FREQUENTLY ASKED QUESTIONS

Fuel and Spark, or Fuel Only?
When embarking upon a MegaSquirt installation, you have the choice of either controlling just your fuel curve or controlling both spark and fuel.  Technically, the ideal tune can only be found with control over both parameters, provided that the person doing the tuning knows what they're doing.  Often times, the stock ignition system with stock timing curves can be employed with a decent amount of success.  My recommendation is that if you choose to control spark as well as fuel, you should a) have a need to do so, and b) know what you're doing.  The only time you should *need* to play with your stock timing curve is if you turbocharge your car and the stock ignition timing results in detonation and/or preignition.  Many people turbocharge their cars with the stock ignition in place (Dodge Neon owners, for instance) with up to 80% power increase over stock levels while running the stock ignition timing and adjusting only the fuel curve with a device such as the MegaSquirt.  When in doubt, ask someone who has had firsthand experience and knows what they're talking about.

The decision of whether or not to run ignition control with the MegaSquirt also decides the complexity of your installation.  If you choose to employ a fuel-only solution, you simply need to tap into just about any signal on the car that pulses once per engine revolution in order to tell the MegaSquirt how fast the engine is spinning... exact crankshaft/camshaft position is not needed for fuel calculations.  In this configuration, a MegaSquirt can be installed on any car in almost exactly the same manner.  If you need to run ignition control, the problem becomes more complex.  Specific modifications to the MegaSquirt itself are often required, and the MegaSquirt must interface with existing hardware on your vehicle in a very specific way.  We offer MegaSquirts modified for a few specific ignition configurations.  The most complete reference for MegaSquirtnSpark setup can be found on the MegaSquirtnSpark Extra Setup page. 

Bear in mind that in almost all MegaSquirtnSpark installations, the MegaSquirt can simply gather RPM and crankshaft position data from the stock sensors/trigger wheels and leave the ignition in control of the stock ECU, if so desired.  This gives the user the freedom of controlling spark when they feel up to the task (i.e. after they've conquered fuel control), without having to re-do a bunch of wiring.

Spark Control: Interfacing With Your Stock Ignition
In order for us to be able to set you up with a MegaSquirt that will control ignition AND fuel, the MegaSquirt needs to get its tachometer signal from a sensor in the stock ignition system that is tied to crankshaft or camshaft position.  This hardware varies from car to car.  If your car isn't a Neon (420A engine), an Eclipse (4G63 engine) or a GM engine with a distributor, we don't know exactly how to connect to it.  This is where you'll need to do some homework in order to use those stock components.  Here are the questions we need answered:

Universal questions:

• How many cylinders does the engine have?
• Turbocharged, or naturally aspirated?

• What type of sensor (or "trigger") is in the distributor?  Is it a VR or a hall sensor?  Engine gurus on online forums dedicated to your car (there's one for every car, I swear) will know the answer to this question.

Distributorless ignition

• Do you have a toothed wheel on the crankshaft that the stock sensor reads from?  How many teeth does it have?  All toothed crankshaft wheels have at least one missing tooth or one inter-tooth gap filled in order to give the ECU a starting point for maintaining timing.  When you count the teeth on a wheel, take this into account.  For example, on a Ford EDIS car, the wheel is called a "36-1" because the wheel has 36 teeth (at 10-degree increments), but one is removed.  Consequently, there are actually 35 teeth, but it's a 36-tooth pattern, so it's referred to as a "36-1" wheel.  Here is a picture from Boost Engineering, a supplier of EDIS parts.
• Which type of sensor (or "trigger") reads the toothed wheel?  Is it a VR or a hall sensor?  Again, ask an engine guru... he'll know.
• Is your stock ignition "coil on plug", or "wasted spark"?  Coil on Plug (COP) systems put a small coil on top of each spark plug, so there is no fat spark plug wire going to a remotely located coil.  Wasted spark systems use a coil pack that is connected to the spark plug with a traditional spark plug wire.

