I've got an electric fuel pressure gauge. When installed it showed about 31-32psi for idle, in the last six months that has progressively gone down. At first it dropped to 30psi. I changed the fuel filter and no difference. It stayed at 30. Then it went't 29, changed fuel filter again, stayed at 29 and so on. Now it sits at 27psi at idle (brand new fuel filter) and when driving and letting off it goes down to 25psi. WOT used to be about 50 and now it is 48.

I'm going to check the pressure with another gauge to make sure the gauge isn't reading wrong. Any ideas if another gauge gives the same results?

 

Another guage is a good idea. Also keep in mind that under light throttle/high vacuum conditions, cars/trucks pull back fuel pressue for economy reasons, and they don't need higher pressure. Remember the boost sensitive regulator is also vacuum sensitive. As for your declining readings, how many miles do you have?

 

50K miles

There is no pull back on the pressure under light throttle and has never been. Only under no throttle.

 

Lena, anytime you are at low load (idle, light-part throttle cruise, decel) you have vacuum pulling the fuel pressure down. Your base fuel pressure should be around 39 psi. That's checked with the truck idling and the vacuum line OFF the regulator. When you put the vacuum line back on the regulator, it should be pulled down to about 30-32 psi. The more vacuum you have, the lower fuel pressure will be pulled down. Now if the truck was not supercharged, when you go WOT, you'd have zero vacuum and would see base fuel pressure. Since we are supercharged, you have a boost sensative regulator which steps fuel pressure up based on boost pushing on the regulator. We also have the two stage voltage system, that switches the pumps to full ground at WOT, which is why if you watch the gauge, it looks like a switch in fuel pressure from PT to WOT. I'd start with checking base fuel pressure and see what you are at. Hope this helps.

 

ok, replaced the pumps... this changed nothing.

Then began looking under the hood for any vacuum line problems related to the fuel pressure regulator... noticed that the two rubber lines that come off the EGR pipe were blown off. Had this problem before when one of her cats got clogged. Got that cat blown out, now it seems the other is clogged. D@MN Bassani cats!!!!

My question is, since a clogged cat effects boost, does it also effect vacuum and cause the vacuum on the fuel regulator to be low?