Dear all,



I have a 1994 Mazda RX-7 FD running Haltech Nexus R3, with a new engine which recently completed its initial break-in.



I went for a test drive today and it went mostly well, except for a sudden fuel pressure drop during one quick 2nd gear pull, causing the engine to lean out momentarily. Noticeable stutter during acceleration, and it showed in the logged data as well.



It happened twice during that pull, each only lasting 0.15 to 0.2 seconds. When it happened, fuel pump output voltage (25A HCO4) was steady at around 14V, but the high side current went from over 13A to ~7.5A. Expected fuel pressure is at 365 kPA (53psi) but actual fuel pressure dropped to 60 kPA (8.7psi).



Besides that, my fuel pressure at idle is always a little lower than expected, and it’s always unsteady during a pull.



The car has:

- Stock, unopened 13B-REW short block

- Single Turbo EFR8374

- Walbro 400LPH intank fuel pump

- ID1050 primary, 1700 secondary

- IDF750 fuel filter

- Radium -8 direct mount fuel pulsation damper

- Radium primary & secondary fuel rail

- Holley hydramat in the tank



My questions were:

1) What could cause random fuel pressure drop like this? Is it electrical, or a physical resistance in the fuel delivery?

2) How far does the measured fuel pressure deviate from expected value is generally considered acceptable?



New to the forum and looking to learn. Thanks a lot!

 

How is the pump wired

 

How much fuel in the tank?
Drop in pressure and amps with steady voltage may indicate air was sucked in

 

No mention of FPR? Did find some years ago the 2000s era turbosmart one we were running caused erratic readings when the fuel requirements and boost went up, one of the newer, bigger versions cured it.

 

As FDAuto helped me in the past, I recently encountered a similar (if not the same) issue...

https://www.rx7club.com/haltech-foru...aries-1168297/

To answer your number 2 question, I've left the acceptable fuel pressure differential at 270kPa. so, 30kPa margin. I might back it off to 35 or 40 as I've tripped it a single time since with a hard stab at the throttle . This seems safe enough to me.

 

was it with a full tank of gas? hard turn?