We can almost always set up the hardware in the MegaSquirt to work with your stock hardware, provided that we have accurate and complete answers to these questions.  Without this info, you'll be buying a MegaSquirt that may or may not work on your engine.  Keep in mind that once you receive your MegaSquirt, you'll need to set up the firmware with MegaTune so that the timing settings for your stock hardware are correct.  I recommend installing MegaTune (grab the latest version in this location) and playing with settings before actually setting up the MS on the car.

EFI Conversion: Which Parts Do I Need?
There is a collection of parts that are common to every speed-density EFI system that the system must have in place in order to operate.  These parts can be purchased from us, found in a junkyard, taken from a donor vehicle, etc.

• ECU (MegaSquirt, in this case)
• Fuel injectors and injector rails
• Fuel pressure regulator
• High-pressure fuel feed and return lines
• Intake manifold suitable for fuel injector mounting, or a TBI system
• Throttle position sensor (or wide-open-throttle switch)
• High-pressure electric fuel pump designed for EFI duty
• Exhaust Gas Oxygen (EGO) sensor
• Intake air temperature and coolant temperature sensors
• Manifold Absolute Pressure (MAP) sensor (internal to the MegaSquirt)
• Wiring to tie it all together
• Ignition system (either a distributor or the hardware necessary for a distributorless setup)

How Do I Wire It Up?
The installation procedure for a MegaSquirt varies on every vehicle to some degree.  The procedure depends on a few key questions you'd need to answer for yourself:

1) Do you want to put your stock EFI system to work for you? 
   If the stock ECU and wiring are left in place, installation is fairly simple.  Stock injector wires can be used, many sensor wires can be tapped (sensors will be covered in detail later), and the stock power wiring can be used.  For instance, you don't even need to run your TPS power and ground wires, you simply need to tap into the center wire of your stock throttle position sensor with the TPS SIG wire.  The same logic applies to the stock narrow-band O2 sensor.  The stock ECU can often control the fuel pump and idle air control functions for you as well.  Lastly, the stock main power relay can be used, with the MegaSquirt running from the "on while key on AND during cranking" power wire.  As for fuel injectors, all you need to do is disconnect the fuel injector switched ground leads (not the common +12V leads, which can be left in place) and connect them to the outputs of the MegaSquirt.  The same logic applies to the ignition coil(s), once the proper wiring and modifications are in place for ignition control.  New temperature sensors usually need to be wired separately, which will be explained later.  For this type of installation, a Relay and Power Distribution Board isn't really necessary, since all of the features it provides are already built into your stock wiring.  Save yourself some money and do without it, unless you want to totally isolate your MegaSquirt wiring from the stock system.

2) Converting from a carburetor, or just want to ditch your stock wiring and ECU entirely?
   If you'll be starting from scratch with your EFI system for one reason or another, you'll need to do a bit more wiring and buy a few more system components.  We advise you to carefully consider all ramifications of removing the stock ECU from your car without a good reason... for instance, a Neon's ECU feeds the crankshaft position sensor (a necessary component) a 9V supply voltage, which would require additional circuitry to run without the stock ECU.  Alright... back to the wiring.  What you'll probably want to do is get a Relay and Power Distribution Board.  This board offers fuses, relays, and a central wiring hub that you'll likely find either useful or essential in your installation.  We offer this board for sale, as well as a range of cable kits with which to connect the Relay and Power Distribution Board to the MegaSquirt.  Once you have your MegaSquirt and Relay and Power Distribution Board installed in the car, wiring the system is fairly simple.  Each output terminal of the Relay and Power Distribution Board is labeled with its function, and these labels correspond to the labels stamped on the wires in our harness kit.  It makes installation a breeze, relatively speaking of course.

