MS Tuning & Fuel Pressure

[eliotmansfield]

Just a thought; Are you sure your FPR is referenced to manifold [absolute] pressure? I.e. have you got a pipe going from your fuel pressure regulator to your
throttle body?

Eliot.
http://www.mez.co.uk

68dime wrote:
> Okay. So I'm fouling plugs like crazy, and the exhaust smells like fuel.

This combined with the fact that the power is good when you get on
it seems to indicate that the upper right part of the VE table is
ok, but that the cruise and idle (middle and lower left) are too
rich.

> Also, his RPM bins start at 1300 and go up to 6000, and jump at one
> point from 2800 to 4300. Is this a valid way of setting up a fuel map?

Well, it sounds a little strange to me. I'd have at least one bin well
below idle, say at 500, then try to narrow that gap in the middle a bit.

> The visual version of the VE table shows a very sharp plateau between
> those RPM's. It seems like a more stable curve would be desirable.

Yup, I think you and I agree on that:

http://www.not2fast.com/efi/spacing.shtml


> car also doesn't want to idle very smoothly, and I'm wondering whether
> the fuel map starting at 1300 RPM might be part of the problem there.....

Seems likely.

> pressure that is higher than I need. I am using a fuel pressure
> regulator that I think should dial it back to within reason, but if all
> the tuning that I'm doing is going to be defeated by this fuel pump
> situation, please let me know.

Changing the fuel pressure will indeed require a retune, but don't worry
about it, as soon as you've tuned it once, you'll get engrossed in tuning
and want to do it again anyhow.

--
Eric Fahlgren http://www.not2fast.com/

(posted by email)

[68dime]

Just a thought; Are you sure your FPR is referenced to manifold [absolute]
pressure?
I.e. have you got a pipe going from your fuel pressure regulator to your
throttle body?

Eliot.
http://www.mez.co.uk

Yes, I am. Actually, on my setup, there are two fuel pressure regulators. We used a stock 280Z fuel regulator, and tied that into the Megasquirt and ran vacuum lines to the manifold. I was running so rich, initially, that I suspected fuel pressure might be too high. The 280Z FPR came from another car, and I didn't have much faith in it.....so we added an MSD adjustable fuel pressure regulator to the system, and that seemed to help some.

outlet from fuel tank --> fuel pump --> supply line --> fuel filter --> fuel rail --> MSD FPR --> 280Z FPR --> return line to tank

The 280Z FPR has a vacuum line which connects to the intake and to the Megasquirt ECU.

On another topic entirely, I have a question about the VE table and the color-coded fuel map. What do the different colors represent? Specifically, what do the blue and red areas of the curve tell me? I can't find reference to this in the documentation -- probably just not looking in the right place -- and was curious about what those areas represent.

[eliotmansfield]

That doesn't seem right to me. Why two FPR's?. At the very least they should both be referenced, but ideally bin the 280z one and keep the [referenced] adjustable one.

[68dime]

Ideally, I would. But the adjustable FPR can't do vacuum. It's simply fuel in / fuel out with an adjuster screw for the pressure.

That doesn't seem right to me. Why two FPR's?. At the very least they should both be referenced, but ideally bin the 280z one and keep the [referenced] adjustable one.

[eliotmansfield]

Then it's not suitable for fuel injection. Your FPR has to be referenced to manifold pressure/vacuum - otherwise your VE numbers will be all over the place (which i believe youre seeing).

See fuel pressure regulators under:
http://www.megasquirt.info/manual/minj.htm#supply

Eliot.

[68dime]

I see what you mean. Although, the problems that I've been having with plug fouling predate the installation of the second fuel pressure regulator.

Thanks for the advice. I'll go back to the stock FPR and see if that helps me in my effort to build a better fuel map.

Then it's not suitable for fuel injection. Your FPR has to be referenced to manifold pressure/vacuum - otherwise your VE numbers will be all over the place (which i believe youre seeing).

See fuel pressure regulators under:
http://www.megasquirt.info/manual/minj.htm#supply

Eliot.