Fuel Pump Help needed

My 47 with a 212 and an AC type AP numbered fuel pump is reading 1.5 psi while turning the motor over( so not running). The car when driving acts like it is fuel starving and stalls at low speed like coming to a stop The manual says 3.5 to 4.5psi is needed. Is that measurement running or non running as I have tested?

The manual mentions cleaning the screen which I assume is in the top of the glass sediment bowl. If the screen is clogged does that keep the psi reading low?  Or, does the 1.5 I'm reading tell me rebuild or new fuel pump?

Any help much appreciated.


  • You should have the 3.5 to 4.5 when ever the pump is pumping, engine turning over or running. Yes a clogged screen could do it, also if your flexible fuel line is collapsing when suction is applied.  The fuel pump could also be bad.  Good luck.
  • When bench testing the pump I'm getting the 3.5 to 4.5. When the pump is installed I'm getting .5 at best and it is not pulling any gas. I have an inline fuel filter mid way under the car with plenty of fuel flow. there are no obstructions in the line before entering the pump. This is the same pump that has been in the car running for 10 years.  Any Ideas?
  • When you pump it by hand you are getting full travel of the lever. So when in the car you are not getting full travel. Pump must be worn out somewhere inside. It can be taken apart and rebuilt if you can find a kit.  It is possible that the cam lob it runs on is worn, but not likely. Good luck.
  • I took it apart. The diaphram is like new. The input screen above the sediment jar was clean. Not sure what else could cause problems the pump is pretty simple. Sure hope it's not a worn cam. I guess pump replacement will tell.
  • Geoff
    Geoff Senior Contributor
    Is the spring intact?
  • Yes the spring appears and acts normal
  • Excuse me but maybe the lever sticking from the pump into the engine block might be under the lever that goes up and down instead of above it...sorry but I can't explain it better...the same thing can happen if you remove the oil pump and the lever isn't in the proper position cheers ken
  • Geoff
    Geoff Senior Contributor
    Could be crud stuck in a valve. 
  • ken1962 I think you are on to something here.  I again bench tested the pump after replacing the two fiber valves. Using a hose and a glass jar of gas I hand pumped it and it gushed gas like it should.

    So again I remounted the pump to the block cranked the motor and no fuel came out and less than .5 lbs pressure.

    Is there a trick to aligning the arm to the camshaft when mounting the pump.

    On other non flathead vehicles I have replaced fuel pumps and I recall having to put a fair amount of pressure on the pump when installing thereby compressing the arm while 
    bolting down the pump.  On this one only a small amount of pressure is needed to hold the pump to the block while bolting it down.

    Again this was a running vehicle that started fairly easy but stalled at slow speeds when the pump was removed.
  • Toddh
    Toddh Member
    You should be able to use a light and look into the block to see the fuel pump eccentric so you know where the FP arm needs to go. You’re correct that you should feel spring pressure when installing the pump.  
  • tough to look up inside without removing the inner fender. Tried using a mirror and a light didn't help much.  Put my finger up in the area where I think it contacts the cam shaft. Feels like a groove in the camshaft vs a lobe. Not sure what that means.
  • Lance Walker rebuilds this sort of pump and is a wealth of information on them.  If the diaphragm is in bad shape, it won't push much fuel.

    The amount of pressure needed to align the pump for mounting depends, in part, on the position of the eccentric on the cam.  Sometimes you luck out with this and the low area is aligned with the pump arm, but sometimes, and more often,  the pump is in need of a rebuild.
  • when bench testing, the pump arm has 1/2 in of free play before feeling the resistance of the diaphragm and again, during bench testing fuel is pumping what appears normal. When installed the pump acts like it never actuates beyond the 1/2 in of free play travel and moves no gas.
  • That 1/2 inch of free play is your problem

  • So if I understand correctly these fuel pumps should have no free play and the diaphragm should actuate from any movement of the arm?
  • There should be no free play.  If there is movement of the arm without resistance then there is a problem.
  • Thanks to all who responded sounds like it's time for a new pump
  • pseftoncomcastnet
    pseftoncomcastnet Senior Contributor
    edited April 2023
    More familiar with the stepdown engines, but do you have the right spacing with the gaskets between the pump and the block? On the stepdowns there is a spacer plus gasket or gaskets that the fuel pump bolts pass through and a correct distance between the block and pump. If you use too many gaskets and have too much distance, the arm will not be fully actuated by the cam

  • same pump and same 1/4 in metal spacer that was on the running motor for the last 10 plus years. I still don't think it's the pump but I have ordered one so we'll see.
  • The real problem is you thought the job would be done in 15 minutes however the Hudson gods thought otherwise. Major problems you put off take no time at all once they actually break yet small "yep this should be easy" take forever and always involve 1. Cuts to the fingers, 2. More swearing than talking, 3. Praying to the almighty, 4. Swearing at the almighty, 5. Swearing at your partner, dog, cat, interested onlookers. 6. Promises to the almighty you'll never ever try and do this again, 7. Resolve to sell the car, wash your hands of the problem or storm off slamming the door and breaking the hinges so that you have now 2 jobs to do ....coming back later you find you have put it together wrong, incomplete, used the wrong spring etc etc and curse yourself for being stupid ....look at the Hudson and say " I bloody well hate old cars" the next day saying to your partner "drove the Hudson this morning and boy was it a great drive, I certainly love having it around" The partner just hands you a coffee and says " the garage door is hanging off the hinge" you say " no problem fixed in 15 minutes" and it starts again .....
  • jjbubaboy
    jjbubaboy Senior Contributor
    edited April 2023
    Oh heck yeah Ken!!
    LMAO at that one!
    Showed it to the wife and said, " see I'm not the only one"!


  • Old Fogey UK
    Old Fogey UK Expert Adviser
    My own experience, Ken.
    Those Hudson Gods have it in for me every time I start a "simple" job !