Download Megasquirt EX, Installation Instructions document revision 1.4

Megasquirt EX, Installation Instructions
document revision 1.4
(Includes also the version equipped with wasted-spark ignition)
General
Megasquirt EX is a programmable engine control system, based on Megasquirt v2.2. The
printed circuit board has been completely re-designed and also some other modifications
have been done. The unit uses Megasquirt Extra software, which includes an ignition
control and many other improvements, compared to the original software.
MS Extra features:
- Ignition control
- 12x12 maps for fuel and ignition advance
- many other additions, see the web site of MS Extra SW
Megasquirt EX changes:
- A proper connector for vehicle wiring, instead of D-type data computer connector
- Variable-reluctance (inductive) sensors supported (Marelli, Nippon-Denso, Honda, etc)
- Pre-amplifier for Lambda sensor
- 1, 2.5 or 4 bar MAP sensors
- Wasted Spark distributorless ignition for 4-cylinder engine, without an external control
unit like Ford EDIS
Links:
Megasquirt EX home page:
http://www.netikka.net/ville.vieri/ele/ms-ex/index.html
MegasquirtnSpark-extra Firmware for megasquirt
http://megasquirt.sourceforge.net/extra/
MegaSquirt Electronic Fuel Injection Computer by Bowling & Grippo
http://www.bgsoflex.com/megasquirt.html
ECU location and installation
ECU must be located so that it is not subjected to excessive moisture or dirt. An example
of good location is underside of the dashboard – the programming connector for the
laptop is also then easily accessible. Installation into the engine compartment is not
recommended.
Installation should be done according to the wiring diagram. A brief description of
sensors and other components needed is given in this document.
Sensors
Timing sensor (pins 15 and 16)
This sensor produces the timing signal that is needed for timing the ignition and injection
pulses. This is the most important sensor of the engine management system. The ECU
also calculates the engine RPM from this signal.
The sensor is located, for example, inside distributor or near crank shaft pulley. The latter
one is the recommended way, because then the timing will be more accurate and the
highly sensitive timing sensor is located away from high-voltage cables that always send
big amount of radio interference. Cam shaft pulley might also be used.
Unlike the original version of Megasquirt, this version is designed to be used with VR
(variable reluctance) sensors. A suitable type is, for example, SEN8x-series from Magneti
Marelli. The sensor is used in Ford Cosworth and several Italian vehicles. Also NipponDenso and Honda sensors can be used. The resistance of the sensor is optimum when it is
in range of 200 to 800 ohms. Some sensors may require a load resistor in parallel with the
sensor to decrease sensitivity to disturbances. Some sensors may produce too small signal
for the ECU, but this kind of sensor have not yet been met.
The timing sensor and its wiring are very critical when talking about disturbances and
overall reliability of the system. The voltage level of the sensor signal is small and the
input impedance of the sensor amplifier of the ECU is large, so it can easily pick up
disturbance from, most generally, from ignition parts, like the ignition coil and wiring.
The sensor wiring must be of shielded type, preferably coaxial. The shield will be
connected to pin 15 of the ECU. This is a dedicated grounding pin for the timing sensor.
No other wires are allowed to connect into this point. The sensor ground also must not be
connected to any other place, like the chassis of the vehicle.
Coaxial cable can be obtained from electronics store. It looks like an antenna cable of a
car stereo. This kind of cable may also be used.
If the sensor is installed near the crank shaft pulley, the pulley will be equipped with
timing teeth that the sensor will be reading. The teeth will be equally spaced and their
total count is the number of engine cylinders divided by two. For example, four-cylinder
engines will need two teeth with 180 degrees spacing. An 8-cylinder engine will need 4
teeth. Spacing is then 90 degrees. The tooth may be located 0…120 degrees before the
top-dead-center – this is the point where the timing tooth points towards the sensor.
Check this range also from the MS tuning software of the PC (Megatune, etc.). For a
typical sensor, the clearance between the tooth and sensor is around 0.5 mm. Suitable
diameter of the tooth is 5…6 mm and it should be flat-top.
