Jumpering the DIYPNP Main Board to the
Adapter Board
Basic Jumpers
Now that we've assembled the main board and adapter board,
we'll install the basic jumpers to provide the DIYPNP with
power, grounding, sensor inputs, and injector outputs. These
jumpers simply run from a pin on the lower edge of the DIYPNP
main board to the appropriate holes in the adapter board. If you
don't have one of our application spreadsheets handy for your
car (check our available DIYPNP Models
page for these), you'll want to consult a pinout of your stock
ECU. You'll also want to get a copy of the setup spreadsheet
from our
DIYPNP downloads page, as this can
help organize the process.
Once you've got an ECU pinout, the first step
is to figure out how the pin numbering on the DIYPNP matches the
pin numbering on your own ECU. On some models, it's quite
simple; the Bosch 55 pin board, for example, always simply
numbers its pins 1 through 55, and the numbering scheme does not
change from car to car. On the Nippondenso-derived connectors,
each manufacturer had their own numbering system, which
sometimes changed depending on how many of the connections are
used. So you will need to match the factory wiring pin numbering
system up to the DIYPNP pin numbering system first. Here is how
the pins on the DIYPNP connectors are numbered. Click on the
pictures for a closer, clearer view.
N42 pins:
N76 pins:
The above two connectors are just shown
as examples, the DIYPNP supports many others as well, click here
for a full list.
Once you've identified which pins you'll need
for the stock ECU, you'll need to match them up to the output
pins on the DIYPNP. We'll start by matching up the basic
connections for power, sensors, and injectors. We'll cover RPM
input, ignition control, and some of the advanced input and
output functions once this is complete. Here are the pins we're
going to focus on for now, and what the pins do. You'll be able
to find them all along the lower edge of the mainboard.
-
IAT – Intake air temperature sensor
input
-
CLT – Coolant temperature sensor input
-
TPS SIG – Throttle position sensor
signal
-
O2 SENSOR – Oxygen sensor input
-
FUEL PUMP – Signal to drive a fuel pump
relay.
-
INJ 1 and INJ 2 – Each of these headers
has four connections and can drive four high impedance
injectors.
-
12V – Use these connections to supply
12 volt power to the board.
-
VREF – 5 volt reference voltage for
sensors.
-
5V – 5 volt power voltage from the main
board voltage regulator.
-
SG – Signal ground, for sensor returns.
-
GND – Power ground.
The locations of the jumpers on the main
board that you'll be using in this step are marked in yellow on
the picture below.
Power and Ground
As you've noticed, there are five separate types of power and
ground connections on the DIYPNP. Each of them has its own
specific purpose. Here is what each connection does.
12V: This connection powers the DIYPNP. Connect it to
the pin(s) which get 12 volt power when the ignition key is in
the Run and Start positions. We've provided you with several 12V
pins in case your ECU has more than one. These should not be
connected to any pin that receives 12 volt power when the key is
off, but only to 12 volt switched power connections.
VREF: This connection provides a 5 volt reference
voltage for the throttle position sensor, and can be used for
some other types of sensors, such as external MAP sensors. These
connections are usually marked with something like "5V," "VREF,"
or "Reference Voltage" in the factory wiring diagram. Caution:
Do not let the VREF connection be shorted to ground - this will
shut down the DIYPNP.
5V: The DIYPNP has a second power supply for 5 volt
circuits that are isolated from the main reference voltage.
Usually you won't need to connect this to any external wires
(it's more useful for onboard circuits), though if you run
across a Hall effect or optical sensor in the external wiring
that needs to be supplied 5 volt power, use this jumper.
SG: Sensor ground. If you have common ground wires
coming back from external sensors, connect the pins these wires
use to the SG jumper. This is to reduce the amount of noise in
signal wires.
GND: Power ground. Connect any ground wires that go to
the engine block, battery terminal, or chassis ground to the GND
jumpers.
Sensors
The throttle position sensor, temperature sensors, and O2
sensors are fairly straightforward to hook up. The VREF and
sensor grounds are covered above; now here's what to do with the
sensor input pins themselves.
IAT: The intake air temperature sensor may be a
freestanding sensor, or it may be built into an air flow meter.
It generally has two wires, the signal wire and the sensor
ground wire. The signal wire goes to IAT and the ground wire
goes to SG. Usually the ground wire will merge into another
ground wire in the external wiring; in the rare event that you
find an IAT sensor where neither wire connects to others or has
a clear function, it can be wired up either way.
CLT: The coolant temperature sensor wires up exactly
the same way as the IAT sensor.
O2 SENSOR: Narrow band O2 sensors come in one, three,
and four wire flavors. With a one wire sensor, simply connect
that one wire to the O2 SENSOR jumper. Sensors with more wires
will also need the signal ground connected to SG, but they'll
generally work OK without the heater circuit connected. It just
takes them longer to warm up. The DIYPNP does not read wideband
sensors directly, requiring an external controller. If using one
of these, wire the controller's analog output to the O2 SENSOR
jumper.
TPS: The TPS's signal wire goes here. It is usually
marked in the diagram about which is the signal wire. If it
isn't, you'll need to test the TPS with an ohmmeter. Observe the
resistance as the throttle opens and closes. Each pair of pins
will behave differently:
The resistance between the VREF and ground pins will remain
constant.
The resistance between the ground and signal pins will be low
with the throttle closed and high with the throttle wide open.
The resistance between the VREF and signal pins will be high
with the throttle closed and low with the throttle wide open.
If your sensor behaves like this, it will be pretty
straightforward to connect it to Megasquirt.
If the resistance jumps from infinite (or near infinite) to near
zero, you have a switch type throttle position sensor, or
possibly a seriously defective potentiometer type TPS. These do
not provide very much information that Megasquirt needs, as it
can tell if you are at idle or full throttle by the MAP sensor
information. You can still use MAP based acceleration enrichment
and ground the TPS signal pin through a resistor.
Fuel Control
INJ1 and INJ2: These are your injector outputs. The
DIYPNP is batch fire normally, so you will be using two outputs,
each of which can drive one low impedance or four high impedance
injectors. The INJ1 and INJ2 jumpers connect to the injector
wires on the adapter board. Usually the best way to pair them is
by firing order - connect the first cylinder to fire to INJ1,
the second to INJ2, the third to INJ1 again, and so forth. This
isn't a hard and fast rule, and some harnesses will make the
injector pairing choice for you. Usually it'll run fine with
pretty much any injector pairing anyway, though some pairings
may be a little bit smoother.
FUEL PUMP: This pin supplies a ground for the fuel
pump relay. Most ECUs will have a ground pin for the fuel pump
relay wired straight to the ECU, so you just have to find this
wire on the adapter board and connect it to the FUEL PUMP pin on
the main board. Some cars, however, have the fuel pump
controlled by a switch in the air flow meter. If this is the
case, you have two choices on most cars:
- Leave the air flow meter in place and don't connect the
FUEL PUMP jumper to anything. The fuel pump will still
operate more or less normally.
- Remove the air flow meter and connect the FUEL PUMP
jumper to a wire previously used by the air flow meter. At
the air flow meter connector, splice the wire that is now
going to the FUEL PUMP jumper to the wire that goes to the
fuel pump relay.
This picture shows a DIYPNP partially jumpered. Note that
these jumpers are being put in on the underside of the board -
the main board is marked on both sides, although not all adapter
boards are.
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Next Page in the Docs: Ignition Control >>>
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