HAILERS

Three different fuel gauges, same result. Using either a vac pump or a pressure pump, I can make the factory fuel pressure regulator hold any pressure b/t 28psi and 50psi. Drive the turbo, third gear, up hill, stomp peal, boost goes up and fue pressure goes to 48psi. Give me a cold day and I can hit 50psi fuel pressure. Enough said. Its variable b/t 28 and 50...

RETed

This might be the reason why the FD guys claim theirs to be rising-rate...
The original Mazda system was designed to vent the FPR vacuum fitting to atmosphere, so unless you converted your FPR to see both vacuum and boost, it's still technically a two-stage system due to the stock design.



-Ted

NZConvertible

According to the FSM, the FPR solenoid is only there to provide max fuel pressure to the rail for the first 50sec after starting "to prevent percolation of fuel during idle after the engine is restarted." This only occurs if coolant temp is above 65ēC and intake air temp is above 60ēC.
That's what I said! It's a linear rate regulator. It's output pressure is kept at a set pressure above manifold pressure. In a rising rate reg, the difference between fuel pressure and manifold pressure rises as manifold pressure increases.

RETed

I knew about that part, but I left it out on purpose...

Uh, it might work rerouting the stock FPR vacuum line, but if you keep everything intact like stock with the orange solenoid, it's just switches between 30psi and 35psi.&nbsp It does NOT rise stock!



-Ted

HAILERS

The stock fuel pressure regulator after the 50 sec bull ****, rises and falls in proportion to the foot pedal, on a turbo car, from 28psi to 50psi. Its as simple as that. Step on the pedal and the pressure will rise incrementaly. Idles at 32psi and as you step on the pedal slowly rises to 50psi if your engine can put out 10psi boost. Let off the pedal at full boost and the fuel pressure will drop to 28psi until you apply foot pressure again. If your car does not work like that, I suggest you get it fixed.

RETed

Are you talking about modified FPR or the stock system with the solenoid still intact?



-Ted

NZConvertible

That's how the stock system should work. The FPR solenoid only opens under the conditions I stated above, meaning no vacuum is applied to the FPR and providing pressure to the fuel rails as if the manifold was at atmospheric pressure (which is higher than at idle). When it closes, a normal vacuum signal is sent to the FPR, and it's output rises and falls with manifold pressure.

HAILERS

Very much a stock unit. I know about the 50 sec nonsense. On the whole the regulator sees vacuum 99.9 percent of its running time, so I don't pay attention to that feature. I also have a stock fuel pump. When idling and I pull the vac hose off, I get the 37plus or minus psi. When the vac line is on, and idling, the fuel pressure drops to about 32psi. If I drive the car,as I accelerate, the pressure goes up incremently and If you stab the accelerator, it will go to 48psi fuel pressure on my car with the temp what it is today, 80degrees. I've seen 50psi on those 35degree days. If I watch the vac side of the boost gauge, when it hits zero, the fuel pressure gauge hits 40 at the same time. When going into the boost phase, the fuel pressure hits48psi at the same time the Autometer hits its phony reading of 8 and 1/2 to 9psi. As the boost drops, the fuel pressure drops. I don't think a lot of the fpr solenoid *hot start*feature. They might as well have plumbed it directly into the intake manifold and used the solenoid for something useful. We had a thread on this solenoid and its uselessness last fall on this forum. I can simulate my driving experience in the driveway using the pressure side of a MITTYVAC and a fuel pressure gauge connected to the fuel rail. Can even do it in the driveway on the N/A car. I'm pretty sure its one and the same regulator. Has the same characteristics. Whatever.

Keith

OK Ted, you can't have it both ways. Make up your mind. In an earlier thread, you said that boost has no effect on injector PW. In this thread, you are saying that there is no pressure increase when there is boost. So, either we have exactly the same fuel sent to the engine from 0 psi boost to 10 psi boost, or one of the above has to change. Personally, I agree that there is no change to injector PW on boost, so increasing fuel pressure in proportion to boost would solve that problem perfectly by injecting more fuel due to pressure increase at the same injector PW. Since Hailers has verified this (at least to my satisfaction) and this method has been used on many automobiles (Saab, Ford, etc.), it must be the way it works! Either that, or the fuel maps necessary to keep our engines from detonating would mean a way rich mixture except under full boost, so that we need to drive our cars WOT all the time to make sure we don't foul plugs and carbon up engines every 10 minutes! (Actually, there is a little bit of truth to that, now that I think of it, but for different reasons, I think.) Just my 2 cents worth (probably not even worth that much!).

How's that for puttin' on the 'ole gloves! Seriously, no offense to anyone intended, just havin' a real nice thread here!

Irv, Keith's dad

RETed

Now, you're getting me confused!
The other threads were about boost to the BOOST SENSOR not affecting fuel delivery.&nbsp I still stand by that conclusion.

This FPR thing is a whole nother ballgame...&nbsp I've gone through the Fuel section of the Mazda factory service manual, and there is no proof that the FPR orange solenoid switches under boost.&nbsp But, there is no proof of the FPR raising fuel rail pressure under boost either.&nbsp My SPI fuel pressure gauge showed that fuel rail pressure didn't budge under boost - it stayed at 40psi (running Walbro 255lph upgrade fuel pump), so I'm a bit puzzled myself.&nbsp The SPI fuel pressure sender died after 1 week of use, so my readings were all bad and get thrown out the door.

I've got into this beef with the FD guys, and they are adamant about their FPR's being a true boost-dependent FPR also...




-Ted

NZConvertible

Aargh! Not boost dependant, absolute manifold pressure dependant! The difference between fuel pressure and manifold pressure remains constant, from Hailers figures it seems to be about 40psi. So idle vac of around -10psi (20inHg) gives idle fuel pressure of +30psi. Full boost of say 10psi gives 50psi. The numbers may be off a bit, but the theory holds. Every EFI system I've seen does this, turbo or not. The fuel pressure on a turbo engine just goes higher because the manifold pressure goes higher. The FD guys may think they have something special, but it ain't!
In a rising rate FPR, that difference (40psi in our example) isn't constant, it "rises", hence the name.
The orange FPR solenoid doesn't switch under boost (no one said that), it's only vents vacuum to raise fuel pressure to a constant setting for 50sec after starting if coolant temp is above 65ēC and intake air temp is above 60ēC. That's it!

fast13b

Friends don't let friends drive stock...

HAILERS

I'm curious why Ted's car only registers 40psi max. The range of fuel pressure that the fpr regulates is from 28 to 50psi. The only time I ever will see a steady pressure of approx 40psi, is when and if I disconnect the vacuum line from the stock fpr. Then and only then do I ever see a solitary figure. By the way I am totally ignoring the 50sec bs on startup here. Its not worth talking about. Put the vacuum line back on the fpr and the range is 28-50 dependent on how much boost pressure is available or how much vac is being applied to the fpr. It makes me think his/your car is not plumbed into the intake manifold or there is a stoppage in the vac line.