FPR the problem? or look elsewhere?

[lnkncontiverto]

I've only had my car on the road with my new combo for a few hundred miles so I haven't turned the wick up yet, just to make sure everything is working properly. Boost is set at 18psi currently, with alky.

Fuel pressure is set where it should be at 43psi (line off), which should put it at 38psi (line on). Starting the car cold, everything is where it should be. The problem I am noticing is that once the car gets fully warmed up, the fuel pressure drops down to as low as 32psi (line on) at idle. I have noticed that sometimes when I go WOT I see a touch of KR (0.7degrees).

My FPR, BTW, is one of those older units with the billet top and the stock Bosch bottom end. I picked it up used, but everything has worked well for the first few hundred miles.

I don't think I have any vacuum leaks, I'm seeing voltage of 13.7 or higher on my SM, my walbro fuel pump (new) was confirmed by Full Throttle to be from the 'safe' batch, and everything is dandy when the car's cool. Is this a failure mode for a fuel pressure regulator? or should I look elsewhere for why I'm knocking and have a low pressure reading? I'm anxious to get this sorted out so I can get it tuned for higher boost. Thanks!

 

[Rich Gio]

Tagging along...

I see the same thing, to a lesser degree, with my new accufab reg. I start out at 43 line off/39 line on, and once the engine gets to temp I'm seeing 41 line off/37 line on. The next day I start the car.... same issue!

 

[ttppll]

I had the same problem. I reset the fuel pressure while the car was warm and the knock went away.

 

[87GN_70GS]

I've only had my car on the road with my new combo for a few hundred miles so I haven't turned the wick up yet, just to make sure everything is working properly. Boost is set at 18psi currently, with alky.

Fuel pressure is set where it should be at 43psi (line off), which should put it at 38psi (line on). Starting the car cold, everything is where it should be. The problem I am noticing is that once the car gets fully warmed up, the fuel pressure drops down to as low as 32psi (line on) at idle. I have noticed that sometimes when I go WOT I see a touch of KR (0.7degrees).

My FPR, BTW, is one of those older units with the billet top and the stock Bosch bottom end. I picked it up used, but everything has worked well for the first few hundred miles.

I don't think I have any vacuum leaks, I'm seeing voltage of 13.7 or higher on my SM, my walbro fuel pump (new) was confirmed by Full Throttle to be from the 'safe' batch, and everything is dandy when the car's cool. Is this a failure mode for a fuel pressure regulator? or should I look elsewhere for why I'm knocking and have a low pressure reading? I'm anxious to get this sorted out so I can get it tuned for higher boost. Thanks!

You need to know what your vacuum is. The line-on fuel pressure will drop by the vacuum amount. Of course you will need to convert units. But 20 in Hg of vacuum is really close to 10 psi. So if you're pulling 20" Hg of vac at idle, your line-on base fuel pressure will drop from 43 to 33 psi.