Quote:
Originally Posted by oldskoolaudi
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To verify if this is a pump/filter/regulator issue you will need to hook up a fuel pressure gage ($20 at Harbor Freight) to the schraeder valve on the fuel rail and read rail pressure. With the key in the run position it should be 51 +/- 3 psi. and only take 2 or 3 seconds to reach that pressure (if it rises slowly you have a clogged filter or bad pump, see NOTE 1 below to identify). Next step, start the engine and let set at idle for 1 minute (high vacuum), pressure should now read 36 to 46 psi. Now disconnect vacuum line from pressure regulator to simulate full load, pressure must increase 6 to 10 psi.
NOTE 1; If pressure did not come up to 51 +/- 3psi, repeat test while gradually pinching return hose to fuel tank. Rapid rise in pressure reading at rail with each pinch verifies pressure regulator is bad. No rise in pressure verifies fuel pump is bad.
A $10 digital voltage indicator that plugs into your cigarette lighter will tell you the condition of your battery (turn key to run position (NOT start), voltage displayed should be over 12.5 volts). The condition of your alternator (start engine, wait 10 seconds and voltage displayed should be 13.7 to 14.7 volts).
Fixing a problem by throwing parts at your vehicle is expensive and frustrating. Diagnosis seems to be turning into a "lost art" not only in the DIYing area but the dealer/indy shops too......and to ALL DIYers, buy a Bentley Manual, it's all there in black and white and saves you from "I had that same issue that was fixed by "INSERT MY FIX HERE" responses". These will leave you with an empty wallet and broken vehicle, NO fun.
These vehicles are MUCH too complex to have issues resolved with the same part every time WITHOUT PROPER DIAGNOSIS. Only fools and neophites think in this manner.
Sorry for the rant, but this is a pet peeve of mine and it has been building up for over 15 years. Several BMW forums I have been a member of (E46Fan is a BIGGIE) have turned into fastest response is right and max post count is ALWAYS right (even though they hit that response count by going on once a week and responding to every thread with a "k".
The tool required to diagnose this issue cost less then 1/3 a tank of gas, why guess and throw part at the problem????