255lph fuel pump

do i have to have a fuel regulator with a walbro 255 pump if i have a safc2?
thanks
tyler

Yes, absolutely. An adjustable FPR is the only way to control fuel pressure over-run.

k, thanks

NO! if you are properly tuned with a SAFC, all you have to do is lean out the fuel trim for lower rpms so you don't bog. FPR is only really nessecary if you wish to fun higher fuel pressures, which is for people who don't want to shell out for a safc, or cars that are putting so many horses to the ground that they actually need the extra pressure. A SAFC will be fine with a wally. As a side note, if your hp goals are not over 400, then a 190 is the better way to go...its a little less noisy. Fuel pressure overrun is well....the wrong term. Since you are probably running a bigger turbo, your car will just need more gas, not more pressure, and your ecu is not used to the extra gas, so the idle gets fucked up. This happened to me when I put on my EVO III. a SHORT term solution (as in until you get the money) to the SAFC is to raise your idle a small amount, so that when you do get the extra fuel, your car will use it and not die

NO! if you are properly tuned with a SAFC, all you have to do is lean out the fuel trim for lower rpms so you don't bog. FPR is only really nessecary if you wish to fun higher fuel pressures, which is for people who don't want to shell out for a safc, or cars that are putting so many horses to the ground that they actually need the extra pressure. A SAFC will be fine with a wally. As a side note, if your hp goals are not over 400, then a 190 is the better way to go...its a little less noisy. Fuel pressure overrun is well....the wrong term. Since you are probably running a bigger turbo, your car will just need more gas, not more pressure, and your ecu is not used to the extra gas, so the idle gets fucked up. This happened to me when I put on my EVO III. a SHORT term solution (as in until you get the money) to the SAFC is to raise your idle a small amount, so that when you do get the extra fuel, your car will use it and not die

Let me try to correct some of this misinformation before it spreads too far ;) Tuning with an AFC or any other device is completely independant of and has nothing to do with fuel pressure tuning. Leaning out to compensate is a piss poor bandaid. The whole purpose of upgrading FPRs is to run LOWER pressure. Shit, you can simply increase spring pressure on the stock FPR if all you want to do is raise pressure. B&M Command Flow for example. The onyl way to lower pressure (back to stock) is with a regulator that is larger and can bypass more fuel to the tank. Fuel pressure over run is absolutely correct. The pump puts out too much fuel, the regulator can not bypass enough, and pressure rises. You have over run the regulator. You can also call it fuel pressure creep. Same thing that happens with boost creep. Wastegate can't bypass enough exhaust gass, boost pressure rises.

Fuel pressure should absolutely be set properly to base pressure with the hose off, and change with boost on a one to one ratio. That means it has to DROP in vacuum situations (99% of the time the motor is running). 2 inches/HG is equal to one psi. So if idle vacuum is 20", the reg needs to drop 10 psi from base pressure. Base pressure is 38 psi for 1Gs, 42 for 2Gs. A stock reg will not be able to get to 32 psi with a 255, high or low pressure version. In fact, the 190 even overuns the stock reg slightly, but its not enough to cause much trouble. Without DSMlink, I never even noticed it was there, until I got a fuel pressure guage. ;)

Moral of the story is if you want the motor to run properly the way it was designed to, fuel pressure has to be correct. If you dont mind half-assing it, it can be tuned around. A matter of personal preference as usual, but I know exactly where I stand on this subject. I have even go so far as to run a larger return line back to the tank, since that is the next bottle neck after the regulator. ;)

by fuel pressure overrun do you mean the rise is pressure in regards to higher boost levels? The SAFC will trim the fuel so that the engine gets (with an wideband o2) almost perfect trims, and these will not over work the (upgrade) pump or overrun the pressure reg. With 16psi of boost, the FPR rises to 60psi. With the afc, , the trim can be leaned out so that your wally won't pump 190, or 255 lph at WOT, it will reduce the load on the pump so it does not add as much fuel, thus keeping the fuel pressure at the correct level. 450cc injectors at WOT at apprx 100 LPH will have to be tuned so that the that is he gets a 190, his fuel pump will only run at 52%, which will provide the same amount of fuel. Only if his fuel pump was running at a rate higher than he needed would his pressuer overrun. his pump at 52% will pump the same amount of fuel as 100% stock. This value of course increases as he upgrades his car, so say he needs an extra 12% fuel than he gets with his 100LPH, he would tune so that the wally runs at 64% vs his ecu reading WOT. If he did not have the SAFC tuned, the fuel pump would run at full voltage, pumping 190LPH, creating way to much fuel, and overrunning the FPR.

