Let's get technical: Tuning the ECU for mpg

[GasSavers_bobski]

Wide-band sensors are nothing new - Honda has been using them for years. The '92-95 Civic VX, '96-05 Civic HX, '00-06 Insight and '01-05 Civic Hybrid all use wide band oxygen sensors to operate in lean-burn mode. The lean burn system is designed to go as high as 22:1 A/F ratio if the conditions are right.

[Bill in Houston]

The guy with the 30 mpg Explorer uses some kind of custom ECU programming to try to increase his gas mileage. If you are interested, you can search here for "30 mpg Explorer" and try to find the thread where I linked it, or just google "30 mpg ford explorer scuba quest" and you will find the Explorer board where he posts.

[DrivenByNothing]

I was out of town for the weekend. I'm happy to see that there's some good discussion occurring.

Interesting stuff about the LC-1's ability to be 're-geared'. They're priced reasonably well, so the ability to adjust the output is icing on the cake (very good icing).

I didn't realize that Honda was using WBO2's, but it sure helps to explain why the prices were so high when I was checking for my friend's HX.

Another friend of mine has mentioned an MR2 that's running to different programs for race and economy. I'll see if I can get more info, but I remember being impressed when I heard it.

[DRW]

Here's how to get a dual image in the 1990-1994 Eclipse chip. Maybe the MR2 is similar? http://www.dsmchips.com/dualimage.html Usually one half of the chip has a tune suited for regular pump gas, and the second image is setup for race gas. This way you don't have to re-tune if you add race gas at the track. Just flip a switch.

Like it said in the Megasquirt link, there's not much reason to have a HP tune and a seperate economy tune since when you want economy, you're at light throttle. So tune the light throttle maps for economy. When you want power, you're at full throttle, so the full throttle maps are tuned for power.

[DRW]

Aha. Here it is. I found an old post I wrote about stuff that can be changed in the ECU to save gas. Each one is just a little thing, but it all adds up.

"This is just the stuff I'm doing with my ecu. The stock ecu in my car controls just about every aspect of how the motor runs, there are very few mechanical controls. This will be a shotgun approach, I'll list everything in my notes. Each one of these items can be changed to optimize FE and tailored to a drivers particular habits. It's up to each individual to examine their car to see if improvements can be made in each area.

Idle speed control (isc): regulated by a stepper motor, 0 steps is closed, 120 steps is fully open, 30 steps is base/normal.
-ECT based offset when starting to crank, added to base isc depending on ect. This is how high the engine revs when first started.
-Timer that counts down starting-to-crank isc offset, this is how quickly the revs drop to idle after being started.
-Starting to crank fuel enrichment aka choke. How much extra fuel is added when starting the motor.
-Starting to crank countdown timer used to decrease choke enrichment. Has two speeds; enrichment decreases quickly at first, then slower.
-Starting to crank timer threshold between quick and slow timer.
-Target idle speed based on ect. Lower your idle speed, especially when the engine is cold and running most rich.
-Rolling idle speed, isc steps added to base when car is moving. Also based on ECT, higher when cold.
-Threshold where car is considered moving/stopped.
-ISC offsets added to base if A/C is on, power steering pressure is up, and ? somthing else.
-Coasting fuel cutoff, cuts fuel when engine rpm is above threshold and throttle is closed. I lowered the threshold so I can coast longer in gear with the fuel off. A side benefit is that there is very little engine braking available at lower rpms, so I can keep the car in a higher gear and coast longer. Useful when EOC is not appropriate for the conditions.
-Accelleration enrichment fuel adder based on ECT, how quickly the throttle is opened, and a timer used to taper off accel enrich.
-Warmup temperature threshold for determining open loop vs. closed loop (31*C on my car), and warmup2 used for closed loop/cold engine enrichment vs. closed loop/fully warm engine (86*c).
-fuel trim update temp, based on ect. Below this temperature threshold the fuel trims are not updated.
-ECT based fuel enrichment table. Runs richer at colder temps, decreased to standard enrichment as airflow goes up.
-EGR solenoid duty cycle map, based on load and rpm. Adjust EGR use at individual rpm/load points. 56 datapoints.
-EGR solenoid modifyer based on ECT, less EGR at cooler engine temps.
-Rev limit. Fuel and ignition are cut off above this limit. Could be useful if someone is using weak valve springs?

-Ignition timing map, 192 points based on rpm and load. On my car there are a few areas on the map where timing is decreased in order to smooth the power delivery, such as when the turbo is spooling up. There is another area where timing is decreased to make the car feel more torquey, such as low load at 1000 to 1750 rpm. Standard theory is that timing should go up as rpm goes up, and timing should go down as load increases. But at low load/low rpm it starts with low timing, then timing increases as load increases from load level 1 (lightest load) to level 4 (out of 12 levels). The difference is significant, about 6 degrees less timing at light load vs. load level 4. The stock timing map 'FEELS' nice, power surges as you step on the throttle. I changed the timing in that area so it's flat, no increase or decrease from level 1 through 4, and I found I can back off the throttle much farther once up to speed. In other words, I'm using less throttle to maintain 35mph.

