Last time we went to the mazda dealership, me and Fanis(aka FxF) helped the RX-7 specialist mechanic to measure the fuel pressure of an FD. We did the Fuel Pressure Hold Inspection (page F-96 on the FD manual), the Fuel Line Pressure Inspection (page F-97) and found both normal. When we measured the Fuel Pump Maximum Pressure (page F-101), we found that the pressure was 410-420 kPa when the manual says that it should be around 490-740kPa{5.0-7.5 kgf/cm2, 71-107 PSI} max. The same day we measured another 3 FDs and found the found the same results as above. What is wrong? All the fuel pumps have been on the cars for more than 4-5 years. Is the workshop manual wrong? Or have we got to replace the fuel pumps as a precaution and reliability modification? Does the aforementioned measured pressure have an affect on performance? Would a fuel pressure regulator help the (maybe) faulty maximum fuel pressure (410-420 kPa)? None of the above 4 pumps made any noise.

 

Well today me and Dimitris checked the Fuel Pump Maximum Pressure on his car and found the following:
His idle fuel pressure is the lowest permitted 190kPa of 190-220kPa recommended (Mazda).
His Fuel Pump Maximum Pressure is also the lowest permitted. 490kPa of 490-740kPa recommended (Mazda).
We later on installed a fuel pressure regulator and pushed the pressure to 240-250kPa at idle.
Went for a drive and the car seemed transformed. Better low end-mid range pull, but starvation again after 5000rpm. The car has a gutted out precat, no air-pump, no A/C.
We viewed all the fuel pressure fluctuations while driving from the Mazda fuel pressure tester.
Pretty sure by now, that the car needs a new fuel pump. Thinking of installing a Supra or a Cosmo pump.
Question is should we reinstall the fuel pressure regulator (took it out after the run)? We know that the FD fuel system is very complicated (goes from 220kPa to 740kPa at WOT). Is there any potential harm to the engine?

Fanis

 

Well I may have over exaggerated when I used the term starvation. All I am saying is that the owner and me, have the feeling that the car above 4500-5000rpm doesn’t pull like it should. The car does not show signs of fuel cut and goes all the way to the redline, but seems as if something is holding it back….
The boost patterns are the same as a stock car. Maybe a momentary overboost of 11-12psi sometimes, I think due to the gutted out downpipe.
We know what the normal ECU can take on mods. But we found the normal fuel pump to be on the down side, probably because of its age. We (dimitris) does not want to pay 800(!!!) euros to buy a new mazda pump, so he is going to buy a bigger one probably supra which will be cheaper too.
As for the tests we did with the FPR I could have dyno figures too, but dimitris doesn't have a cigarette lighter in his car and I can't connect the G-Tech meter.
We have the feeling that whatever we do the car above 4500rpm is lean. It doesn't pull as it should. Probably this is due to the aged fuel pump and that is why we go to all this trouble.
Any suggestions?

 

upgraded fuel pumps are really not that expensive (at least in the US). I wouldn't think they'd be too much more over there. I would say go for it, get a bigger one, and put the new FPR back in. It certainly can't hurt, and it's not worth blowing an engine over.