Here are the important sensors that tell your Renix era Jeep engine how to run. The Renix computer was used from 1987 to 1990 and operates very differently from the later MOPAR engine controllers. It was designed through AMC’s partnership with Renault. Parts are still available for most of these from Amazon.
Crank Shaft Position Sensor.
The Crankshaft Position Sensor (CPS) tells the computer how fast the engine is spinning and where in the cycle the pistons are located. It generates a voltage based on teeth passing in front of the sensor. There are three gaps in the teeth located around the flywheel that correspond to the three different top dead center positions of the pistons.
It is a hall effect sensor that rarely goes bad. However, I have had alot of trouble with the connector used to connect the sensor to the wiring harness. Often unplugging and re plugging the sensor will cure problems associated with it.
As this sensor is critical to all other computer functions in the Renix control scheme, it is good to carry a spare. Available from Amazon.
Throttle Position Sensor
The throttle position sensor (TPS) tells the computer how far open the throttle plate is. If you have an automatic, transmission, it also sends a separate signal to the transmission controller to aid in downshift calculation.
If you have a manual transmission, the sensor will have only the one circuit to send a signal to the ECU. For some strange reason, he manual version is more expensive to purchase. You can use the cheaper auto version and just not connect the square plug.
It this sensor is bad, you may experience a stumble passing from idle to open throttle. The computer will make a guess and usually compensates pretty well for a failed sensor.
Manifold Air Pressure Sensor
The Manifold Air Pressure (MAP) sensor measures the engine vacuum. This data combined with the Throttle Position Sensor and Intake Air Temperature sensor allow the computer to calculate how much air is being used by the engine. This number is then used to calculate how much fuel to inject by controlling how long the injectors stay open.
The AMP sensor gets its pressure reading off the back of the throttle body. The plastic tube is connected to a rubber plug that can pop out. If it does, the engine will run very rich but it will run.
Problems with this sensor are more likely related to the small and brittle plastic line connecting it to the throttle body. If it is really bad, you can get one from Amazon.
Intake Air Temperature Sensor
The intake air temperature charge sensor is used to determine the density of the air coming into the intake. This data is combined with the MAP and TPS sensor data to calculate how much air is being drawn in.
I have not been able to find this sensor available. I used one from a ZJ and changed the wiring. It seems to work just fine. The later Cherokees did not use this sensor.
Oxygen Sensor
The oxygen sensor closes the control loop and provides freed back to the computer how good of a job it did in determining the amount of fuel to mix with the air for combustion.
The Jeep Renix uses a heated O2 sensor. The heater helps get the sensor up to operating temperature more quickly when the engine starts form cold condition.
The O2 sensor has a limited life depending on the quality of fuel it is given. The Jeep engineers predicted it to last around 2750 hours and set a remained to change it in the dash. A maintenance required light will come on at that time. There is no way to reset the timer, so just pull the bulb.
You will need a scan tool or something that can read the O2 sensor to actually determine if it is functioning properly. When correct, the readings will rapidly change from rich to lean as the computer makes adjustments.
The engine will go into closed loop if it is successfully controlling the mixture based on this signal. If the readings are not changing, the engine will operate in open loop and usually run just fine but possibly consuming more fuel.
The sensor is available from Amazon.
Cam Shaft Sync Signal
This sensor is located inside the distributor and may only be available as a unit with the distributor. It is used by the computer to determine with of the pistons is at top dead center when the engine starts. This helps the computer time the injector pulses to the valve opening better.
However, it it does not get this signal the computer makes a guess and goes on about its business. You can run without this sensor and possible never know it was missing.
A whole distributor is not much more money than just the sensor, If you need to change the distributor for other reasons it is available from Amazon.
Knock Sensor
The knock sensor listens to vibrations caused by pre ignition. The computer will retard the ignition timing based on the knock reading. The original style sensor is no longer available but there is a new style that looks to be more robust and plugs and bolts right in.
Idle Air Controller
While not a sensor, this device can affect how the engine runs. It is a stepper motor valve on the throttle body that bypasses air around the throttle plate to control the idle speed.
While most engines experience stalls when this valve fails, as often as not this valve fails in the open position causing a high idle condition on the Renix Jeeps. It may be possible to clean it, but the plunger is pretty fragile and it may be best to replace it.
It is available from Amazon.