Machupo

iTrader: (6)

Forgive me if this has been directly discussed before, if it has, i'm a moron @ selecting keywords for search


Something I was discussing with Sharif when I was down there last month was the cause of the rough start that plagues many built / blown motors with much larger injectors and sky high fuel pressures.

While much of the explanation was over my head, I picked out a bit that due to the very high fuel pressure at startup, the engine is somewhat flooded and so it takes a couple tries / more work.

My question is: Is this a requirement for a high-hp (read: high fuel pressure) engine? If my idea of how a rising-rate fuel pressure regulator works, you should be able to design a more "normal" fuel pressure setting at idle / low rpm, but once you get into boost, the 2:1 or 3:1 (or whatever you need) unit will increase the fuel pressure to whatever levels you need in order to deliver the correct amount of fuel. This in theory would allow you to start the car as if nothing were amiss, but you'd have plenty of fuel once you got on it.

Am I way off-base / a complete moron, or has this idea just not been tried yet?

Thanks in advance!

Brandon@Forged

Well, there is a base pressure that FPRs have. I'm not sure what the idle fuel pressure or start-up fuel pressure is, but if you find out an average you can just find the FPR with a base pressure that goes as low as that.

Here's a FPR that used to be used in the AAM kit, I think they started using something else since then.

http://www.aeromotiveinc.com/product...uct.phtml?p=10

That lowest base pressure you can set is 30 PSI, which, i'm guessing, is a little high for start-up/idle.

BTW, i'll see if I can find a FPR with boost reference for you if I can get some fuel pressure numbers from Sharif at start-up/idle.

Machupo

iTrader: (6)

Brandon -- thanks for the reply -- checking the SM, the stock fuel pressure is supposedly 51 psi (on page EC-54 of the SM)

maybe it's the fact that the startup/idle fuel pressure is too low w/ the RRFPR? beats me basically, I just know that it was something to do with fuel that was causing the rough starts (multiple tries) -- and trying to brainstorm a way around it.

Since i'm moving to Deutschland, I'll probably be without local tuners, so i need to see if I can figure out a lot of the reliability issues before I move!

Thanks again,
-nick

Brandon@Forged

Thanks for the SM quote.

With a return fuel system, it could be entirely different (and probably is). I'll check with Sharif to find out what FP he's seen with the AAM-Walbro setup.

You can always have Sharif fly out! LOL

Machupo

iTrader: (6)

LOL -- well, when the real goodies go on, you know for sure i'm driving back out to Charlotte to get it all done

Oh, and i'll be right down the road from Der Nürburgring -- we'll have to have a My350Z event

mpowers

iTrader: (7)

You will most likely need around 44-48 psi for start up. Info from a 300ZXTT service manual, the fuel pressure is bumped up for start up. Then for idle around 37 psi after start. I would think the info would be relative.

Machupo

iTrader: (6)

thanks mike

Machupo

iTrader: (6)

bump

mpowers

iTrader: (7)

Hope it helps Nick...

Sharif@Forged

iTrader: (92)

Hey Nick, hope all is well.

Here is the jist of the issue.

The engine needs a richer mixture to start the car when cold. This is why, regardless of fuel pressure, the built return system cars always start up nicely when cold. However, when the engine is warm, the ECU dials in a leaner mixture, but with larger injectors, and higher than normal fuel pressures, you occassionally end up with a mixture that is too rich. Stock fuel pressure 52psi running through 280cc injectors.

The idea with the return system, is to run as little fuel pressure as possible, while still meeting your fuel requirements up top. This can vary from car to car. Some cars, like GMAN's only need about 40psi of fuel pressure to deliver 550whp...others might need 50psi. From my experience, the cars start nicely when warm, if fuel pressure is in the 35-45psi range. Above that, they tend to falter a little bit.

If you do have to run higher fuel pressure, a blip of the throttle at first crank, is all thats needed to bring the engine to life.

dynamic6er

iTrader: (1)

Also, allowing the fuel pump to cycle fully (~2 sec) when key is turned to the on position can help with start up. Are you having to pump the throttle slightly or have you noticed that this helps to get the car started?

Sharif@Forged

iTrader: (92)

Machupo doesnt have a return fuel system yet. He is just gathering info on that. We are going to be installing a forced induction kit, fuel system etc..shortly.

Machupo

iTrader: (6)

yup (i'm on the phone w/ the insurance folks right now figuring out why the stupid adjustor/appraiser hasn't looked at my car yet).

thanks for the info, Sharif

overZealous1

iTrader: (27)

i wait for fuel pressure (1-2 secs) then hit the key, fires right up everytime hot or cold, and no hitting the gas.

Sharif@Forged

iTrader: (92)

Did I miss something? Was your car damaged?

Machupo

iTrader: (6)

https://my350z.com/forum/2003-2009-nissan-350z/148541-2003-350z-track-vs-200-pound-4-pointer.html

leemik

iTrader: (2)

I just went through some fuel problems with the AAM FPR and Sharif is right on.. When I had my AAM FPR the thing wouldn't dial below 52psi at idle..this resulted in rough warm starts..

So I bought a nice SARD FPR off ebay and this thing dials right down to 43psi at idle.. I don't have any problems now starting the car warm or cold..

--mike