The mounting brackets of the sensor must be very rigid to prevent any vibrations, causing
erratic timing or extra timing pulses. The sensor mounting must be so good that it cannot
be bent out of shape by bare hands!
If it is noticed that the timing sensor collects some extra timing pulses or another
disturbances and the sensor cable is of correct type and correctly assembled, the problem
may be cured by connecting a parallel resistor to the sensor. It has resistance of 1…15
kilo-ohms and it will be connected between pins 16 and 15 of the ECU connector. Too
small resistance will cause weak sensor signal and cause missing pulses. This is probably
noticed as missing RPM data while start attempt of the engine.
HALL sensors may also be used while this has not yet been tested. The supply voltage of
+5V may be wired from the pin 9 and the sensor ground will be connected to pin 15.
Threshold voltage of the sensor input should then be raised. This can be carried out by
changing the resistor R18 from 1 k to 10 k .
Phase sensor (pins 14 and 15)
This option is used only with Wasted-Spark ignition on four-cylinder engines. On others,
the pin 14 is not connected.
This sensor tells which cylinder pair (1-4 or 2-3) will be ignited at the next. The
instructions for assembling and wiring the sensor are exactly the same as with the timing
sensor.
When using the wasted-spark ignition, the timing sensor will be mounted so that the teeth
are towards the sensor when the crank shaft is at the position 120 degrees before topdead-center.
For the phase sensor, only one tooth is mounted. It is located 20 degrees after the timing
sensor tooth. That is around 100 degrees before the top-dead-center. Clearance of this
sensor is chosen 0.2 mm smaller than the timing sensor, to ensure that this sensor
receives a steady signal before the timing sensor when starting the engine.
‘Hold ignition’ –option should be activated for a couple of pulses from the software, in
order to let the ignition logic to stabilize before firing up the engine at the startup phase.
Lambda sensor (pin 13 and ECU chassis ground)
Lambda sensor measures the oxygen content of the exhaust gas. From this, the ECU can
calculate the fuel mixture in the engine. The sensor type to be connected directly into the
ECU is the zirconium based type that is often referred as a narrow-band sensor. Wide
band sensors are also supported. Signal is wired from its amplifier.
The sensor may be of heated of non-heated type. The latter one is more critical to the
mounting place, because it needs heat from exhaust gases. The right mounting point is 15
cm after the collector of the exhaust manifold, or with turbo engines, 30 cm after the
turbo.
12V supply voltage for heated sensor will be wired separately.
This signal is also very sensitive so it must be wired in the same manner as the timing
sensor. The sensor ground will be connected to the shield of the cable and this will be
connected to the chassis of the ECU. The signal pin is number 13.
Intake temperature sensor (pin 12 and ECU chassis ground)
This sensor tells the ECU the temperature of intake air or charge. In normally aspirated
engine, the sensor will be located in the air intake pipe near the intake or filter. On
pressure charged engines, the sensor is mounted in the intake manifold or intake pipe
after intercooler (if used). The latter is the recommended way – then, the engine will not
heat up the sensor when turning off a hot engine. This might yield some hot start
problems.
Particularly with pressure-charged engines, it is important to use a sensor that reacts
quickly when the air temperature changes. This kind of sensor has small NTC element
that is located in the air stream. A suitable type is, for example, BOSCH 0 280 130 085.
Also an ordinary NTC-resistor can be used, provided the nominal resistance is suitable.
For a sensor having a typical resistance of 2,5 k at room temperature (20 °C, BOSCH
and others), suitable reference resistor values inside the ECU is 1,8 k and 15 k in
parallel (see the schematic and component assembly pictures, RB1A and RB1B).
This sensor is grounded to ECU chassis if there is a separate ground wire.
Engine temperature sensor (pin 11 and ECU chassis ground)
This sensor measures the temperature of the engine coolant. The sensor is located into the
cylinder head or case of thermostat.
See the comments about the nominal resistance and reference resistors from the chapter
named ‘Intake temperature sensor’. The reference resistors are RB2A and RB2B.
