Running "Lean" with a Resistor Divider on the Air Temp Sensor

[JohnnyGrey]

Sorry, won't work on modern OBD engines. The O2 sensor checks your air/fuel ratio and will correct it. Plus, 5-10 degree difference will do next to nothing as far as fuel trim.

That's correct. Racers do the resistor mod because they race at WOT, which is open loop mode. Your IAT is ignored in closed loop operation where fuel is concerned. This mod is worthless, so don't waste your time.

Thats also not to mention that a lean burning engine emits more NOx emissions which is nasty stuff. Factory equipped lean burn engines have a special catalytic converter to deal with this.

Worst case scenario is about 25% more NOX emissions than at stock levels. Leaner than a certain point, and they get lower again. Hydrocarbons also drop when leaning out, so the tradeoff in pollutants is not worth fretting over.

Also, don't try resistors or offsets on a narrowband O2 sensor. It's essentially a digital device.

[steensn]

Originally Posted by JohnnyGrey

That's correct. Racers do the resistor mod because they race at WOT, which is open loop mode. Your IAT is ignored in closed loop operation where fuel is concerned. This mod is worthless, so don't waste your time.



Worst case scenario is about 25% more NOX emissions than at stock levels. Leaner than a certain point, and they get lower again. Hydrocarbons also drop when leaning out, so the tradeoff in pollutants is not worth fretting over.

Also, don't try resistors or offsets on a narrowband O2 sensor. It's essentially a digital device.

I was going to take a look at the sensor that is running on my 1996 Aspire. Anyone have a data sheet on the O2 sensor for a 96 aspire?

Either way, there has to be a way to fool the engine ECU to a certain level to make it run clean. The other option is to get a $550 dollar SW hardware package for a laptop to make it run leaner, but I don't want to spend that kinda money.

This isn't impossible, but all you are saying is do it on the O2 sensors instead of the intake as long as you do the mod correct for your sensor. I still see a benifit of being able to run leaner at any given air temp so that you can take it one step further than a HAI, isn't this what the sport is all about?

People are putting pizza pie pans instead of hubcaps to maybe get .5 mpg change... this is obviously has a better potential for improvement than that.

[JohnnyGrey]

I was going to take a look at the sensor that is running on my 1996 Aspire. Anyone have a data sheet on the O2 sensor for a 96 aspire?

It's a narrowband sensor, just like every other narrowband on pretty much every other car.

Either way, there has to be a way to fool the engine ECU to a certain level to make it run clean. The other option is to get a $550 dollar SW hardware package for a laptop to make it run leaner, but I don't want to spend that kinda money.

There is. You have to buy a wideband sensor. A laptop cannot make it run leaner because your engine still doesn't have the proper sensors to maintain a lean mixture.

This isn't impossible, but all you are saying is do it on the O2 sensors instead of the intake as long as you do the mod correct for your sensor. I still see a benifit of being able to run leaner at any given air temp so that you can take it one step further than a HAI, isn't this what the sport is all about?

I'm saying adding any amount of electronics to a narrowband O2 is ineffective not because leaning isn't effective, but because it won't accomplish leaning. The IAT is flat-out ignored in closed loop mode. Your scangauge will show improvement because IAT is part of the formula it uses to compute fuel usage, but when you go to fill up, you'll realize that you've burned more fuel than it thinks you did and that there was no improvement.

People are putting pizza pie pans instead of hubcaps to maybe get .5 mpg change... this is obviously has a better potential for improvement than that.

Of course it is. I found a 10% improvement, but I leaned my car out properly, with a wideband. Trust me, I've screwed around with narrowbands, and you have no way of knowing what mixture you're running at. To run at your most efficient AFR you need:

1. A wideband O2 sensor
2. A signal converter circuit
3. Good injector-based instrumentation or fillup method (NOT ScanGauge!)

[steensn]

A laptop cannot make it run leaner because your engine still doesn't have the proper sensors to maintain a lean mixture.

The laptop SW set would change the mixture setting to run leaner. We have lots of OEM SW interface tools at work that you can modify settings on different control modules to change settings. Just like someone wanting to run richer, you could use it to run leaner by modifying the flash memory. I just don't think I could get access to a 1996 Ford Aspire setup. What you are changing is the control algorithm rather than the sensor. The settings are not fixed, you just have to be able to change them.

So my best bet is what you have done and that is to get a wideband sensor... so, where do you get one? What modifications have you made? Is there already a thread on this? Any results?

[tasdrouille]

Originally Posted by JohnnyGrey

The IAT is flat-out ignored in closed loop mode. Your scangauge will show improvement because IAT is part of the formula it uses to compute fuel usage, but when you go to fill up, you'll realize that you've burned more fuel than it thinks you did and that there was no improvement.

The fuel mass is computed from the air mass, of which iat is a correction factor. In closed loop the fuel mass is calculated from the input of various sensors, and is corrected from the output of the ho2s. Ever heard of fuel trim?

Where did you get that iat is part of the formula the sg uses to compute fuel usage? I never read that anywhere.

And even if you don't touch the ho2s and do the iats resistor mod, you still retain the timing advantage given by the mod.

