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When do you absolutely need a non-stock fuel pressure regulator

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94EclipseGST

15+ Year Contributor
334
0
Sep 1, 2003
Des Plaines, Illinois
I've done all of the stage 1 & 2 mods. I've also upgraded to a B16G turbo. Got a MAFT and stage III dsmchip. FMIC is in the closet and will be installed this summer for sure.

Anyway, no matter what I've done (including fixing all boost leaks) I run rich. So much so that I bog at high RPMs. Aside from my sidemount heat soaking, I'm wondering if it could be that I do not have an aftermarket fuel pressure regulator.

I have a Walbro 255, 550cc injectors.

So, the question is, when do you absolutely need a non-stock fuel pressure regulator? Is this what is causing my problems?

Thanks in advance.
 
When upgrade your fuel pump to someting bigger than 190lph.
 
Well, what a unique set of search criteria! LOL

So, will not having the fpr cause the problems I'm having?
 
More then likely i had similar problems till i installed my aeromotive. It is amazing what stable fuel pressure can do when your tunning.
 
When you go with biggger injectors then you need one but otherwise no. I am running a 255HP on 450s and stock reguator and no problems at all with fuel.
 
TSIfreek said:
When you go with biggger injectors then you need one but otherwise no. I am running a 255HP on 450s and stock reguator and no problems at all with fuel.

Injectors don't have anything to do with it. Just because you don't see the problem doesn't mean there isn't one.

95 GSXracer said:
Think of the high base pressure you get from a sotck reg and a 255 as boost creep on your turbo. You can rightly call it fuel pressure creep. I used to get boost creep to 18 psi on my 14b. The car ran well with 18 psi, so was anything wrong with that? You could say no, because it ran fine, or you could say yes, because I had limited control over boost, and the WG wasnt doing its job. Same thing with fuel pressure creep. The issue is that more often than not, the fuel pressure creeps enough that your fuel trims are completely bolixed and closed loop runs like shit, and economy goes down the shitter. If you are tuning logger/afc style, you will jsut adjust your low trims to try to make up for it. If you are running DSMlink however, the problem is so obvious, it'll drive you nuts. Trust me

So again, it all depends on how you look at it, and what your goals and concerns are. For a low HP daily driver I dont think its worth running around with banjaxed trims 99% of the time. For a track car that spends most of its life at WOT, who cares. For street cars I personaly suggest using a FPR for the 255, or if thats not in the budget, and you are sure you arent going to go over say 120-125 mpg traps, just go with the 190 and drive it on. I've seen it do 124 mph, very capable pump. And the fuel pressure creep is minimal. Without DSMlink you would be unlikely to notice it.

I hope this helps. L2RTSiAWD hit the nail on the head, but some people just refuse to listen w/o explanation.
 
indeed. 255's will overrun the stock FPR and run more pressure into the fuel rail than should be. thus when the injectors open more fuel is pushed through in a single pulse than should be.

my buddy had a 255 with stock fpr. tuning was sketchy at best. he finally got a afpr and WOW, it made worlds of difference. he was running so rich up high that when we installed the fpr we richened out his safc and he was still running lean up high(cause he was pulling so much from the injectors to compensate).

if you have a 255, you need a fpr. simple as that.
 
Look on vfaq.com under "Fuel". Somewhere is a comprehensive test of psi vs. flow rates for OEM, 190 and 255 high and low pressure pumps. Know that the base fuel pressure is too high for a stock regulator and a 255lph, piece this information together and you will come up with a suitable explanation.
 
SAFC-2 Works great for tuning the fuel curves. I love mine. Feel quite a bit of a difference with a little tuning, get killer gas mileage (32 hwg) and hit good boost without bogging or going too lean. Definetly worth the money.
 
The problem with a 255lph and the stock regulator is you get inconsistent fuel pressure at different loads/rpm. You simply can't tune it out because it's never the same, it all depends on load and RPM of the engine. Load and RPM are infinitely variable so it's just not possible to tune it out with a chip or AFC.

When you have a 255lph pump you need an AFPR. You should not buy the pump with out the regulator. Thats like rims without tires. Just because you can put the rims on and maybe get the car to move, doesn't mean thats the way it's supposed to be.
 
^^^Um.......I think you have your answer! :thumb:
MB

Oh yeah, been there done that. Does not work properly without.
 
Echo5Zulu said:
SAFC-2 Works great for tuning the fuel curves. I love mine. Feel quite a bit of a difference with a little tuning, get killer gas mileage (32 hwg) and hit good boost without bogging or going too lean. Definetly worth the money.

An safc has nothing to do with an afpr. That is like comparing apples and oranges.
 
Purchased the Aeromotive kit. I'll probably have it after the holiday. I'm crossing my fingers that this solves the problem. I can't even dyno my car because the bog and studder. I thought I had all the necessary parts for tuning, but I guess not.
 
I was running the 255 w/the stockfpr, and I was way rich. installed the aeromotive and it just rune so much better. mpg are up at least 5-6mpg more and you can feel the difference in the way the car pulls. definetly a great investment.
 
