Hey guys,

So I have a v6 converted to a cammed LT1. I just installed my fuel pressure gauge today in my a-pillar.

Fuel pressure at idle is about 39psi. At WOT, it goes down to 20psi.

I read that if the regulator goes bad, it leaks gas into the vacuum line. How much gas are we talking about here? A couple drops here and there or a trickle? I'm waiting for the engine to cool off right now so I can go check the vacuum line that goes to the regulator but I had to pull the vacuum line off when I was putting the fuel pressure sender onto the fuel rail valve and I vaguely remember as I whipped the vacuum line around out of the way that a few drops of liquid might have come out. I just thought it was condensation.

I've got a racetronix pump and a new fuel filter I plan to throw in later this weekend but I just wondered if I need to stop at the local race shop and buy a regulator too. Should I just install the pump and filter first and then recheck the pressure?

 

You should not find any wet fuel at all in the vacuum line. The only way fuel could get out of the regulator and into the vacuum line would be if the diaphragm in the regulator is damaged. There shouldn't be any "condensation" in the vacuum line either.

 

Thanks for the info, Fred. I did take the vacuum line off and did not smell a really strong smell of fuel in the vacuum line. Plan to check it again after a week or so.

I replaced the pump today and the fuel pressure is holding steady at about 42. I noticed the fuel pressure goes up at 3/4 and WOT throttle - is this normal?

 

Yes. Fuel pressure increases as intake manifold vacuum drops. That's the purpose of the vacuum compensation line on the FPR - it keeps the DIFFERENTIAL pressure constant, not the fuel rail pressure (your gauge measures the rail pressure).

An injector is an "orifice", and the flow rate through the injector is controlled by the difference in pressure between the rail pressure and the intake manifold pressure. To keep the DIFFERENTIAL pressure at 43.5psi, the rail pressure will rise toward 43.5psi at "0" vacuum (you will approach 0 vacuum at WOT), and will drop proportional to intake manifold vacuum at any other throttle position.

 

Thanks - your wealth of knowledge (and your willingness to share it) is appreciated!