WEIRD Issue with o2 Sensors 997.1RS
06-07-2023, 02:23 PM
#1
Rennlist Member
Thread Starter
WEIRD Issue with o2 Sensors 997.1RS
So... thought I'd share this. I have my RS in the shop getting a few things done. Basic annual service, replacing the transmission mount, plus put the 997.2 shift cables/shifter in the car (removing the cup parts), and a few other bits. Car is quiet now! I forgot the feel of the stock cables, it's good, but you feel a slight bit of rubbery :-) But that is ok, I'm old and this is now a street car.
Before I brought the car in, I'd scanned codes and noticed an 02 sensor error pending. (no CEL). I cleared it to see if it would come back. At the time I looked at it only briefly and thought it was a post-cat/cat efficiency error thinking to myself oh ****, there is another $5k on a set of headers. Anyway, it came back and threw a CEL while at the shop. It was the pre-cat sensor, so we just replaced them both.
Then the car started running like ****. It would start and idle fine. But any loading of the car it started bucking and felt like it was pulling timing/closing the throttle.
The tech hooked up the PIWIS and starts logging stuff and sees the new o2 sensors are not communicating with the ECU. What is odd is the old sensors were, but maybe they were tired or their range/band was out of spec or maybe something changed on the latest sensors, anyway....
My car has no tune/software installed, although I did have a basic Cobb tune when I ran the cup headers for use on the track. That was removed about 3 years ago.
So turns out, it was a pretty easy issue to fix.
My tune software was custom build for my car. When the COBB writes the ECU, it modifies all the various bits to 'install' the tune. When you remove it, it reverts back to a factory 100% as delivered code. It turns out, there was a bug in the older COBB access port firmware that in some cases, once in a while, the re-write to the stock firmware would leave certain bits in a weird state and sometimes would manifest themselves like this. BBI's engine builder / tuner has seen this and knew exactly what the issue is. The fix was simply to update the access port firmware, download the latest and install an off the shelf tune in the car, and then remove the access port. So now it's back to a factory delivered ECU firmware. Problem fixed.
Posting this as an FYI for anyone running a Cobb, they are pretty popular and a good device. Glad I kept it even though I haven't used for some time.
Before I brought the car in, I'd scanned codes and noticed an 02 sensor error pending. (no CEL). I cleared it to see if it would come back. At the time I looked at it only briefly and thought it was a post-cat/cat efficiency error thinking to myself oh ****, there is another $5k on a set of headers. Anyway, it came back and threw a CEL while at the shop. It was the pre-cat sensor, so we just replaced them both.
Then the car started running like ****. It would start and idle fine. But any loading of the car it started bucking and felt like it was pulling timing/closing the throttle.
The tech hooked up the PIWIS and starts logging stuff and sees the new o2 sensors are not communicating with the ECU. What is odd is the old sensors were, but maybe they were tired or their range/band was out of spec or maybe something changed on the latest sensors, anyway....
My car has no tune/software installed, although I did have a basic Cobb tune when I ran the cup headers for use on the track. That was removed about 3 years ago.
So turns out, it was a pretty easy issue to fix.
My tune software was custom build for my car. When the COBB writes the ECU, it modifies all the various bits to 'install' the tune. When you remove it, it reverts back to a factory 100% as delivered code. It turns out, there was a bug in the older COBB access port firmware that in some cases, once in a while, the re-write to the stock firmware would leave certain bits in a weird state and sometimes would manifest themselves like this. BBI's engine builder / tuner has seen this and knew exactly what the issue is. The fix was simply to update the access port firmware, download the latest and install an off the shelf tune in the car, and then remove the access port. So now it's back to a factory delivered ECU firmware. Problem fixed.
Posting this as an FYI for anyone running a Cobb, they are pretty popular and a good device. Glad I kept it even though I haven't used for some time.
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