Author Topic: Fuel Pressure? (Read 3249 times)

tumbler · « **on:** February 13, 2010, 03:02:39 PM »

Where should my fuel pressure be at on my 93' 318i? I checked it today (car in neutral) and it was around 40-41psi, then when under acceleration is was 38-40psi, what should it be at?

ClubSport · « **Reply #1 on:** February 14, 2010, 10:08:34 AM »

Under accel it should climb a few psi. My 95 had 40 at idle and 50 at WOT. Where are you measuring it?

RED IS 91 · « **Reply #2 on:** February 14, 2010, 03:08:41 PM »

At the tank you should have between 42-43 psi on the supply side .I believe since you have an electric pump with a fuel pressure regulator then the pressure should be pretty constant.

ClubSport · « **Reply #3 on:** February 14, 2010, 08:16:42 PM »

No, the pressure should climb up to about 50+, to make up for the difference in manifold vacuum between idle and WOT.

tumbler · « **Reply #4 on:** February 15, 2010, 08:45:31 AM »

Thanks for the replies. I was measuring between the tank and the engine, just before the fuel filter (which i replaced recently). These measurements were all taken with the car out of gear. Sounds like I might be looking at getting a new fuel pump?

flyinglizard · « **Reply #5 on:** February 15, 2010, 09:04:42 AM »

40 Is fine. It drops for an instant under accel as the injectors dump fuel and the vac is low, as the vac come up the pressure comes up a little. The 50 is a little high, spec wise, but the car has plenty of correction to get the right fuel air ratio. It will run the same, as long as you have over about 38#. Many gauges are a little off. If the pump /check valve holds the psi for the 20 min test, runs quietly and builds hot pressure fast, it is OK.
The hot pressure, affects hot starts, along with some injector leak down.
I doubt that the car wil run any different with a new pump.
If it is 20yrs old, change the pump, filter,injectors.
pS my book says 43+-1

flyinglizard · « **Reply #6 on:** February 27, 2010, 09:36:05 AM »

can you give us any results?? TIA. MM