Now im pretty sure that this is correct, but if I have made some error, please correct me.

by fuel pressure overrun do you mean the rise is pressure in regards to higher boost levels? The SAFC will trim the fuel so that the engine gets (with an wideband o2) almost perfect trims, and these will not over work the (upgrade) pump or overrun the pressure reg. With 16psi of boost, the FPR rises to 60psi. With the afc, , the trim can be leaned out so that your wally won't pump 190, or 255 lph at WOT, it will reduce the load on the pump so it does not add as much fuel, thus keeping the fuel pressure at the correct level. 450cc injectors at WOT at apprx 100 LPH will have to be tuned so that the that is he gets a 190, his fuel pump will only run at 52%, which will provide the same amount of fuel. Only if his fuel pump was running at a rate higher than he needed would his pressuer overrun. his pump at 52% will pump the same amount of fuel as 100% stock. This value of course increases as he upgrades his car, so say he needs an extra 12% fuel than he gets with his 100LPH, he would tune so that the wally runs at 64% vs his ecu reading WOT. If he did not have the SAFC tuned, the fuel pump would run at full voltage, pumping 190LPH, creating way to much fuel, and overrunning the FPR.

Now im pretty sure that this is correct, but if I have made some error, please correct me.


Eh, let me give this a shot. I think Kevin may have used too many big words ;) :biggrin: Just kidding.

The Walbro 190lph and the 255lph provide more fuel by being able to run the pump at higher pressures more efficiently. Consequently, this causes the pump to increase fuel pressure all the time, not just at WOT. Idle and cruising is probably where you will notice most of the issues with a higher pressure fuel pump without an adjustable fuel pressure regulator. Since fuel pressure rises 1:1 with boost pressure, eventually the boost pressure will catch up to the fuel pressure (assuming you're using a higher pressure fuel pump and no adjustable regulator) and the car will run fine.

However, it's at idle and light cruise conditions where the higher pressure pump overruns the regulator and causes problems. The SAFC cannot compensate for this because the fuel pressure overrun is a mechanical problem, nothing with the ecu or electrical system. This is exactly why the only solution is an aftermarket adjustable fuel pressure regulator that can mechanically handle the extra pressure from the fuel pump and bleed it off so that fuel pressure will be consistent and where it should be.

I'm not too great at explaining things like this, but that is where Kevin shines. I think he just didn't get into quite enough to really explain why this happens. $10 says that when he comes back and reads this we'll get a 10 paragraph essay :sunglasse I don't know how he continues to type this stuff, but it's awesome :)

by fuel pressure overrun do you mean the rise is pressure in regards to higher boost levels?

The FPR returns un-needed fuel to the tank. You are right, fuel pressure rises with boost pressue equally, but it also decreases when the engine has vacuum. In some off-throttle vacuum situations, desired fuel pressure is as low as 32psi. The stock FPR cannot reduce the pressure that much, and you may end up with more fuel pressure than your car needs/thinks it has. Obviously you can see how this could lead to a problem.

Yes, you can work around this with electronics, especially if the pump is only slightly too large (190lph). For some people, the point is to understand the need for the FPR, and buy it in order to maintain the best running condition of the car. Some people may choose to work around it, or not even notice it. Kevin says that the problem is most clearly visible while logging with DSMlink.

With the afc, , the trim can be leaned out so that your wally won't pump 190, or 255 lph at WOT, it will reduce the load on the pump so it does not add as much fuel, thus keeping the fuel pressure at the correct level.

No, No, No!!

