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Car Forum / BMW Cars / April 2004HELP!! 540i auto - gets close to rev danger zone then loses power and shakes!
UK 1998 540i auto Same problem.. I've been having a problem for a few weeks whereby if I drive the car with full accelaration, I notice the revs almost go into the red zone but before it does, power is cut to one of the bank of cylinders (confirmed by BMW) and the car shakes and runs like a dog! If I stop and turn the engine off and straight back on the problem completely vanishes until I rev hard again. This happens at any time of day with any engine temperature. It doesn't do it in regular 'D' mode but does if use the kickdown. It also happens in manual mode if I don't change gear quick enough (but isn't the car meant to 'protect' itself and change gear for me???) I'm no techie but it seems as if the part of the car that's meant to change gear isn't changing and the part of the car that protects the engine cuts power to a bank of cylinder?!?! Any help would be greatly appreciated as I'm at my wits end!! Steve PS BMW here in Dundee have cleared all faults, tested the coils by swopping banks over (misfire still on same side) and are suggesting a new engine management unit!! > UK 1998 540i auto > Same problem.. [quoted text clipped - 5 lines] > vanishes until I rev hard again. This happens at any time of day with > any engine temperature. --SNIP-- I had a similar problem on my 740, turned out to be faulty catalysts. Although they had not failed, they were starting to break down, and when they get hot they block the exhaust flow causing the misfires on the relevent bank (one cat per bank). Hope this helps?!? > > UK 1998 540i auto > > Same problem.. [quoted text clipped - 14 lines] > > Hope this helps?!? Yes, I've had the identical thing happen to my '98 540i6 some 2 years ago. I also know of other 540i owners who had the identical problem. The 540i has 2 SEPARATE catalytic converters. If one bank is blocked you'll probably have problems with some or all of the 4 cylinders. I have been posting this advice to a number of people with this sort of symptoms. When a modern car ages the catalytic converter is a primary source of such problems because its failure is inevitable and imminent at certain age and mileage. In North America, the cats come with an 8-yr/80k miles warranty. My dealer replaced both cats for free when one failed but it was their discretionary decision. Michael > > UK 1998 540i auto > > Same problem.. [quoted text clipped - 12 lines] > they get hot they block the exhaust flow causing the misfires on the > relevent bank (one cat per bank). I also had a similar problem on my 1997 6-speed 540i, and it was a catalytic converter. They're quite expensive, by the way--glad it didn't happen until 137k miles, though. Mark Folsom > UK 1998 540i auto > Same problem.. [quoted text clipped - 16 lines] > swopping banks over (misfire still on same side) and are suggesting a new > engine management unit!! BTW, get a record of the fault codes. They should pretty well tell you if it is a catalytic converter problem or not. It is not a good idea to clear fault codes without first recording what they are. Swapping parts to look for a problem is an expensive way to troubleshoot - only recommendable if done under warranty. Michael Thanks for the info guys!! Science question: So, when revving hard, the car's producing a higher volume of exhaust gases which pass over the cat and cause it to heat up and expand and thus block off the cat and cause back pressure - the more gas, the hotter it gets and the greater the cat elements expand?. The engine management system detects this and shuts down a bank of cylinders to protect the engine? Is my thinking correct? When revving in idle, *sometimes* I hear a rattle from under the car - like pennies in a glass jar - I rev to eg 4000rpm and when the revs are falling to around 2000, I get the sound. This only happens now and again - could this be pieces of the cat rattling about? It not under my seat but sort of in the passenger side cheers Steve |
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