Vacuum pressure and fuel pressure questions

[kaspr]

I have a '95 Ultra, and in the process of replacing my fuel pressure regulator, I noticed a few things:

1. The fuel pressure regulator is regulated by the boost pressure from the supercharger, not vacuum pressure from the vacuum block. This boost pressure is 18" hg at idle. Is 18" normal?

2. When I hook up my vacuum pressure tester to a vacuum line from the vacuum block, it's 20" hg at idle. Is that normal?

3. At idle, fuel pressure runs 33 psi. When I take the boost source off the regulator, it goes up to 41 psi. I understand for my car I am supposed to get 41-47 psi without any vacuum/boost source hooked up. With a new regulator shouldn't I be getting more than the bottom of that range? Is 33 psi normal for idle with the boost source connected? What does everyone else get?

4. When I rev up the engine, the vacuum and boost lines initially decrease, and then stabilize to the idle pressure, even if I'm revving at a steady 3000 rpm. Is this normal to experience no reduction in vacuum pressure even though I'm revving the engine up? If this is not normal, then it is causing my fuel pressure and boost pressure (via the boost bypass valve actuator) to be lower than normal when revving up.

Any and all comments are welcomed on any of the above questions. Thanks!

[BNaylor]

Your engine vacuum readings look acceptable. Normal engine vacuum ranges from 15 in hg to 22 in hg which corresponds to the green area marked on a typical automotive vacuum gauge.

If the fuel pressure reading deviates more than 5-7 psi when vacuum is removed and reconnected the fuel pressure regulator is suspect.

Also, fuel pressure is checked at fuel pump prime at ignition to ON not start which should be in the 41-47 psi range. Look for the highest reading, repeating a few times.

In reference to para 4, when revving the engine and once reading stabilizes vacuum should match or come close to that of the readings at idle then that is normal. The drop as you rev or accelerate is normal because engine vacuum decreases.

[kaspr]

Thanks for your help, bnaylor. I think I'll try to get that fuel pressure regulator exchanged, since it sounds like it is causing my pressure to be a little too low.

If anyone knows what fuel pressure they get, as well as vacuum pressure both from the vacuum block and boost source, I'd love to hear.

Thanks.

[BNaylor]

Which version of the supercharged 3.8L (3800) engine do you have in your '95? The Series I or II. I've got the vacuum specs from both of my L67 Series II 3800 someplace.

The vacuum readings will be different depending on where you take the reading since the source could be from the throttle body or off the supercharger/UIM.

[kaspr]

I have the Series I 3800 SC. I don't believe they used any Series II SC until '96. From the throttle body, I get 20" hg, and from the supercharger I get 18" hg. The vacuum line for the fuel pressure regulator comes from the supercharger. I'm sure the Series II specs wouldn't be much different, so I'd love to hear them.