Ok guys, my mallory 4309 guage is jumping continuously up and down between 2-6 psi continuously. I cannot figure out why? Should I replace my fuel filter and recheck it? I want to run 5psi but the dang needle is jumping up and down so much i cant. Carb is an edelbrock 1405 600cfm, fuel pump is stock TBI pump.

I had that exact problem with mine, with the stock in tank TBI pump. I think the problem is the small return line. I know others have had problems like that with it, I just can't remember off the top of my head what exactly was the cause.

I also remember when I turned the pump on with the motor off, it the pump ran for more than a second, it would alsomost start surging. I could hear the fuel lines jumping because of the pressure differential. So with that in mind I would bet it's the small return that's causing that.

ok, anyone else?? Thats sound very probably, apparently you are megasquirting now huh? lol

yea, I had bad karma with carbs

anyone else know whats causing this, it seems like the fuel pressure spikes to whatever the reg is set to then opens the return valve then repeats the process. The I am not getting a constant psi just a jumping open/colse/open/close/open/close. I have a cheap mrgasket guage on there is that why??

If your gauge is jumping I think you have the fuel line and return line hooked up backwards on the regulator.

Just got mine running and my 4309 floats between 5 and 6 with the gague jumping but when I installed it my bouced from 1 to 6 and it was a bad connection at the fuel pump relay. Jiggling the relay connector made a difference. After tightening the clips in the connector to the relay mine is always 5-6 now.
Buzzman1

Just had this problem in my 454SS truck when converted to carb using that same regulator (the truck also uses the same size 3/8" feed and 5/16" return line as your Camaro).

Cut to the chase here.... the pickup assembly in the tank was all rusted to crap and drawing air into the line/leaking. New sender assembly cured it, but I also upgraded the in-tank pump at the same time. So I can't say for sure that the pickup alone was definitely the problem, but after the repair/upgrade she's rock-solid on the gague. The basic idea here is that any air in the system drives that style of regulator bonkers.

If the lines are in good shape they are perfectly adequate in size to do the job.

I'll bump this to save a new thread.


I'm having a similar issue with my 4309 except the fuel pressure stays constant until I'm ideling down.

For instance: Rev the motor and let it come back to idle......about 1800 RPM's to idle the fuel pressure gauge will very quickly jump back and forth from 3-9 PSI.

It is fairly constant at idle and when revving the motor except as described above. Also, every once in a while the regulator seems to make a clicking type of noise.

Any idea what could cause the pulsation in the limited situations above???

Only time I ever had issues with a really inconsistant guage reading was when I had a vacuum line attached to the top of the 4309 - that vacuum fitting is for superchargers or something, and just causes havoc with a normal set up.

But recently, my fuel pump is kinda pulsating. When pump is running, but engine is not, it "thumps" in the tank - and I haven't figured this issue out yet - but it's something to do with the pump, and the noise is defintely in the tank. Everything still works fine, car runs great, and Ive been driving it this way for months. It doesn't do this when motor running, just when engine off nut pump on (I have my pump rigged to a relay so it comes on with the key and runs as long as key is on).