Custom EPROM Features

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Rev Limit and RPM Features

Idle Speed: By changing the ECU's target idle speed, the car can be made to both idle smoother and gain drivability, especially when used with modifications that normally hinder the aforementioned items (large cams, highly modified intake tracts, etc).

 

Rev Limiter:  In a more highly modified DSM, the powerband will other continue past the stock limit of 7500 rpm.  Increasing this limit will allow the car to create more power under that curve, making it ultimately faster, and increasing the usable powerband.

 

Stutterbox (2-Step Rev Limiter:  By utilizing a conditional lower rev limiter, the driver has that ability to launch at full throttle, which allows a launch with boost, and greater consistency.  The stutterbox can be had in several verities, with varying speeds, and varying conditions under which it is active.

 

No-Lift-To-Shift (NLTS, aka Stuttershift):  An extension of the stutterbox, NLTS gives the driver a lowered rev limiter whenever the car is rolling and the clutch is pushed in.  This allows the driver to shift at redline without lifting off the throttle, while the motor's speed will still decrease as though he did lift.  This allows for a smoother shift, and more rapid boost onset in the next gear, without any additional synchro wear.  In addition, the chips can be programmed to use the upper clutch switch, which is much more effective in controlling engine speed than the lower switch utilized by TMO.

 

Anti-Lag (ALS):  Currently, the anti-lag feature is compromised solely of retarded ignition timing while stutterboxing.  This increases the energy of the exhaust stream entering the turbo, which is crucial to building boost on the line with larger turbo.  An external switch can be added on any car without A/C, allowing the ALS to be turned on when needed, and off when driving normally.

 

Tuning Features

Fuel Cut Removal/Increase:  There are two main options with regard to fuel cut; fuel cut can be simply removed (my suggestion), or it can be set at a raised value at the request of the driver, based on a datalog (not an arbitrary percentage increase).

 

Open/Closed Loop Control:  The ECU has a set of maps which determine when to switch from closed loop (low load, 14.7:1 AFR) to open loop (higher load, AFR determined by the fuel enrichment map, and generally richer than 14.7:1).  By increasing the range of this map, and the values across the whole range, the car will be driven at higher engine speeds and higher throttle angles before it switches to open loop.  This will generally increase gas mileage, and will also give you the ability to cruise at high sped if you feel so inclined.

 

Conversely, the user can also choose to decrease the values of this map, which will cause the ECU to transition to the open-loop tables earlier and more frequently.  The result would likely be decreased gas mileage and increased power.

The ability to lock the car in open loop for tuning purposes allows the fuel maps to be trimmed and calibrated perfectly, before the car is put back into normal closed-loop operation.  This guarantees accuracy of fuel tuning done later down the road.

 

Double MAF Hz For Datalogging:  All of the information that is transferred to a datalogger is stored in one-byte segments.  As such, every feature has a limited range and resolution.  With the standard resolution of about 6 Hz, the MAF Frequency is limited to a peak of 1606Hz on the datalogger, which most people are able to max out with ease.  As such, there is not a good way to view airflow beyond this point.

By slightly changing the code that stores the MAF Hz value to be datalogged, the chip can make it so that the value on the logger is half of the true MAF Hz.  This will double the operational range to about 3200 Hz maximum, while still having a perfectly acceptable resolution of approximately 12 Hz.

 

Knock Decay Adjustment:  The stock ECU has a "knock decay" factor, which prevents the knock sum from dropping back to zero as soon as detonation stops occurring.  Instead, the knock sum slowly tapers back down to zero, at a rate such that it often will take a whole gear before it gets there.

The decay speed can be modified, in order to speed up this process.  Now, obviously one needs to tread carefully, but generally speaking the factory knock decay rate is a conservative feature designed to keep people out of trouble when the make big mistakes.  On a car that is tuned well and monitored regularly, gains can be found by speeding the decay rate up by up to a factor of two.  It can be made even faster than this, but at that point it is very much at the vehicle owner's discretion.

 

Intake Air Temperature and Barometric Pressure Lockdown: When a device such as a VPC or a MAFT is used, the barometric pressure and intake air temperature signals to the ECU are locked down, and any changes in mass airflow are reflected in the airflow Hz input.  However, this has two downsides: first of all, it uses up two 0-5 volt inputs that could be used for other purposes, such as datalogging or a method of changing options like stutterbox speed.  Second of all, and especially with the older VPC units, you are depending on electronics within the MAFT or VPC control box to feed the correct signal to the ECU.  If the temp and pressure are locked down in the code, you no longer even need to wire the VPC/MAFT into the air temp and barometric pressure wires at the ECU!

