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Tuning / Mod's:


Decided to make this a seperate page as this is quite an extensive subject.

This page is layed out as several subjects...

Install & Tune, A word on M.A.P Sensors, Sharing Coolant Sensors, Air Density Correction,



ECU and WiringFuel systemIntake Manifold

Install &Tune...

After confirming the operation of the E.C.U, using the Stimulator, It was installed into the vehicle along with all sensors and wiring. Engine operation using the Carburetor was retained whilst operation of the new E.C.U was monitored using Megatune. Convinced of the reliability and function of the E.C.U, wiring and sensors it was time to install the remaining components. I.E: Intake manifold, Throttle Body and Fuel System. This was done over 2 days, counting time required for chemicals to cure. Running the basic default Firmware and Fuel Table the Engine was started for the first time on a nice warm Spring day. The Engine fired up, warmed up and even drove quite well! This was a massive relief and in no time tuning had begun...

With the later AutoTune features introduced, soon after, in Megatune and several tanks of fuel the system runs well and I'm saving about a 1/4 tank of gas a week! Performance is awesome along with good economy when cruising. Decided farely early in the game to try the 12x12 Fuel Tables, and other neat User adjustable features, of MSNS-Extra. MSNS-Extra Firmware and matched Megatune with Manuals can be found here.

Now running Firmware version 029Y4 along with a couple of Mod's (See below). Tuning is still ongoing as fine points are tweaked. The fuel table has been fine tuned to where I'm reasonably happy using MegaLog Viewer which has come a VERY long way since it's humble beginnings. I recommend using this! I seem to get better results with smaller Log files, say 10 - 15 minutes worth.

For those interested, Here are the latest MSQ and VE Fuel Table along with a complete copy of my current Car directory for Megatune .

A Word On M.A.P Sensors...

At the time of Firmware install, The only real support provided was for the original E.C.U mounted Manifold Air Pressure sensors. One of these was used initially when the E.C.U was being bench tested. During this testing I managed to trash my 2 Bar sensor by getting moisture into it! This made me decide to adapt the system to the more robust, bullet proof GM sensors. With a small Mod' to the E.C.U Circuit Board, the external sensor input was fed into the spare X11 pin (See Circuits). This required hunting down the information required to build new and files for compilation into the Firmware...

Here are the Excel sheets which include the Algorithms, Plots and Figures for both the 1 Bar and 2 Bar GM M.A.P sensors. Initial use of the existing 1 Bar sensor was later upgraded to a seperate 2 Bar sensor just in case a 'Blower' might come onto the scene.

Part number for the 1 Bar GM sensor is 16006835 and for the 2 Bar GM sensor is 16009886 or 12569241. Both these sensors can be obtained from RockAuto and, although both use the same pinouts, The connector is keyed differently!! Pinout is A: GND, B: OUTPUT and C:Vref (+5V).

Sharing Coolant Sensors...

Problem: As I wished to retain the original E.C.U for Ignition and Timing I would either have to install a seperate Coolant Temperature Sensor or retain the original Sensor and share it between the two E.C.U's. The latter was the best choice as space was at a premium and, after all, the original sensor is of the correct type for both E.C.U's.


Sensor Circuit
Sensor Circuit

The circuit on the left shows how a typical Coolant Sensor is wired into an E.C.U. Because the sensor(R2) is shared between two E.C.U's, one E.C.U does not require a Bias Resistor. However, in order to calibrate the Sensor readings the Bias Resistor value in the existing E.C.U(R1) must be known...

1: Determine the value of R2(Sensor). Unplug it and and measure it!

2: Re-connect the Sensor, turn on the Ignition and measure the voltage across it. This will be called Vo.

3: Calculate the Original E.C.U Bias Resistor value using...

Existing E.C.U Bias Resistor(R1) = R2 x (5 - Vo) / Vo

4: The Fuel injection E.C.U can now be used with NO Bias resistor and, as the Temperature / Resistance curve is known for the Sensor, a new lookup table can be built using the above calculated Bias Resistor value. This is done by using a program such as EasyTherm. The New .INC file is then compiled into the firmware and copied to the Megatune Car1/MTCFG directory.

The Existing E.C.U Bias Resitor value calculated for this vehicle was 362Ohms. R7 is removed from the circuit and the Coolant Sensor output is tapped into and run in conjunction with the original GM E.C.U. The recalculated table can be found here. The accuracy of this mod' has been checked against a Digital Thermometer and also against the Manifold Air Temperature sensor reading when the Engine is cold.

Manifold Air Density Correction Modification...

Problem: This is a common issue reported by a lot of user's with this system. That is the problem of over compensation for M.A.T when the vehicle has been left to sit for a period of time whilst hot. The M.A.T Sensor becomes 'Heat Soaked' and the E.C.U applies too much lean correction for the unrealistic readings. Result... Engine runs like 'shite' until moving air cools down the sensor again! I have also noticed that the system can be tuned almost perfect one hot day and run too rich the next cold day. The lookup table seems to be a little much for many applications.

Solution: The Firmware MegaSquirt'n'Spark Extra version 029Y4 has user adjustable compensation for this issue based on Coolant Temperature. I have tried it but the truth is, the problem still exists even when using the MAP Temp' option... I have found that a combination of moving the sensor right up to the intake filter and modifying the file works well. See below. Mod: I decided to simply alter the lookup table when I was using the early code and this does help.. The E.C.U reads this table based on Manifold Air Temp, as a direct percentage, and uses it to alter the injector pulse widths accordingly. I used Excel and have changed the table values as follows...

Any correction above 70Deg-F (100%) is reduced 50% and any correction below 70Deg-F (100%) is reduced 20%. The Excel sheet can be found here... Simply modify the formula for extra or less correction (*0.5 or *0.2 part) and copy and paste the results to your file. This seems to work very well and produces a much more stable tuning platform and better hot start and running. Here's both the original and the modified tables for comparison. DONT FORGET TO COMPILE THIS INTO YOUR FIRMWARE!!



ECU and WiringFuel systemIntake Manifold


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