Post by Don GreenfieldMy engine misfoires or fails to fire under throttle at about 3,000 to 4,000
RPMs, generally going uphill, and generally after running the fuel tank down
to nearly empty and then refilling. Any ideas?
You should not let your car run till the tank's almost empty. It can
damage your fuel pump - many BMWs need a certain amount of fuel to
cool the fuel pump. IMO, if you hit 1/4 full you should refuel.
Otherwise, your symptoms are consistent with the fuel filter being
fouled by dirt from the sediment in your fuel tank. Fuel always has
some dirt in it - if you don't replace the filter regularly and run
the tank down too much you can increase the concentration of junk in
your fuel lines enough to cause driveability problems.
I've read that if it gets bad enough some of it can get past the
filter and damage the engine. I stay away from ratty-looking gas
stations that sell gas at rock-bottom prices.
BTW, when your engine misfires it is also likely that unburnt fuel
from the misfire will get dumped on your catalytic converter, greatly
hastening its demise. Cats are extremely expensive items to replace.
Since you are also likely to stop and park your car after it misfires
or run out of fuel, the chances of unburnt fuel wrecking your cats
"goes up exponentially".
I once had a nasty experience when a valve cover gasket leak turned
into an engine misfire problem - it killed one of the 2 cats in my E39
V8. Lucky for me it was all under warranty but that's one bad thing
that can happen when the engine "misses". Interestingly enough, the
BMW shop manager told me it was fine to keep driving the car till they
could schedule me for service - I told him where to go.
Don't let your fuel tank run down past 1/4 full and don't drive it
when it "misses".
Michael