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Alright, so I just moved to Colorado and they have the IM240 Test here. Vehicle has no CEL, and my first run around I only had high NOx issues. I fixed 2 exhaust leaks I found, and a intake leak. Cool, makes sense. Go back in, and now I have high HC and high NOx. Checked for vacuum leaks, and can’t find a single vacuum line.
Catalytic converter and O2 sensors were replaced ~13,000 miles ago. Vehicle mileage is 122,766 miles.
No CEL, no hesitations, proper idle, no smoke, no funky smells from the exhaust.
I have been googling and searching for people with similar issues for days now. Came across this community a few times. Figured, I should join and use the combined minds. Attached are diagnostic graphs and ECU readings during the test.
The first common link is a failed/lazy O2 sensors. Did you replace with OEM sensors?
I did replace the upstream and downstream with new OE spec Denso sensors. It did cross my mind I could’ve got a bad one. But the voltage reading from the ECU look normal under the graphs.
edit—
I’ve been going back and forth on this since I got the results. I finally just bit the bullet and ordered a OBDII scan tool that does live data graphing so I can determine if I have a lazy sensor or one that has a bad heating element.
O2 wave forms will show it the best.
As already suspected, a lazy O2 or a failing CAT.
Was the replacement CAT aftermarket?
I see it was 13k miles ago since replacement but i'd fault the cat first since your B1,2 S1 voltages look in spec.
Although real time data is best to find out.
It's an entirely new exhaust from the Heads to the back. The old Cat never went out, but it came from Rust Country when I was living in AZ. It started to just deteriorate, so I got a new Header with the EGR port, and Factory upstream O2 sensor locations. Than I built from the headers to the tips, with all custom 2.5" all the way, but a high quality 50 state legal with Numbers 4way catalytic converter. In the factory location, and downstream sensor in the factory location. My other 2 vehicles I have the exact same Catalytic converter, and custom exhaust on passed with flying colors. So I am more inclined to say a lazy O2 sensor, or heater that is not working. I don't at the moment have an OBDII scan tool that can show O2 wave form, so I ordered one as the good O2 sensors like I put in are pricy, same for the catalytic converter. It's supposed to be here tomorrow, so I should be able to look at the wave forms and determine lazy, or bad heater on one of or multiple O2 sensors. I'll definitely reply with results, and my findings.
The header bungs are just in the standard position. It’s an aftermarket OBX race header. Which heads up do not fit! Correct flange, O2 sensor bung location and, EGR tube port. But, the bottom half of the header does not fit. I fixed by making two small 2” flanged spacers to keep removal easy. I’ll try and get some pictures tomorrow.
Here are some clips and pics I did find on my phone
Rear O2 will not affect fuel mixture.
The Front O2’s does.
So even if its bad, your Nox and hydrocarbons wont change.
Rear O2 looks like its reading rich.
Like the Cat’s efficiency is below threshold on pic 1.
Waveform of a rear O2 with a good working cat should be slow wave increments and be at middle to low voltage readings.
Rear O2 will not affect fuel mixture.
The Front O2’s does.
So even if its bad, your Nox and hydrocarbons wont change.
Rear O2 looks like its reading rich.
Like the Cat’s efficiency is below threshold on pic 1.
Waveform of a rear O2 with a good working cat should be slow wave increments and be at middle to low voltage readings.
picture 1 & 2 are B1S2 which is a upstream O2 sensor. Third one is on my bad is B2S1 which is a downstream sensor during load. At no load shows a slow proper oscillating signal. Same with B1S1 which is the other upstream sensor. With B1S2 (upstream) not oscillating properly and getting stuck on the rich and lean side of the signal is making half the motor act rich or lean. Which explains the NOx and Hydrocarbons.
edit—
nvm I got bank and sensor flopped in my head. Yes it would appear that new cat is not working properly.
02-26-19, 06:45 PM
High HC & NOx in emissions testing. Stumped
