Good Engine Start-up Tip
 

I don't know if anyone else has catloged this before, but it should be helpful.

One of my friends is an engineer at Honda and he told me that at least on Honda vehicles you should be able to get better mileage by turning the key to "ACC" prior to engine start-up for 1-2 minutes. The reason being that in this state, there are element heaters on some of the wide and narrow band fuel mixture sensors that are activated. Then, when you do do turn on the engine and start driving these sensors should be able to effectively adjust the fuel/air ratio.

I don't know how far back this tip works for Hondas, or if it will work for other vehicles.

Who will commit to try it and see if it makes a difference?

I get the premise of heating those sensors; what I don't get is turning the key to "acc". Wouldn't it need to be on "run"?

It wouldn't work on pre-OBD2 cars, and I think some of the OBD-2a versions still didn't have heated sensors.

While heating the sensor surely will have some effect on mippigs, it'll be well within the noise of day to day variation, and unable to be tested without serious testing procedures. The O2 feedback sensors have very little overall effect on AFR compared to the other sensors in the control loop.

ProtractedSilence -

I just enabled this for my previously non-heated narrow-band 02 sensor. Now I can *see* the 02 sensor in the exhaust manifold heat up using my digital AFR gauge :

http://ecomodder.com/forum/showthrea...2-a-10921.html

My post-cat 02 sensor is already heated, so nothing to do there.

However, it doesn't appear that my ECU/PCM is taking advantage of the pre-heated 02 sensor, or at least I can't prove it. My reason for doing this mod was for emissions and *hopefully* quicker switching to closed-loop operation after EOC and engine-off at stoplights.

I think anyone can test your friend's advice if they have a ScanGauge and all of their 02 sensors are wired for self-heating. The driver just has to compare how fast the car goes into closed-loop operation.

I agree it's a small benefit, but I like the idea of it nonetheless.

CarloSW2

Looking at the videos, the driver turns the key to the on position and not ACC. This makes more sense. On ACC there shouldn't be any juice going to the sensors.

thatguitarguy -

That's right, I use the RUN position because the AFR gauge doesn't work unless it's in the RUN position.

I just did a test. I set the key to the ACC position and I waited for a bit. Then I set it to the RUN position. If the heating element had been on, the gauge would have shown "L" for lean when I changed to the RUN position. This did not happen, so the heating element (at least on my car) will only heat up in the RUN position.

CarloSW2

IIRC, the heated sensor on saturns (HO2S) is the rear one. It is basically a sanity check of the front (non heated) one so the computer knows when to throw a cat or one of a few o2 sensor codes. Pretty sure most obd cars have at least a rear heated sensor but not necessarily a front one, and the front one is the one that you "drive" on.

dcb -

I agree, but Honda is really good with emissions, so (these days) all of their sensors are heated. For instance, on my wife's car, both her sensors are heated :

Replacement Oxygen Sensor - Front or rear - Fits 2003 Honda Civic EX 4 Cyl 1.7L
You should be able to eyeball your sensor. If you see 1 or 2 wires, it's probably unheated.

I think the second sensor is always heated because you can't count on the exhaust being hot enough to make the sensor work. It's more than a sanity check, it's for keeping the cat healthy.

CarloSW2

From an EPA perspective, the rear sensor is there to double check that the front sensor is being responsive, and so it needs to be heated so it can tell when the front sensor comes "on line". It is also to see that there is actually less O2 downstream of the cat, to make sure that the cat is actually doing something. But the sensor immediately downstream of the engine should be more accurate and thus the primary sensor.

FYI, it may never run the obdII o2 sensor/cat converter readiness monitors if you have a heated front sensor and always heat it up before starting the engine.

I haven't been able to find a 2nd sensor on my Civic. There aren't any wires at the cat or anywhere on the exhaust except for the O2 sensor sticking out of the front of the exhaust manifold. Pricey, but easy to get to.

So this is another reason for turning the car to "run" before putting your seat belt on, then start the coasting down the driveway, popping the clutch to start the engine.
I like this.

thatguitarguy -

Yeah, I went looking at partstrain.com for your 1995 Civic, and it wasn't clear that there was more than one 02 sensor. It did look like *most* of the sensors were 4-wire, but there were unheated sensors too. Maybe your Colorado(?) Civic has a different exhaust configuration.

Also, a 1995 car is pre-OBDII.

CarloSW2

I think the car was built in Canada and the original owner bought it in MI and brought it with her to CO. I think what counts is that it's not a CA car. I guess those are all different because of CARB.

It is OBDI and it was throwing a code at me for the heater circuit on the O2 sensor. I changed the sensor, and it is a 4 wire, and when I did, I looked all over the exhaust system and found no other wires. I always thought the important one was in the cat, but this one doesn't even have one in the cat.

Some people think that the older cars are more polluting because of fewer sensors and a less complex system, but when cars like Civics and Metros use that much less fuel in the first place, they are less polluting by nature.

Most cars only have two of them after 1996. Pre-1996 are OBD-I compliant, and don't need Cat checks, but they were optional to manufacturers.

Newer Porsches have this option of pre heating the sensors. You trun the key and watch the display on the dash.

Well that justifies a $2900 battery!! :p

I can test this but I don't have my MPGuino assembled yet :( I am running my block heater daily at this point on my VX. I always set the key to on and let the CEL and upshift light go out before cranking the motor over (this allows the fuel pump to prime and the car to start quickly). I have a yellowtop Optima deepcycle battery in my car (41Ahr) and can easily let the key sit in the "ON" position while I get my kids in the car and get them buckled and set to allow my Wideband to heat up.

that is funny.
to call it technological evolution, ya know, like everything before vtec...

they are mimicking an electric choke.

alot of japanese (the first I knew of, aside from diesels) have a bell even for carb cars (35+ years), wait for the bells to stop and then start, it avoids rich conditions, sometimes the little fuel pumps know to give it a squirt, if given a few seconds before hand..pumping once or twice of course before hand. that is a big big confusion for our retarded planet.

Oddly, I don't remember any kind of "bell" on any of my old japanese carb'd engines, including my Honda CRX and my older Subaru Justy field car.