MAP Tuning Fuel System Status Logic

Status Levels

There are 4 main fuel system status levels defined in FlashPro Map based tuning on the Civic Si.

• 2 - Closed Loop
• 1 - Open Cold - O2 sensor is cold and is warming up
• 4 - Open Driving - Driving, WOT and/or sometimes overrun
• 8 - Open Error - An error has been detected in the fuel system (usually Primary O2 sensor failure)

Closed Loop

Closed loop is used during idle, cruise and part throttle. The ECU applies fuel trims (STRIM) to the fuel tables (Fuel Low, Fuel High and associated compensation tables) to reach a 14.7 AFR. 14.7 is the generally accepted target for the cleanest combustion of standard gasoline fuel. The calculated STRIM value is based on feedback from the Primary O2 sensor.

Open Loop

Open Loop is a static state where the ECU literally inserts the amount of fuel dictated by the appropriate fuel tables for the current running condition of the engine without applying any feedback based short term fuel trims (STRIM) to the tables. Most people will be familiar with Open Loop as it relates to WOT fueling. WOT fueling for an NA engine generally targets 12.6-13.5 AFR depending on the modifications to the engine and where it makes the best power. The ideal WOT Open Loop target for Forced Induction vehicles (supercharger, turbocharger, nitrous) is between 11-12 AFR, again depending on the modifications and what provides the best detonation resistance vs misfiring.

Open Loop Control

Engine Startup

When the car first starts up, the primary O2 sensor is too cold to accurately read the AFR. The ECU knows this and stays in Open Loop until the primary O2 sensor starts reading. This process usually takes 15-20 seconds from the time you start the car. After that it switches to Closed Loop and starts applying trims to reach 14.7 AFR.

Wide Open Throttle

When you go WOT, the ECU will switch to Open Loop depending on a couple factors.

1. The MAP pressure / RPM as it relates to the MAP WOT Determination pressure table
2. The WOT Lambda tables as they relate to the magic failsafe in the ECU for the Minimum Fuel Enrichment value

Fuel Overrun

In between shifts, the car's MAP pressure drops very low. This is called overrun. During this time the car reverts to Open Loop operation momentarily. You may see fuel statuses of Open - Cold (1) or Open - Driving (4) in between shifts or on deceleration while in gear. This is by design since the O2 sensor can't provide feedback quickly enough during shifts to control the fueling properly. Thus the ECU has to rely on the Low Fuel / High Fuel tables in the low load columns for the appropriate fueling.

Primary O2 sensor failure and Limp Mode

If the Primary O2 sensor fails to respond to the ECU within a reasonable time after the car starts up, the car will go into an error status on the fuel (8). In this state, the ECU will run statically in Open Loop. Most (99.9%) of tunes are not safe to run in Open Loop statically. It is highly advised that if your Primary O2 sensor fails that you replace it as soon as possible and avoid driving the car except to get it to a place to get the sensor replaced.

MAP WOT Determination pressure

This table provides you RPM based load values that tell the ECU when to switch to Open Loop.

At low RPM these values are high, so it'll take more MAP pressure to invoke Open Loop operation. If you find that you're not entering Open Loop on the low cam at WOT, check the pressure values in this table and lower them if necessary. If you are still not entering Open Loop on the low cam, check your WOT Lambda Adjustment tables..

To help understanding how this table works, I'll explain how the table depicted above affects the ECU's operation:

Below 3500 RPM, the ECU will run in closed loop below .85 BAR (Barometric Pressure), this load pressure correlates to the 8th column in Hondata's MAP based calibrations. If .85 BAR is exceeded, the ECU will switch to Open Loop operation.

As the RPM increases, the values in this table slowly decrease, thus allowing Open Loop operation at lower Barometric Pressures. This is because as the RPM increases, so does the heat the engine produces at a given load. Fuel is not only used to make power, but also as a means to cool the engine and stave off detonation. So above 4500 RPM the ECU only needs to reach column 7 for MAP pressure (.75 BAR) to invoke Open Loop, and at 8000 RPM it only takes .55 BAR (between column 5 and 6).

In between the provided indices, the ECU will interpolate the needed pressure dynamically. So in between 3500 and 4500 rpm, the pressure needed to switch to WOT will vary based on how close you are to each of the indices.

WOT Lambda Adjustment Tables

The values in this table control the targeted transient throttle behavior related to tip in enrichment (the initial moment where you punch the gas). Unfortunately Honda's logic surrounding this table has a built in failsafe that can have an unexpected impact.

If these values are set to target an AFR that is too lean, the ECU will remain in Closed Loop during WOT. This will cause the engine to run sluggishly and you'll experience decreased performance as a byproduct. At WOT the engine should always go into Open Loop, anything that prohibits that will decrease performance.

It has become an accepted best practice to leave these values alone when using Hondata's MAP based tuning. Unless you explicitly know what you are doing, the potential to cause issues by editing these tables far outweighs the potential for some kind of improvement in the tune. If you really want to edit them, it's suggested that they only be made richer, never leaner.

It should be noted that a few parts manufacturers have been supplying basemaps for their parts that have these values set high to force the engine to run in Closed Loop at WOT. The idea behind this being that even though the car won't run smoothly, the fuel will at least be reasonably safe until the car can be tuned by a professional. Make sure your tuner is aware of these tables and has them set to the stock values provided by Hondata before tuning commences.

You may think that your tuner would know about this, but it is an issue unique to MAP based tuning on the Civic Si. KPro does not have these tables, so KPro experience does not beget a tuner that will know how to handle this. Protect yourself and your investment in your tune. Take a moment to point your tuner towards this information.

Advanced Open Loop Tuning

Some tuners offer tunes that keep the ECU in Open Loop at all times. This can be done to run the car in a lean burn mode and allow the driver to acheive better fuel economy during cruising and idle. These tunes are not for everybody. This is a very advanced setup that requires a very experienced and seasoned tuner to setup the tune. There are very few tuners I would trust to set this up properly.

A setup like this requires constant attention to make sure that as the seasons change, your temperature compensations for your fuel are working properly. For most people that just want to get a tune and feel that their car is safe, I highly recommend leaving the stock Closed Loop logic enabled.