AFPR pointless ?

[2GturboTALON]

I have been looking and looking and still only able to find one reason to buy an afpr. I know at idle with a big pump you will run rich and this is one good reason to get an afpr but if i have my injectors deadtimed correctly and compensate correctly for my pump is there really any true reason to get an AFPR ?

 

[agentorange313]

I thought cars have a fuel pressure regulator because of the return line.

if you fuel set up had no return line I dont think you need a FPR or a AFPR

Most current car do not have a return line, thats also why fuel filters last longer now.

 

[MrBoxx]

Can you tell me how you're compensating for higher fuel pressure due to a small return orifice in the stock FPR?

It doesn't really matter how you tune your injectors, and it doesn't really matter if you'll run rich at idle or not. If you have any pump larger than a 190, you'll overrun your stock FPR.

 

[dsm-onster]

Controlling deadtime alters midrange where the FPR will flow properly. You're still seeing an issue that tuning can't solve.

 

[LiquidX]

Not to mention on top of what MrBoxx said, but with an AFPR you can change your fuel pressure (obviously) which can help out if you are running close to your limit for IDC. Raising the pressure would essentially give you a "larger" injector.

 

[steve]

Please read some more on fuel pressure overrun and think about what happens every time the the road dips or you let up slightly on the throttle during part throttle operation.


There is no way to tune around a fuel pressure regulator that doesn't regulate.

 

[donniekak]

I run a hotwired 255, and 1000cc injectors, and i have no problems with the stock regulator. I also use the auto (43.5 psi) and n/t (47 psi) regulators. So even if i have slightly higher pressure at low load, it wont be much higher than i'm tuned for. Example, if you over run a stock regulator to 45-50 psi, that can be a big issue when you are tuned for 37 psi. If you are tuned for 47, or 43.5 psi, overrunning to 45-50 isn't to much for the lft to compensate for.
Also, i would imagine the higher volume demand for e85 would help.

 

[steve]

E85 changes the whole deal since, what, about 35-45% more goes out the injectors all the time when compared to gas.

 

[2GturboTALON]

I just wanted some input because i have read countless threads where the overrun only occurs at idle. Well at least from what some people say. Does anyone have before and after logs by chance ?

 

[steve]

Only is incorrect.

It doesn't happen at WOT, or if it does you have bigger issues.

The rest of the time it roughly depends on how much fuel your pump(s) is/are pushing, how much fuel your return port and lines can flow (2G AWD's can have problems in the return line in the tank) and how much fuel your using (flowing out the injectors). If pump flow - injector flow > return flow the regulator won't be able to regulate.

Since injector flow is engine load based, anything that changes the load on the engine can cause the problem to trigger and manifest until the parameters in the equation change.

If all you care about is what happens when the loud pedal is pinned to the floor it's not as big a deal.

 

[2GturboTALON]

I have plans to purchase one but i wanted to get a poll. I appreciate all the input and it helps me understand the fpr in our cars a tiny bit more. I know for the 2G guys we have small feed lines and that also had me thinking a afpr may not do too much more until that is replaced.

 

[turboglenn]

well, I'll add my .02. I ran for a period of about 8 years from the time i sold my first AFPR to getting my second one. During this time i added a 255wally (upgraded from 190), went to a to4e 57trim turbo, 720 injectors and just before getting rid of the first one went to a haltech EMS.

I never encountered any issues with over run, and the main thing that crosses my mind is that if you;'re using more fuel than can be forced through the return to cause over-run then the over run is something you won't have to deal with.. these are just my thoughts... I actually had more issues going back to an AFPR than i did running a stock 2g FPR for many years

But, now that i'm running 2 parrallel 255HP's i definitely noticed some over run at idle, cruise and part throttle, mainly because i couldn't get the FP below 50;ish IIRC..BUT the over run was due to a small return line (OEM) not the AFPR because i had and s still have an aeromotive unit on there, but was using the OEM return line

But personally i think that if you're not over excessive on the fuel system and your turbo and intake tract is balanced enough to use 70% or more of your fuel when WOT , over-run is something you won't have much trouble with.

I went 12.08 @ 119MPH on the 57 trim, haltech with a half street/half track tune (leaner AFR's, and onlyt slightly higher timing similar to a stock 1g) while running 110 leaded fuel, on MT 26'' slicks peg-leg spinning the hell out of one of them all through 2nd

but this is only my theory, i have nothing more than my experiences to back it up, so please no flaming, take it for what it is, an opinion

 

[1995gsx20g]

like donniekak said if your tuned to run on 47psi and in reality its 45-50 you can get by but think of it from the ecu's view. it does not have a fuel pressure input so it only hopes that when they designed it to stay at 43.5psi with no vacuum that it would.

