Sensors and wiring

Can someone please explain the two sensors located on the front to Middle ways on the block on the driver side that are found on the renix era 4.0 engine. I know one is a knock sensor and the other is a temp sensor but what is the purpose of these two sensors and are they mandatory. And also can someone get a diagram of the wiring going to the sensors. Thanks.

The one at pan level is the knock sensor. Has a plug on it like an injector. Good to have, but not critical.

The other is the CTS, Coolant Temp Sensor. Absolutely necessary for proper engine operation.

What are you trying to do?

I did a swap on my 87 I replaced the engine in it with one from a 91. I kept all the wiring ignition manifolds flex plate and other components from my 87. The 91 came drilled and capped for a place for those sensors. Does the coolant temp sensor connect to the pcm or the fan. Also there is a spot near the rear of the head for coolant sensor and a place on the thermostat for one also. I need the wiring for the sensors so I can have my fan come on with air conditioning or around 210/215°F

If you are running the Renix computer, you should really run the knock sensor or if not, bridge across the connector with around a 1K ohm resistor. It is nothing more than a microphone that listens for a knock. If it hears what it thinks is a knock, it will retard the timing. If you simply unplug the sensor and don't terminate the connector, it will pick up electrical noise and think it is knocking and will retard the timing and cut down on your power. Notice that the knock sensor wiring is the only shielded wiring in the wiring harness? Even with a sensor, it can still pick up electrical interference.

The Coolant Temp Sensor on the side of the block feeds the PCM. The one on the back of the head is the water temp sensor for the dash gauge/light.

I snapped my knock sensor off changing the motor mounts a while back. I "glued" it back on. Have no idea if it works but the ol' girl runs fine.

I got a place for a sensor in the rear of the head the thermostat housing the block the radiator and one between a splice in the bottom radiator hose. I wish I had a diagram because that seems like too much.

Maybe I missed it. What year is it? What year engine do you have in it?

Renix era Jeeps, like my 1988 have 3 "coolant temp" sensors. They also have a closed radiator system (no radiator cap).

1. CTS in the side of the block under the manifolds. This feeds the PCM.

2. Water Temp Sensor in the back of the head. This feeds the dash gauge/light.

3. Elect Fan switch located in the radiator, driver side tank. This turns on the elec fan when water temps exceed 220.

There is no port on the thermostat cover. This is for the later years that consolidated the sensors into this one. Some folks covert the closed system to open and need a place to attached the elec fan switch. Another option is a junction in the lower radiator hose.

I think you should take and post a few pictures.

He put a 91 engine in a renix rig, thus the odd T-stat housing.

"3. Elect Fan switch located in the radiator, driver side tank. This turns on the elec fan when water temps exceed 220."

FYI, that sensor does not know the T-stat/engine block temp and acts on the temp it sees in the radiator exit only. If the flow is too slow or or the radiator is scaling up, or the top half of the radiator is full of air and the the sensor sees cold air, the engine can be at 240 F and the radiator exit at 140 F!!!!! I documented that here about 8 years ago with IR gauges and old radiators/clogging up, rew radiator half full of air, and new radiator with now air.

That is why Jeep moved the e-fan temp sensor to the T-stat housing in 91.

I've figured it out guys thank you. I hooked up the sensor to the head which feeds the gauge. I installed the sensor in the engine and also installed the sensor that was once in my radiator to my thermostat housing which kicks the fan on. Thanks a lot.

Glad you got it. Thanks for providing your fix.