Welcome Visitor! Please take a few seconds and zekew64
Member
- Joined
- Oct 4, 2011
- Messages
- 207
- Reaction score
- 2
- Points
- 18
- Location
- Carbondale, IL
- Vehicle Year
- 1992
- Make / Model
- Ford
- Engine Size
- 2.3L I4, rebuilt from a '91
- Transmission
- Manual
After a bit of research, I discovered an easy way to determine if your Ranger's "brain box" is dead, or nearly so; these tests require the use of only a DVOM. Basically, on any older, OBD-1 system, most engine sensors had only two wires going to them, such as the ECT and EGR sensors.
The idea is this: Using the positive probe of the DVOM, probe a sensor's connector (by removing it) or pierce one of the two wires. You'll either have battery voltage, or, as in the case of a heat-style sensor like the ECT, low voltage (the thermistor in the ECT is probably the best sensor to use, as it is close to the battery, and has differing voltage values for each wire). IMPORTANT: Do these tests with a cold engine -- it makes it easier to determine which wire is which.
One wire is the PCM input wire: This wire, if you get battery voltage with the ignition key turned 'ON', means that the PCM is getting power, and has energized, in this case, the ECT circuit.
Alternatively, on the 2.3 Lima engines, you can check for PCM activity on the top Ignition Control Module (ICM) connector. Here is what you need to do: Look for the wire that is blue with a yellow stripe (I believe it is the first wire going from left-to-right as you look at it from the front of the vehicle). This wire is the Dual Plug Inhibit circuit; it should have voltage to it, as the DPI circuit is active only on start-up, to allow only the primary ignition coil to fire the exhaust-side spark plugs. After start-up, the voltage at this wire should be 0 volts, as the PCM grounds this circuit to allow the secondary coil to fire the intake-side plugs per normal operation.
After doing either of these tests, if you have battery voltage (between 12-14 volts), this should be a good indicator that your PCM is on and working. If you have little to no voltage, this is an indication your PCM is very weak or dead altogether.
The idea is this: Using the positive probe of the DVOM, probe a sensor's connector (by removing it) or pierce one of the two wires. You'll either have battery voltage, or, as in the case of a heat-style sensor like the ECT, low voltage (the thermistor in the ECT is probably the best sensor to use, as it is close to the battery, and has differing voltage values for each wire). IMPORTANT: Do these tests with a cold engine -- it makes it easier to determine which wire is which.
One wire is the PCM input wire: This wire, if you get battery voltage with the ignition key turned 'ON', means that the PCM is getting power, and has energized, in this case, the ECT circuit.
Alternatively, on the 2.3 Lima engines, you can check for PCM activity on the top Ignition Control Module (ICM) connector. Here is what you need to do: Look for the wire that is blue with a yellow stripe (I believe it is the first wire going from left-to-right as you look at it from the front of the vehicle). This wire is the Dual Plug Inhibit circuit; it should have voltage to it, as the DPI circuit is active only on start-up, to allow only the primary ignition coil to fire the exhaust-side spark plugs. After start-up, the voltage at this wire should be 0 volts, as the PCM grounds this circuit to allow the secondary coil to fire the intake-side plugs per normal operation.
After doing either of these tests, if you have battery voltage (between 12-14 volts), this should be a good indicator that your PCM is on and working. If you have little to no voltage, this is an indication your PCM is very weak or dead altogether.
