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liljos
11-20-2011, 04:54 AM
can a bad fuel pump have a major effect on the car's idle? if so what can it do, to what degree, and how serious it is. thank you ^.^
btw, it's an m20b25 525. 1990
shogun
11-20-2011, 08:15 AM
from theory not, as in idle it probably needs lowest fuel volume. A fuel pump in general always pumps more than is needed, the excess is fed back into the tank via the fuel return line.
whiskychaser
11-20-2011, 08:38 AM
I wouldnt think so either. Have you checked and found your fuel pressure is lower/higher than expected?
liljos
11-20-2011, 11:12 AM
i haven't done a fuel pressure check, but a mechanic said that my fuel pump is bad and that it stops working after the car is warmed up.
today i'm doing a fuel pump change to the tre-340 BMW 255 LPH Fuel Pump - TREperformance.com (http://treperformance.com/i-656-bmw-255-lph-fuel-pump-many-years-and-models.html)
i also had another question, what the mechanic said above, is that even possible?
whiskychaser
11-21-2011, 06:31 AM
Anything is possible. You can get dry joints on a relay. The car warms up, metal expands and there is no contact. Result: car wont start.
The trick is diagnosing the problem. To confirm I would warm the car up and jumper the fuel pump relay. If it doesnt run and you have 12V at the pump its a fair assumption the pump has had it. Maybe he did that
shogun
11-21-2011, 07:35 AM
also check fusible link
BMW E34 Website (http://www.bmwe34.net/E34main/Maintenance/Electrical/Fusible_link.htm)
Tiger
11-21-2011, 12:21 PM
The question is how old is that fuel pump? The youngest E34 is 16 years old. Fuel pump failure in BMW is a common issue.
liljos
11-21-2011, 12:30 PM
The question is how old is that fuel pump? The youngest E34 is 16 years old. Fuel pump failure in BMW is a common issue.

yesterday i did a complete fuel pump overhaul and changed to a tre performance 340 pump. i got the car started for a few minutes and in those few minutes my idle seemed cured but then the car shut off so now i don't know what the cause is
shogun
11-21-2011, 04:25 PM
crankshaft position sensor tested?
liljos
11-21-2011, 05:27 PM
crankshaft position sensor tested?

not yet. i'm waiting till wednesday to go pick up a muiltimeter. best part is there's no school this whole week so i can really get down to the problem. and if you don't mind, how could that cause a problem?
BMW4LIFE
11-21-2011, 07:17 PM
One thing I noticed when a fuel pump is going bad (have gone though 2 now) is that your car feels like its weak and when you give it the beans it dies.

Do you hear that 'whin' on the rean right of your car when you click the key over to position 2? You should!
liljos
11-21-2011, 07:26 PM
I've actually never heard that 'whin'. if that means that it's priming then no I never have. I have yet to see if it works with this new fuel pump.
BMW4LIFE
11-21-2011, 09:28 PM
Have you heard a "Hiss"?

It is a distinct sound that is unmistakable...but it seems it is hard to describe! ha!
liljos
11-21-2011, 11:43 PM
i've never heard anything at all when in position 2
BMW4LIFE
11-22-2011, 06:17 AM
Position 2 is when all the lights come on your dash but you havent started the car right?!

If not then position 3...

This is where the fuel pump is engaged and ready for ignition.
liljos
11-22-2011, 08:11 AM
Position 2 is when all the lights come on your dash but you havent started the car right?!

If not then position 3...

This is where the fuel pump is engaged and ready for ignition.


minne is position 3. theres off (1), acc (2), and on (3). on is where you just described above and i haven't heard anything with the old pump in. it'lll be another day before i go back and test the car again with the new pump.