Fuel Pressure Regulator Works Backwards From Intended
 

Set up a FPR on my '90 motor, but as the title suggests I get backwards results. As I increase the pressure, the motor gets less fuel. I have it set up as required; from the rail to an in/out port, and bottom port to the tank return. Still have stock rail with stock FPR if that makes a difference.

https://cimg4.ibsrv.net/gimg/www.mia...8f3120413b.jpg
I know Ive got the lines correct, because when I pinch the return line after the FPR the pressure increases.

How do you know the motor gets less fuel? Are you sure you've got it plumbed correctly?

.. wait.. do you have this regulator running from the tank before the rail?

It should go tank - rail entry - rail exit - in FPR - return FPR - return to tank.

Theres a direct relationship between the number on the pressure gauge and the number on the wideband display. Also the motor would tend to die after a (very lean) rev.

Ive checked the fuel lines from the pump to the rail, and verified visually just about 10 times that the line Im using is coming from the return side of the rail.

setup is tank->filter->rail in->rail out->FPR in/out->FPR return->tank

One option I have to get around this is to use the FPR to convert to a returnless rail, but Id like to leave that as a last resort. I dont even know if the rail has the proper flow characteristics to make that happen. I'd like your thoughts on that as well.

The only thing that makes sense to me if you accidentally have it hooked up backwards - the return line is the most-forward hardline in the engine bay, source is behind that.

I'll make absolute confirmation that fuel is coming out of the correct hardline in the morning.

Do you still have the stock FPR installed? If so, that will prevent the upstream AFPR from working.

Well the trickle charger took it's sweet time, but I was able to confirm the lines are correct.

The regulator builds pressure fine, I'm not sure I understand the science behind this.
Anything I can do about it without getting an aftermarket rail?

https://www.ebay.com/itm/MAZDA-RACIN...Vh6I:rk:1:pf:0

Looks like the one Braineack used. https://www.miataturbo.net/engine-pe...erience-57044/

There's another one $5 cheaper if you look for "mazda fpr adapter". I ran a dual feed rail so.. ymmv.

Some others have left the original FPR and added one after it, but I don't remember who, or how they plumbed it.

Keuzy, if you want to use -AN connector to replace the stock FPR, the correct P/N is FT061-001. The one shown on-line for Miatas, in various places, WILL NOT FIT.