# Science Fair Question

I am a teacher in Chicago, and one of my students wants to test if there is less car emissions when the car is in neutral vs. drive. We were curious if anyone knew of a way to test the car’s emissions without going to the emissions test center.

Sure, see if you can get your hands on a gas analyzer. Check with some of the technical colleges around your area and see if they have one they can loan out. If there is a Vo-Tech school, they should have one if they carry an automotive certification class.

I assume you mean while idling?

Busted Knuckles had a good idea. A community college automotive instructor might be happy to assist your student in testing this. Speak with the department chainman.

It may even be a great learning experience for the entire class.

Loves labor lost…In a modern car with a properly working emissions control system, you will detect no difference. The readings will be zero either way…A functioning catalytic converter makes it all go away…

This is not true at all. Modern emissions bring the numbers down, but there is no gas-burner available today with zero emissions unless the engine is off.

Have you ever seen the taipipe fiqures on a (the latest I have seen is probably year model 1999, I can only imagine how low they are on a 2009) The readings are so low the needles barely move and the difference between idle and neutral is going to be very hard to see. My college certainly would not make room for such a experiment,they have classes to run,and no gas analyzer,all theory.Turn students loose with a gas analyzer and that machine will be down probably 80% of the time,the maintiance costs are prohibitive.

Two possibilites,pick a non-cat 60’s gas guzzler or make this a book exercise that cant be verified with the equipment you have access to.

Are you talking about the question of whether or not to put the car in neutral at a stop light? If so, here’s my quickie approach. I bet the concentration of pollutants in the gas is no different, drive vs. neutral. That’s what all those sensors and cat converter, etc, do. What will differ is the total volume of gas. So you’ll get a rough answer to your question by measuring the volume put out in a given time. How to do that? One way-attach a known volume bag to the exhaust pipe, time how long it takes to fill it up in each condition. Less time = more emissions.

One simple thing you could do is if you buy one of the more upscale (like maybe \$40) home carbon monoxide detectors, they have a little LCD screen that tells you the PPM concentration.I know on my old VW, putting the CO tester anywhere near the tailpipe would make it go off-- I’d be curious if that’s still the case on newer cars.

I agree with texases though, that the concentration is probably no different, but it might be interesting to measure the difference in the volume of exhaust gases.

Engineers know the answer to this question already. I have been told that my car uses more fuel in park than in drive with the brake on. It is because the emissions programming assumes that the PARK situation might be for some time while the stopped in drive is probably relatively temporary. You can get away with lean mixture for a while, but the catalytic converters need to be kept hot so if sitting in PARK, the computer commands more fuel to be dumped in.

Why would enginners assume that because you are in Park that the engine would be running longer than if you where Drive? The logical conclusion if you are in Park is that the engine will soon be shut off.

There must be more information added to the transmission in park situation to conclude that a fuel adjustment to keep the cat. efficient is required,like a time parameter or a sequence of events that leads the computer to believe the cars operation is to continue and not shut down.

It makes sense to me, but I am a moron for the most part. This is the way I understand it. If you stop with your foot on the brake in D, you will not be stationary for that long. The mixture can go lean because it will go rich when you accelerate shortly. If you stop in P and shut off the engine immediately, it does not matter what you have been doing with catcon cycling in the few seconds between going to P and shutoff. If go to P and assume a relatively long idle period, you have to keep the catcons cycling, and somewhat rich to function.

Gentlemen, the student will learn far more if we refer him to someone who can teach him how to test for the answer (which is what he asked for) than if we tell him the answer.

Teach a man to fish…

Good point. While i assume an automatic transmission the net carbon emission would likely be less. The best test would be an instantaneous read out from a dealer type equip that shows the fuel rate. An autotrans holds a bit of torque on the engine in drive. This goes away in neutral. The net fuel difference might be shown on a dealer scan. Find a local dealer with a sense of fun.

For those of us that don’t know please explain “fuel rate” and how it relates to emissions. Remember your plan must be fully cooked,don’t expect the Dealer to do any thing but hook up the scan tool and let you at it.