Author Topic: Pressure regulator or fuel pump failing? (Read 2504 times)

tumbler · « **on:** August 06, 2009, 03:14:43 PM »

I'm driving a '93 318is.

What is a good way to test whether my lean condition is caused by a faulty fuel pressure regulator or my fuel pump?

Unplug the pressure regulator's vacuum line and test to see if the car drives differently?

tumbler · « **Reply #1 on:** August 07, 2009, 08:42:09 PM »

Is there a port where I can get a vacuum gauge to measure the manifold vacuum pressure without screwing with the fuel pressure regulator? Then I could test to see what happens to the fuel pressure as the vacuum drops or rises.

1991 E30 M42 · « **Reply #2 on:** August 07, 2009, 09:44:16 PM »

the line that goes to the charcoal canister

tumbler · « **Reply #3 on:** August 08, 2009, 08:17:09 PM »

So heres what I'm thinking. As I approach WOT, the vacuum should be decreasing. So, if my fuel pressure regulator is working correctly I should see a steady increase in fuel pressure as the vacuum decreases?

After writing that out, it seems like my idea won't produce any conclusive results because it could still either be a fuel pump or fuel pressure regulator issue if the fuel pressure isn't increasing when the vacuum is dropping...Anyone have any thoughts?

B318M42W · « **Reply #4 on:** August 13, 2009, 10:43:43 AM »

get your fuel pressure tested at a garage? I know there is a flow test that you can perform... the fuel flow AFTER the regulator should be around 875ml/30sec. at idle. not 100% sure of my #'s but that is a way you could try. too little fuel = pump, too much = regulator.

on a side note, if you have a lean situation, it can also be caused by a wrong air reading... (MAF or O2)