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Old 02-02-2011, 10:06 PM   #3
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Join Date: May 2008
Location: Markham
Posts: 458
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.
You could have a bad/clogged fuel injector in cylinder 4 or quite simple the plug could be bad internally. Does the tip of the #4 plug look different from the others....that should tell you what's happening.

You don't have to use a Magna flow Performance CAT, you can use any of the CATs sized for Mustang or Camero. In the past I've had good luck with Catco CATs, emissions not a problem and no performance issues.
'99 E39 540iT

Last edited by MLue1; 02-02-2011 at 10:09 PM. Reason: clarifying comment
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