Could I have great fuel pressure when cranking but not when running?

[Ponchonutty]

Still battling my lean condition on my HUGE Pontiac 301 on a freshly rebuilt quadrajet.  When a fuel pressure gauge was installed and the engine cranked over, I had 7psi.  Didn't think about installing a gauge inline and drive it to see if the psi drops off.  Thoughts?

[Cadman-iac]

It's possible that you have a bad pump, but an inline gage while you're driving would definitely tell you if that's the problem.
 I've experienced brand new pumps that would put out beautiful pressure when first fired up, but shut it off and restart and the pressure then drops, fluctuates, and pulsates more than that first time.
 It also drops the hotter the engine gets or the more you drive.
 I finally got sick of trying to "adjust" for that and went back to an electric pump with a good regulator.
 However even with the electric pump and a good regulator, i still experience a change in pressure, it's just not as pronounced as with the mechanical pump.
 I bought an Aeromotive regulator made in America that cost me 220 bucks over 4 months ago or more now.

 But it's definitely worth looking at your pressure during the issue. Anything else is just guessing.

[Ponchonutty]

It's possible that you have a bad pump, but an inline gage while you're driving would definitely tell you if that's the problem.
 I've experienced brand new pumps that would put out beautiful pressure when first fired up, but shut it off and restart and the pressure then drops, fluctuates, and pulsates more than that first time.
 It also drops the hotter the engine gets or the more you drive.
 I finally got sick of trying to "adjust" for that and went back to an electric pump with a good regulator.
 However even with the electric pump and a good regulator, i still experience a change in pressure, it's just not as pronounced as with the mechanical pump.
 I bought an Aeromotive regulator made in America that cost me 220 bucks over 4 months ago or more now.

 But it's definitely worth looking at your pressure during the issue. Anything else is just guessing.

Well I am grasping at straws at the moment.  Everything I can possibly think of has been checked more than once except for this.  I did a compression test when I first got the car and all were around the same.  Now that I have more miles on it, doesn't mean things have changed though.  Starts and usually idles fine even when hot.  Don't really want to go to the electric pump route especially since I have a small fortune in new stainless lines but if push comes to shove!

[lightning boy]

Have you checked the sock in the tank?

[Cadman-iac]

Have you checked the sock in the tank?

 Yes, that's a good point.  Also, check your tank for dirt/debris that could be being drawn down and over the sock. When the suction is gone, the crap will float free from the sock and your cranking test will be normal.
 Something like a tank coating coming off, you didn't mention how old your car is, but with a 301, I'm guessing it's a late 70's or early 80's Firebird.

 How did it run prior to your carb rebuild?

[Raoul Ross]

Gas Cap?