fuel pressure regulator

[mostlygobitshow]

I was wondering if since I have an aftermarket fuel pump on my 91 gst with 16g, DO I need to get a new fuel pressure regulator. COuld this be why the car hesitates when I punch the gas. Is it getting too much fuel so it can't even combust or what? Thanks for any help you guys can give me!

 

[daren_p]

Could be but need a little more info. What size is your fuel pump?

 

[BluemeanieTSi]

I was wondering if since I have an aftermarket fuel pump on my 91 gst with 16g, DO I need to get a new fuel pressure regulator. COuld this be why the car hesitates when I punch the gas. Is it getting too much fuel so it can't even combust or what? Thanks for any help you guys can give me!

aftermarket pump - yes. end of discussion

 

[EclipseOwner95]

aftermarket pump - yes. end of discussion

Uhm...negative, you don't need an AFPR when you install a high volume fuel pump, especially in a 1g, I had a stock regulator for 2 years with no problems, I reccently installed an AEM AFPR so I could raise the fuel pressure.

 

[boostedinaz]

Uhm...negative, you don't need an AFPR when you install a high volume fuel pump, especially in a 1g, I had a stock regulator for 2 years with no problems, I reccently installed an AEM AFPR so I could raise the fuel pressure.

Depending on the pump it may not be necessary, but it is a big help.

By the way your reasoning isnt that great. "I ran a 60-1 on 450 injectors for a month" oh then that must be ok then right???? Just becasue it has be done doesnt mean it is the best way or the even the right way.

I would put on one becasue alot of the bigger pumps (255) will over run the stock regulator, and even though your car might run fine, it will run rich at idle. This can cause poor fuel milage and make it hard to tune for a nice idle.

 

[EclipseOwner95]

Depending on the pump it may not be necessary, but it is a big help.

By the way your reasoning isnt that great. "I ran a 60-1 on 450 injectors for a month" oh then that must be ok then right???? Just becasue it has be done doesnt mean it is the best way or the even the right way.

I would put on one becasue alot of the bigger pumps (255) will over run the stock regulator, and even though your car might run fine, it will run rich at idle. This can cause poor fuel milage and make it hard to tune for a nice idle.

That wasn't my reasoning, it was to raise the pressure for my 780's on the 57 trim thanks. But as I stated before, even my rewired 255HP did not over run the stock regulator, 2g's are the ones that have the problems with the stock FPR being overrun. Most if not all 1g's don't have many problems with them being overrun.

 

[mavisky]

The problem is that we don't know what fuel pump he has. If he has a 190lph then he's fine on the stock regulator, if he's on a 255 then he'd probably better go to one if he wants the best possible tune. It's not mandatory though and you won't damage anything, your wot tuning will be just fine, it'll really hurt the midrange though. Look at it this way, let's say you are on a stock fuel pressure regulator and running 15 psi, here's how the fuel situation might work out.

motor at 0 boost - fuel pressure at 45 psi (assuming 7psi overrun)
motor at 5lbs boost - fuel pressure at 45 psi (7psi overrun is still higher than base +boost level)
finally motor at 7lb boost - fuel pressure will be correct at 45 psi
motor at 10lb boost - fuel pressure still correct at 48 psi now
motor at 15psi max boost - fuel pressure at 53psi

At any boost level above whatever the base + amount of overrun the car will run right. But as you can see until it reaches that level the car is running rich, now it gets less rich as boost builds, but it will still hamper flow. In real life this situation may not level off at 7psi like in my example. It may be as high as 15psi before it evens out, someone would have to pull the hose off of their stock 38psi 1g regulator and see what it comes to on the guage with a 255 installed. Take that pressure - 38 and you'll have the boost pressure your car will have to reach before your fuel pressure starts rising at a 1:1 ratio again.

 

[beat90tsi]

Mavisky is right, you're only raising your fuel pressure when your engine doesn't need it at all, and consequently running leaner than you normally would at high RPMs under load.

But to get back on topic, the pump he has matters, with any upgraded pump, the AFPR is preferred, but if he's running a supra pump or something else that large, he's in desperate need of a regulator ASAP.

 

[BluemeanieTSi]

"Running any bigger fuel pump (no matter if Walbro 190 or 255) and bigger injectors without AFPR is a half-assed application. One can see people running their S-AFCs at -20% to maintain an acceptable A/F ratio while the IPW table, timing and fuel pressure curves look like an ass and the car knocks like a bi*** (and they blame it on "phantom knock"). Maintaining a proper fuel pressure and timing curves are the key to any successful tuning - which is impossible to achieve without AFPR if bigger than stock fuel pump and fuel injectors are utilized.

