Help 2008 bmw 328i with misfires on 1,2,3 cyl and power loss

[mrgizmo04]

But that said, depending on how much of your honey comb from the cats traveled downstream and is clogging the muffler, you might need new cats to pass next smog. Sorry, not trying to confuse the issue here.

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[Tigre77]

Thankyou mrgizmo04,
so today I took of the exhaust and lots stuff came out I would say like 2 lbs so hopefully this would fix it.

[bmwdirtracer]

Take the entire rear exhaust off (you'll need help); stand it up with the forward end , on a concrete floor or similar (you'll need help, probably a six foot ladder too!), and gently bang the flange on the pavement. Note that I said GENTLY; you're just rattling a buch of ceramic honeycomb out of the resonator and/or muffler.

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Oh good, you did that I see. After putting it back on, recheck the backpressure!

[Tigre77]

Yes sir I did exactly that I’ll put back today and check pressure thanks again

[Tigre77]

So installed the exhaust back on and the pressure on the exhaust is now 4psi post cat at 3000rpms so still clogged right

[bmwdirtracer]

Yes. It absolutely needs to be LESS than 2 psi under all circumstances. Recommend you test your gauge: remove the rear exhaust again, and retest at secondary sensor hole. backpressure would of course be zero

[Tigre77]

Ok I’ll try that, but is there something a muffler shop can do to unclog it or do I need a replacement?

[Tigre77]

Ok I did as you said took off the exhaust after the o2 and test the gauge and it’s at 0psi then I completely took out the exhaust again and banged on it with a rubber mallet and a whole lot more stuff came out and did it till no more came out.
put back the exhaust and I’m still at 4psi at 3000rpm still clogged

[bmwdirtracer]

Yep, still clogged....this is indisputable. There are quite a few "cat-back" systems available for your car. Some are stupidly noisy, by the way. Personally, I'd look for someone who just put a "performance" exhaust on their car, and wants to sell the stock system.

[Tigre77]

Ok thankyou but I went ahead and try and clean out soon more gunk out and put it back on and now I’m at 1.5psi back pressure, is this good enough you think?
also I have 1psi at the pre cat

[bmwdirtracer]

1.5 psi is considered within acceptable limits, engine revving, of course.

[Tigre77]

So I’ve been driving the car for two days and I’ve put 100 miles on and it’s been driving excellent no hesitation or warning lights,I’ve been also monitoring the cooling system and it’s working as it should so I’m really happy with the car and how it drives.
thanks to all that have helped me out here on this site and specially bmwdirtracer you have been a blessing and you saved me thousands so I hope this thread helps someone and if there’s anything I can do to help or help this site keep goin please let me know thankyou!

[bmwdirtracer]

Glad to have been of help.