My setup is nowhere near stock anything; it's an S5 TII long block with an S4 front cover/OMP and an S4 ECU/knock box etc using an S5 AFM. It's not even in an RX7. :laugh: Anyway, here's my questions:

The stock fuel pump setup uses the resistor and relay to knock voltage back to around 9v at idle or under low load situations, it also is there to help prevent hot restart flooding and that is one reason I'd like to keep it; if I stall the car (very possible given my driving skilz) I want to be able to restart it quickly without flipping switches etc. Also, under boost the relay bypasses the resistor to supply full voltage to the pump, thus raising the pressure/volume. I know this is basic RX7 101 etc but bear with me, I'm going somewhere with this.

I'm using a MSD 2225 fuel pump, when using the stock resistor setup the car runs like *** and has no power, won't even go over about 2 psi boost. So I've bypassed the resistor to supply battery voltage to the pump at all times. My concern is that by disabling the stock rising voltage setup it may be possible for the engine to go lean under boost. Is anyone using that pump and if so have they experienced that problem?

The Walbro '255' pump has a better voltage/pressure curve than the MSD so it may be a better solution. So is anyone using that pump in a TII and if so is it working well, particularly with the stock resistor setup?

Last question: I still have the stock solenoid for the fuel pressure regulator which I understand is there partially to address hot restart flooding. I've seen where there's people bypassing it to use direct manifold vacuum. Again a stupid question: if that's done is it necessary to use a vacuum check valve to prevent problems under boost? Does bypassing it lead to the hot restart problem?

 

"My concern is that by disabling the stock rising voltage setup it may be possible for the engine to go lean under boost."
If you disable that system, you are disabling the 9v kick down, not the 12v normal operating condition. If you bypass everything, you are just getting 12v. It won't lean out. You're thinking of somehow always running 9V to the pump. That's probably not possible, and a big NO NO anyway.

Some people will say the 255 pump will overwhelm the stock regulator. A new pump on old stock equipment makes that a possibility. Personally, I don't know. I run the walbro pump, but I am on a standalone ECU and aftermarket regulator.

The stock fuel pressure solenoid is used to bypass any vacuum going to the regulator during cranking, so the car gets maximum fuel flow. That's why as the cars get older, they run richer and richer (as compression lessens) and start flooding easier.
edit: from the FSM, spelling mistake and all "to prevent percolation of the fuel during idle after engine is restarted, vacuum is cut to the pressure regulator increasing fule pressure"

 

never heard of a vacuum check for the fpr.
like beef said, you'll be running rich, not lean

 

Okay, so the normal condition is battery voltage to the pump. That's good to know. I fiddled with the car today, bypassed the vac solenoid and verified that under load and boost the fule pressure is hanging pretty steady at ~42 PSI. That's a bit higher than the FSM says but I'd rather be a little high than a little low.