Also since the fuel pressure changes with an increase/decrease in vacuum the ecu knows that this change is linear to the map based on VE. And since the ecu has less efficient ways of constantly GUESSING VE(in closed loop) compared to you tuning for a steady factor it makes the hole calculation not 100% perfect and i just wont settle for that.

with a fpr being overrun the relationship between vacuum and fuel pressure may not be as linear as you may think.

 

[Black95TSIawd]

the overrun that 2g's are experiencing have ZERO to do with the stock fpr and EVERYTHING to do with the return siphon in the gas tank. Drill it out larger and boom, no more overrun. Stock FPR works, its just difficult to actually monitor your pressure. Its a good idea to have a gauge and it is usually hooked up to an aftermarket AFPR.

 

[turboglenn]

the overrun that 2g's are experiencing have ZERO to do with the stock fpr and EVERYTHING to do with the return siphon in the gas tank. Drill it out larger and boom, no more overrun. Stock FPR works, its just difficult to actually monitor your pressure. Its a good idea to have a gauge and it is usually hooked up to an aftermarket AFPR.

Good point, just remember that the siphon tube only applied to the GSX, as the T doesn't have one. My oer run came from the stock return line (only after adding a second pump in tank though)

 

[1995gsx20g]

Good point, just remember that the siphon tube only applied to the GSX, as the T doesn't have one. My oer run came from the stock return line (only after adding a second pump in tank though)

i never heard about any of this.. i would like to hear some more please?

 

[steve]

I never encountered any issues with over run, and the main thing that crosses my mind is that if you;'re using more fuel than can be forced through the return to cause over-run then the over run is something you won't have to deal with.

It's hard at idle and low loads on gas to use more fuel than flows back via the return. I think I've explained before, fuel pump flow has to be <= injector flow + return flow under all conditions or the regulator will overrun.

Also since the fuel pressure changes with an increase/decrease in vacuum the ecu knows that this change is linear to the map based on VE. And since the ecu has less efficient ways of constantly GUESSING VE(in closed loop) compared to you tuning for a steady factor it makes the hole calculation not 100% perfect and i just wont settle for that.

Keep in mind that on MAF equiped cars VE drops out, the air flowing though the MAF directly effected by the real VE. (except when you have leaks)

The ECU makes no adjustments for fuel pressure changes because the whole point of the regulator is to maintain a constant delta pressure across the injectors so they always flow at the same rate regardless to manifold pressure.

the overrun that 2g's are experiencing have ZERO to do with the stock fpr and EVERYTHING to do with the return siphon in the gas tank.

From what I've seen and read people hit the flow limit of the return port before they hit the flow limit of the tank return port on 2G GSXs. Once you fix the regulator issue it doesn't take much before the tank becomes the restriction.

 

[95blackGsTurbo]

I like Donnie run a rewired 255hp with a stock regulator. No issues at all. I even have a pressure gauge mounted to monitor fuel pressure and no issues. Granted it is a new OEM unit but I have never been a fan of AFPR because it really isn't something that 75% of this board needs. Just another expensive shiney part. It isn't uncommon to run a stock or EVO regulator down here on 2g's. Some guys are even successful with a 255 and inline or dual 255hp pumps. This overrun thing really seems to be more of a 1g issue.

 

[1995gsx20g]

are we talking about closed loop or open loop with the MAF based system?

Keep in mind that on MAF equiped cars VE drops out, the air flowing though the MAF directly effected by the real VE. (except when you have leaks)

this is what i was trying to say in my jumble of words. but if the fpr is being over run then that means pressure is never at a steady constant in relationship to vacuum correct?

The ECU makes no adjustments for fuel pressure changes because the whole point of the regulator is to maintain a constant delta pressure across the injectors so they always flow at the same rate regardless to manifold pressure.

 

[steve]

are we talking about closed loop or open loop with the MAF based system?

Why does it matter? Fuel trims are only there to correct for the small differences between real world part behavour and the mathematical model. Most of the time that a working car is in open loop it's usually consuming enough fuel that the regulator isn't being overrun. The second you lift off the throttle, things change.

if the fpr is being over run then that means pressure is never at a steady constant in relationship to vacuum correct?

Correct, if the regulator is being overrun there is no pressure regulation and fuel pressure doesn't track manifold pressure while it's happening.

 

[1995gsx20g]

Im pretty sure i understand this a lot better now, thank you steve