injected sedans that don't appear to have issues with under bonnet heat, I seem to remember someone mentioning it was present there for flow and to maintain constant pressure to each injector. Could it be that modern cars use this solution to counter a totally different issue then that which motivates Healey owners to implement a return line?.

    Ray(64BJ8P1)

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    Re: Fuel pressure

    With an electric pump in a street you can prevent vapor lock by mounting the pump at the rear of the car below the fuel tank rather than mounting it in the engine bay. This keeps engine heat away from the pump and pumps work better as pushers than pullers.
    Doug L.
    '64 Morris Mini Cooper-S 1275
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    Re: Fuel pressure

    I have a double-ended SU pump. If I need more flow, I can turn the other end on.
    John, BN4

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    Yoda Michael Oritt's Avatar
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    Re: Fuel pressure

    John--

    I have one as well--rebuilt/converted a few years' back by Dave DuBois--and have it wired so that I may select BETWEEN one motor or the other via an "On-Off-On" switch mounted through the bulkhead behind the driver's seat. I assume you have wired your pump so that one of the "On" positions connects both sides of the pump to a hot lead.

    Please correct me if I am wrong but--assuming proper motor operation and unimpeded flow--why would running both motors supply more fuel and/or more fuel pressure? I have always assumed that the limitation of flow and pressure is a function of the pump's design and operation and not a lack of power to it.

    Best--Michael Oritt
    1954 Austin-Healey 100 Le Mans
    1959 Elva MK IV Sports Racer
    1961 Ginetta G4

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    Re: Fuel pressure

    My 911 has two facet pumps either of which can be switched on . I just tried both on with the guage refitted as it's not something I usually do. I can confirm both on gives 3.5 psi as does one or the other. I didn't bother checking delivery rate. In neither case did the webers flood.
    The twin pumps is a nod to the race cars of the 70s which ran two pumps for reliability.
    Fuel injection systems require a constant output and high pressure. The system design often includes an accumulater to further reduce pump related pressure fluctuations. They usually run recirculation too. Very different to our relatively simple installations.
    In essence an SU pump will give 3 to 4 psi and doesnt really need a regulator as the float valves on SU cars can cope with that pressure.
    Double ended pumps may deliver more volume I'm sure some one will chime in with an answer. Recirculation is a good way to ameliorate for vapour lock if its a problem for you after all the usual heat protection has failed.

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    Yoda Michael Oritt's Avatar
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    Re: Fuel pressure

    Haasad--

    Though the double-headed pumps might be a good thing in a race application my understanding is that they were primarily fitted to cars with two fuel tanks, such as some of the Jags and, I believe, Aston-Martins, and that they were set up to select between tanks versus run simultaneously.

    Best--Michael Oritt
    1954 Austin-Healey 100 Le Mans
    1959 Elva MK IV Sports Racer
    1961 Ginetta G4

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    Obi Wan RAC68's Avatar
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    Re: Fuel pressure

    Hi All,

    Self regulating pumps, as the intermittent SU or possibly the continuously running Facet, were designed to maintain a max fuel delivery line pressure. If this is correct, adding pumps will not add additional line pressure but will only stimulate the self regulating internal function the pump employs.

    Also, the 2-headed SU pump uses 2 triggering heads to activate 2 solenoid coils on a single central pump chamber. The regulating function of the pump is to maintain a max fuel line pressure and is shared between the 2 halves of the pump. As a result, the pump would maintain the same max fuel line pressure whether running 1 or 2 halves simultaneously.

    Is my understanding correct?
    Ray(64BJ8P1)

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