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9 MPG.......Help........What is the correct way to test the o2 sensor

C85D4x4

C85D4x4

NAXJA Member #1311
Location
Ohio, Brecksville
96, 4.0, AW4, 34" LTBs, 4.56, 145000 miles


The o2 sensor is 2 months old (Bosch replacement)



What is the correct way to test the o2 sensor ?

I tried to test the voltage the way the manual told me by unplugging it........but the manual did not tell me which wire to test. I got mixed results with each wire (2 white, 1 black, 1 grey) but I never got much of any volt reading at all.

Also, I have replaced plugs(champs), wires, cap, and rotor, Oil. I checked and also a muffler shop checked for any leaks in the exhaust manifold. I also have checked the CTS and MAT sensor.



I still cant see this engine needed to eat so much gas, even with my 34 LTBs.


Any Ideas guys???
 
34" ltbs (swampers measure a lil higher, im guessing they might be 34.5) are a big, and heavy tire, and those huge lugs dont mesh well with the road efficiently. consider yourself on 35" tires, but with 4.56s you should be getting pretty descent milage. how does the engine run? does it sound like it runs smooth or does it kinda of "chug" in comparison to other 4.0Ls?
 
34" ltbs (swampers measure a lil higher, im guessing they might be 34.5) are a big, and heavy tire, and those huge lugs dont mesh well with the road efficiently. consider yourself on 35" tires, but with 4.56s you should be getting pretty descent milage. how does the engine run? does it sound like it runs smooth or does it kinda of "chug" in comparison to other 4.0Ls?
 
What about your engine temperature? Are you sure your getting up to at least 195? Otherwise you are in "rich" mode all the time. If you disconnect the sensor and test it, you will not get voltage. You would test the plug from the harness for voltage.
 
Hallo. Bosch sensors are mostly Zirconium ones. They generate a voltage by themselves. From 0 till 1 Volt. 0 is rich and 1 is lean.
There are 4 wires. One for the signal to the ECU. One for the grounding.
The 2 others are for the heatingelement.(mostly grey or white, but depends on year).
The problem with testing is, that they have to heat up about 600F.
So you can do a difficult test under your Jeep with piercing probes or do a bench test and heat it up yourself. :scared:

I renew my O2 sensor each 100K km.


'92 XJ
 
Last edited:
emr1101 said:
34" ltbs (swampers measure a lil higher, im guessing they might be 34.5) are a big, and heavy tire, and those huge lugs dont mesh well with the road efficiently. consider yourself on 35" tires, but with 4.56s you should be getting pretty descent milage. how does the engine run? does it sound like it runs smooth or does it kinda of "chug" in comparison to other 4.0Ls?
Click to expand...

I didnt get much better MPG with 32" bfg a/t. The engine seems to run great.....not sluggish at all.

winterbeater said:
What about your engine temperature? Are you sure your getting up to at least 195? Otherwise you are in "rich" mode all the time. If you disconnect the sensor and test it, you will not get voltage. You would test the plug from the harness for voltage.
Click to expand...

Temp. is right in the middle of the gage. so its good.

wim hoppenbrouwers said:
Hallo. Bosch sensors are mostly Zirconium ones. They generate a voltage by themselves. From 0 till 1 Volt. 0 is rich and 1 is lean.
There are 4 wires. One for the signal to the ECU. One for the grounding.
The 2 others are for the heatingelement.(mostly grey or white, but depends on year).
The problem with testing is, that they have to heat up about 600F.
So you can do a difficult test under your Jeep with piercing probes or do a bench test and heat it up yourself. :scared:

I renew my O2 sensor each 100K km.

'92 XJ
Click to expand...

I tryed it when I was under the jeep..........but I still do not understand how to test it the correct way?
 
Quote:but I still do not understand how to test it the correct way?

Hallo. In fact you don't, you will need a scope to do a real test.
Put the leads of a DMM in the connector . Look at Volts.
Heat up the end of the sensor with a torch.... Better to buy a new one. :dunce:
 
winterbeater said:
Does this mean that the o2 sensors check the temperature of the exhaust gas, not truly the oxygen level?
Click to expand...
If I'm thinking clearly here (not always a guarantee) the stuff an O2 sensor is mad eof reacts to O2 in the exhaust and creates a chemical reaction, generating voltage. The level of voltage generated by this reaction tells the computer how much O2 is there. Over time the sensor runs low on it's reactant and the voltage output drops, telling the computer there's less O2, so the vehicle adjusts fuel to compensate.
 
winterbeater said:
Does this mean that the o2 sensors check the temperature of the exhaust gas, not truly the oxygen level?
Click to expand...

Hallo. Well, the chemical reaction is only working by heat.:flamemad:

Zirconia sensor

The zirconium dioxide, or zirconia, lambda sensor is based on a solid-state electrochemical fuel cell called the Nernst cell. Its two electrodes provide an output voltage corresponding to the quantity of oxygen in the exhaust relative to that in the atmosphere. An output voltage of 0.2 V (200 mV) DC represents a lean mixture. That is one where the amount of oxygen entering the cylinder is sufficient to fully oxidize the carbon monoxide (CO), produced in burning the air and fuel, into carbon dioxide (CO2). A reading of 0.8 V (800 mV) DC represents a rich mixture, one which is high in unburned fuel and low in remaining oxygen. The ideal point is 0.45 V (450 mV) DC; this is where the quantities of air and fuel are in the optimum ratio, called the stoichiometric point, and the exhaust output mainly consists of fully oxidized CO2.

