Fuel Pump Issue |
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hcpcjj
Member Joined: 01 July 2010 Location: Charleston, WV Status: Offline Points: 395 |
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Posted: 10 Mar. 2016 at 4:45pm |
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When I last parked the Jeep (46 CJ2a) it was facing uphill. Another problem (which I think I have figured out) was allowing the fuel to bleed back into the tank after the engine was shut off, leaving the glass bowl on the pump & filter dry.
When trying to start the Jeep yesterday, I could not get fuel to the pump. This is a new pump, but I had another known good pump and put it on. Same issue. I can blow through the line from the pump back to the tank. It is all clear. The lines are all new anyway. The same issue with the cap off, so I know it's not a venting issue. The tank has approx. 6 gallons in it. I can apply pressure at the tank opening and get fuel to the pump, which then pumps it up to the filter & carb at which point it will stay running. I guess the question is, should a good pump be able to pump from the tank, even if the lines are dry?
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RSR_MK
Member Sponsor Member Joined: 22 May 2009 Location: Cabool Mo Status: Offline Points: 657 |
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Yes, a good pump will self prime. I would check for air leaks between the pump and tank.
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hcpcjj
Member Joined: 01 July 2010 Location: Charleston, WV Status: Offline Points: 395 |
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No air or fuel leaks that I can find.
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cpt logger
Member Joined: 23 Sep. 2012 Location: Western Colorad Status: Offline Points: 3022 |
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Do you have a glass bowl either on the pump or on the fuel filter? If so, do you have a lot of air bubbles with the engine running?
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hcpcjj
Member Joined: 01 July 2010 Location: Charleston, WV Status: Offline Points: 395 |
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Glass bowl on the pump and clear filter. I've not noticed any air in either while the engine is running, and it runs well. The only issue that I have (and I believe it is a problem with the Solex carb), is that after the engine is shut off - all of the fuel bleeds back into the tank. I'm waiting on a float for my Carter rebuild, so hopefully it will take care of the issue. I initially thought it was the fuel pump, but new pump did the exact same thing.
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RSR_MK
Member Sponsor Member Joined: 22 May 2009 Location: Cabool Mo Status: Offline Points: 657 |
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Your fuel pump has an inlet and outlet check valve. Fuel should not run back from the Carb or back to the tank. Its not likely both pumps would have bad checks but it is possible.
If you can not pump fuel from the tank with a new pump but can "push" it to the pump with pressure it is either a bad check valve in the pump or air is getting in the line between the pump and tank. It may not leak fuel. I would check my connections between the tank and pump. |
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hcpcjj
Member Joined: 01 July 2010 Location: Charleston, WV Status: Offline Points: 395 |
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I just capped the fuel pump end of the line, and put a vacuum pump on the tank end. I can pull & hold vacuum - so no air leaks. I went ahead & put new brass fittings on the pump itself, but I still have the same issue. I assumed that the bleed back was caused by a needle valve issue in the carburetor, allowing fuel to flow back into the lines, but from what you're saying, the fuel pump shouldn't allow the fuel to bleed back into the tank - so you think 2 bad fuel pumps? I can actually see air bubbles forming in the filter & fuel pump bowl after the engine is shut off. You would think if there was an opening in the line that fuel would be leaking somewhere. As a side note, if I manually actuate the new pump (that I took off), I don't feel any vacuum on the inlet side, but have pressure on the outlet side. I don't even know if I should feel vacuum. |
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Oilleaker1
Member Joined: 06 Sep. 2011 Location: Black Hills, SD Status: Offline Points: 4406 |
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Other than junk holding your inlet check valve open , the glass dome can leak by the gasket but not leak fuel. Will fool you. Ask me how I learned this!
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Green Disease, Jeeps, Old Iron!
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RSR_MK
Member Sponsor Member Joined: 22 May 2009 Location: Cabool Mo Status: Offline Points: 657 |
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OK, if your line will hold vacuum then I agree that’s not the issue. Is it possible that you have rust or other crud in your fuel tank and lines. Normally this will show up as carb issues first but if you have a filter between the pump and carb it could be isolated to the pump and its check valves. Anything in the fuel that could keep a check valve from sealing would effect either fuel pump. I found a small lead shot in the intake side once. It was letting fuel back to the tank and would not pump well at all. I guess someone had cleaned the tank with shotgun pellets and did not get them all out at one point. |
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cpt logger
Member Joined: 23 Sep. 2012 Location: Western Colorad Status: Offline Points: 3022 |
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Bolding mine. Not necessarily. Fuel is much denser or less viscus than air is. Air will leak in or out through a much smaller hole than fuel will. Since you did a good vacuum test on the fuel line from the tank to the fuel pump, we can eliminate that from the problem. The line only, not its connections at either end. However, if the leak were at the tank end it would not cause the leak back issue. I also suspect that the leak is in the cork gasket for the fuel pump bowl. IIRC, It is in the fuel circuit upstream from the pump, thus protecting the pump from contaminants, IE: crud. If this gasket leaks it does not matter that the fuel pumps valves are sealing well. The faulty cork gasket will allow air to enter the fuel line which will allow the fuel to drain back into the tank. If the cork gasket is sealing well, it will prevent air from coming into the fuel line & this will prevent the fuel in the line from draining back into the tank. The fact that you can feel pressure at the outlet tells me that the pump & its valves are good. You should be able to feel a vacuum on the inlet side of the pump. The fact that you cannot tells me that the air leak is between the pump itself & the inlet nipple. The only thing between those two is the glass sediment bowl. Thus, my guess as to the cork gasket. It is also a known common problem area for this kind of failure. IHTH, Matt W. PS. RTV is fuel soluble. Do not use it in fuel systems. It will swell up big time & cause you all kinds of problems. AMHIK! PPS. Just because we fixed one leak does not mean that we fixed ALL of the leaks. |
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TERRY
Member Sponsor Member Joined: 22 May 2007 Location: BOULDER COLORADO Status: Offline Points: 3396 |
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Fel Pro 5019 is the fuel bowl gasket.
