View Full Version : How does gearing affect emissions testing?

10-08-2013, 05:50 PM
My 4Runner, that is driven a good bit less than ten miles per year in emissions controlled counties, is due next month. [scam] It passed last time, though it always seems to require the extended test, or whatever they call it, to do so. Since that test, I've regeared from 4.88 to 5.29, and 4.88 was too short for 33" tires. Is that likely to make a difference in its ability to pass, or will the tester just upshift to an appropriate gear? I don't know the test protocol well enough to predict what will happen, but I know they always seem to run it at a much higher RPM than would be required on the street to maintain the test speeds.


10-08-2013, 06:47 PM
I ran 5.29 and 33" tires for e-tests and it usually took the full test but always passed. Since going back to 30" and 4.10 both tests have kicked out after about 30 seconds saying it meets Fast Pass criteria.

Looks like to me that the tester doesn't do anything special, he seems shifts like he's driving it, shifting whenever he feels like it. Although maybe (just maybe) they avoid lugging it because part of the passing requirements is they have to follow the speed line some minimum amount of the time and our junk probably has trouble doing that if the RPMs are too low.

10-08-2013, 06:54 PM

I/M 240 Emissions Test
The I/M 240 emissions inspection tests the carbon monoxide, hydrocarbons, and nitrogen being emitted from the vehicle over a period of four minutes.

The inspector does a visual inspection of emissions equipment.
The vehicle is tested under simulated driving conditions using a dynamometer (similar to a treadmill) to allow the wheels to spin and a large fan to simulate wind while measuring emissions from the tailpipe.
A gas cap seal test is performed after the simulated driving test is complete.
You will be given a vehicle inspection report with details about how the vehicle performed and whether it passed or failed.

Two-Speed Idle Test
The two-speed idle emissions inspection tests the carbon monoxide and hydrocarbons being emitted from the vehicle.

A probe in the tailpipe is used to measure emission pollutants.
The inspector lets the engine run at idle speeds for 30 seconds and readings are taken.
The engine is then sped up to 2500 RPM for 30 seconds and readings are taken.
The engine returns to idle speed for another 30 seconds and readings are taken.
You will be given a vehicle inspection report with details about how the vehicle performed and whether it passed or failed.

Diesel Opacity Test
Vehicles that run on diesel fuel will be given a diesel opacity test.

An opacity meter is used to measure how much the air pollutant obscures sight through the exhaust smoke.
You will be given a vehicle inspection report with details about how the vehicle performed and whether it passed or failed.

Dynamometer Test
All-wheel drive/traction control vehicles must be inspected using a dynamometer that examines the amount of force or torque the vehicle produces. The dynamometer will spin both front and rear wheels together. Each Air Care Colorado station has at least one of these dynamometers.

If you have an Obama phone, maybe you can qualify for this... :D

Economic Hardship Waiver

You may qualify for an economic hardship waiver if you are getting financial aid from an approved program, and your failed vehicle is your only method of transportation. There are no minimum repairs required to qualify.

If you believe you qualify for the hardship waiver, call the Colorado DMV at (303) 205-5603.

10-08-2013, 06:56 PM
I have an '85 runner and it has always passed on the fast pass. I had 4.88's with 33" tires and now currently 5:29's with 35's. But all of my recent tests were with 31" tires. I always ask for a driver who is very good at shifting gears at the emission station. And I always tell them it is an older tired engine so help it along. And that has been my method.

10-09-2013, 08:34 AM
Thanks guys. It sounds like I should be OK..


10-09-2013, 10:04 AM
On my test last Saturday, they bumped the O/D off and it kicked up all the numbers across the board. They wouldn't let me copy the data down but it was higher from the glance I was able to get.

10-09-2013, 11:50 AM
when i was having trouble passing mine the guy was generous enough to do stuff liek short shift it and start in 2nd gear. it helped a lot.

10-09-2013, 01:56 PM
I just passed last month in my automatic 85 4Runner with 5.29's on 32 inch mud terrains no problem. I had the ECT set on "PWR".