Has anyone had a problem keeping the pressure set using a mallory 4309 bypass regulator? I've got an in tank 255lph electric pump and installed a 4309 regulator to bring the pressure down. I couldn't get the pressure down far enough with just the mallory...I was only about to get it down to 10psi or so. Following some advice I installed a second dead-head regulator after the mallory to bring the pressure down to 5-6psi. The problem I'm having howerver, is that it won't stay set at 5-psi.

I'll run the pump with the car off (Pump is wired to turn on with the ignition 'on'), and I can set the pressure to 5psi. I'll turn the car on and run the car, and it'll be at 10PSI!? Then I'll turn it down to around 5psi with the car running, but it'll be at like, 2psi iwth the car off. However, the next time I start it, it might be at 10psi? I'm so confused. With the bypass, shouldn't it be the same all the time?

Has anyone else had issues with the single mallory not being enough to bring the pressure down to 5psi?

Has anyone had issues with it not remaining steady to get a good reading?

I've currently got it so wher eit reads about 4psi with the car running, but then yesterday I checked it when I started it before work, and it was at 10psi again? Just looking for other people's experiences.

 

I dont see any 3709 regulator...? What regulator do you have?

 

Wow, I was way wrong. It's the 4309

 

you might have a bad regulator. it its not letting you adjust the psi down to 5-7 on just the mallory unit, something isnt right.

 

Agreed with Travis. I have a Walbro 255 in-tank with a Mallory 4309 regulator in my 454SS truck and it's got no problem holding 6 PSI where I set it. Ditto the identical system I installed on my previous 92 Camaro (which I ran with both a stock TBI pump and a Walbro 255, requiring almost no adjustment at the regulator after the change).

If the pressure is creeping up with the 4309 my first suspicion would be an obstructed return line. Out of the box with no adjustment or spring change they supply about 4 PSI.

 

I am sort of having the same problem. I'm using a gas tank from a 92 Z28 TPI in my 86' conversion. After installing my 4309 and adjusting it to its lowest psi my gauge cruises past 15psi. I installed a mech pump and ran a hose to a gas can to check if it was my gauge...around 8psi so I don't think its my gauge. In the Mallory directions it says that if your return line is too small that you won't be able to adjust the pressure correctly. Has anyone had any issues similar? Did you have to change from the 5/16" to a 3/8" return???

 

theres tons of people running the mallory unit on stock return lines with 0 issues. its a possibility that your return line has some sort of blockage, as damon suggested for the OP.