Failed CO High Speed Smog

[bluemoney]

I have a 1990 SHO MTX. I removed the spout all the time to make it pass, this year I just failed the high speed CO. The car runs great and no codes and good gas mileage. Here are two year ago readings and this year, only put about 500 miles on it in two years:
CO at 15MPH 1698 RPM Max 0.52 Meas .20 Pass
CO at 25MPH 2699 RPM Max 0.43 Meas 0.12 Pass

This year:
CO at 15MPH 1579 RPM Max 0.52 Meas 0.08 Pass
CO at 25MPH 2746 RPM Max 0.43 Meas 1.53 Failed
Please help with suggestions on why so high this time and how to fix or troubleshoot. Thanks Larry

 

[luigisho]

http://www.smogtips.com/failed-high-carbon-monoxide-CO.cfm

Those numbers are way different from year to year.
Maybe swap in new O2 sensors? I would consider new plugs for good spark to burn the fuel and I probably would clean the MAF sensor filament just to make sure air:fuel was good.
Maybe swap inspection stations?

 

[rubydist]

I assume the other measurements (NOx, HC) are okay.

If so, then your high CO readings are due to one of these: fuel pressure regulator issue (pressure too high, leaking, etc.), fuel injector leaking (not turning off, too much fuel), bad mafs (not reading air accurately), bad oxy sensor (not reading ratio correctly).

Since the readings are fine at some speeds, that suggests that it is not the fuel injector failing to shut off, nor the fuel pressure regulator being bad, so I would look at cleaning the mafs and changing oxy sensors. Since there are no codes present, that suggests that the oxy sensors are bad.

 

[bluemoney]

http://www.smogtips.com/failed-high-carbon-monoxide-CO.cfm

Those numbers are way different from year to year.
Maybe swap in new O2 sensors? I would consider new plugs for good spark to burn the fuel and I probably would clean the MAF sensor filament just to make sure air:fuel was good.
Maybe swap inspection stations?

All new plugs and wires, compression good and valves set properly. The specs here were the same from 2 years ago. I'll clean sensor and change air cleaner. Thanks Maybe I just didn't drive it far or long enough to teach the computer, since the battery needed changed, so did that and drove it down to smog place. Thanks

 

[bluemoney]

I assume the other measurements (NOx, HC) are okay.

If so, then your high CO readings are due to one of these: fuel pressure regulator issue (pressure too high, leaking, etc.), fuel injector leaking (not turning off, too much fuel), bad mafs (not reading air accurately), bad oxy sensor (not reading ratio correctly).

Since the readings are fine at some speeds, that suggests that it is not the fuel injector failing to shut off, nor the fuel pressure regulator being bad, so I would look at cleaning the mafs and changing oxy sensors. Since there are no codes present, that suggests that the oxy sensors are bad.

All the other readings are great, I do pull the spout to help the HC readings. All new plugs and wires, compression good and valves set properly. The specs here were the same from 2 years ago. I'll clean sensor and change air cleaner. Thanks Maybe I just didn't drive it far or long enough to teach the computer, since the battery needed changed, so did that and drove it down to smog place. Thanks

 

[luigisho]

If you still fail after all that, you should consider O2 sensors as they are part of the data input for air/fuel mix.

 

[bluemoney]

If you still fail after all that, you should consider O2 sensors as they are part of the data input for air/fuel mix.

I have both on order and will try that, I will post the out come of my results. Thanks

 

[luigisho]

I think you are onto something about clearing the pcm memory with battery install

 

[Devin]

All the other readings are great, I do pull the spout to help the HC readings. All new plugs and wires, compression good and valves set properly. The specs here were the same from 2 years ago. I'll clean sensor and change air cleaner. Thanks Maybe I just didn't drive it far or long enough to teach the computer, since the battery needed changed, so did that and drove it down to smog place. Thanks

Make sure to drive it ******* the way there and have it hot. I failed on a SLO, got some outrageous estimate to replace the Cats and O2 sensors, but the tech told me to get it nice and hot before testing, and I passed with flying colors.

 

[rubydist]

there is also some stuff you can buy at the auto parts store that will help you pass the test.