Thread: Fuel pressure gauge install 93 classic

Not to sure thats the way it works PhillipA My understanding is ,The 14CUX reg just maintains 2.5bar(above atmo) in the rail by dumping more fuel as inlet manifold depression increases .The Flapper begins at a high inlet manifold depression ,idle @ 17inshg or .578 bar and as inlet manifold depression decreases (down to 0-5 Inshg or 0.17-0 bar)the reg increases the fuel rail pressure from 28 to 38 PSI or 2 bar to 2.66 bar.and it does this quite rapidly probably to give a slight accelerate pump effect ?
So ignoring that , if inlet manifold depression is low (numerically !) then the throttle plate will be wide open and more fuel is required .Inversly , if the inlet manifold depression is high (numerically) the throttle plate will be almost closed thus requiring less fuel .

In your post below the reg supplies 2.5 bar above manifold absolute pressure. When the manifold absolute pressure drops, the injection pressure above atmospheric drops to 1.8 bar but the difference between the fuel pressure and the manifold remains at 2.5 bar. Believe me, they are both exactly the same. If you remove the vac hose off the reg on either engine it will run extremely rich due to the increased pressure over manifold pressure.

Fair enough bee utey , I dont disagree with that . the end result is the same , clearly illustrates why a Fuel pressure gauge (permanently istalled) can be quite useful.!! to observe this variation of 1.8bar to 2.5 bar as load is varied .

Hi all, I've installed my fuel pressure gauge. Photos will come later, but I ended up putting a t piece not far from the fuel filter. T piece cost me $12 including compression fittings/olives etc. The guy at Enzed also quickly tapped a 1/8th npt thread for me. I wired it through where my old air suspension wiring harness went through the floor. Interesting readings.... I'm getting about 44psi with ignition on and on idle I get just on 40 psi. The pressure doesn't change much except when I stab the accelerator as it will go to about 43psi and then drop to 37 and then work up to 40psi again. Seems a bit high though? My new fuel pump arrived today so this is with new fuel pump.

Interestesting Milld . So your gauge is telling you that at WOT (thats ZERO in the manifold) you get 3 Bar (43 PSI) and at idle (lets say 17insHG or -.5bar you get 37 psi or 2.55 bar.(mine, a LS1 Commy pump,on flapper , idles at 38 and will run up to 48 on WOT loaded,which is along way from what a Flapper should do which is 28 idle 36 WOT,cruize ,above 7 inshg 42psi)
Whether people realize it or not picking up 25% rail pressure on dutied out injectors does make a substantial difference!!
Your results show that fuel regulator is almost working the opposite of the way it was designed to do . eg ,lowest Fuel pressure at the highest inlet manifold Vac , and highest pressure at the Lowest manifold Vac. The Transition is not Linear either.(all this tells you that the next most imortant gauge is the VACUUM gauge , very underated !!!!