Hey guys, we're having an issue with our 2010 S where the air fuel ratio will not adjust at all with varying throttle inputs, rpms, or boost levels. It is staying at 14.7 all the time until you let off throttle then it might dip down to the 13s. I put a new engine in it about 8k miles ago and this is when I noticed it while making sure it was running good during the first drives and it's been babied so no major damage is done hopefully. I haven't been able to find a solution anywhere online so hoping someone has experience. It threw two misfire codes since it's been happening and that's it.

The car has a catless downpipe on most of the time, but I switched back to the stock dp to see if it would fix the issue but it did not.

 

What is the status of the primary O2 sensor? If the primary fuel ratio monitor doesn’t change with engine operation, I would assume something amiss with the sensor.

 

Last I checked it was reading it just seems like the computer is trying it's hardest to maintain stoich afr for some reason.

 

Well, the ECU's job is to maintain the correct fuel ratio....

If you are driving down the road, I would expect the A/F ratio to go in the 13's or below under load, and go above 15 on throttle lift or overrun. If its not doing that, and holding steady at ~14-ish, yeah, something is wrong. I would try swapping out the sensor before blaming the ECU.

 

Replaced the wideband (upstream) O2 sensor and it's still doing the same thing. Any ideas anyone? The computer is commanding 14.7 pretty much all the time even if you're driving aggressively. I took a log via torque. Does this look wrong to anyone else? To me I would think the fuel ratio should be dropping down to the 11s when I'm at 60%+ throttle and 7+ psi of boost. I tried to keep throttle moderate since this could damage the engine.

 

I get it now, you’re looking at the wrong column! Look at the “Measured” column, and you’ll see the A/F ratio change during driving conditions. The “Commanded” column is the target. I don’t see anything wrong with that log.

 

Yeah I understand that, the target should be changing based on different driving conditions because that is what the car tries to achieve with the measured afr. To not see the commanded or measured afr drop below 14 at all while in the throttle should point to something being wrong, and the car doesn't know it.