Problem after cat by-pass install...HELP!

[ckeasterling]

Saturday I installed a set of cat by-pass pipes on my '99 C4. Took the car out for a 15 minute drive and it ran great! Later I drove about 10 miles to a store and CEL came on but this was expected. Left store and drove 20 miles to my parents house. About 2/3 of the way there the engine started running roughly and it kept getting worse. The CEL also started flashing. I disconnected/reconnected the battery at my parents house to reset the computer and the car ran great again. Unfortunately I had to do the disconnect/reconnect battery thing three times on my way back home. When I got home I noticed the right exhaust tip (left cylinder bank) had black soot all around it. The left tip was normal. I decided I had damaged one of the O2 sensors and thought if I switched the sensors from one side to the other, the opposite bank would start burning rich and I could pinpoint the bad sensor by process of elimination. Well last night I first switched the two after-cat sensors, reconnected the battery, and took the car out for a drive. Left bank still started running really rich after a few miles, just like before. I let the engine cool, switched the other two sensors, reconnected battery, went for a drive. Same problem, left bank running really rich. I guess my next step is to re-install the OEM pipes but I really don't think that will cure the problem and I really like the sound and performance improvement of the by-pass pipes. Any suggestions will really be appreciated. Thanks!

[1999Porsche911]

Have you hooked up your scanner and looked at the fuel trims for each bank as well as the O2 sensor readings?

[ckeasterling]

Have you hooked up your scanner and looked at the fuel trims for each bank as well as the O2 sensor readings?

<{POST_SNAPBACK}>

99P911,

I don't have a scanner but looks like I'm gonna need one. I guess the laptop software versions are a lot better than the comparably priced hand held units? Autozone has a $150 Actron handheld. I'm just anxious to dive into this. Thanks!

Edited September 20, 2005 by ckeasterling

[1999Porsche911]

Have you hooked up your scanner and looked at the fuel trims for each bank as well as the O2 sensor readings?

<{POST_SNAPBACK}>

99P911,

I don't have a scanner but looks like I'm gonna need one. I guess the laptop software versions are a lot better than the comparably priced hand held units? Autozone has a $150 Actron handheld. I'm just anxious to dive into this. Thanks!

<{POST_SNAPBACK}>

Alot of people use the autoengenuity software and are happy with it.

http://www.autoenginuity.com/

[Costa]

I was always under the impression that you cannot just bypass the cats and expect the car to run correctly. I assumed that the engine management would have to be modified to allow for the fact that the O2 sensors after the cats are now giving the same readings as the pre cat O2 sensors.

Since you have just bypassed the cats then I would expect that the engine would run as you have found because the engine management is trying to adjust the fuel mixture etc to get the O2 sensors after the cats to read correctly. Since the cats are not physically there, then the engine management will never be able to run correctly as it assumes that the cats are still present.