Fuel pressure regulator

[spectr019]

Hey hey, I have a re-wired 190 pump, 550cc injectors, and I tune with an SAFC II unit. I'm running a ported FP Big28. I have no knock problems at 21 psi and everything has been going well for a couple years now with the set up. I'm happy where it all is, but without upgrading the entire system, would I see any difference (better tuning perhaps) putting in an aftermarket fuel pressure regulator? I understand that the 2G AWD (which I have) fpr has a base of 43 psi, which is good. Just curious if getting a higher flowing unit would be advantagous. Thank you

Ben

 

[DGajre777]

An aftermarket fuel pressure regulator (AFPR) is NOT a higher flowing unit.

When you get a big pump like the 255 or the supra denso pump, you need to get an aftermarket fuel pressure regulator to turn down the fuel pressure to 43psi (on a 2G). Good AFPRs raise fuel pressure on a 1:1 ratio to boost.

Short answer to your question is if your car is running fine, don't worry about an AFPR. The issue of needing a AFPR on a 190 is debatable. Some people will say you should get one anyways, most will tell you that you don't need it on a 190.

Also, did you try searching? There are many many threads on here about this.

 

[spectr019]

thank you for the quick response. Yes I searched for awhile today while at work, and found some people saying that having an upgraded fuel pressure regulator is a 'higher flowing unit', some saying that it isn't, and some saying that putting one in there will help feed the engine more fuel. I have always leaned towards the non-necessity of one with only a 190, and now that I have a wiseman's opinion I can feel pretty settled about not getting one. I'll search a little more in depth next time. Thank you though.

Ben

 

[snox135]

A aftermarket AFPR is a higher flowing unit. That is why we upgrade it. When you install a bigger pump it can over run the stock FPR, causing the fuel pressure to be to high. This over run occurs because the stock unit can not flow enough fuel out the return line to maintain pressure.

It is debatable whether you need it on a 190 pump. Most say no, but it sure won't hurt anything.

 

[1992awdlaser]

I agree with what DGajre777. They do have the ability to bypass more fuel than a stock regulator, so I could understand where you would say it flows more. If you want to know if you need a fpr hook up a fuel pressure tester and see what your pressure is at idle with the vacuum line disconnected. I would bet it is not higher than stock.

 

[snox135]

Doing that will not always tell you if you are over running your regulator. That is why you can not tune out over run. You don't know when it will happen and won't.

 

[1992awdlaser]

Nine times out of ten it will over run at idle if it is going to over run it. It won't do it at wot though.

 

[JeffGST]

My post in another forum

The Truth :

After tuning countless DSM's with a 255HP and no AFPR

2G AWD's = Need an AFPR
2G FWD and all 1G's = Not necessary, but still helpful.

Fuel pressure overrun only affects idle and light throttle situations. This is basically any normal street conditions. Fuel Pressure overrun occurs when there is a greater amount of fuel flow than a regulator can bypass through the fuel return line. This means that fuel pressure is higher than intended, therefore the injectors spray more fuel into the motor than is required. Thus a rich condition.

In the situation of the 2G AWD, the reason for the huge overrun conditions that occur is not solely because the regulator is completely taxed, but it is the design of the fuel tank. Mitsu designed the 2G AWD tank as a plastic saddle tank that travels up and over the rear driveshaft. You basically have 2 separte fuel tanks that are connected by a hump in the middle that is above the driveshaft. There is a siphon in the tank that transfers fuel from one side of the tank to the other. THIS IS THE REAL RESTRICTION, not the stock FPR. By enlarging this siphon, 2G AWD owners can drastically reduce fuel pressure at idle to what it is intended to be.

All 1Gs and 2G FWDs do not have this drastic of a problem since there is no saddle fuel tank. The stock FPR's are still slightly overran but it is easily tuned out.

Once again this overrun problem only affects idle and part throttle conditions and has no effect on WOT tuning. So in essence, you are able to tune this rich condition out in the low RPM's if you know how much the overrun is. With a decent engine management, you are able to reduce fuel injector duty cycles in the lower airflow regions where overrun is most effected.

If a 2G AWD owner were to purchase an AFPR, it would not solve the problem. Only enlarging the siphon in the tank will completely rid it from overrun. There are still tricks that you can perform with an AFPR that will compensate for 2G AWD overrun, but that is a completely different thread.

 

[turbosax2]

How do you determine how much the siphon should be enlarged to still keep enough vacuum for the siphon to function correctly?