 

Tuning Options

 

Global Injector Compensation:  In order to compensate for larger injectors and/or modified base fuel pressure, the global "injector size" factor in the ECU is changed to suit each distinct car.  The base settings will be determine by the change in fuel flow, and the finalized settings will be chosen after test runs are made with a datalogger.

The end result of global injector compensation is a car that runs correctly, while using larger fuel injectors, and still giving the ECU the true airflow signal.

 

Injector Deadtime Adjustment: Larger injectors tend to have more massive moving parts, so they take longer to open once the ECU activates them.  If you do not account for this, the car will run leaner at shorter pulsewidths, which often causes abnormally positive corrections at low engine speeds when using a device like a SAFC, VPC, or GCC.

By changing the deadtime map in the ECU, the car will idle like stock on larger injectors.  As with the global setting, initial changes will be made based on the injector size and manufacturer, and then the settings will be finalized using datalogger information.

 

MAF Compensation:  In order for the car to run properly, the ECU needs to have an accurate picture of the true airflow entering the engine.  However, in a lot of cases people use MAF sensors that are not stock, in order to gain other properties (higher flow, higher metering capabilities, better design, etc).  There is a table within the stock ECU code that modifies the MAF signal, before it is used in the fuel and timing calculations.  With simple changes to this map, you can make it so that the ECU receives fairly accurate airflow readings, even with extremely hacked mass airflow sensors, or sensors that didn't originally come with the car (2g sensor, MAFT, etc).

This allows the 2g MAF to be a plug-and-play solution (no extra tuning necessary), and also allows people to use the very economical solution of a severely hacked 1g MAF.  A hacked 2g MAF can also be used for cars that need the capability to meter upwards of 50 lb/min of airflow.

 

Custom Fuel Map:  The stock ECU has a single primary fuel map, that is used whenever the ECU is in open-loop operation.  This fuel map is an enrichment map, which multiples the calculated pulsewidth for a stoichmetric AFR by a value in order to richen up the air to fuel ratio.  By changing the map, the fuel curve at all points in open loop can be modified.  The stock map is not designed with performance in mind, but rather a myriad of desirable traits for a mass-produced vehicle.  By even changing to a recontoured base map (shown below), there will be solid gains in power, throttle response, and detonation resistance.

 Enrichment Comparison

 

Custom Timing Map: There is also a primary timing map, which is used by the ECU to find a base timing value at every engine speed and load.  This timing value is then modified by other variables, such as knock retard, "octane" retard, and intake temperature corrections.  Like the fuel enrichment map, the timing map is modified to provide the best possible performance for each individual car.  The stock timing maps have quite a bit of features which simply are not optimal, and these problems are all fixed with an EPROM tune.

Below, you can see a comparison of a stock timing map to a modified base map.

 Enrichment Comparison

 

 

Future Projects and Goals

Factory Boost Gauge Utilization:  One of the highest priority projects is to use the factory boost gauge to display other parameters, such as timing advance, knock, or injector pulsewidth.  In addition, with a MAP sensor installed, the gauge could be programmed to display true boost pressure, using the stock scale, or a new scale (to extend the range).

The current status of this is the gauge will display the aforementioned values, but the scaling is off.  Once the scaling is worked out, it will be an option.

 

TMO-Style Stutter Speed Selection:  The current adjustable stutterbox uses a knob to be mounted in the dash, which will input a signal into one of the 0-5v A-D inputs on the ECU.  While this works great, some people like the decreased complexity of utilizing all stock hardware to make stutter speed changes.  As such, an interface with the stock boost gauge is in the works.

 

MAP or Airflow Per Rev Based Timing Retard:  When a car is flowing a decent amount of air (300+ horsepower), it is very common for that vehicle to reach the highest load level on the fuel and timing maps.  At this point, if the load increases any more, the timing will not change; it will stay locked at the value at the current engine speed on the highest load level.  In some cases, this causes knock as the boost spikes up on initial boost onset.

A system is in the works which will retard timing beyond the highest load level, based on either MAP or airflow per rev.  The current goal is for the system to be completely automated, except for the choice of rate of timing retard.  Beyond that, the ECU will automatically detect when the highest load level is reached, and then actively retard timing based on the distance past that load level in MAP or airflow per rev.

 

 

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