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BOULDER 48 2A
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RSR_MK
Member Sponsor Member Joined: 22 May 2009 Location: Cabool Mo Status: Offline Points: 657 |
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I would agree with Matt, it sounds like you have a leak to atmosphere within the pump body. Let us know what you find. Mike |
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Carlsjeep
Member Joined: 15 Jan. 2011 Location: Taylorsville Ky Status: Offline Points: 2642 |
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Are the screws that hold the two halves of the pump with the diaphragm in between tight? Is your oil diluted with gasoline?
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Life is only as good as you make it.
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hcpcjj
Member Joined: 01 July 2010 Location: Charleston, WV Status: Offline Points: 395 |
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OK. I have to know. How can the dome leak air, but not fuel? I disassembled the new pump and the check valves appear to be free & clear.
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RSR_MK
Member Sponsor Member Joined: 22 May 2009 Location: Cabool Mo Status: Offline Points: 657 |
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Think of Gortex, its engineered to repel
water yet is breathable. It comes down to particle size. Air will travel thru a smaller opening then
fuel or water. |
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Oilleaker1
Member Joined: 06 Sep. 2011 Location: Black Hills, SD Status: Offline Points: 4406 |
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I rebuilt the double acting fuel pump on my '53 Willys Pickup. The metal dome, on top that is the fuel part was sucking air, but not leaking fuel. After walking home and towing my pickup, and finding no fuel at the carb and plenty of fuel at the fuel pump inlet, I tightened the dome down again on the brand new cork gasket. Been running fine ever since. With a glass bowl, you would have seen it bubble profusely. Loosen and tighten yours while running to see this and prove what I said to yourself. I've seen the same thing with Bruce W's Jeep when it had a obstructed fuel line. I've also seen non sealing loose check valves cause low or no fuel supply. Junk in the seat. Non vented caps or tank, loose fuel lines. So, you have the fuel lines checked, loosen the fuel line at the carb and hold a catch can there and crank her to see what's going on. John
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Green Disease, Jeeps, Old Iron!
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Wily-46
Member Joined: 15 Apr. 2015 Location: Missouri Status: Offline Points: 160 |
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I had that same problem on an SBC years ago. I could apply air pressure to the tank to prime the pump and it would start right up and run for a while, but then it would eventually die and act like its running out of gas. Replaced the fuel pump and all the lines..still same problem. It ended up being the lobe on the cam. It was wore to the point that it would no longer pump regularly. Check the wear on the arm of your pump and see if the cam is hitting it. You can take it off and dry it off and mark it with a sharpie. Take your coil wire off so it wont fire, put the pump on and turn the engine it over a few times. Pull it back off and see if the sharpie is worn. If not, you have a cam issue.
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Bruce W
Member Joined: 29 July 2005 Location: Northeast Colorado Status: Offline Points: 9611 |
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(Bolding Mine) The fuel inside the line from the tank and inside the dome (both on the "suction" side of the system) are under VERY little pressure, even at rest. There is the weight of the fuel in the tank pushing on the fuel in the line, but the Jeep tank is not very high above the pump, so that does not matter much. The pump's job is to reduce the pressure in the line so that atmospheric pressure in the tank will push fuel thru the line. When the pump is working, there is less pressure in the line than there is in the air outside the line, so either at rest or pumping, there may not be any leakage from the inside out (fuel), but there is air under 14.7 pounds (more or less, depending on altitude and weather) of pressure on the outside trying to get in. Air leaking from the outside in, a leak you cannot see, except for the bubbles in the pump dome or in your clear plastic fuel filter. And if you have any obstruction on the tank end of the line, or a kink or something in the line, the pressure inside the line and the dome can easily go below zero PSI! With the ever-present 14.7 PSI of air trying to get in. In every "help me" post on this forum, there are always several who say, "I had that exact same problem....", well, I'll throw one of those in here... A friend at the Colorado Fall Colors Tour was having fuel delivery problems, we changed fuel pumps on the trail which seemed to help at first, but soon, back to the same problem. He had several hose-and-clamp splices in his fuel line, but I could not convince him that he could have air leaks at these points and that they could be his problem. He went to town and bought an electric fuel pump, which I helped him install right at the outlet from the tank. I told him that if I was right about the air leaking in that he would know when the electric pump was turned on. When the installation was complete and the electric pump was turned on, his fuel line became a sprinkler! We replaced some hose and clamps, and tightened some other clamps, and stopped the leaks. He still maintains that the electric pump solved his problem. Oh, well, it's the end result that counts, right? BW
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It is NOT a Jeep Willys! It is a Willys jeep.
Happy Trails! Good-bye, Good Luck, and May the Good Lord Take a Likin' to You! We Have Miles to Jeep, Before We Sleep. |
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