Tester Concepts and Ideas

The ECU edge connector needs to come from a dead 914-type ECU - don't get the early VW ones, they are apparently a poor match. The wiring harness plug can come from nearly any D-Jet equipped car. The project box comes from Radio Shack, as do the banana plug sockets. Total cost should be around $50.

With this type of box, by connection to the wiring harness plug, you can use a DMM to test the injector resistances, contact trigger point operation, throttle position sensors (TPS) switch functions, manifold pressure sensor (MPS) primary and secondary resistances, TS1 and TS2 resistances, system voltage, start signal, etc. By plugging the ECU into the other side and starting the car, you use an oscilloscope to measure the injector pulse widths, watch for trigger contact "bouncing", etc.

A more ideal tester would split the harness from the ECU connectors. By bridging the connectors, you would realize the straight-through breakout box. A split box would permit substitution of all of the components, enabling emulation of the functions. For example, a circuit that simulates the trigger contact points could be substituted, permitting simulation of any engine speed in a static (engine not running) state. In combination with substitution of power resistors for the injectors, and vacuum pump control of the MPS, virtually any engine operation mode could be simulated and the pulse widths measured. This idealized tester describes the basic EFI Associates models, which had the added advantage of an integrated pulse meter, which is more convenient than an oscilloscope for rapid measurement of injection pulse widths.

In the future, I hope to include diagrams for the construction of a split breakout box, along with trigger contact simulation and pulse width meter circuits.

By the way, I know of at least three other D-Jetronic testers that I don't have listed here. One was a sophisticated unit from Sun that a guy in Australia sent me some info on, it had an integrated vacuum unit and some sort of dwell meter for measuring injection pulse widths by an analog method. And lastly, I saw a picture of a huge bench tester that Bosch developed for the engineering of the MPS and other system components. If anyone knows of other testers, please email me with details.