Application Notes
1.8L Moss/Jackson Racing/Sebring
supercharger
1.6L Moss/Jackson Racing BBK (big
boost kit)
1.8L Moss/Jackson Racing/Sebring supercharger
To alter fuel delivery, SOME 1.8L Moss/Jackson Racing/Sebring supercharger kits use a modification to the
intake air temperature sensor. This modification tricks the Engine Control Unit
(ECU) into thinking that the air temperature is much colder than it actually
is. The ECU responds by adding fuel, which is needed because of the extra air
provided by the supercharger. Neat trick.
A problem with this setup is that too much
fuel may be delivered at idle, when the supercharger is not adding air. Some
1.8L supercharger kits use an 'Idle compensator module' to address this situation.. This compensator basically disabled the resistor that is
switched into the air temperature sensor circuit when not under boost. Several
owners have experienced drivability problems with the 'Idle compensator module'
as it switches in and out of boost. Many have disconnected the boost switch.
Others have replaced the module with a fixed 15 K ohm resistor.
Unfortunately, the 'resistor trick' will
trick the ACU as well as the ECU. This will render the ACU air temperature
compensation inoperative. (The ACU will otherwise function normally.) Although
you might think that you could remedy the situation by connecting things in the
proper order, it's not that simple.
Further complicating matters, Not all Moss/Jackson Racing/Sebring 1.8L kits use the same
air temperature setup. Some use the 'Idle compensator module' and some don't.
Later versions of the base kit do not use a modification to the air temeprature input at all, but use an Auxiliary Fuel
Pressure Regulator instead. But, it is our understanding that the Big Boost Kit
(BBK) uses both!
To properly connect the ACU, you will need
to know if your kit uses a fixed resistor and/or an 'idle compensator module'
or not.
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If your kit uses an AFPR
only, make the air temperature connection to the ACU as per the standard
wiring diagram. Do NOT use the 15K option. There are three work-arounds
for the 1.8L Moss/
|
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Note: Bipes Automotive does not recommend or
endorse any change in installation of the supercharger. Bipes Automotive does not accept responsibility
for any alterations that you make to the fuel delivery system.
Fixed
resistor instructions
Some Jackson Racing supercharger kits for
the 1.8L engine include a wiring harness that inserts a 15K ohm resistor into
the air temperature circuit. ACU units shipped after
If your kit included an 'Idle compensator
module', you can only use this option if you have disabled the module by
disconnecting the pressure switch (some owners have found that disconnecting
the switch fixes a hesitation or stumble problem). Please note that we are not
recommending or endorsing any change in installation of the supercharger. Bipes Automotive does not accept
responsibility for any alterations that you make to the fuel delivery system.
Here's how to enable the ACU option:
1. Remove the four screws from the bottom of
the ACU.
2. Remove the bottom cover.
3. Locate the jumper near the center of the
board.
Jumper in the 'normal' position.
4. Remove the jumper from the two posts
towards the back (connector end) of the unit. Re-install the jumper on the two
posts towards the front (LED end) of the unit.
Jumper
in the '15K' position
5. Replace the bottom cover.
6. Re install the 4
screws.
To use this ACU option, you must
connect your ACU as shown below:
Note that the air temperature connection to
the ACU must be made from the air temperature sensor, and not the ECU. Your
supercharger kit may have included any or none of the components (resistor,
idle compensator module, pressure switch) illustrated in gray. If your kit has
a pressure switch and an idle compensator module, this ACU option will only
work if you have disconnected the black wire between the pressure switch and
the idle compensator module. Bipes
Automotive does not recommend or endorse any change in installation of the
supercharger. Bipes Automotive does not
accept responsibility for any alterations that you make to the fuel delivery
system. (Did we say that often enough?)
1.6L
Moss/Jackson
The 1.6L BBK (big boost kit) uses an AFM
Module (in addition to an AFPR) to manage fuel.
The AFM Module is well-behaved and does not alter the air temperature
sensor's output. The ACU will work properly with the AFM Module, but you must
connect the ACU air temperature input to the junction between the air
temperature sensor and the AFM Module, not at the ECU.
The ACU is also well-behaved and will not
affect AFM Module operation.
Nitrous Oxide
If you are running nitrous oxide, you may want
to retard timing when the nitrous is on to avoid knock. The ACU can be set up
to add 3, 4, 6, or 8 degrees of retard across the board when you engage the
nitrous. You can easily do this by using a common automotive relay. Refer to
the wiring diagram below.
This
illustration references the 1.6L ECU pins and wire colors, but the application
works equally well on the 1.8L engine.
Here's how it works:
The airflow and RPM retard maps are
disengaged by connecting the airflow input to ground. The air temperature input
is connected to a set of relay contacts that switches to ground when the
nitrous is engaged. When the nitrous is not on, the ACU thinks the air
temperature is very cold, and it adds no retard. When the nitrous is on, the
ACU thinks that it is very hot, and it adds the total amount of air temperature
retard. You program the amount of retard via the air temperature switches.
|
Switch
5 |
Switch
6 |
Nitrous
retard |
|
open |
open |
3 degrees retard |
|
open |
closed |
4 degrees retard |
|
closed |
open |
6 degrees retard |
|
closed |
closed |
8 degrees retard |
In this application, set switch
1 to the 1.8L setting (closed position), even if you have a 1.6L engine.
|
Switch
1 |
Engine |
|
open |
1.6L - n/a |
|
closed |
1.8L - Nitrous |
In-dash timing adjustment
If you're willing to forego air temperature
compensation, you can easily connect a control to your ACU to adjust timing up
to 8 degrees right from the driver's seat. This can be a useful temporary
connection. It allows easy adjustment of base timing to help experiment with
just the right amount of timing retard that is needed in a particular
application. Once you've determined your car's particular needs, you can set
the programming switches appropriately, reconnect the temperature compensation,
and disconnect the in-dash control.
