Adjustable Fuel Pressure Regulator

[afree029]

This may sound like a dumb question but I have good reason for asking.
I have an adjustable fuel pressure regulator (Mid-America brand) installed but the fuel pressure is reading lower than normal. When I first start the car it reads about 38 but after it warms up a little it drops down to around 25 with the FPR vacuum disconnected. I have turned the pressure reguator bolt both Clockwise and CCW but see NO noticeable change in pressure.
Whis way is supposed to increase pressure CW or CCW?

I have the stock unit that I am considering putting back on but thought I would probe the forum a little first for some advice.

 

[rrubel]

Clockwise raises it on mine; I'd expect yours to be the same. You're tightening a spring. Mine you have to turn a LOT to get any noticeable difference, so maybe you didn't adjust it enough.

[RICHR}

 

[afree029]

Thanks for the info. I thought that was the way I remembered it working when I first installed it but it has been a while. I actually turned it from min to max and saw no change. I did a few more checks and it looks as though the in tank pump fuel pump pressure is low. Actually it starts off around 38 and then drops down to about 25. I am going to replace it with the Edelbrock high volume version as I need the additional fuel delivery capability for other mods that I plan to add. Thanks again for the info.

 

[rrubel]

Glad to be of help.

[RICHR]

 

[Tuna]

Don't forget to replace the fuel filter also while you replacing the pump.

 

[Hib Halverson]

Let's talk about A-FPRs
First, an adjustable fuel pressure regulator is neither needed nor desireable on a stock or near stock L98. Nor is a high-volume pump necessary. Now, you mention modifications but did not specify what they are. It is true that once the engine is modified past a certain point, increased fuel delivery may have to be addressed.

Secondly, if the intent of the A-FPR installation is to raise fuel pressure because the stock or near stock engine suffers from symptoms of low fuel pressure, ie: it running lean, then it's better to fix the problem (ie: vacuum leak, restricted fuel delivery, faulty injectors, etc) rather than going to the adjustable regulator. In addition, if you have 38 psi fuel pressure which drops to 25 once the engine warms up, regadless of what kind of regulator you have, there's a problem somewhere because the Factory Service Manual requires a range of 40-47 psi, when testing according to the FSM. I'd put the OE regulator back in, then diagnose the system for low fuel pressure, first. Once you have the system operating properly, then come back and modify the fuel deliver system, if necessary.

Third, keep in mind that with 25 psi fuel pressure, your engine is going to be so lean at WOT that damage due to detonation is possible.

Fourth, that you adjust the A-FPR through the range in its adjustment and see no difference is another hint that something is amiss in the fuel system.

 

[afree029]

Excellent info and advice. The adjustable fuel pressure regulator was one of those spur of the moment bolt on miracle devices that I am sure many of us are guilty of purchasing at some point. Falls in line with the air foil I suppose. But anyway I installed it and pretty much set it to the stock pressure which was fine for several years. Recently I noticed a dead spot in acceleration at the lower RPM range which is what lead me to my current state. Actually I have done a lot of troubleshooting to arrive at the pump replacement decision. I have replaced the filter. Cleaned both the return and feed lines. Verified the diaphragm in AFPR to be operational and not leaky and made sure there was no blockage in the fuel rails.
I also realize that I could go with stock pump but I am planning ahead for a new set of AFR heads, a different cam, a Nitrous setup and maybe even a new intake and plenum setup.

 

[Hib Halverson]

(snip)
I also realize that I could go with stock pump but I am planning ahead for a new set of AFR heads, a different cam, a Nitrous setup and maybe even a new intake and plenum setup.

If this is an L98 in this 88 you have, with AFR heads (excellent choice, BTW) and cam, a different intake is required because the big restriction with the L98 is the intake manifold and plenum. The money you spend on the cam and especially the heads will be partially wasted unless you change the intake, too.

Add nitrous oxide to all that and, yes, you probably will need a high-volume pump.

In fact, my recommendation would to not use an A-FPR at all.

I'd add the high volume pump, then go up an injector size and, finally, have someone burn the right calibration into a PROM for you. Done right, it will require dyno tuning.

Trying to tune that set-up with an A-FPR will be a fool's errand.

 

[afree029]

You've pretty much decribed exactly what I have in mind.
Still having difficulty deciding on which heads though. I've read a lot of varying opinions about the AFR heads and a lot of good things about the Brodix Race-Rite series. Still gathering info at the moment. Any recommendations?
I definetely see a different intake in the future with either Siemese or Large Tube runners.
The hard part is trying to do the mods in a logical order as I can't afford to implement all of them at same time. I'm trying make sure I do the research up front and once again I really appreciate the advice. It has been duly noted.