Well I just swapped in my old walbro 255 hp pump. It has been sitting in my old tank (with gas) for a little over a year now. Prior to that, it has seen maybe 6,000 miles. I ruesed the braided line running from the pump to the sending unit to handle the pressure. I turn the key and hear it prime. Turn a little further and she fires right up. Success!, or so I think. Then I check the fp, it's at 15psi at idle. A little higher than stock but not bad. Then I rev and the PSI drops by 2. Rev a little harder and it drops 3-4psi. Not good obviously. I can't test it with a load on it, as I am currently changing out the rear end.

When I first turn the key the gauge jumps almost back to the 6 o'clock position then goes to 15 psi, and finally after the pump disengages, it drops back to 0psi.

The pump does not seem to be fluctuating when running.

Before I go and replace my entire harness and buy another pump, I was wondering if it could be my regulator? Can these things go bad, or possibly something with the diaphram? The main reason I changed the pump while running the 305 still was because my plugs were white as snow.

I never had problems with the pump with my old setup and I was running a Holley 670 with 85pph delphis at 21psi. Adjustable regualtor of course and the only drop off in pressure was maybe 1psi for half a second when first put underload. I was running the stock harness as well.

Any help would be apprieciated, if I can avoid droping the tank or redoing my harness, that would be very nice. So should I mess with the regulator and buy a new diaphram, or would that just be wasting time and money? Thank you

 

Also just fyi, I swapped pumps, but not tanks do to the condition of the sending unit and tanks themselves. Also this is the 255 high pressure unit, the thing should be good to 110psi or so.....also, I am going to check the voltage at the connector outside of the tank. The votage should be 12v, right?

 

So your using a stock regulator now but where using a holley unit before, correct? One possibility could be that the regulator cant handle all the excess flow without any load on the fuel system, causing a pressure rise with the pump just running. Revving the motor would help remove some of the excess fuel that cant return at the stock pressure, thereby causing the fuel pressure to drop.

 

That is actually a pretty good theory dimented. I wish I would have taken a bit more care in monitoring the stock unit's habits. But it sounds about right, I think the stock pump was putting out right around 12psi or so. I'm gonna play with it a little more tomorrow as well as check the voltage.

One thing I am noticing is that the fp gauge is bouncing around a little bit. Oh well. I guess the only way to really test the setup is to test it under load, and go ahead and make my regualtor adjustable.

Thank you for the help, I am keeping my fingers crossed!