3) Do you know exactly how your stock temperature sensors are controlled by the stock ECU?
   If you want to use your stock intake air temp and coolant temp sensors, you have to do one of two things: a) know exactly how they're driven by the stock ECU, or b) remove the stock ECU from the picture entirely.  The problem is essentially this: The stock computer puts a fixed-value resistor in series with a temperature sensor, and then drives the series circuit with a supply voltage.  The voltage is balanced between the sensor (a thermistor, or thermally varying resistor) and that resistor (often called the 'bias resistor'), and that balance is measured in order to calculate temperature.  Knowing that resistor value, one could simply tap into the stock sensor signal.  There are instructions here for doing so in this archived YahooGroup message.  If you don't know how to tap your stock temperature sensor signals, we recommend purchasing and installing new GM temperature sensors (which we offer), and running the wiring independently of the stock sensor.

First off, here are the basics:

   a) Make sure you're not using your huge soldering gun (for pipes, etc.) to do the job.  A $7 Radio Shack 25W soldering iron is perfect.  Ideally, a temperature-controlled soldering station can be used, but if you already had one of those, you'd probably already know how to solder the connector...  I built my MegaSquirt and my harness with a $7 iron.

   b) Heat the part with the soldering iron and then touch the *part* with the solder. This is to ensure that the flux is flowing across the part instead of burning up on the iron. The flux cleans the surface and helps the solder to flow across it, so if you burn the flux up before it hits the part, the solder might not flow and the joint could be 'cold' and may develop into an open circuit at some point.

Now for some photos... (click on a photo to see larger version)
(Note: Don't solder the sensor return wires to the pins that I did if you're running a relay board... this harness doesn't use one.  With a relay board, there should be a main ground wire in the center, and a sensor return wire on pin 19.)
 

Soldered ground wires	More soldered ground wires
Soldered signal/power wires	Completed connector (somewhat redundant heat shrink, perhaps)

Here's the process:

1) Lightly tin (coat with solder) the pins on the connector. This shouldn't take too much heat. Add enough solder that the 'cup' shape in the pin is full to the point of being almost leveled off with solder. This will serve as a sort of reservoir when the wire is soldered on.

2) Using needlenose pliers, make sure the strands of the stripped wire are nicely packed together. Cut and re-strip to about 1/16-1/8" if the strands are too bent to be completely straightened.

3) Completely tin the stripped portion of the wire. I found it easiest to hold the wire down with something (a vise, a book on a table, etc.), apply heat to the very *tip* of the wire, and touch the solder to the *side* of the stripped portion of the wire. The solder will very easily 'wick' into the wire. Make sure all sides of the stripped wire are tinned, but don't put so much solder on there that it balls up on the wire. If it does, get it hot and quickly shake the excess solder off of the wire.

4) Hold the connector in some kind of vise. Grab the edge of the connector with a pair of Visegrips if you don't have a vise, and just set it on the table. The Visegrips will keep the connector from moving around too much while you're using your other two hands to do the soldering.

5) Lay the tip of the wire onto the top of the solder cup (don't worry if it doesn't fit *into* the solder cup, it's too big), and apply heat with the soldering iron to the side of the stripped wire. The iron will melt the solder in the wire, and that will in turn melt the solder in the connector pin. The excess solder in the connector pin will supply all that is needed for the connection, so no solder needs to be added. As soon as the solder has completely flowed between the wire and the pin, remove the heat while still holding the wire in place for a second or so. The solder will freeze up, and you'll have a good solder joint. 

Note: Be sure to keep the joint small (i.e. don't add too much solder or smash the tip of the wire outward while soldering), and there should be very little risk of shorts between the pins.  If you want to be really sure, you can use 3/16" heat shrink tubing on every *other* pin to prevent shorts between adjacent pins.  Just be sure to remember to slide the tubing over the wire before you solder it!  Carefully applying heat with a lighter or a match will work just fine on the heat shrink tubing, if you don't own a heat gun.

More info will be added here as the questions are asked!