Hey guys. First post here. I am trying to create an interface board for my 1985 VW Vanagon. I have swapped in an engine from a 2000 Subaru Forester. The Subaru engine used a lot of sensors that are no longer necessary when running in the Volkswagen. The interface board seems like it would be relatively simple to build, I am just absolutely new to creating circuit boards/interface boards. All it needs to do is have the wire plug into it and send the ecu a voltage that the sensor would normally send to it when operating correctly. I have all the voltages I need, I just don't know how to go about making this. I am pretty good at figuring things out and really just need a push in the right direction as this is all new to me.

Above are two pictures that will help in reverse engineering this. I appreciate any help in advance.

Thank you,
Jacob Norton

 

All it needs to do is have the wire plug into it and send the ecu a voltage that the sensor would normally send to it when operating correctly.

I would start by looking at what you have and what you need. Sort of subtract the have from need. Where you may run into a problem is all of the need may not be simple fixed level signals. Just using a MAP sensor for example:

Analog MAP sensors have a three-wire connector: ground, a 5-volt reference signal from the computer and the return signal. The output voltage usually increases when the throttle is opened and vacuum drops. A MAP sensor that reads 1 or 2 volts at idle may read 4.5 volts to 5 volts at wide open throttle.

The MAP sensor as well as other sensors provide varying outputs so it is not just a matter of providing a simple fixed milli-volt or voltage signal. Things like how the ECU senses engine RPM can be another issue as there are inductive sensors and hall effect sensors as well as the various pressures and temperature data. Providing fixed levels is not a problem, the changing signals is what will be difficult. Again, I would start with what you have and what you need.

Ron

 

Ron,

I appreciate the reply. Most of the sensors are for the fuel tank. Things like fuel level, fuel temp, fuel tank pressure. These all have ranges that the ECU needs to see the voltages inside of. I figured I would just set them all smack dab in the middle of the expected ranges.

Jacob.

 

The fuel pressure and temperature are they both 3 wire sensors?

 

Ron,

I appreciate the reply. Most of the sensors are for the fuel tank. Things like fuel level, fuel temp, fuel tank pressure. These all have ranges that the ECU needs to see the voltages inside of. I figured I would just set them all smack dab in the middle of the expected ranges.

Jacob.

Jacob,
Then I would just think about using potentiometers. Normally the ECU provides 5 VDC to most sensors. I would take that 5 VDC and Ground and place maybe 10K Ohm pots across 5 V and Gnd and take the outputs off the pot wipers. You will need to know the typical sensor outputs. That should get you started.

Ron