Unstable Fuel Pressure

[ykf7b0]

UPDATE; I recently installed a large cannister type fuel filter to replace the small inline but my problem still exist. It's falling from 7.5 psi down to less than 3 at high rpm and the engine stalls out. Could it be my Mallory 140 pump is getting weak?

 

[493charger]

Where exactly is the pump located? Pics would be worth a thousand words...

 

[ykf7b0]

Pump is located above the rear axle housing on the passenger side and it is below the fuel pickup.

 

[ykf7b0]

I now have a Painless Wiring Fuel Pump Relay on the way and I'm thinking that installing it might give the the fuel pump a boost of voltage and amperage and also provide me with a safety feature that I should have already had. I'm going to give it a try before I give up on the Mallory 140 pump.

 

[HT413]

Pump is located above the rear axle housing on the passenger side and it is below the fuel pickup.

But is it below the bottom of the tank? I dont run an electric pump because i run a stock fuel tank and every electric pump i saw needed to be mounted below the bottom of the tank (not just below the pickup connections) preferably with a sump installed. It could be with fuel slosh your pump is intermittently up above the fuel, which could cause pressure fluctuations on the suction side and actually cavitate the pump.

 

[67 coronet]

see what happens when you have stable voltage,but sounds like the pump aint cutting it or you may have to modify the tank for a sump.if your street motor is hot enough you may have reached the point where you need a sump design tank feeding your pump.honestly,if you wiring fix dosnt solve your prob,try replacing or rebuilding the pump first.even the g rotor pumps can wear out.

 

[ykf7b0]

But is it below the bottom of the tank? I dont run an electric pump because i run a stock fuel tank and every electric pump i saw needed to be mounted below the bottom of the tank (not just below the pickup connections) preferably with a sump installed. It could be with fuel slosh your pump is intermittently up above the fuel, which could cause pressure fluctuations on the suction side and actually cavitate the pump.

It is at or below bottom of tank and it has been this way for the past several years. Only recently has the pressure been an issue. Thanks!

- - - Updated - - -

see what happens when you have stable voltage,but sounds like the pump aint cutting it or you may have to modify the tank for a sump.if your street motor is hot enough you may have reached the point where you need a sump design tank feeding your pump.honestly,if you wiring fix dosnt solve your prob,try replacing or rebuilding the pump first.even the g rotor pumps can wear out.

That will be my order of action. Thanks!!

 

[ykf7b0]

I've got the relay installed and the preliminary test shows good steady fuel pressure and is a definate improvement. When I get the chance I will carry her down the road and get the rpm's up for at least a quarter mile to see iif the pressure will hold.

 

[ykf7b0]

After a hard test drive I have learned the fuel pressure is not holding. Have any of you had experience with rebuilding these Mallory 140 Series pumps? I can send it back to Prestolite for a rebuild or I can get the rebuild kit and attempt this myself. Recommendations and opinions are appreciated!!!

 

[ykf7b0]

I was running a fuel return with 3/8 aluminum line that was feeding into the small 1/4 inch vapor relief/return on the factory style fuel sending unit. I am in the process of installing a -8 AN bulkhead fitting into the upper portion of my stock fuel tank for the fuel return. I'm hoping this will alleviate my fluctiating fuel pressure problem. Would you recommend that I install a tube on the inside of the bulkhead fitting to force the returned fuel to the bottom of the tank to eliminate the chance of aeration therefore causing another fuel delivery problem? or, do you recommend that I let the returned fuel spray out from the bulkhead fitting and decrease the chance of fuel pressure inconsistencies?

 

[ykf7b0]

Bump!