Fuel Pump problems.....again

[datsun_dom]

Hey guys so im having some reoccurring issues with my Z and im ready to burn the car to the ground at this point. So i bought the car almost a year ago and it was converted to just an electrical fuel pump when i got it. the car ran fine for a few months maybe like 5 or 6 i cant remember. Anyways one day the fuel pump started to go out so i replaced it with the K&N pump from MSA and that lasted about one month. So before i ruled that pump was no good i blew out the gas lines replaced all the filters and took a long look into the gas tank with a borescope btw such a fun tool to use. and found nothing out of the ordinary. I even rewired the whole pump putting my own relay in just so i could eliminate the electrical aspect. the pump ended up being bad and i replaced it and put a holley pressure regulator in it. the car runs good at 3 PSI. Well this started about a week ago where on hills in 4th the fuel will cut out. trust me i know exactly what it feels like by now. Now the fuel pressure barely builds past 1 PSI and if i give it gas the pump doesn't build anymore pressure it just uses up the gas in the lines and dies. So im kinda at a loss right now and the only thing i can think of doing is putting a mechanical fuel pump back on and replace the electrical again. Another option for me cuz im pretty sure the SUs arent balanced and i might just do the holley comversion cuz that was part of my plan anyways. PLZ HELP

[NewZed]

1 hour ago, datsun_dom said:

just an electrical fuel pump

K&N pump from MSA and that lasted about one month.

a holley pressure regulator in it. the car runs good at 3 PSI.

about a week ago where on hills in 4th the fuel will cut out.

 Now the fuel pressure barely builds past 1 PSI and if i give it gas the pump doesn't build anymore pressure it just uses up the gas in the lines and dies.

im pretty sure the SUs arent balanced and i might just do the holley comversion cuz 

You already had one bad pump.  Maybe you got another.  Switching carbs won't fix a bad fuel pump.  Have you confirmed a good power supply and good grounding?  That's a very basic electrical component troubleshooting step.

Are you running it deadheaded or using the return lines.  Are the return lines open?  Are you using a filter before the inlet?  Does it flow enough to supply a gravity fed pump?  Those inlet filters can cause a lot of problems.

Doesn't seem like you've double-checked the basic stuff.  It worked for a while you should be able to make it work again.  If the pump's not designed to deadhead or if you're cavitating due to inlet restriction you can wear the pump out faster.

[datsun_dom]

1 minute ago, NewZed said:

You already had one bad pump.  Maybe you got another.  Switching carbs won't fix a bad fuel pump.  Have you confirmed a good power supply and good grounding?  That's a very basic electrical component troubleshooting step.

Are you running it deadheaded or using the return lines.  Are the return lines open?  Are you using a filter before the inlet?  Does it flow enough to supply a gravity fed pump?  Those inlet filters can cause a lot of problems.

Doesn't seem like you've double-checked the basic stuff.  It worked for a while you should be able to make it work again.  If the pump's not designed to deadhead or if you're cavitating due to inlet restriction you can wear the pump out faster.

I am sure the electrical side is good that was the point of the relay I put in and I am using the return lines and the filters should not be hindering it because the flow before was good going through the filter so I don't see how it would magically start to hinder it?

[datsun_dom]

And the pump I used is supposed to replace the mechanical fyi

[NewZed]

If you're sure that everything is right then the only solution is to replace the pump.  Because it went bad, it had to have gone bad.  It must be the pump because you are positive that everything was right when you put it together and magic would be required for anything to change.

See the logic problem?  If you're positive, then the only thing left is a bad pump.  Maybe try a different brand of pump.

[datsun_dom]

Ok ill try that thanks

[Firepower]

First off I’m assuming it’s a 240z- as you don’t say.  If so, i think you could have clogged mesh fuel filters in the float bowls -they sit in a banjo bolt that’s holding the inlet tube to the float bowl.  You remove the lock washer thing, and then crank a 17mm wrench or socket to get them out.

Also your float levels could be wrong.  Going uphill you aren’t filling the bowls up because the float(s) valves are stopping flow.  When the bowls empty the engine dies. Some pumps break if you have them on & then block fuel flow.  So you need to run the return lines, if that’s the case.

I had an electric pump on mine for a while, it’s no better than mechanical imho.  I stopped at a light smelled gas, and I had blown a hole in a brand new hose between  fuel rail and float bowl.

The electric fuel pump kept running at 4psi  because the engine was still running float bowls stayed full at that point.   I was lucky not to have a fire.  Do NOT defeat the Datsun electronics in your fuel pump harness.  It reads the oil pressure and won’t run the electric fuel pump if the engine isn’t running.  Having to carry a can of starting spray to get things going is a small price to pay to avoid death.