[cfg83]

tasdrouille -

Originally Posted by tasdrouille

The fuel mass is computed from the air mass, of which iat is a correction factor. In closed loop the fuel mass is calculated from the input of various sensors, and is corrected from the output of the ho2s. Ever heard of fuel trim?

Where did you get that iat is part of the formula the sg uses to compute fuel usage? I never read that anywhere.

And even if you don't touch the ho2s and do the iats resistor mod, you still retain the timing advantage given by the mod.

Last summer I replaced the IAT sensor with different resistors. I got progressively better MPG on the SG, but I didn't believe it. Others have had similar results with long term resistor swaps that 1) didn't effect driveability and 2) didn't effect their observed fuel usage.

CarloSW2

[JohnnyGrey]

The laptop SW set would change the mixture setting to run leaner. We have lots of OEM SW interface tools at work that you can modify settings on different control modules to change settings. Just like someone wanting to run richer, you could use it to run leaner by modifying the flash memory. I just don't think I could get access to a 1996 Ford Aspire setup. What you are changing is the control algorithm rather than the sensor. The settings are not fixed, you just have to be able to change them.

Here's the catch: this only works in open loop mode, which we're not interested in. In closed loop mode, fuel tables are only used for a starting point, and the O2 sensor is god.

The fuel mass is computed from the air mass, of which iat is a correction factor. In closed loop the fuel mass is calculated from the input of various sensors, and is corrected from the output of the ho2s. Ever heard of fuel trim?

ONLY IN OPEN LOOP MODE!!! Seriously guys, I'm getting tired of repeating it by now. Ever heard of long term/short term trim? These are tables that are in the ECU's SRAM that you don't have access to. They're created according to the O2 sensor's output that cancel any wacked out values you put in the fuel trim tables. See that thing on your scangauge that says CLSD LP ? That means your ECU is running off its own tables and ignoring yours.

Where did you get that iat is part of the formula the sg uses to compute fuel usage? I never read that anywhere.

It's true. If you had some real fuel instrumentation that would give you GPH or injector pulse widths, you'd see that tricking the IAT sensor causes only a blip of difference until the O2 corrects it. Then pulse widths go back to the exact same value they were before. The SG on the other hand truly believes that the ECU is injecting less fuel, even though it's not.

And even if you don't touch the ho2s and do the iats resistor mod, you still retain the timing advantage given by the mod.

You might, or you might not. Something tells me that this is one area where the OEM squeezed every bit of economy and performance out of the engine possible on the given fuel. In fact, many engines are eqipped with piezoelectric knock sensors because they constantly flirt with the bleeding edge of detonation. The IAT serves as a starting point and the ECU will see what it can get away with. If you move the starting point well within the knock region, you may cause damage to your engine.

[cfg83]

JohnnyGrey -

Originally Posted by JohnnyGrey

Here's the catch: this only works in open loop mode, which we're not interested in. In closed loop mode, fuel tables are only used for a starting point, and the O2 sensor is god.

...

I agree.

CarloSW2

[tasdrouille]

Put the resistor on a switch, go out for a drive, cruising in closed loop. Now look at your A/F meter and flip the switch. Nothing will happen to the A/F since we're in closed loop right? You won't see it jump and then be corrected right?

[JohnnyGrey]

Put the resistor on a switch, go out for a drive, cruising in closed loop. Now look at your A/F meter and flip the switch. Nothing will happen to the A/F since we're in closed loop right? You won't see it jump and then be corrected right?

It will jump because it's working off of tables that have been confirmed by the O2 sensor. Then it will lean out for a second or so, then quickly be corrected by the O2 sensor back to normal. When you take the resistor out, it will go rich for a second or two, then it will go back to normal. Let me illustrate what happens when you do the resistor trick...

ECU: "Intake air is 90 degrees, I'm switching between lean and rich."
O2: "Mixture is lean."
O2: "Mixture is rich."
O2: "Mixture is lean."
O2: "Mixture is rich."
O2: "Mixture is lean."
O2: "Mixture is rich."
IAT: "Air coming into the engine just got 100 degrees hotter."
ECU: "Holy #$*#, I'd better cut back on fuel fast!"
ECU: "Let's see what my tables say I should be injecting based on the last time I dealt with 190 degree air..."
ECU: "OK, I'm cutting fuel delivery by 20%"
O2: "Mixture is lean."
O2: "Mixture is lean."
O2: "Mixture is lean."
O2: "Mixture is lean."
ECU: "I've over compensated, adjust the trim tables and increase the fuel a bit."
O2: "Mixture is lean."
O2: "Mixture is lean."
O2: "Mixture is lean."
O2: "Mixture is lean."
O2: "Mixture is lean."
ECU: "I'm still off. Adjust the tables some more and increase the fuel."
O2: "Mixture is lean."
O2: "Mixture is lean."
O2: "Mixture is lean."
O2: "Mixture is lean."
ECU: "Wow, I'm really off. Injecting even more fuel."
O2: "Mixture is rich."
ECU: "OK, we're back to normal again."
O2: "Mixture is lean."
O2: "Mixture is rich."
O2: "Mixture is lean."
O2: "Mixture is rich."

Everything above happens within about 2 seconds.