The ECU will try to maintain the proper A/F ratio at part-open throttle only - based on the O2 sensor readings, in which case it will compensate for the increased fuel pressure by shortening the IPWs. However, the ECU ignores the O2 sensor output at WOT and will not compensate for the pig-rich mixture. It's not the ECU that dumps the fuel with the stock injectors at WOT, it's the increased fuel pressure that supplies more fuel at the same IPWs. The fuel cut itself comes only from aproaching the MAS threshold, which happens when people install a bigger fuel pump or injectors and crank the boost up. In this scenario, the car will run pig-rich even more since one has 11:1 A/F to beging with, increased fuel pressure from the bigger fuel pump and increased fuel pressure in 1:1 ratio with the increased boost level from the fuel pressure regulator and longer injectors pulse widths (matched to the increased airflow) on top of it.
In real numbers, the stock base fuel pressure is 36 psi and 47 psi at full stock boost level of 11 psi. Once someone installs let's say Walbro 255HP and runs 18 psi of boost, the base fuel pressure goes from 36 psi to 48 and from 47 to 66 psi at full boost - and at increased IPWs (until one hits fuel cut). The result is a car running awefully rich.
In my opinion, running any bigger-than-stock fuel pump without AFPR is a half-assed fuel system modification that may cauise problems when it comes to tuning.

Some people claim that one can successfully run the Walbro 190 without AFPR. Then their IPW maps are stretched to hell due to their S-AFC settings jumping across 20% across the board just to compensate for a fuel pressure curve that looks like an ass and changes any time one turns his headlights or turn signals on. Then they slap on a set of 660cc's and run the bi*** at -30% S-AFC settings with timing that looks like it came straight from Chevy 350 while they wonder where the "phantom knock" came from.
____________________

as i stated before it has nothing to do with HOW much boost your're running.

if your base FP is 42psi then at 7psi you'd have 51psi fuel pressure
if your base FP is 60psi then at 7psi you'd have 67psi fuel pressure (and you'll be wondering why you're running stupid rich with hardly any psi)

you now not onlly have to tune for 7psi but you have to tune around the fact that your injectors are operating at a larger volume.

REGUARDLESS of how much boost you plan to run if you want a good timing curve and good tuning you need to run a regulator. if you choose not and think otherwise then don't."

 

[beat90tsi]

One thing a lot of people fail to realize is that when your car is in running in vac (90% of operation) it runs lower than base fuel pressure, and with a bigger pump, it never runs as low of a pressure as it is supposed to, and is why your car will not have optimal performance, despite the fact that it might run.

My car will start and run with the MAF sensor unplugged, that doesn't mean it's fine.

 

[mavisky]

Okay lets take your numbers then since it sounds like you've seen them first hand. Now from what I know you have a few different things to deal with when it comes to maintaining fuel pressure. You have the pressure that your regulator is set to, in this case its a 1g and you say that's 36psi. You have the amount of pressure applied to the diaphragm through the vacuum hosing, you used 18psi so I will as well. Where people run into issues is that the stock regulator can't move enough fuel at the regulator's base opening to keep the pressure in the rail at 36psi, you claim this rise in pressure is equal to 12 psi in the rail for a total of 48psi in the rail with a 255.

so if we take this formula

regulator pressure + vacuum source - base overrun = total fuel pressure

since you state that the base raises 12 psi you could replace this with this equation.

regulator pressure + vacuum source - 12psi = total fuel pressure

What I know about the overrun issue is that the stock regulator can't open up enough to flow the volume of fuel the 255 puts in the rail at lower pressures, but at higher pressures the diaphragm opens up enough to let the fuel out. This may be where my teachings came from the wrong people.

on an adjustable regulator setup it makes sense that you wouldn't have the overrun problem so your formula would look something like

regulator pressure + vacuum source = total fuel pressure

 

[beat90tsi]

uh....riiiight

I think the bottom line is....

AFP w/o AFPR = FUBAR fuel tuning

 

[steve]

What I know about the overrun issue is that the stock regulator can't open up enough to flow the volume of fuel the 255 puts in the rail at lower pressures, but at higher pressures the diaphragm opens up enough to let the fuel out. This may be where my teachings came from the wrong people.

