Fuel Pressure Adjustments. afpr ?'s ALL GO HERE
 

As with the other "ALL GO HERE" Posts...

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So, if you have a questions relating to Adjustable Fuel Pressure Regulators. Or adjusting your fuel pressure...

Please post here. Of course, after you have searched, and after you have read the related articles..

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My walbro255 fuel pump is so strong it overcomes the AFPR at 17PSI. I'd like to run 13-14PSI which is recommeded by the programmer for my custom chip.

Someone suggested lowering the voltage to the fuel pump? How would i go about doing that?

Appartenty the fuel lines themselves are my restriction....

Would getting a lesser/cutting the spring in the FPR lower the PSI?

Instead of cutting the spring I recommend drilling out the weld that is in the bottom and make it adjustable, get a fuel pressure guage and fitting to dail it in exactly. I used blood sweat, and tearing, and a wood bit in my cordless drill but I got it. It was tough but its gone. cut a notch in the screw and use a flat head to adjust it.

I have the VAFPR and I can't for the life of me get the fuel pressure to go down. I've been turning the little adjustment screw CCW (lefty loosy) and it just stays at 16 psi. Should I be turning it the other way???

Tony

I already have an AFPR, its adjusted as LOW as it can go. That is why i need other means of lowering the pressrue, such as lowering the voltage to the fuel pump...? or getting a lesser-spring?

What AFPR are you using? If its aftermarket with a stiffer spring just reuse the spring from your stock regulator.

I wish it were that easy. Its turbo city's kit, it didnt come with a spring... this one is from my original FPR.

is there a certain size/demensions on the spring i can use to find another one?

Yeah, it's not what you'd expect. Clockwise lowers the pressure, counter clockwise raises it.

Haha, wow, then I must be frickin killing my fuel pump! I guess it makes sense though if you think about the threads and what not

Any advice on how to lower my fuel pressure?

I'm tired of my truck always running rich, and the extra PSI is playing hell with my computer/driveablility. The custom chip is set for the stock 13PSI... never had any problems till i replaced that damn fuel pump with the Walbro 255... heh

-AFPR is adjusted as low as it can go, and i can only get as low as 17PSI... i want to have 13-14PSI.

-I'm using the same spring as the old 5.7 FPR.

Options?

-Drop the tank, use a stock pump...

-Lower voltage to the fuel pump... how?

-Find a replacement spring, one of lesser tension.. where would i find a specific spring like that?

-Tempted to just cut the existing spring... but you loose the base of it, and all the tension rests upon one coil-end.

hmm.. i'd say, cheapest one first... but no ghetto riggin'. :p

any advice on this one?
thanks!

check with lon @ top down solutions. he has a spring that corrects this problem in vafpr installations, i don't know if the same one would work on afprs.

This is why i recommend the 190 pump. The 255 is way overkill and is made to support something like 700+ hp. Get the 190 and be happy.

what is the 190?

It's the walbro electric pump that flows 190 lph instead of 255 lph. I'm not even sure if they make it for our cars, but I know they do for a lot of other cars. I think 255 is just too much for the low fuel pressure tbi requires.

but, if you're using a fuel pressure regulator, it wouldn't make any difference, would it?

depends, some guys actually can't get the pressure down to where they want it again because the 255 is just too powerful even with the regulator bottomed out

if that happened, you could always put a standard regulator in line before the throttle body in addition to the one after it, couldn't you?

I guess you could, but most are for carbs with around 6-7 psi, not 13 or so like tbi. I think the better thing to do would be a high flow pump designed for tbi like turbo city sells or something similar. I believe those are capable of 30 psi and wont overload the tbi regulator either. The 255 was designed for a really badass multiport system like tpi or lt1 or ls1 and is designed for around 50 psi, not the low 13 or so of tbi.

For anyone who is interested, you can make your fuel pressure adjustable and not have to disassemble it to adjust it. Just find a spare allen wrench and grind down the long end into a flathead screwdriver. When you want to adjust fuel pressure, just stick the allen wrench-driver thingy through the hole and adjust all you want. It's not great, but it works.

I've toyed with this idea, maybe someone will find it interesting enough to do. To make the pressure adjustable without pulling anything apart, why not replace the stock screw with one that extends down, beyond the end of the regulator, out that hole in the tbi, and ends in an 8mm or so hex, so you just have to reach under there with a little wrench to turn it?

Did that make sense?

Makes perfect sense, and that is pretty much what turbo city does with theirs.

It makes sense. But the only thing is that you would have to attach a washer to the bolt so it wouldn't fall out or not allow you to adjust. You could probably just weld it on now that I think about it.

I wish I wish I had a lathe. Then I could just turn the whole thing as one piece.

Yep..did it several years ago. Tap the hole for a 3/8-24 bolt and here ya go.:)

This is actually the part that you tap.

is that all there is to it? tap the hole? or do I have to drill it out first?

drill out the weld, remove the screw, and then replace it with a bolt long enough to fit the regulator?

3/8-24tpi ?

From what I remember remove the weld, the hole will be close enough in size, tap the hole 3/8-24 SAE, add the bolt.

but I'd need a 3/8" bit to drill the weld out all the way correct?

No not 3/8. The drill sizes are smaller than the actual size of the bolt to allow metal to be left for threads. For a 3/8-24 tap you would use a .328" bit or a 21/64" bit for the decimal challenged. :)

Why is everyone allways trying to lower their fuel pressure? In general wouldn't you want more fuel pressure?

TPI Cars seem to respond very well to uping the fuel pressure. Our TBI cars don't?

If the injectors are changed to larger ones you might need to adjust downward. If stock with added airflow mod's.....yes you would turn it up to adjust the fuel curve if you needed to.

because a lot of our cars come rich from the factory.

190:

http://www.autoperformanceengineering.com/

Correct. Also, when guys go with bigger injectors (after heads cam and tuning) they may need to lower the PSI. They can either run high flow at low pressures or run low flow at high pressures. This depends on injector size though.

yeap, but I would rather run smaller injectors at a higher psi. I feel that it would give a better spray of fuel and better atomization.

Anyone want to fill me in on how to install a fuel pressure gauge so I can read whats going on? I don't really know where it even goes or how I would install it.

You can splice in any mechnical fuel gage. Summit makes one for like 30 bucks. Try a few searches to see what comes up. There should be a few decent threads containing part numbers and such.