4k major loss of power

[Headmaster]

Hi all, 04 zhp w/155k, sharked, afe intake. List of service in last 25k:
V/c and gasket
Ccv
Thermostat and water pump
Ofh gasket
Vanos seals
New plugs @ 120
Gas disa
Maf @ 125k

So here the problem that has me and my indy stumped. I'm throwing codes for banks 1&2 cats bad (cat problems usually show bank 1 or bank 2, rarely borh simultaneously). Symptom is major power loss from 4-5 k, power returns at 5 k. We've double checked all mechanicals and everything appears ok. Cat flow readings look ok.. Software? Shark? Car has updated dme... Thanks in advance

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[gmurphy]

Most likely just the DISA valve. After market software can decrease the effects of the 4k dip. I have Dinan stage 1 and it has reduced it enough to the point of not noticing it.


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[az3579]

Most likely just the DISA valve. After market software can decrease the effects of the 4k dip. I have Dinan stage 1 and it has reduced it enough to the point of not noticing it.


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It was already replaced.

[jsfbmw]

Looks like a well-cared-for car. Even after reading what maintenance items you replaced, my first guess was going to be DISA. as gmurphy suggests. New parts can go bad. I guess more basically, you have fault codes; so what could trigger "bad cats" code?

It's like you need to have a monitor in place as you drive to capture what various sensors and values are reported.

The return of power at 5k, does it continue to redline? The fundamentals of gas, air, and spark, in the correct volume at the correct time need to be examined. Not to be redundant, but issues at 4k rpm usually point at DISA or other airflow controls. Looking forward to hearing the root cause. Good luck.

[gmurphy]

It was already replaced.

Mine was replaced and still did it until my DME was flashed with the software.


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[az3579]

Mine was replaced and still did it until my DME was flashed with the software.


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Which he also had done...

[gmurphy]

Which he also had done...

Flashed with Dinan S1 is what I meant. I can't feel the dip anymore. Before it was very noticeable. OP Good luck in finding the source of the problem.


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[Hornung418]

Didn't see the Oxygen Sensors in that list. They are pretty pricey...but the labor is super easy. Highly recommended if you can do it yourself. Would also recommend the Fuel System Maintenance at 120k+ miles. That is to say, Fuel filter and Pump. These cars are getting up there in age, so even if it doesn't have the mileage, things tend to fail if they are made of plastic and rubber.

Give your Vacuum lines an inspection, too. They can influence the a/f mixture.

[jorbon]

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