To install this control, you'll need to
obtain two components - a 10K ohm potentiometer (linear taper preferred) and a
13K ohm resistor, rated at 1/4 watt or more. These components are readily
available from electronics stores such as Radio Shack Connect these components
as shown in the wiring diagram. Note that the ACU air temp input is not
connected to the Miata's air temp sensor in this
application. This input is connected to the center lead of the potentiometer.
Wire to the outside leads of the potentiometer and the resistor as shown.
In-dash timing adjustment wiring diagram.
This
illustration references the ECU pins and wire colors for the 1.6L engine, but
the application works equally well on the 1.8L engine.
To use the control, rotate the potentiometer
fully counterclockwise. Set the display to indicate retard. Set the air
temperature switches to 1 degree of retard for every 15 degrees C temperature
change. Start the engine and let it idle. You should see no LEDs lighted. If
you see four LEDs lighted, and these extinguish as you rotate the control
clockwise, reverse the connections to the outer leads of the potentiometer.
With the engine idling, adjust the control
back and forth. You should be able to light 0, 1, 2, 3, or 4 LEDs. This
represents from 0 to 8 degrees of added retard (2 degrees of retard for each
LED) . Don't be alarmed if the engine idles poorly or
even stalls at the 8 degree setting.
Set the control so that 2 LEDs are lighted.
Now, adjust your base timing manually (using a timing light and rotating the
CAS) to your desired base timing value.
You should now be set up to add or subtract
base timing via the control. For example, if you set base timing to 12 degrees,
then rotating the control fully counterclockwise to extinguish the two LEDs
that were lighted will leave you at an effective 16 degrees of base timing.
Rotating fully clockwise to light four LEDs will put you at 8 degrees base
timing. You should be able to verify this with a timing
light.
The control adjusts timing across the board.
As airflow and RPM increase, the ACU will add more retard to this base value.
The display will show the total amount of retard that is being applied by the
ACU at any time.
(This application requires software version
1.4.)
MAP sensor
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For those not satisfied
mapping airflow to retard, you can map boost to retard instead by connecting
an external manifold air pressure (MAP) sensor to the ACU. A standard GM 2
bar MAP sensor will trigger the ACU to start pulling timing at about 2 psi of
boost and will pull maximum timing at about 9-10 psi of boost. Refer to the
table below.
ACU
boost-to-retard map with external MAP sensor. (The
ACU LEDs column is with the ACU set to display Airflow.) |
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To use the extrenal
MAP sensor, connect it per the wiring diagram below. Basically, you just
connect the airflow input of the ACU to the MAP sensor instead of to the Miata's airflow meter. To power the MAP sensor, you must
connect it to +5 volts. Fortunately the Miata can supply this voltage at the
ECU or at the airflow meter assembly. For example, on the 1.6L engine, +5 volts
is available at ECU pin 2K, which is connected to the airflow meter assembly
via a green with red stripe wire.
MAP
sensor wiring diagram.
This
illustration references the ECU pins and wire colors for the 1.6L engine, but
the application works equally well on the 1.8L engine.
In this application, set
switch 1 to the 1.8L setting (closed position), even if you have a 1.6L engine.
|
Switch
1 |
Engine |
|
open |
1.6L - n/a |
|
closed |
1.8L - External MAP sensor |
Use switches 2-4 to select the
boost-to-retard map that you desire. For example, if your turbocharger develops
up to 6 psi of boost, and you would like to pull 5 degrees at maximum boost,
select 0.8 degrees of retard per psi of boost (6 psi times 0.8 degrees/psi =
4.8 or about 5 degrees). Remember that in this application the ACU will reach
maximum boost-mapped retard at about 10 psi. More than 10 psi will not result
in additional retard.
Boost-to-retard map
(approximate) with GM 2 bar MAP sensor
|
Switch
2 |
Switch
3 |
Switch
4 |
Degrees
of retard |
|
open |
open |
open |
0.4 |
|
open |
open |
closed |
0.5 |
|
open |
closed |
open |
0.6 |
|
open |
closed |
closed |
0.7 |
|
closed |
open |
open |
0.8 |
|
closed |
open |
closed |
1.0 |
|
closed |
closed |
open |
1.2 |
|
closed |
closed |
closed |
1.4 |
External Temperature Sensor Application Note
Some Sebring/Jackson Racing/Moss
supercharger kits for 1.8L Miatas use a resistor in the air temperature sensor
line to the ECU and an "Idle compensator module" to adjust fuel
delivery. This setup makes it impossible for the ACU to read the correct intake
air temperature. The cleanest solution to this problem is to install a separate
air temperature sensor (thermistor) for the ACU.
To install an external thermistor for the
ACU, you need to add the three external components as illustrated in gray.
These components may be obtained from the electronics distributor Digi-Key for under $15 inluding
shipping. The thermistor value is 2K ohm at 25 degrees C (Digi-Key
part no. KC001T-ND). The resistor values are 2.7k ohm
(Digi-Key part no. 2.7KQBK-ND - the minimum order
quantity is 5) and 5.6k ohm (Digi-Key part no.
5.6KQBK-ND). Visit Digi-Key online at digikey.com to place an order.
The thermistor should be mounted in or near
the intake air stream (near the air filter would be suitable). The resistors
may be mounted anywhere convenient. You may be able to mount them right at the
ACU connector. The thermistor may be connected to ground almost anywhere,
including most metal parts of the car or engine. Take care to properly solder
wires to these parts and insulate the connections (shrink-wrap tubing is
recommended).