FUEL PRESSURE

TOM-WA-
TOM-WA- Senior Contributor
edited November -1 in HUDSON
I just installed an inline fuel pressure gauge to monitor the fuel input to the carb from the pump...

Very strange when the car is first started I get a steady reading of about 6 PSI from the pump.. BUT WHEN THE CAR REACHES OPERATING TEMP THE PRESSURE DROPS OFF DRASTICALLY TO 0 PSI?

Any thoughts on this and could it be a reason why the car will NOT RUN and shuts down when I get to operating temp?


THANKS


TOM

Comments

  • GrimGreaser
    GrimGreaser Senior Contributor
    Running just the mechanical pump? Sounds like vapor lock is the culprit. Have the right spacers inbetween the pump and the block? 1/4" I believe. I made a spacer out of some pine, sealed good but still wasn't enough to keep the pump cool.
  • TwinH
    TwinH Senior Contributor
    Try putting a handful(or baggy full) of ice around the pump when you see the pressure
    dropping. If the ice brings the pressure back up your dealing with vapor lock.
  • RonS
    RonS Senior Contributor
    This is a mechanical pump, right? If your pressure drops like that, check for blockage in the tank or lines. I know it only when hot, but, connect the gauge, anyway, to the gas tank side of the pump in order to check your vacuum. If the reading is not above 6hg there is a blockage. I knew some one who put some additive in the gas filler and unknown to him the seal went in as well and floated around for years. We need to eliminate any chance it is blockage. Carry ICE WATER pour it slowly on the pump then see if the starvation goes away. Soak a old sock with ice water fold it and push it under the float bowl to keep the gas cooler there as well.Do the vacuum test first.RE Spacers: A/C installed two sleeves and two washers made of a fiber phonalic material between the bolts holding the fuel pump to the block. This was supposed to help keep engine heat from transfering to the pump. JEGS parts sells a 6" x14" mylar pad that fits nicely between the pump and exhaust manifold.
  • TOM-WA-
    TOM-WA- Senior Contributor
    Ron:

    Thanks for all your assistance.....I think that I have isolated the problem to Major Vapor Lock.....I ran the car up to temperature and drove it up the street until it stalled..I got it home immediately and poured cold water on the fuel pump and the pressure gauge immediately went from 0 back up to 6 psi.

    Now the issue is what to do about it.. This problem just surfaced in the past few weeks and I never have had it before running the same pump and configuration..Hell its only about 55 degrees outside also.


    Thanks,

    Tom
  • [Deleted User]
    [Deleted User]
    If this problem just recently started, Think back, is there any thing that you might have changed? If so that may have caused your problem, if You haven't changed anything, all can recomend is what I did to my '54 Hornet Special. I cut my line from the pump to the carburator and ran a rubber fuel line over to the inner fenderwell to a see thru in line filter then another rubber line to the carb. I know there are other ways but this has worked for Me and I have not vaporlocked in 5 years. Oh Yeah, I made a bracket to hold the filter in place.
    Bob Hickson
  • [Deleted User]
    [Deleted User]



    Here's how mine looks.
  • hudsonguy
    hudsonguy Senior Contributor
    One way to completely eliminate the vapor lock is to follow Walt's advice and run a return line from the front to the back. In my case it completely eliminated vapor lock, and that was a major problem with my car at one point. Granted it is rather involved to do it right, but it sure works well.

    55 degrees huh? It's supposed to near three digits in southern WI today, with high humidity, so I wish I was where you are! Good Luck
  • RonS
    RonS Senior Contributor
    I was wondering, did you use 1/4 steel line or rubber back to the fuel filler neck?
  • [Deleted User]
    [Deleted User]
    Walt here, use 1/4 inch steel brake lines, 2 five foot lenths and they have connections on each end so just get a coupler and join together. Attach with tie straps to the original fuel line on the right side inner rocker panel. If you install an AMC pump you can get away with it, but best to install an electric fuel pump also, for when the car sits longer than a week, today's gas dries out, so just turn on the pump, wait a minute, pump the pedal, and off she goes, not killing the battery. The complete story on how to install is in Walt's volume one tech tip book. Walt Mordenti
  • TOM-WA-
    TOM-WA- Senior Contributor
    Finally:

    Sometimes Less is better... I described the problem I was having and got LOTS AND LOTS of input...Obviously I considered all the options and based on what I read I thought that I had had figured out from the input that I was experiencing an strange case of VAPOR LOCK that just came out of the blue.

    I was all set to install an electrical fuel pump and just figured that for whatever reason VAPOR LOCK was the problem and I would live with it..

    Don't know why but I decided for some reason today to pull the fuel pump and put back on the old one that I had sitting around for years.

    Wellllllllllll.. LOOKS like that solved the problem..no loss of fuel pressure, no VAPOR LOCK and so far it's back to running like it had in the past.


    Sometimes we we create bigger problems when the issue is minor and was probably the very FIRST thing that we should have done.


    Thanks for all the assistance..


    TOM
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