GM Chevrolet Cosworth Vega E.F.I. - ein D-Jetronic-Fahrzeug

Here is a picture of the top of the Bendix ECU circuit board.

Also, here is a picture of all of the EFI components.

What we call the "speed sensor" is probably the equivalent of the "trigger contacts" you mention. It is a reed switch, and it is synchronized to the distributor, so that the ECU knows when to open each injector. While it is called a speed sensor, its main function is to tell the ECU where the engine is/when the valves are open/closed. In doing this it also tells the ECU the engine RPM. I will try to get a good photo of it an post it.

We are trying to make a new schematic, not a new ECU. Some members have built their own ECU using modern components and a laptop. All I am trying to do is document for our website the technical specifications of our original Bendix system.

Mark

Hi Mark,

interesting, Bendix has already used a few ICs at that time.But of course they still need transistors. Without that they aould not have been able to interface the MAP sensor. However that means also that they should have done some tuning as well.

The 0 180 150 030 injector seems like the yellow one, just ist has no fuel hose connected to it. I will follow your work whenever possible. An interesting project!

Hi Mark,

having looked at your ECU picture, I believe to see some tuning resistors there as well.

The injector is the yellow one, but it is a 280, not a 180.

I do not know enough about electronics to say whether the resistors are tuning resistors or not. I have heard that phrase used (tuning resistors) but only with regard to the circuit inside the Coolant Temperature Sensor and the Air Temperature Sensor. They have identical components inside, and use the temperature sensitive characteristic of a 2n2905 transistor to measure the temperature. The circuit is a Vbe multiplier circuit with the transistor and either two or three tuning resistors. The sensors output voltage that ranges from about 2.4v when cold to about 1.7v when hot.

As I understand it, the ECU "reads" the CTS voltage and uses it to adjust the injector pulse width to ensure the proper fuel mixture at that coolant temperature.

Mark

Hi MArk,

0 180 was a typo, should read 0 280 150 030 .

What is CTS, does it mean MAP sensor? The tuning resistors in good old Bosch tradition are the ones that are above the PCB board in a kind of bridge.Such tuning is needed in analogue electronics to compensate for tolerances in switching levels and amplifications of semiconductors. Bosch has up to 42 of them. Bendix seems to have digitalized of that circuit what they could by using ICs. E.g. the flip-flop reading the trigger contacts could be an IC if you switch to 5V level.

All I am trying to tell you is that when you rebuild such an ECU, you will also need to tune the analogue part. It is not just copying the components of an original PCB.

CTS means Coolant Temperature Sensor. This sensor is located in the thermostat housing.

ATS means Air Temperature Sensor. This sensor is located in the intake manifold.

They differ in the way the temperature sensitive transistor is physically "connected" to the medium (coolant or air) being measured. The CTS uses a thermal paste to connect it to the case of the sensor which comes in contact with the coolant.

According to the shop manual: "The ECU receives the [output[ signal from the water [coolant] temperature sensor and uses it as one of the factors in determining the amount of fuel enrichment required. As coolant temperature rises, the output of the temperature sensor is changed. With this change, the ECU recalibrates the need for fuel enrichment and changes the duration of the fuel injector opening."

The ATS uses a spring, one end of which slips tightly over the head of the transistor, and the other end of which presses tightly against a small aluminum disc which comes in contact with the air. (This disc is electrically isolated from the sensor body.)

According to the shop manual: "The air temperature sensor is locate in the bottom of the inlet manifold, in the number 3 intake runner. The sensor incorporates a temperature sensitive transistor that transmits varying amounts of current to the ECU. The current flow becomes a factor in establishing the need for fuel enrichment."

Hope this helps.

Mark