i was thinking of installing a fpr to better manage my fuel to air mixture. will it make a difference in hp gain or am i just wasting my money?

does anyone know someone who has one installed?

 

Your engine already has a fuel pressure regulator. There is a good photo of it in the Haynes book on page 4-10 and the Chilton book on page 5-6. Your fuel to air ratio is managed by the Engine Control Module (the computer), the Oxygen Sensors, and the fuel injectors. I don't see how installing a second regulator would provide any benefit, unless the factory unit is defective. If that were the case, the factory unit should be replaced.

 

Daniel, I have been confused about this for a while. The way I under stand it is...

The A/F ratio is controled by the ECU when you are at PT via the O2, MAF, IAT, EngT, TP, RPM etc. sensors input for good emissions control. At WOT the ECU switch's to a a pre-rogramed fuel MAP and ignores the O2 sensor's. But is the ECU capable of changing the preprogramed MAP based on the ratios it obtains during PT operation. If thats the case than an FPR is of no use to raise pressure because the computer can and will compensate or re-learn its WOT MAP. If it can not re-learn then an adjustable FPR my be worth a few HP, ~2-3hp at most. Please clarify this for me if you know how it works.

I have added one because of my hi flow fuel pump and NOS. I keep the FP at the stock 43psi@WOT. I use the Paxton EFI regulator at works fine. Unless you are running NOS or SC the stock FPR works fine. A better choice would be the Apexi S-AFC for a NA Maxima.

 

I truly don't know. The factory service manual is the source of most of my information. That book tells a lot about replacing a broken part but mighty little about design considerations such as the internal logic of the ECU.

 

I'll E-Mail Rich and see if he replys...

 

"A fuel pressure regulator will be of benefit to the Maxima, since the ECU does not re-learn at WOT. PT the computer will use the input from the O2 sensor to regulate the injector duty cycle. At WOT it goes into a "pre-fab" map (The same one we modify, FYI) and open injectors for a set time. In that instance, higher fuel pressure will deliver more fuel. Remember that in order to double fuel flow, you must QUADRUPLE fuel pressure for the same size lines, etc etc, and this is not recommended. Your fuel rail pressures should remain below 60-70psi except for a system where you have ultimate control over everything (i.e. read fully built race motor, forced induction, with stand alone engine management.) Fuel pressure risers are generally used for slightly modified vehicles, and only when changing the injector size/fuel pump is not an option.

Please let me know if I can be of any further assistance.

Richard Schroeck
UPRD Sales/Tech"


So it looks like an FPR will do some good on the Maxima. Thanks Rick for finally putting this to bed.

 

After a careful reading of Mr. Schroeck's response, I reached this conclusion: A non-stock fuel pressure regulator will provide a performance benefit ONLY at Wide Open Throttle, and ONLY if your Engine Control Module has a chip with a non-stock preprogrammed fuel management map.

I can see that your engine, running "on the bottle" would benefit from increased fuel at WOT. In fact, it needs more fuel because the introduction of an oxidizer (such as NOS) without additional fuel to be oxidized would provide no power gain. It might even cause harm, in the same way any lean mixture can cause harm.

BLUMAX (the originator of this thread) is running a stock engine. I don't believe a fuel pressure regulator would give him any performance advantage.

Do you agree? Disagree? Think we need more information?

 

[QUOTEAfter a careful reading of Mr. Schroeck's response, I reached this conclusion: A non-stock fuel pressure regulator will provide a performance benefit ONLY at Wide Open Throttle, and ONLY if your Engine Control Module has a chip with a non-stock preprogrammed fuel management map.

I can see that your engine, running "on the bottle" would benefit from increased fuel at WOT. In fact, it needs more fuel because the introduction of an oxidizer (such as NOS) without additional fuel to be oxidized would provide no power gain. It might even cause harm, in the same way any lean mixture can cause harm.

BLUMAX (the originator of this thread) is running a stock engine. I don't believe a fuel pressure regulator would give him any performance advantage.

Do you agree? Disagree? Think we need more information? [/I][/QUOTE]

I would disagree, kinda.

The ECU fuel map that controls injector pulde width at WOT is not modifiable except for by reprograming the ECU. It cant learn and reprogram the WOT fuel map. So to get more fuel you could raise the system preasure and at WOT you would get more fuel, at PT the ECU would modify the injector pulse width to compensate fot the additional pressure in an attempt to stay in a low emisions state.

I dont think that this would benefit a vehicle with just an intake, down pipe and exhaust much more than a few peak hp. The increase in preasure would cause changes accross the entire power band, some good, some bad. To see those gains you would need to do some time on a dyno. So the cost is not worth it. ~$200 for the regulator and plumbing parts & $150 for dyno time.

If you had cams, head work and some more serious engine work you would benifit much more and it becomes possibly financialy plausible.

A better solution is the APEXI S-AFC so you can fine tune the fuel curve across the entire power band. Their is perhaps ~10hp peak to be gained their. ~$300 for the SAFC & $150 for dyno time. Perhaps worth it.

Or a reprogramed ECU...

In BLUEMAX's case I would say to spend your money on other performance options first before trying an FPR. But because he has some air flow modifiers he might benifit from a litle more fuel. But if $$$ is tight, try other things first.

I had to go with one because the fuel pump I have uprgaded to is too strong for the factory FPR to control, I was getting ~52psi. Thats tooooo rich. I now run ~43psi. I havent tried to tinker with the preasure yet, not enough time in the day, my wife is pregnant and was due yesterday sooooo my play time is short.

Whatcha think.

[Edited by MardiGrasMax on 10-27-2000 at 04:20 PM]