Installed NOS Fuel Pump--Oddity Observed

[rickf]

Pressure drop across a fuel filter should be zero if it is a quality filter and clean. At least with the amount of fuel we are talking about flowing. If you were flowing 20 gallons an hour there might be a measurable resistance but we are talking about 4 GPH at 60 MPH solid for an hour.

[A45WV]

Sorry for the delayed new input, but I'm still in the working world, etc.

Yesterday, I changed the fuel line from the pump to the filter, and also the filter. Still seeing the same pulsing behavior. Filter still empties shortly after engine shut-down. The situation Doesn't seem to affect operation once the engine is running. I test drove it at varying speeds up to about 45 mph with no issues. I suppose i could buy the pressure gauge and give fuel pressure a look, but again--the condition does not appear to be affecting starting or running in any way.

Unless y'all have some other input, I'm about to decide not to worry about it any more, lol.

[Horst]

The fact that the filter gets empty quickly makes me think that one of the valves in the pump is not sealing correctly.

[A45WV]

The fact that the filter gets empty quickly makes me think that one of the valves in the pump is not sealing correctly.

I guess that is possible. Then again, I've read posts from many (in multiple forums) describing the emptying filter phenomenon--to the point that I've seen people talking about putting a check-valve in line to keep it from happening?

Just odd.

[rickf]

The "check valve" is a correctly operating fuel pump. If it is actually draining back to the tank and fully draining out the filter then you have a pump issue and and it is not one valve, it is both of them. And yes, you could put in a check valve to prevent the drainback. But that is not going to help you when the valves in the pump get worse and the pump stops pumping. But, with that said, if you are seeing pulsing on the end of the fuel filter housing then the pump is plenty strong and the valves are fully closing. If the pulsing you are seeing is actually the gas in the filter then what you may be seeing is the pump pushing gas up and pulling some of it back again through a bad valve. Was this NOS pump still in the original box and foil wrapper? If it was then there was a date of manufacture on it. If it was not then two things, one is you do not know if it is actually NOS and the other is that even if it is NOS you can for the N in that equation since it has been exposed to air for lord only knows how long and that natural rubber diaphragm will be dried out along with the rubber flapper valves. Also keep in mind that a lot of people offering these quick and easy fixes have very little mechanical experience and just pass on what they have heard from others like them on the net. And THEY will be the ones to flame me.

[A45WV]

The "check valve" is a correctly operating fuel pump. If it is actually draining back to the tank and fully draining out the filter then you have a pump issue and and it is not one valve, it is both of them. And yes, you could put in a check valve to prevent the drainback. But that is not going to help you when the valves in the pump get worse and the pump stops pumping. But, with that said, if you are seeing pulsing on the end of the fuel filter housing then the pump is plenty strong and the valves are fully closing. If the pulsing you are seeing is actually the gas in the filter then what you may be seeing is the pump pushing gas up and pulling some of it back again through a bad valve. Was this NOS pump still in the original box and foil wrapper? If it was then there was a date of manufacture on it. If it was not then two things, one is you do not know if it is actually NOS and the other is that even if it is NOS you can for the N in that equation since it has been exposed to air for lord only knows how long and that natural rubber diaphragm will be dried out along with the rubber flapper valves. Also keep in mind that a lot of people offering these quick and easy fixes have very little mechanical experience and just pass on what they have heard from others like them on the net. And THEY will be the ones to flame me.

Understand all. It was a new pump in a box--no foil wrapper. I also have a new commercial NAPA pump (FUP B0275P: https://www.napaonline.com/en/p/FUPB027 ... sionRank=1) that I could potentially install/adapt with hose just to see if what you're describing goes away with the NAPA pump.

If I do anything, it would be to replace the pump and see what's what. That said, I just drove it around for 10 miles or so in all driving regimes and had no issues. Started it multiple times--facing uphill, downhill, etc...no issues.

[rickf]

It sounds like there is nothing wrong with the pump. As I said, the way the filters are built the inlet and outlet tubes are not directly on the end of the filter, they are inset a little so air will usually be in there depending on the angle of the filter. Drainback is something you are not going to notice until the vehicle has sat for a week or two and the gas in the carb bowl has evaporated a bit And you do not have a full bowl to work with right at startup. If all the gas in the line has drained back to the tank it is going to have to crank for a bit to get it back to the pump and up to the carb to fill the bowl. That would be a good time to watch the filter. After it has sat for a couple of weeks look at the filter and then try to start it while watching the filter, two people would be good here. If you get gas moving in the filter instantly pump is good. If it takes five or more cranks before you get any gas moving, especially if the engine has started, then you have a drain back issue.

Now, if it sits for a month or more I would not expect the lines to still be full. No rubber valve will hold forever. As long as it runs good under normal circumstances I would not worry about it, you already have a spare. If it ain't broke don't fix it.

[rickf]

I just looked at the link you have for the NAPA pump and I do not believe that is the correct pump. That looks like a V8 pump. You would be looking for a 60's slant 6 pump. And this is only my personal opinion but I am not totally convinced that the cam shoe on the civilian pumps lines up on the cam exactly the same as the military pumps. I have never had one of each on hand at the same time to do any measurements so if you do get the right pump check the angles on the cam shoe. The pump will work, hundreds of people are using them, I just wonder about cam wear.