This sensor is grounded to ECU chassis if there is a separate ground wire. If the sensor is
of 1-wire type, it is grounded via the engine.
Throttle position sensor (pins 9, 10 and ECU chassis ground)
This sensor (TPS, throttle position sensor) measures the opening angle of the throttle
butterfly. It is actually a potentiometer that contains two variable resistors. Their ratio
changes with throttle position. The sensor uses +5V supply voltage (pin 9) from the ECU.
This voltage must not be connected to any other device (excluding the potential HALLsensor mentioned earlier) or be short-circuited.
The sensor usually has 3 pins. W-pin of the sensor is connected to the pin 10 of the ECU.
Before doing the connections, the correct pin-out of the sensor must be determined, if not
known. It can be found using an ordinary multi-meter (with resistance measurement
range) as follows:
-
Find the two pins that have constant resistance between them, regardless the
position of throttle. These are two end-pins, called pins 1 and 2. Those are
connected to +5V supply (ECU pin 9) and to the chassis ground of the ECU.
The pin that was left is the W pin. Connect this to pin 10 of the ECU
Find the end-pin out of the two that has smallest resistance with W pin when the
throttle is closed and the resistance will increase when throttle is opened. This is
the pin connected to ECU ground. Another one is the +5V supply pin.
The sensor will be connected so that the W pin is having voltage near zero when the
throttle is closed, and near +5V when throttle is open.
Throttle position sensor can be burnt if connected wrong way (by connecting W to
ground or +5V).
Outputs
Fuel pump relay (pin 8)
This output controls the fuel pump relay. It is active-low. That means that the ECU will
connect the pin to the ground when the pump is activated. The fuel pump relay coil is
connected between the output pin and +12V supply. The output has internal protection
diode so no other components are needed.
Ignition control signal, cylinders 1 - 4 (pin 7)
This signal controls the ignition amplifier, if the ECU is used for ignition control and not
for injection alone. This signal is routed to the ignition amplifier. Suitable types are, for
example, 7-pin Bosch-modules ’0 227 100 137’, ’0 227 100 139’ or similar.
The ignition coil is located as near the ignition amplifier that possible. The wires are kept
short, especially the module ground wire and minus wire of the coil, going to the module.
Those signals are strong sources of electromagnetic disturbance that can interfere with
sensor signals. A bypass capacitor (for example 0.47µF) is connected between module
ground and plus terminal of the coil. If there are problems with interference, a similar one
can also be connected between minus terminal and module ground. In that case, the
capacitor has to withstand large pulse currents and have at least 630 V voltage rating.
A strong grounding cable placed between the ignition ground and cylinder head of the
engine – this provides return path for ignition currents.
Ignition parts must be located as far from sensors as possible. Any cables of those two
groups must not be bunched together.
The ignition coil to be used with these ignition amplifier modules may be of ordinary
breakerless type that has primary resistance of 0.5…1 Ohm.
Ignition control signal, cylinders 2 - 3 (pin 6)
This option is used only with Wasted-Spark ignition on four-cylinder engines. On others,
the pin 6 is not connected.
This pin controls the ignition amplifier of cylinders 2 and 3. The connections are made in
the same manner as with the pin 7.
Injector outputs (pins 1…2 and 3…4)
The ECU has two output stages for controlling the injectors. The first one is connected to
pins 1 and 2 and another one to 3 and 4. The high-impedance injectors having resistance
of above 10 ohms can directly be connecter. Low-impedance types will need series
resistors.
Pins 1 and 2 are internally tied together, as are pins 3 and 4.
It is worthwhile to use both of the injection banks – this will share the load of injectors
and it will also be possible to select non-simultaneous injection from the software.
Like Megasquirt v2.2, this ECU does not support PWM-control of the injectors. Some
modifications must be done prior activating this.
Other pins
+12V Supply (pin 5)
This is the supply voltage of the ECU. This is wired from the battery via a relay
controlled by the ignition lock. A 1-amp slow-burn fuse will be connected in series – the
unit itself does not have an internal fuse. Do not use +12V routed from the ignition
lock – this voltage may decrease very low during starting.
