Is my fuel pressure too low

[Bob Yates]

I have an 86 C4 with TPI L98. I just bought a fuel pressure gauge. I believe the pressure should be 47psi but I can only get 34psi on the gauge. I have about a year ago replaced the fuel pump and sack filter and the in line filter about a month ago. Could my pressure control valve be weak.The car runs Ok but I feel it could be a little quicker. It seems to peter out to quick. Would this lower pressure cause low power. Any advice would be helpful....Thanks in advance.....Bob Yates

 

[rrubel]

Low pressure could cause low power, esp. at higher (for an L98) RPMs. Did you check the pressure with the vacuum line on or off the regulator? Stock for an 86, btw, is IIRC 38.
[RICHR]

 

[Bob Yates]

I checked it with the line on....Do I check it with the line off and if my pressure goes up then my pressure regulator is bad?

 

[jester]

I believe the specified pressure is with the vacuum line disconnected.

 

[rrubel]

Jester's right. The pressure should be lower with the line on.
[RICHR]

 

[Bob Yates]

Well now I'm really in a pickle. Today I rechecked the pressure and it was 38 psi.I disconnected the hose and the pressure went to 45 psi. My GM shop manual says the pressure should be between 41-47 psi .So that means my pressure regulator is OK ....Right !!! But I've read that higher fuel pressure gives you more power,so should get an adjustable regulator and up the psi? Don't saw the limb off on me now. Let me hear from you

 

[rrubel]

If you're getting 45 PSI with the hose off, then you're fine. Don't mess with it (and replacing the regulator requires removing the plenum, which can be a real pain on a higher-mileage car).
[RICHR]

 

[Bob Yates]

This may sound strange but since I've checked the pressure it is running better. Could air have been in the rail and I bled it out when I removed the gauge. I have 55,000 miles on the clock. That's not bad for an 86. thanks for you info......Bob Yates

 

[rrubel]

I don't *think* you could get air in the rail, though I guess it's possible (my dad once had an air bubble in his car's fuel line). Maybe you had a loose connection with the vacuum line or something.
[RICHR]