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The car is cammed and bolt ons and has been for 30k miles. Recently it threw P0131 and P0151 on my way to get the emissions done. The rear oxygen sensors are tuned out. I replaced the sensors and it didn't change anything, I replaced the MAF sensor and also no change. I feel like I've sprayed the entire engine bay down with brake cleaner looking for vacuum leaks while it's idling and can't seem to locate one. What should I check next? It idles like it's about to stall but smoothens out when you give it throttle.
Can you graph your O2 sensors ??…they should be switching between 200-800mv’s…also look at your fuel trims…if they are greater than 10% we have a lean condition…if they exceed 10% raise the RPM to 3000 RPM…if they decrease you have a vacuum leak somewhere…I use propane to look for vacuum leaks since it is not as flammable as something like Brake Kleen…when the engine has cooled down and with ignition on and engine off you should see 450 mv’s (bias voltage) on your scan tool…this may be a wiring issue if that bias voltage is stuck low below 50mv’s…signal wire may be shorted to ground so the car may be running rich…don’t know why you changed the MAF for an O2 “circuit” code ??…it is ALWAYS a good idea to let us know the model year as a minimum…you should put that info in your profile.
Can you graph your O2 sensors ??…they should be switching between 200-800mv’s…also look at your fuel trims…if they are greater than 10% we have a lean condition…if they exceed 10% raise the RPM to 3000 RPM…if they decrease you have a vacuum leak somewhere…I use propane to look for vacuum leaks since it is not as flammable as something like Brake Kleen…when the engine has cooled down and with ignition on and engine off you should see 450 mv’s (bias voltage) on your scan tool…this may be a wiring issue if that bias voltage is stuck low below 50mv’s…signal wire may be shorted to ground so the car may be running rich…don’t know why you changed the MAF for an O2 “circuit” code ??…it is ALWAYS a good idea to let us know the model year as a minimum…you should put that info in your profile.
I've read that bad MAF can cause similar issues, replacing the cheap easy stuff first. The car is a 2016 Z06 m7. Here's what the oxygen sensors and fuel trims were doing, I gave it throttle towards the end
I'm not used to looking at this live data which may be some kind of phone app but you normally look at "millivolts" and not volts...it looks like the sensors or the wiring may be the issue...if the O2 is stuck lean the ECM will schedule more fuel and that is why your fuel trims were negative....disconnect BOTH O2 sensors and with ignition ON what does your app read...you should see 0.45 volts...if you see that your wiring is fine...WHERE did you buy your O2 sensors ??
I'm not used to looking at this live data which may be some kind of phone app but you normally look at "millivolts" and not volts...it looks like the sensors or the wiring may be the issue...if the O2 is stuck lean the ECM will schedule more fuel and that is why your fuel trims were negative....disconnect BOTH O2 sensors and with ignition ON what does your app read...you should see 0.45 volts...if you see that your wiring is fine...WHERE did you buy your O2 sensors ??
With both unplugged they are pegged at 1.89 volts like the rears. Also threw codes P0030 and P0050. Oxygen sensors are OEM ACDelcob from Rockauto
With all 4 at 1.89 volts sounds like all 4 O2 signal wires are shorted to power…never seen that before…with a DMM if you have one see if the violet/gray for bank 1 and violet/white for bank 2 show near 12 volts at the harness connector…you can also remove the 15 amp fuse upper left of the wiring diagram and see if that 1.89 volts disappears on the scan tool…if you have headers check the O2 wiring harnes…a scan tool will only show 1-2 volts and not 12 if shorted to power.
With all 4 at 1.89 volts sounds like all 4 O2 signal wires are shorted to power…never seen that before…with a DMM if you have one see if the violet/gray for bank 1 and violet/white for bank 2 show near 12 volts at the harness connector…you can also remove the 15 amp fuse upper left of the wiring diagram and see if that 1.89 volts disappears on the scan tool…if you have headers check the O2 wiring harnes…a scan tool will only show 1-2 volts and not 12 if shorted to power.
Thank you for all your help, when you said both are shorted to power I figured it out. The shop didn't secure the plugs for rear 02 sensors and one melted. It was bad enough that the wires inside were touching. I cut off the plug and it immediately fixed it and I was able to get my emissions testing done today.
Oxygen sensor codes, terrible idle.