General information about assembly
Grounding the ECU
Sensors (excluding the timing sensors) are grounded to the screw connection at below the
back-side heat sink of the ECU. From this point, a heavy-duty grounding cable is routed
to the cylinder head of the engine.
+12V supply for injectors, ignition and fuel pump
+12V supply for these devices if wired from the battery via fuse and fuel pump relay
contacts. Rating of the fuse is dependent on current consumption of those devices. A
heavy-duty cable must be used and the cable should be routed far from the sensor wiring.
If the fuel pump is very large or there are several of them, it is good to have a separate
relay for the fuel pump(s). This relay is controlled by the fuel pump relay of the ECU.
Initial system tests
Before the start attempts of the engine, some initial tests for the equipment should be
carried out. During these, the ECU unit must be powered and connected to the PC
running the control and monitoring software (for example, Megatune). These test
methods can also be applied for other versions of Megasquirt or commercial systems.
Ignition system test
Prior this test, the fuel pump relay must be energized by disconnecting its control wire
from the pin 8 of the ECU and tied to ground. Then, +12V supply is available for the
ignition amplifier and coil. Fuel pump can be prevented from turning by taking its supply
wire off.
Disconnect the high-voltage cable from distributor and leave this a few millimeters away
from the cylinder head. This leaves a spark gap for ignition voltage. Disconnect the
control signal of the ignition module from the ECU and scrape some metal part connected
to vehicle ground with this wire. The high-voltage cable should now give some spark.
While doing this, it is monitored that the sensor values measured by the ECU do not
change – especially the RPM display in the control software must stay in zero! If the PC
beeps, the software shows some odd RPM readings or other non-appropriate values, there
is a problem with sensor wiring, shielding or grounding. There is no reason to continue
further before these are corrected and the operation during spark interference is stable.
Odd timing signal and other disturbance can cause corruption of ECU memory, including
the settings or the firmware itself. However, the case with this should be better with
newer SW revisions than 029v.
With the versions equipped with wasted-spark, the testing is done in the same manner,
but with some exceptions: The high-voltage cable is disconnected from spark plug rather
than distributor and both of the ignition modules/coils will be tested, one at a time.
Tests prior starting
At the next, the fuel pump relay and ignition control wires are connected back to the
ECU. The high-voltage cable of ignition is left as it was during the previous test and also
fuel pump will remain non-connected.
Check the correctness of all the temperature sensor readings, and test and calibrate the
throttle position sensor.
Turn the engine with starter and check with timing-light that the ignition advance is
correct. Check also, that the spark is continuous, regular and strong. The RPM meter of
the software should show a correct RPM – this is around a few hundreds of RPM,
depending on the engine.
If there is problem with spark, it may be caused by interference with the timing sensor or
wrong setting of starting RPM value in the software. The default value in Megatune is
300 RPM that is too small for a typical 4-cylinder engine, for example.
The default ignition advance during starting is 10 degrees.
When the ignition advance is correct and spark OK, the engine can be tried to be started.
Prior that, calculate the theoretical values for injection settings according to the general
Megasquirt documentation.
Troubleshooting the most typical problems
-
-
-
Problems with starting
o Starting RPM setting wrong
o Wrong fuel mixture
o Timing sensor interfered by ignition
o Wrong ignition advance
Uneven engine running, does not accelerate
o Timing sensor interfered by ignition (especially when the RPM meter in
the SW shows double RPM momentarily).
In this case, try the parallel resistor for the timing sensor.
o Bad/wrong ignition coil or leads
o Timing sensor fastened poorly
Software beeps and/or RPM meter in the software shows odd readings
o Weak signal of timing sensor (maybe too small resistance connected in
parallel with the timing sensor, wrong sensor type or sensor clearance too
wide)
o Timing sensor interfered by ignition
This is the first version of Megasquirt EX installation instruction document. It is updated continuously and
it contains also a version equipped with wasted-spark ignition – the text related to this is written in italic.
The updated versions are kept on the home page of the Megasquirt EX.
Ville Vieri, 8/2011