The FPR will try to maintain Fuel Pressure = BASE pressure + MANIFOLD pressure. On a good 1G engine with about 18 in hg vacuum the manifold pressure will be about -9 psi and fuel pressure should be about 27 psi. At 0 psi manifold the fuel pressure will be 36 psi and at 20 psi boost the fuel pressure should be 56 psi. Draw a line between these points and you'll know what the fuel pressure should be. The problem with overrun is the stock regulator outlet can't flow enough volume to keep the pressure from rising and until the excess volume drops off the regulator won't follow that pressure line. It's not the higher fuel pressure that fixes the problem ( it does help the outlet flow more) but that the engine consumes more fuel that causes the regulator to start regulating again.

So your formula is off because there isn't a fixed overrun, it varies depending on engine load.

Steve

 

[Burnett03]

My car runs fine without a FPR and i run 255pump and 680cc injectors. Notice i said it runs "fine" It runs rich at mid throttle, rich at idle and wastes gas. Still runs 12s but doesnt run and have the gas mileage as it should. This is why i orderd a FPR today. Hopefully it will make the tuning a bit easier and get rid of that rich smell at idle and when i come to stops.

 

[steve]

My car runs fine without a FPR and i run 255pump and 680cc injectors. Notice i said it runs "fine" It runs rich at mid throttle, rich at idle and wastes gas.

Maybe you should just say it runs
I'm not picking on you since you recognise you have the problem. Too many others think the fact that they run 12's means they don't have overrun. What it really means is they don't understand and they have never checked their fuel pressure to see that it's not linear anymore.

I don't think stock regulator really able to handle much more that the stock pump. I saw a 2 psi jump in pressure just putting a unrewired 180lph 3kGT pump in. Not enough to worry about but gives you an idea where overrun starts. Of course not all stock regulators are exactly the same and YMMV.

Steve

 

[mavisky]

So your formula is off because there isn't a fixed overrun, it varies depending on engine load.

Steve

So the theory that the car can attain a 1:1 rising rate at a certain point is still correct, but rather than a certain psi it depends on the total volume of fuel the motor is devouring at the time. I see now, in that case the equations would be wrong, but the idea that at lower boost you would be monster rich while still maintaining a good wot tune are still correct. What's worse is that any area under which you're overrunning the fpr it would vary greatly depending on rpm/boost/throttle opening which would make it nearly impossible to tune for correctly. For some who've been around for awhile this is why some people were trying to setup a gm map sensor to replace the tps signal on an s-afc. That way it would change maps based on boost/rpm levels which would closer approximate the motors actual fuel needs than throttle position/rpm in order to improve low boost overrun conditions where on large injectors you could be in a very rich state which is not only slow, but also slows spoolup which means its going to take you longer to get to an area where you're making the power you should.

 

[Downtime]

Thanks, for those words of wisom you have answered all questions i had about afpr and why it is needed.That's what i like about this board you can really get some good info here.

 

[DSMnewbi]

So the only thing limiting the stock regulator is the outlet? Couln't you drill it bigger, tap it, and it would run fine with a bigger fuel pump?

 

[turbo90gsx]

Thats alot of good information on AFPR's. I have had a 255 pump on the stock 1g regulator for probably a year now, and I now understand alot of the symptoms that my car has. I have the "rich" bumper if you know what I mean. Im really considering getting an AFPR now.

 

[mavisky]

So the only thing limiting the stock regulator is the outlet? Couln't you drill it bigger, tap it, and it would run fine with a bigger fuel pump?

The problem lies in the inlet area of the regulator, the diaphragm size itself, and the outlet. Pretty much the entire thing.

 

[CSEclipse]

i've been running a supra fuel pump with 660's and still don't have a AFC or FPR and running very rich... I was going to get a AFC (I or II not sure yet?) first but now i think im getting the FPR, thanks for all the info

 

[boostedinaz]

i've been running a supra fuel pump with 660's and still don't have a AFC or FPR and running very rich... I was going to get a AFC (I or II not sure yet?) first but now i think im getting the FPR, thanks for all the info

So you have a fairly large pump and injectors and have no way of contolling either of them????

I would get both becasue you will need them to make the car run propely. You car must drive like ass if you are running 660's with nothing.

 

[mavisky]

You realize that with that much extra fuel in there you could've easily washed fuel down past the rings and into the oil thinning it to the point where you would've fried every bearing in the entire motor including risking your turbo?

You need to get at least an safc to lean it out some.

 

[awdsm drft]

EPROMS burned for specific injector sizes own tuning.

 

[steve]

EPROMS burned for specific injector sizes own tuning.

EPROMS burned for specific needs > any piggyback. But this is pretty far off topic.

Steve