-Ign timing corrections based on ECT. timing is increased below19*F.
-Ign timing corrections based on air temp. The stock map decreases timing at temps above 100*F and below 48*F. I changed it to increase timing between 73* and 19*F, with a max increase of one degree at 48*F. and tapering off above and below that temp. My change was based on the theory that colder air lowers the octane requirement of the fuel. It's also possible that the engineers might have reduced timing in this area so the power would not change with temp since their buyers might complain when the weather warms up that power is lacking. Just a thought.
-Open loop fuel map. 168 points based on rpm and load. Specifies a target A/F ratio depending on the rpm and load level. Only used during open loop.
-Open/Closed loop thresholds based on rpm/throttle position. Changes the point where open loop is used. I raised the thresholds so I can dip into the throttle at low rpm without going into open loop, and so I can stay in closed loop at higher rpm.
-Open/Closed loop thresholds based on rpm/airflow. Same as above, try to stay in closed loop longer.
- A/C on/off threshold based on throttle position. WOT shuts off A/C. Lower the threshold so A/C is off during anything greater than light accelleration.
-Closed loop O2 feedback cycling speed. How quickly the O2 sensor cycles up/down.
-O2 feedback stoich trigger. Stock is set to .5 volts. Can be changed in .02V increments, may affect emmissions.
-O2 feedback increase/ decrease values,wide range. How much fuel is added/ removed from base fuel calculation in order to get the O2 sensor cycling.
A wide range is used to help find .5v and center the short term trim. Used for the first 4 seconds each time after returning to closed loop.
-O2 feedback increase/decrease values, narrow range, used after 4 seconds to increase O2 sensor cycling speed and limit wide excursions from .5v Based on airflow and rpm. Different tables are used depending on Federal or California market.
-O2 feedback timer. Stock is set to 4 seconds. Whenever the throttle goes from closed to open the wide range O2 cycling is used for the first 4 seconds, then narrow range cycling kicks in. This can be changed to reduce the ammount of time spent in wide range cycling. May improve emmissions.
-Dash pot. Timer used to decrease fuel gradually when throttle is closed. Helps smooth the transition between open to closed throttle. Stock timer is .75 seconds, ie fuel stays on for .75 seconds after throttle is closed.

All of the above is adjustable simply by changing a number in the hex code.

OK I think that's it for the stock stuff that could be adjusted to improve FE. There are also changes that can be made to match any modifications to the vehicle, such as different fuel pressure, different size injectors, different or modified airflow sensor. These help keep the car running optimally with other hardware."

And then there's Multi stage Lean Burn Code. Yeah, this is more than just a few changes, but once you open up the box, there's no going back!

[Spencyg]

This guy knows his Hex, AND he is working with an OBD1 computer. OBD2 doesn't allow you to change variables in the EEPROM, and as mentioned earlier, all the Import manufacturers are using proprietary code to control their machines. All this being said, IF you are running an OBD 1 car (pre-1996) AND you are at peace with the programming gods, than this puts you many steps ahead of the rest of us who faint at the sight of code...

Spence

[minic6]

When working with this type of modifications remember to add in a thermocouple in the manifold to monitor temps.

[GasSavers_Willard]

Originally Posted by Spencyg

What year is the Volvo?

My 84 Turbo has Bosch CIS with the 'little screw'.

I found this post while searching for some info on the P07 ignition maps. I was at the dyno this past weekend with my D15Z1 (has modifications) getting the P28 ECU tuned (burnable chip) and was chatting about a fully controllable ECU. I was just wondering how agressive/safe Honda was with the P07 ignition maps under lean burn conditions.

If I were to use a "full control" ECU it would be nice to have a good starting point for the ignition maps (lean and normal burn).

[ashiga]

I just raised the closed loop threshold (throttle position x rpm) for all values on my D16Z6 P28 ECU with chrome, I'm hoping to get better mileage as I'm a hard driver but I usually keep my foot below WOT. I changed the threshold values to about 80%. That's an idea I just had, so I'll tell you if I get bad mileage which I think is unlikely to occur as when I had a wideband, the stock basemap produced 12.5 AFR when in open loop.

[pgfpro]

I hate closed loop.

Have you tried running only open loop and build your own fuel/ign. maps. You can dial your tune in way better then stock when running in closed loop as long as you have a wideband for reference. Major gains can be made over stock by running in open loop with a good map.