Auto Service World
Feature   May 1, 2004   by Jim Anderton

Homegrown EFI, Part 2

Learning precision soldering and making a stimulator

Last month, we gave an overview of a homegrown EFI controller that uses off-the-shelf Motorola control electronics to create a fuel injection ECU good for anything from Harley-Davidson to the mighty Rolls Royce Merlin. But assembling this project requires a more delicate touch than anything commonly encountered in automotive electrical systems, beginning with the tools required.

Outside of the lowest wattage soldering iron you can find, this is a basic set of tools. Surgical forceps work in very tight spaces, while the fine needle nose pliers are ideal for bending leads. The diagonals are also tiny, with spring-open jaws that are extremely sharp.

Solder wick is a great way to fix mistakes. Heat the joint, and the copper braid sucks up solder by capillary action. Plunger-type sucking tools are also available for the same purpose.

Preparing the iron is very important. It’s a switchable 15/30-watt pencil type, here being tinned with rosin-core electronic solder. If the tip won’t tin cleanly, wipe on the damp cloth and try again. If it still won’t take, you may have to cool the tip and sand with emery cloth.

Here’s the stimulator circuit board and some of the components as they come from the electronics store. The stimulator simulates the vehicle’s sensors and fuel injectors, allowing you to calibrate the MegaSquirt ECU off the vehicle. Components are all off-the-shelf and are available through electronics supply houses or by mail order/Internet.

Clean and neat. The board has the part codes printed on it, so it’s hard to mess up the installation. This board is almost ready to go.

Assembly is straightforward. According to the instructions, bend the leads of each component and feed the leads through the predrilled holes on the board. Then solder on the back side. Note the homemade heat sink.

Drop a resistor on the floor and can’t remember which one it is? There’s a colour code, but it’s much faster to use your VOM. This one’s a 1 kohm-1/4 watt unit.

MegaSquirt is an open-source project freely available on the Internet for anyone who’s looking for a truly universal fuel injection controller that uses off-the-shelf parts, including commonly available sensors from major manufacturers like Ford and GM. Visit megasquirt.html for background, system descriptions and examples of successful installations. Down with carburetors!

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