HAILERS

No. This was a stock series four turbo, 1987. I just got the engine hot(read 185*F) and then watched the afr as I pulled the green/red from the ECU and then reinstalled it. Did it several times. Next time I'll just hook up the fuel pressure gauge and do the same thing with withdrawing. reinstalling the green/red wire. I'm fairly well versed on how the FPR solenoid works. Not a player in what I did/will do later....again.

EDIT: But then again, why repeat my last mistake? The FPR has a vacuum on its diaphram and opens a passage of a given size. Unless the vacuum is changed, the opening won't change. So, if you speed the pump up by removing the green/red wire, the pump outputs more pressure, but the opening in the FPR does not change size. Pressure rises in the fuel rail due to that. How much? Not all that much, but it has to rise. No way around that.

slo

iTrader: (1)

Pressure doesn't have to change the FPR just bypass's more fuel back to the tank, there is probably a limit perhaps its the point at which the pressure on both sides of the FPR is equal, thats probably the limit.

NZConvertible

The S4 ECU only reports faults on inputs, not outputs (the relay control is an output). Even the S5 ECU which does monitor the relay, takes no action for output errors, only input errors (see the FSM).

Common knowledge. Ignoring carbs because they're irrelevant, all EFI FPR's work in basically the same way and do the same thing.

Actually 2-speed pump systems are not uncommon.

We can keep saying that back and forth all day, or we can just stick to actual information...

Like I already said, we're talking about a stock function and a stock fuel pump. Any talk of reaching the FPR limits is irrelevant to this discussion because we're nowhere near that.

Attached is a cutaway pic of the FPR from the Mazda FC Training manual. You can see that the only way the diaphragm can move is if the manifold pressure on one side changes or if the fuel pressure on the other side changes. If fuel rail pressure increases, the diaphragm will deflect, the valve will open more and more fuel will be bypassed BUT, the fuel pressure in the rail must increase for that to happen. In other words this very simple device cannot maintain a fixed pressure. Referring to the pic, can you explain how it could?

You claim keeping fixed fuel line pressure is the FPR's primary purpose, with injector pressure differential being a secondary role. Here are few links I found quickly about FPR's. They all mention maintaining the injector pressure differential but not one mention anything about a constant pressure anywhere else in the fuel system.

http://www.240sx.org/faq/articles/fu...gulator_wo.htm
http://www.mirafiori.com/~thad/fi/fpress.html
http://www.xspeed.com.au/tech_features.php?tech_id=24
http://www.autoshop101.com/forms/h22.pdf

The last one is interesting because it also describes the same 2-speed fuel pump system in Toyotas.

slo

iTrader: (1)

You answered your own question above, the fact is this very simple device does maintain a relatively constant pressure across varied input pressure and varied injection time (which also varies the input pressure as seen by the FPR) and how it does that:

"If fuel rail pressure increases, the diaphragm will deflect, the valve will open more and more fuel will be bypassed BUT, the fuel pressure in the rail must increase for that to happen."

pressure increases, fuel is bypassed relieving that pressure, or rather keeping the pressure constant to a point, even if the pressure drifts some based on the input pressure its not going to be much.

Your contracting your original statement...

In any case this is so far off the original topic, as to be pointless in continuing.

NZConvertible

Can you remember or find those AFR numbers?

This is the bit you're not getting. If the extra pressure was completely "relived", the valve would move back down and the pressure would increase again. The only way for the valve to move up and stay up is if the rail pressure also increases and stays up.

So now the pressure isn't constant, but drifts a bit (presumably up). This is exactly what I've been saying. I didn't claim some massive pressure increase, only that it does increase and that increase does cause a richer AFR.

slo

iTrader: (1)

No you claimed that FPR's can't compensate for upstream pressure changes. Which is so clearly incorrect.

Don't you remember:
Quote:
Now you say that the pressure isn't constant but that there is some increasing drift, which I can infact agree with, and which I would call fuel pressure and volume overcoming the FPR.

these points are so clearly opposite,

So which one is it?

You are completely contradiction yourself....

This is a pointless discussion and far beyond the original thread.


And no the extra pressure is relieved but the diaphragm finds a point at which spring pressure (and vacuum) is balanced with rail pressure.

NZConvertible

You claimed that changing the pump's speed (and hence its outlet pressure) had no effect on fuel pressure because the FPR compensates (somehow) and maintains the rail pressure where it was before. This is not correct, the FPR can't compensate for upstream pressure changes in this manner. In this case (the pump's 2-speed system, the thread's topic), when the pump is slowed, fuel rail pressure drops. When it's increased, the pressure rises. Simple.

I said from the beginning the pressure didn't remain constant. You did. That's my whole point...

Yes it does, but this point is at a higher input pressure, i.e. a higher pressure in the rail. It's impossible for it to work any other way. Assuming a constant manifold vacuum (idle, cruising), the only way the valve in the FPR can move is if the fuel rail pressure changes. Pressure goes up, valves opens a bit increasing flow, pressure stays up.