I think you are confused here. The SAFC does not change how much your fuel pump will run. The fuel pump runs the same no matter what you do (unless you run more or less voltage to it). Changing FP is the job of the FPR. Thus, a higher flowing fuel pump will overrun the stock FPR.

In conclusion you NEED an AFPR with a 255 (the stock FPR can handle a 190).

wow, im starting to get confused!!

riff22, sinple asnwer is yes. you'll need one.

k thanks

bump.

they are right. alot of ppl have this issue or question and dont understand what is going on with their car after the pump install.

I think everyone pretty much cleared up the things that I saw in whathits post. Its ok to be wrong about these things, if you have a good attitude like this guy does. Makes for some good discussions.

I'm not going to reiterate what everyone after me posted. But I'll go into some fundamental pressure control basics and flow vs pressure. For reference, I have a bit of experience with these things, not only from cars, but at work. I work with high vacuum systems at work, in the millitorr range (atmospheric pressure is 760 torr, for reference).

"Flow" is movement of a mass of volume over time. Liters per hour. Pounds per minute. Etc. I think we all know what flow means.

Pressure is a force exerted by the fluid on the things it comes in contact with. The lines. The filter. Even the pump that is pumping it.

Fuel pumps dont produce pressure. They produce flow. They move fuel. Movement is flow. Bigger pumps flow more. If you hook up a fuel pump in a bucket of water and let it run free, it will move a ton of fluid, but at no pressure. In order to have pressure we need a restriction to push against.

In our case, the restriction for the most part is the regulator. The regulator is simply an automatic mechanical valve that will restrict the flow back to the tank just enough to maintain the pressure we want. If pressure is too low, the valve will close more. If the pressure is too high, it will open a little. A pumps flow varies with many factors (pressure, voltage, etc), so this regulator valve has to be dynamic, changing constantly to adapt to chaning conditions. So think of pressure as excess flow.

If you have finally wrapped your head around how a wastegate works, this is the same exact thing. Thats why I tried to compare reg over run to boost creep. I like to call it fuel pressure creep to make the point.

The more fuel the motor is consuming, the less needs to be returned to the tank. This is why this is not really a problem at WOT. When the motor is not consuming a lot of fuel, like at idle, 99.9% of what the pump is pushing up to the motor gets returned right back to the tank. So the regulator has to be able to flow the same amount that the pump does and all of the feed lines. I think everyone understands why you wouldnt run a 4 guage power wire to your amp, but run a 18 guage ground wire, right? So why do people upgrade to high flowing pumps, larger feed lines, less restrictive filters, bigger fuel rails, etc, but keep the same puny regulator and return line? ;) Same principle...

In our case, the fuel pressure has to vary with boost or vacuum on a one to one ratio. It is not to add more fuel when under boost! Lets assume base fuel pressure (no boost or vac signal, also known as "hose off" base pressure) of 42 psi. Boost has gone up to 10 psi. Now the pressure across the injector is only 32 psi. Fuel flow through the inector for that same pulse width will drop. If we use a 1:1 regulator, lets see what happens. Base pressure is 42 psi. Boost pressure goes up to 10 psi. Fuel pressure goes up to 52 psi. Pressure differential across the injector is still 42 psi. Same goes for vacuum. Remember that 1 in/hg equals half a psi (.49). So if you have the hose on, base set to 42 psi, and 20" of vacuum, it should drop 10 psi. Fuel pressure should be 32 psi. As seen in wagons example.

Now, lets look at the large pump vs stock reg situation closer. Lets say that at idle we have 50 psi fuel pressure. This is a common number. sticking with the 42 psi base pressure example, at everything 8 psi and below pressure is too high. At 9 psi boost, the regulator will set fuel pressure to 51 psi, 10 pounds of boost, 52 psi, ect. So when you go over 8 psi in this example, the regulator regains control. So at WOT when it really matters, we have control over fuel delivery. But also note that 99.99 precent of the time the motor is running, it has no control over fuel pressure.

So it becomes clear that our closed loop (feedback control) pressure control is purely mechanical. Pump flow vs restriction and consuption.