One last question. Once I get this bad boy installed (it will be here Friday, if UPS doesn't screw up), how do I determine the new settings. Obviously, the stock 38 isn't going to cut it.

I have 550cc injectors and 255lph fuel pump. All other mods are listed if you need those.

Thanks,
 
94EclipseGST said:
One last question. Once I get this bad boy installed (it will be here Friday, if UPS doesn't screw up), how do I determine the new settings. Obviously, the stock 38 isn't going to cut it.

I have 550cc injectors and 255lph fuel pump. All other mods are listed if you need those.

Thanks,
The stock fuel pressure setting is what you want to set it to. You are not to the point where you need to run increased fuel pressure. Remember, it rises 1:1 with boost anyway. Make sure you mount a gauge on the regulator so you can see what you are setting it to (otherwise you are working blind). :dsm:
 
99gst_racer said:
The stock fuel pressure setting is what you want to set it to. You are not to the point where you need to run increased fuel pressure. Remember, it rises 1:1 with boost anyway. Make sure you mount a gauge on the regulator so you can see what you are setting it to (otherwise you are working blind). :dsm:

You can run with 45psi base though (like 2g) which si just fine. If you set the afc you can run anything. Some guys at the track run 60psi base on 660cc injectors and go low 11's with a SAFC and hacked MAF FYI...
 
I do have a gauge--it comes with the kit that I ordered.

Okay, now I think this is making some sense. I was under the impression that I had to raise the pressure to cure the overrun. So if I'm understanding you correctly, because the fpr has 1:1 that raises with boost, that actually cures the overrun problem.

Sorry to be such a noob on this subject. I struggled so long with learning tuning, this is a whole new aspect for me. I'm trying to learn how the fpr fits into my tuning.

Thanks again to everyone whose helped.
 
94EclipseGST said:
Sorry to be such a noob on this subject. I struggled so long with learning tuning, this is a whole new aspect for me. I'm trying to learn how the fpr fits into my tuning.
This VFAQ will probably have everything you need to understand the functions of an afpr and how to setup the base pressure properly. Good luck.
 
94EclipseGST said:
Okay, now I think this is making some sense. I was under the impression that I had to raise the pressure to cure the overrun. So if I'm understanding you correctly, because the fpr has 1:1 that raises with boost, that actually cures the overrun problem.
No; here, I'll try to explain it for you. Inside the regulator, there is an orifice. The regulator uses that orifice to regulate pressure and to allow unneeded fuel by so it can run back to the tank. What happens is, when you install that huge 255 pump, it flows a shit-ton more fuel to the motor/regulator. So much, that the orifice in the stock regulator is too small to handle the added volume and it begins to be overran. It's capability to return the correct amount of fuel to the tank is compromised. Because of this, the pressure begins to rise and that causes the vehicle to run a rich mixture; which hurts performance and gas mileage.

The difference is that the aftermarket adjustable regulator has a larger orifice that will handle the flow from the 255 pump. And it has the adjustable screw on top to adjust the pressure applied to the diaphragm which in turn raises or lower your fuel pressure.

I hope this helps you better understand the regulation process of fuel pressure. :thumb:
 
Thanks oldman and 99gst_racer. Very helpful information. Once again, you both get cool points! :thumb:
 
I got the kit today, but the damn fuel rail adapter is too small--the holds don't match up with the fuel rail. I went to Murray's and Autozone, they didn't even know what I was talking about and when I showed them the piece, they'd never seen it before.

I'm going to get another one shipped from the vendor that sold me the thing, but I need an adapter now. Anyone know where I can get one?

Right now, I just hooked the stock fpr back up, and attached the Aeromotive to it. I just wanted to see what my pressure was--it was at like 60psi. I was really overrunning the sucker, so that's got to be what's causing my nasty bog and tuning troubles.

Anyway, where can I get this stupid adapter!!!????
 
94EclipseGST said:
I got the kit today, but the damn fuel rail adapter is too small--the holds don't match up with the fuel rail. I went to Murray's and Autozone, they didn't even know what I was talking about and when I showed them the piece, they'd never seen it before.
I had the same problem with mine. The holes were too narrow and it wouldnt fit. Just take a drill or file and widen out the holes. It's the same concept as making a 2G oil drain line fit a 14b. Here's a pic.....
You must be logged in to view this image or video.

The black holes are where the holes are on the flange. The red area is what you want to remove with a drill or file. I did it like this and I've been fine ever since (about a year now).

94EclipseGST said:
I just wanted to see what my pressure was--it was at like 60psi. I was really overrunning the sucker, so that's got to be what's causing my nasty bog and tuning troubles.
Yeah, same here. We tested my fuel pressure right before we installed the AFPR, and I was at 62 psi. OMG


If you don't want to modify your rail adapter, you could always get crafty and make your own. See pic below. I made this in about 30 min. and I used it for about 14 months, trouble free. :thumb:
 

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