QuestionQUESTION: Brad - I have a '31 Chev (original condition) with a fuel pump that doesn't pump. When it stopped working, I removed the top and found that the diaphragm was ruptured. I replaced the diaphragm and the pump still did not work. I replaced both springs and seats (new parts) that put pressure on the diaphragm, but still no luck. I examined the small springs and hexagonal fiber seals on top of the pump and believe them to be in good order. I'm certain that the little springs were in the proper position when I replaced the two valve cap screws. I blew the fuel line out to the tank (many bubbles). Still no luck. I appreciate any ideas that you may have, I'm to stubborn (cheap) to buy a professionally rebuilt pump. Thanks..., JTB
ANSWER: Ok, here is how I would go about checking the fuel pump. Disconnect the inlet line from the pump and attach a vacuum gauge to the pump. Crank the engine and the gauge should read close to 11 inches of vacuum. If it read pressure then the check valves in the pump are reversed. If it read close to 11 inches of vacuum, disconnect the vacuum gauge and attach a pressure gauge, usually a vacuum gauge will also read low pressure, to the outlet side of the pump, crank again and you should see about 3 PSI. If the pressures are OK, then reconnect the inlet side of the pump and go back to the tank. Disconnect the fuel line at the tank, reconnect the vacuum gauge to the line and crank again. If the vacuum is not the same as it was at the pump then you have a small pin hole some where in the line between the tank and the pump. I usually gab a roll of flex (rubber) fuel line off the shelf, connect one end to the inlet side of the pump and the other I drop into the tank, or a five gallon can of gas. The crank and see if the pump will pump fuel. If not then I have a problem with the pump or the cam that drives the pump in the engine is worn enough that the pump will not work. Remember that the cam moves the rocker arm and the action of the cam pulls the diaphragm down against spring pressure creating a vacuum that draws the fuel from the tank. When the car goes over TDC the pressure of the spring under the diaphragm is what pushes the fuel to the carburetor. Let me know what happens.
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QUESTION: Brad - Thanks for the prompt response to my question. I'm a little late in replying, just came into a borrowed vacuum/pressure gauge this AM. First measurement attempt gave zero reading at both ends. I reversed the check valves and got zero vacuum IN and a very very small vacuum reading OUT. I'm fairly certain the original check valve setup was correct, every picture I've seen of this pump shows the domed cap at the exit and the flat cap at the inlet. It seems that the new diaphragm just isn't doing it's job, although I took the top off the pump, cranked and observed the diaphragm undulate up and down at least 3/8 inch (eyeball measurement), which seemed to exonerate the cam lobe. I've got several cores and partial cores so unless you have another suggestion I think I'll replace the large sheetmetal washers securing the diaphragm (possible leak source?) with the more robust ones I find in the other cores. Failing that, I guess I'll attempt to rebuild one of the other cores using the new parts and gaskets I bought for the troublesome pump. Thanks again..., Jere Brunton
ANSWER: I might be a little suspect of the check valves.
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QUESTION: I examined the fiber seals and found them to be undamaged and I cleaned the seats thoroughly with Berryman's and Q-tips. I reassembled and poked the fiber seals lightly from the underside with a tooth pick and they definitely don't stick. Still no vacuum/pressure reading. Is there any check I can make to assure that they're working properly? Just curious, remembering back to the original failure indication (ruptured diaphragm), do you suppose that a check valve malfunction could have contributed to that rupture? I hate to leave the challenge unanswered, but at this stage stage I think we may be beating a dead horse. Let me know if you have a favored vintage part supplier. Thanks again..., JTB
AnswerOK, you are really jogging the old gray matter memory bank. I used to check those check valves by turning the pump body upside down so that I could pour a little gasoline into the cavity and see if in fact the discs were seated properly and hold the fluid from leaking. Those fiber discs will warp and then not completely seal. If you have no vacuum/pressure there are only four things that it can be: 1. the diaphragm is leaking. 2. The check valves are not seating. 3. The cam is worn or the arm is not hooked into the slot in the diaphragm shaft. 4. The housing is porous or warped not making a good seal around the outer rim of the diaphragm. I have no favorite vendors and I usually look in my latest issue of Hemmings for a supplier.