All the AFC, DSMlink, and other electronics can do is control the electronic portion of the system. In this case, the time that the injector is open. This is called injector pulsewidth and is measured in milliseconds, or as a percentage of time open vs available time to be open (duty cycle). The ECU expects pressure to be at base pressure at all times. ~38 psi for the 1g, ~42 psi for the 2g. It tells the injector how long to be open based on these assumptions. If the pressure is too high too much fuel will get though the injector in the time it is told to stay open.

Now, in closed loop operation, the ECU has some adjustability available, and it will use it to try to correct this situation. Lets say at idle fuel delivery is 10% too high thanks to the excessive fuel pressure. The ECU will move the low trims 10% down to compensate. Which is fine. But now there is less room for adjustment for normal things that it adjusts for, like temp changes, running the AC, differences is fuel specific gravity, etc.

We can use an AFC or other device to adjust the airflow signal down 10% instead, allowing trims to move back to center. But its still a bandaid. We have not changed fuel pressure, and the ECU still doesnt know that fuel pressure is wrong. Anc changing airflow signal changes other things as well. If you are setting something like the global slider in DSMlink, the changes you make to compensate for banjaxed fuel pressure are also applied at WOT when fuel pressure is back under control. So you can start to see the nightmare this can cause when tuning. Waaaaay too many variables. When I say that I like my tuning to "make sense" this is what I am talking about. running 550s with 660s settings does not "make sense" and you'll struggle with it forever, or learn to bandaid it, unless you fix the source of the problem.

In order for the ECU to work as it was designed to, and it does a very very good job, certain things have to make sense. Fuel pressure. Air (mass) metering. Injector accuracy. Those are the heavy hitters. One of the reasons that the math always makes sense on my setup is because I spend a lot of time, money, and effort to get those parameters correct.

Hopefully this makes some sense. Its easy to make these posts too simple, or too complicated, and to avoid doing so it takes many words. And this still seems inadequate. ;)

That is some damn good information right there. I think Matt wins $10, although his 4 paragraph estimate was a drastic understatement :p

Or you can be like me and run a 190lph with the stock regulator to avoid confronting this stuff for a while :grinno:

Or you can be like me and run a 190lph with the stock regulator to avoid confronting this stuff for a while :grinno:


Word. Although, Kevin says its slightly noticable even with the 190lph when loggin on DSMlink. I wish I knew what to look for, so maybe he can chime in and let me know :icon16:

What's the word on your turbo, Matt? Is it on the car yet? Are your injectors coming in soon?

What's the word on your turbo, Matt? Is it on the car yet? Are your injectors coming in soon?

Yea man, the turbo has been on the car for a week now. So far, it's quite amazing. Full boost right around ~3800rpm and it pulls damn hard to redline. I have some 880cc injectors on the way, and I'll be taking it to the local track as soon as I can get them on and dialed in. With the stock injectors, I hit 122% IDC :eek: so I'm not going WOT anymore until I get those injectors! The turbo seems to perform quite well, even at low boost. I actually turned the boost up (via the threaded adjustable actuator arm which is badass) to about 19 psi just to see what it feels like, and WOW I was burning through gears like no tomorrow :grinyes: I was a little skeptical at first, but so far this is a great turbo. I MIGHT even drive it over to Atlanta soon to get it on the AWD dyno :) Next mod after injectors is a water injection kit. I want to see how far I can take this turbo on the stock SMIC :smokin:

Now, back on topic!

wow. this thread has just taught me more about fuel delivery than i ever knew. thanks everyone, this is why i love af!!!

Yo, gotta question, but its going to be hard either explaining it or answering it (as what I heard). Okay, my cousin has a 92 Talon Tsi AWD, problem is the Bogging thing. It was pretty bad when ever shifting from high rpms. I'm thinking of buying that DSM from him, but how can you fix the bogging thing? From his mouth, he said that everytime he shifted in high gears, the car/engine would shake shake alot, and yes thats 2-Shakes. I havent been in it yet, but I want that thing. He just got the 255 walbro fuel pump and I was probably guessing it was the fuel regulator? or something thats not letting fuel or something into the engine. help? if not enough explaination, please PM about it. Appreciate it! THANKS!