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Oxygen Sensor Volts Jumping.

R

RebelXJ

NAXJA Forum User
Location
Montreal
I have been running around this issue for a while now of my oxygen sensor jumping between.92-4.96 volts ever since I changed it. No matter what I Am at, idle or going down the highway it always jumps up and down randomly. I have read many post by Ecomike and his seems to differ from my readings. His seem to stay between 2-3 if i recall correctly at 2500 rpms. My mileage has always sucked, average about 160 miles to a full tank and alot of that is highway. The question is, is it the o2 sensor that is funny or do i have another problem. ( ALL TEST DONE RUNNING TEMP )The loop status is closed, and the scanner jumps rich to lean continuously at idle or driving on interstate. Map voltage at idle is 1.7-1.8v, Throttle closed reads 13% on scanner. TPS is adjusted to 83%. Coolant is at 88c, Spark advance at idle is 14-16 degrees, knock sensor reads 0 at idle will go up if i accelerate. Egr will open under acceleration, but closes on idle. O2 sensor continuously goes from .92-4.96v all the time, idle is about 580-620. Jeep is an 87 4.0 Renix. Thanks
 
That sounds a lot like you have an intermittent connection somewhere - check along your wiring harness to the sensor for cracked insulation, broken wires, melted insulation, shorts, and opens. 4.96 volts is very close to the internal supply voltage of the ECU and I believe is the float voltage of the signal inputs, so if you have a connector that is corroded or a broken wire when it comes disconnected momentarily you will see that voltage on the input.
 
I will go check that right now, because my sensor isn't all that old maybe 18 months but haven't drove it but maybe 5000 miles if that.
 
I have visually checked these wires and everything seems to be fine. Is there anyone who know where these wires end up so i can run the resistance from beginning to the end of the wires going to the O2 sensor.
 
Ground is at the dipstick, pin 35 on the ECU (per 90 FSM), the oxygen heater relay on the passengers side fenderwell.

88 C = 190.4 F; why are you running so cold? Thermostat should be 195 F. Replace thermostat with Stant SuperStat Premium 195 degree thermostat.
 
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Why SOOOO COLD..... It is -29 c with the wind factor imagine driving into that. I think that would make sense hell I might be talkin through my hat.It did go up to 92 c.

But I just ran the scanner after sitting for 5 hours in the -29 and what I observed was O2 sensor stay at .92v varied very little, it was in open loop status, and was burning lean, egr was closed. All this lasted about 60 seconds to 90 seconds, then it went to closed loop and the O2 went .92 - 4.9 in random fluctuation, and went from lean to rich continuously according to scanner. If I gave it a small amount of throttle it would go into open loop and close a few seconds later back to closed. Anything Curious?
 
Well i'm still fighting this jeep and wont give up just makes me more determined. I have checked the O2 sensor with meters accord to ecomike and I do have the proper voltages except for when the truck is running, it keeps jumpin from .92. to 4.96 all the time idle or highway. Now I'm getting about 160 miles per tank, I can smell it burning rich as hell i have check the manifold air sensor its fine, tps and coolant temp sender is good and does go into closed loop. Is the O2 sensor defective? since its goes rowdy all the time>
 
This sounds a lot like the wiring fault I suspected still. I'd disconnect both ends (the ECU connector and the O2 connector) and measure resistance from one to the other on the O2 sensor signal lead while having someone shake the wiring harness around. There is probably a broken wire with the insulation still intact that kept you from seeing it in your visual inspection.
 
So basically from what I understand is that you want me to unplug the ECM which is under the dash right? And then run the resistance from the ground on the ECM to the ground on the O2 Plug. I did check the wires from O2 to its own plug and they aren't melted at all, now i just need to know where each wire goes. Correct me if im wrong. thanks
 
Nope... ECM is on the fender wall on the driver side, at least on HO XJs, not sure about RENIX. I want you to unplug the sensor and the ECM and then find the signal wire (will go from the sensor connector to the ECM connector, not sure which pins, hopefully one of the RENIX experts can give that info) and measure the resistance from the proper pin on the O2 sensor to the proper pin on the ECM connector. If it jumps around a lot while someone else is wiggling the wiring harness, you found the problem, and just need to track down where the wire is broken or where the dirty connector is.
 
ECU on the Renix is under the dash, driver's side, between the steering column and the heater box.

Best I can tell on the o2 sensor is ECU ground at B11, and its input to the ECU is D9.
 
OK. In that case, I would say you should measure resistance from D9 on the ECU connector to all the pins on the O2 sensor - only one of them should measure low resistance, that is the one you want to investigate more.
 
OK perfect I will go do that, D9 is the 5V right just for my own knowledge? Also if I don't have any resistance there what else must I check while im out there in the snow so I don't have to come back in.
 
What those guys said..

basically you just want to confirm continuity in the harness from the pcm out to the o2 signal wire, perhaps the heater wires as well. Then make sure you have no continuity to ground, and no power bleeding over either. Keeping in mind you never check continuity on a powered ckt.
 
Yeah, it's the one you are seeing jump to 5V intermittently. If you don't see low resistance there (should be lower than 10 ohms, if it's above that, you definitely have a problem) you should trace the wiring between the two connectors and clean any connectors you find in between. You should also check for frayed or damaged sections in the wire.
 
I checked the resistance from battery and Block to the O2 and its fine now I will have to check the other wires you have been talkin about.
 
Today was the day that I decided to unplug the o2 sensor and check for a difference. HA there wasnt one, and there was 14 volts coming from one wire and 5 from the other. It doesnt make any difference plugged or not. Do you reckon shes shot?
 
nevermind.
 
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The O2 sensor on the Renix engine is different than a typical O2 sensor. If you measure the output in-circuit, you should see it flipping between roughly 0 and 5 volts. It should flip about once a second, maybe a little faster. If you disconnect the connector at the sensor and measure on ship-side harness, you will see battery voltage on the heater pin and a 5 volt pull up from the ECU on the output pin. I think yours is working correctly.
 
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