nismology

iTrader: (8)

I should've done this earlier, but here goes.

Adjusting fuel pressure to 51 PSI is unnecessary.


Running at stock 3.0 fuel pressure with a vacuum source attached is PERFECTLY fine. The presumption was that it would improve fuel atomization and because stock A33B's ran @ 3.5 bar (~51 PSI) that A32 3.5 swaps should use that pressure as well. In retrospect, that was bogus. All running 51 PSI will do is worsen pre-existing cold start issues due to too much fuel at startup (simultaneous fuel injection during startup doesn't help) and may contribute to slightly worse gas mileage since the actual a/f is so far off the target a/f that the ECU corrections in closed loop are more coarse. Even if MPG is unaffected, for all intents and purposes, it's not as essential as I (or others) once thought. The only time raising fuel pressure above stock (43 PSI @ WOT) would be viable or necessary is if you wanted to indirectly advance ignition timing be adjusting a/f via something like a V-AFC or EB or are making so much power that the injectors can't keep up. You could either raise fuel pressure, get a higher capacity fuel pump, or install larger injectors in such a case.

There's still a distinct advantage to converting to a "returnless" fuel system as opposed to the stock FPR mounted on the rail though. By forcing fuel to return to the tank before reaching the fuel rail it stays somewhat cooler, improving power and reducing fuel loss to evaporation. It's hard to quantify exactly how much it helps, but it does to some degree. The theory is very sound and the farther the AFPR is from the engine, the greater the effect (the greatest effect being with the FPR in the tank). IMHO, the ideal fuel setup (for those with 3.0 ECU's) is a remote-mounted AFPR @ stock pressure (unless trying to advance timing indirectly as mentioned earlier) with vacuum applied to it.


Comments or questions?





Note: Only applies if using 3.0 ECU.

97_Roadrunner

iTrader: (2)

I think it should be in the stickys.

KRRZ350

iTrader: (29)

^ Ran stock 3.0 specs w/vacuum right from the start after hearing nismology casually mention it in a few threads, my s/t fuel trims are closer to zero than any 3.0 I've checked.

Kevlo911

iTrader: (36)

I been known dis cuz

chillin014

iTrader: (67)

I didnt ^ !! i'm gonna go turn it down right now mayn! thanks!

krismax

iTrader: (15)

ive never changed my pressure .. i thought this was common knowledge

nismology

iTrader: (8)

This thread is for those that don't know. Both stickies mention 51 PSI.

KRRZ350

iTrader: (29)

lol, I told you that in another thread!

nismology

iTrader: (8)

I've known for a long time as well. Doesn't do n00bs any good if nobody says anything about it though.

chillin014

iTrader: (67)

lol i swear to god i was not ignoring your advice, i do not remember that though. or maybe you said it and i thought you were one of the only guys doing something different, but i didnt want to stray from what everyone else was doin.

okay i'm done whoring the thread.

95turbo gxe

iTrader: (25)

yeah its know that you will run rich with the 3.5 injectors why cut them up to 51psi and make it worse. But hey Good looking out for the ones who dont know!

97_Roadrunner

iTrader: (2)

Noob question.... you said...
So does reducing the fpr pressure slighty below 40psi would be helpfull?

nismology

iTrader: (8)

I would leave it at 43 PSI like stock. FWD VQ35 injectors are not that much bigger than A32 injectors (270cc vs. 259cc).

NmexMAX

iTrader: (22)

http://forums.maxima.org/showpost.ph...49&postcount=8

tavarish

iTrader: (27)

I have mine set at 75psi, but then, I'm not using the stock injectors. Anything near 50psi on these, and it runs really rich.

NmexMAX

iTrader: (22)

Unless you're trying to advance timing indirectly, why are you @ 75psi?

MaxBlack97

iTrader: (11)

and y r u not using stock injectors? Do u plan on boosting soon? check ur PMs on the other forum and reply as soon as u get a chance

SR20DEN

iTrader: (7)

You adjust the fuel pressure according to the injector/ecu combo you're running. If you're using the A33B ECU and the A33B 270/315cc injectors of course you would also want to use the 3.5 BAR fuel pressure. If you're using the A32 ECU the fuel pressure is basically left for you to decide what it should be based on your setup.

nismology

iTrader: (8)

Understood. To everyone that knows better, awesome. This thread is for people that have done the 3.5 swap using the A32 ECU or people thinking of doing it that are going by the stickies and are running unnecessarily high fuel pressure.

tavarish

iTrader: (27)

Because for the fuel to spray correctly in the injectors I have (07 Range Rover SC), I have to set it at 75 psi, or higher. Range Rovers stock pressure is about 80-90psi, so I'm running right at the stock flow rate of a range rover. I have NO CLUE what these things actually flow at, and I haven't gotten them flow tested, but I'm willing to bet they flow much more than stock, as I'm running pretty rich. The only reason I put them in is because they were direct plug and play, had similar resistance (a little higher), and they were free.

I'm running a custom MAF, 3" ID piping, gutted out IM, and I ordered my wideband and Emanage to help tune. Car runs great, but backfires like crazy when I let off the gas. Kinda cool.

95BLKMAX

iTrader: (10)

BAHAHAHAHAH!!!!!!!

jaemax

iTrader: (6)

finished my swap yesterday without the AFPR and was about to post this and found this thread...

MaxBlack97

iTrader: (11)

51 psi doesn't bother me, besides I rather run rich then lean

NmexMAX

iTrader: (22)

In that case why not 75 PSI?

scrhale

Yes, but if my memory serves right, 51 PSI without tune is disgustingly rich ... like pig rich, Jay-Z rich, Bill Gates rich.

OK maybe I exagerated ... but it runs a little rich to the point where you are just wasting gas.

Stabone

iTrader: (8)

It does. I figured it out once I ran the WB and was trying to make corrections with SAFC. I had 40-50% correction just to get it to 13.0 range. Once I changed the FP, I was able to lower the idle back down to 650-700rpm and NOT have to gas the motor every morning.

Otherwise, the car ran well with high FP.

chillin014

iTrader: (67)

What else improved with the tuning?? I'm doin mine soon! Hopefully. On topic, right?

THT

iTrader: (8)

It's funny but I had my pressure at 51psi until I read this thread. Cold starts sucked and required a little feathering of the gas. So I reduced the pressure to 34psi at idle and now, it's even harder to start my car.

nismology

iTrader: (8)

Then raise the FP until you find a sweet spot. Results may vary people.

The primary purpose of this thread is that there's no logical basis in running 51 PSI on the dot just because A33B's run that FP. That's all.

Apparition

iTrader: (5)

haha these VQ guys I tell ya..

spdfreak

I'm making a parts list for a swap so it's good I read this.

We have the choice to run a "T" and then to the FPR which then returns to the tank or...? I'm not sure what you guys are saying. Are you saying use a lower (stock) 43psi or are you saying run it some other way?

Someone please clarify this.

Thanks

scrhale

You will have to run the tee either way. The problem was that people assumed we had to run a fuel pressure regulator on the return line and bump the pressure up to 51 PSI instead of running at the stock 43. NISMO states that it is a waste and creates havoc.

SR20DEN

iTrader: (7)

I also like to recommend putting the FPR on the firewall and tee the fuel return BEFORE the fuel rail. This in a sense converts the system to returnless and will not send heated fuel back to the fuel tank.

nismology

iTrader: (8)

^ ?

spdfreak

Whats the differance if it's heated or not?

nismology

iTrader: (8)

From the first post....