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Renix Oxygen Sensor Relay and Wiring

Black1990jeep

NAXJA Forum User
Location
california
On my 1990 Renix Inline 6 I am trying to understand the O2 sensor circuit for trouble shooting, I have the factory schematic. The O2 sensor heater relay is a single pole, double throw type as seen on sheet 20 of the schematic. One throw terminal goes to the O2 sensor heater and the diagnostic connector via an orange wire, and the other throw terminal of that relay goes to an orange/black wire that splices to the fuel pump.

So when the O2 heater relay is switched one way the power goes to the fuel pump circuit, and when that relay is switched the other way the power goes to to the O2 sensor heater.

Why is this O2 relay hooked up like that, when the O2 heater is on the relay is closed to the heater ( which makes sense) but when the relay turns the heater off, that relay is connected to the fuel pump circuit. that makes no sense to me, what am I failing to comprehend here?

Thanks!:bunny:
 
That's not the way I read my 88 FSM. (perhaps there's a difference for a '90?).

The O2 heater relay on the coil side has a orange lead (pin 5) that connects to the fuel pump relay, but other components as well and C11 on the ECU (Injector feed). This is part of the circuit that energizes the relay. The other lead (pin 2, GRY-YEL) goes to A-7 on the ECU (O2 relay gnd).

On the switch side I see only 2 wires. Pin1 Yellow is the "Key On hot" off the ignition switch. The ORG (ORG-GRY) is the "ON" throw and connects to the O2 heater element and C9 on the diagnostic connector.

The other throw is blank.

Does seem confusing that there are 2 orange wires. Reading these schematics can be challenging as well. Just remember, junctions are indicated by a big dot
 
this is what I found out....

https://www.cherokeeforum.com/f2/o2-sensor-schematic-renix-4-0-liter-260518/

thus the O2 sensor heater is disabled when under wide open throttle, additionally the fuel pump ballast resistor is bypassed via the O2 sensor relays non energized throw position. This gives greater voltage to the fuel pump evidently for the increased flow rate needed at full throttle. also the AC clutch relay is bypassed to off and the egr is disabled. when at full thottle the engine switches to open loop mode for mixture control.
 
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