The voltage produced by the sensor is so nonlinear with respect to oxygen concentration that it is impractical for the engine control unit (ECU) to measure intermediate values - it merely registers "lean" or "rich," and periodically adjusts the fuel/air mixture to keep the output of the sensor alternating between these two states. The time period chosen by the ECU to monitor the sensor and adjust the fuel/air mixture creates an inevitable delay, which makes this system less responsive than one using a linear sensor (see below). The shorter the time period, the higher the so-called "cross count" [1] and the more responsive the system.

The zirconia sensor is of the "narrow band" type, referring to the narrow range of fuel/air ratios to which it responds.
 
Last edited:
wim hoppenbrouwers said:
Quote:but I still do not understand how to test it the correct way?

Hallo. In fact you don't, you will need a scope to do a real test.
Put the leads of a DMM in the connector . Look at Volts.
Heat up the end of the sensor with a torch.... Better to buy a new one. :dunce:
Click to expand...

:confused::confused::confused::confused::huh:

DMM ?????????

Really guys..........I dont know the first thing about electronics.............Please enplane in detail and in general terms..........the easiest way to test the o2
 
DMM=Digital MultiMeter.
 
I've this problem too, but I'm running on 31 BFG ATs.

Muffler shop told me I was running rich, due to the condition of the cat. converter. I have a black ring around the exhaust pipe, and when I changed the plugs, they looked like crap.

I also haven't figured out how to test the O2 sensor.

Wim, does the Jeep need to be running and the exhaust hot to test the sensor? Do you test between the ECU wire and the Ground wire to get a voltage?
 
Lift=less MPG.
Larger tires=greater mass=more rolling resistance=less MPG.
Automatic transmission=fluid coupling=less MPG.

Got a/c? Defrost mode=a/c compressor runs=less MPG.

A failing (not bad yet) alternator bearing can drag MPG down quite a bit. Jp Magazine has been running a series on xj mileage. Check their website.
 
joe_peters said:
Lift=less MPG.
Larger tires=greater mass=more rolling resistance=less MPG.
Automatic transmission=fluid coupling=less MPG.

Got a/c? Defrost mode=a/c compressor runs=less MPG.

A failing (not bad yet) alternator bearing can drag MPG down quite a bit. Jp Magazine has been running a series on xj mileage. Check their website.
Click to expand...

A lift in and of itself doesn't drop mpgs that much.
There are plenty of account of people running 34's/35's getting pretty good mileage.

How much mileage should you lose with lift and bigger tire?
 
I have heard of guys losing 2-3 MPG with a front-high lift, you should be slightly down at the front. How much being higher off the ground would effect MPG I don't know. Someone with ground-effects knowledge would be a better judge of that.

As to tires, that is going to depend on numerous factors. 34 a/t tires will probably impact mileage less than 34 swampers, and the actual weight of the tires I am sure will vary between manufacturers and again, tread type. Not all 34s are made equal.

His gearing is right for the 34s according to most charts I have seen.

The gov says his xj should get 14 city, 18 hwy, 15 combined. If his 9 MPG is combined, then losing 6 MPG without some other factor would seem steep, but just personal driving habits could account for the rest.

PS--those gov mileage figures are for REGULAR gasoline, with E10 you can expect a bit less, especially in cold weather--ethanol is crap in cold weather even with the formula change.
 
Last edited:
Hallo. Running rich can also have to do with a bad T-stat.
Quote;
Wim, does the Jeep need to be running and the exhaust hot to test the sensor? Do you test between the ECU wire and the Ground wire to get a voltage?
__________________
To test a 02 (lambda sensor) in the Jeep in the right way? Forget it. You will need a scope.
When you like to do it on the warm running Jeep ,with a multimeter, use piercing(needle point) probes, which you can use through the insulations of the wires.
I prefer the bench test, you can put the probes of the DMM into the connector. Black is mostly the + for the signal.
Heat the tip of the sensor red hot. And read, but what? The sensor is comparing the reference air with the ambient air , but needs the air from the hot exhaustgas. :roflmao:
Easy to test is the heating element in the sensor now. The resistance have to be more than 30 Ohms.
Use the 2 grey or the white wires.
 
Last edited:
joe_peters said:
I have heard of guys losing 2-3 MPG with a front-high lift, you should be slightly down at the front. How much being higher off the ground would effect MPG I don't know. Someone with ground-effects knowledge would be a better judge of that.

As to tires, that is going to depend on numerous factors. 34 a/t tires will probably impact mileage less than 34 swampers, and the actual weight of the tires I am sure will vary between manufacturers and again, tread type. Not all 34s are made equal.

His gearing is right for the 34s according to most charts I have seen.

The gov says his xj should get 14 city, 18 hwy, 15 combined. If his 9 MPG is combined, then losing 6 MPG without some other factor would seem steep, but just personal driving habits could account for the rest.

PS--those gov mileage figures are for REGULAR gasoline, with E10 you can expect a bit less, especially in cold weather--ethanol is crap in cold weather even with the formula change.
Click to expand...


O yea my 6 MPG is mostly all highway to and from the trails. I dont DD its trail only, but I still want to fix this problem.
 
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