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Old 02-03-2011, 01:26 AM   #4
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Join Date: Oct 2002
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Originally Posted by Dado 540 View Post
Is anyone here using any aftermarket catalytic converters on their E39 540i

I read up some guys running Magnaflow high flow cats on, but im not sure if its gonna pass emissions test for us here in canada. They are actually improving performance.

Im experiencing a missfire at cylinder 4 only when car is given a pedal to the floor (High rpms and higher speed). Check engine starts to flash a few times and then remains on. Once i turn the engine off and them back on everything runs smooth. I swapped out the ignition coil at RMP however the symptom is back, rulling out the faulty coil.

Reading up a bit on these symptoms leads towards a clogged cat or even a faulty O2 sensor. The only code that does come up is the missfire cylinder 4.

Comments and suggestions are always welcome.
A clogged cat will cause all the cylinders at the Bank to misfire not only one cylinder.

Since your car is a 97, the cats are built in the rest of the exhaust. 99+ got them integrated into the manifold.
Why not drop the entire exhaust system and taking it for spin, that will determined if you have a bad cat or not.

Also you can try parts from a different cylinder.
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