found out why car was backfiring running rough

[misfortune]

Dying fuel pump.

What do those run on an 89 535i?

I'll prolly call bma in the morning, though i just don't want to overnight or wait for shipping.

[Dave M]

Good to hear. Out of interest, did it make any noise (the pump) while the car was acting up and how was it diagnosed?

I ask as I'm still fartin around trying to solve my periodic engine studdering issue. I have narrowed it down to the pump, as the hesitations coincide with low pressure readings (I have the fuel pressure gague hooked up on the 'inlet' line from the sending unit and watch it when the engine is idling and hesitates). I then hooked up my multimeter to the power supply wire at the sending unit and extended the wire so I could watch it while driving. I noticed that the voltage does NOT drop significantly prior to the pump quiting. The voltage only drops slightly from 13.1 V to high 12.XX V just after the sputter, which I'm guessing is attributable to the brief loss of engine speed. Did you go through any of these steps in determining it was the pump?

Anyhow, I think I've written enough to warrant another thread, so I may start one.

Dave

[shogun]

rockauto has a lot, also big price differences
http://www.rockauto.com/catalog/x,carcode,1012363,parttype,6256,partGroup,22
Autohaus is very cheap with Bosch pumps
http://www.autohausaz.com/search/product.aspx?sid=telm0fvbq4ntvwy5wmo4hl45&makeid=800003@BMW&modelid=1012363@535I&year=1988&cid=22@Fuel%20%26%20Air%20System&gid=6256@Fuel%20Pump,%20Electric

[genphreak]

rockauto has a lot, also big price differences
http://www.rockauto.com/catalog/x,carcode,1012363,parttype,6256,partGroup,22
Autohaus is very cheap with Bosch pumps
http://www.autohausaz.com/search/product.aspx?sid=telm0fvbq4ntvwy5wmo4hl45&makeid=800003@BMW&modelid=1012363@535I&year=1988&cid=22@Fuel%20%26%20Air%20System&gid=6256@Fuel%20Pump,%20Electric
Isn't it really hard to pull the plastic assembly apart and get the pump swapped over? I thought I'd read somewhere here that it was easy to break the plastic frame, that it was easier to buy a replacement assembly to drop in...

BTW; mine has been noticeably buzzing round the back of the car for years- especially when the level is low. The engine runs fine though, except I have an occasional hard, hot start. Learned to treat it as an engine flood- that is keep cranking. Normally I only crank for 2 secs, with a hard start the trick is to notice the first try, then give it a good 10 secs without stopping. Works every time. My battery is not so hot so she won't go forever. If not, no way- I've learned- flattened the battery twice cranking for shorter perods than that. Best to come back later if that happens. One day I'll buy a pump, the BMA check valve 'kit' was just ordered though. I just keep putting it off... :) Nick