Bypass for o2 sensor?

[xj]

Hey all,

I've just cut the catalytic converter off, and had to put the o2 sensor back, seeing as how its all computer controlled an' all. Have found immediately that when giving it some jandal high rev in 2nd and cruising at 3rd theres now an intermittant miss, and backfire. Not constant, just every now and then. Im only talking in the space of 24 hours after converter was cut out, and im assuming that the o2 sensor has been affected. Any bypass that anyone knows of?

[adogg]

have you removed it all together or moved it?

[xj]

put the sensor back into the pipe that is now where the catalytic converter used to be. its in exactly the same position as it was before.

[TJ]

Your O2 sensor is before the cat converter on a TJ, so it should not be impacted by removal of it. Its possible that the wires got crimped or are loose when you put O2 back in the pipe.

I have had mine replaced with a Bosch unit (I think it was like $130 or so). Otherwise, just swap the sensors between your two TJs and see if the problem is transported or remains with the TJ that is missing a bit.

Otherwise it could be that the cat was just hiding the missfire in its rattle and now you can hear it loud and clear?

[TJ]

Any bypass that anyone knows of?

There is no bypass for O2 as the engine adjusts injector timing and pretty much everything for the mixture based on input from the sensor.

Fortunately for us, export models only have one sensor on TJs (before the cat). I believe ZJs came with two sensors, one before the cat and the other after - which makes it tricky to remove the cat.

Has the sound been impacted by removing the cat? I mean the cat does act like a resonator and muffles it a bit. Is the exhaust any louder now?

[xj]

TJ, if im lying in my back, with my feet to the front of the vehicle, and my head is directly below the muffler, the o2 sensor dives into the top left of the cat. Its set up like this on both of our TJ,s. To cut the cat off, the sensor has to go. I dont know how yours is connected, but thats the way it is/was with both ours.

No it wasnt just hiding a miss, you kinda feel a backfire accelerating full tit, rattly cat or not.

Its a bit "throatier" now, esp when planting the boot, but not so much as to be a bother come WOF time (i hope).

Ill check the wires etc again on the weekend, you might be right, maybe just loose or crimped.

[TJ]

TJ, if im lying in my back, with my feet to the front of the vehicle, and my head is directly below the muffler, the o2 sensor dives into the top left of the cat. Its set up like this on both of our TJ,s. To cut the cat off, the sensor has to go. I dont know how yours is connected, but thats the way it is/was with both ours.

I have just now sent you a couple of photos of how it looks on mine (on yoru personal email addy). It was raining outside, so this is the best I could do without getting wet. I'll see if I can post a photo here.

Its a bit "throatier" now, esp when planting the boot, but not so much as to be a bother come WOF time (i hope).

I am thinking about this "mod".

[xj]

Hmmmm.... interesting indeed. youd have to go 180 deg and look to the top of the cat to see ours, from the opposite side of the transfer case cross member. neither has any indication of ever having one placed where yours is in the pics.
On the first diagram (11.2) draw a horizontal line fron the "2" arrow point across the cat. 3/4 of the way across is where ours are located.

typical i suppose, two different sets of brake pads, 4 different swaybar bush sizings, 5 different serpentine belts, why not have different exhaust setups??

We'll have to get together sometime and compare.

[TJ]

Its a Jeep thing, you wouldn't understand it

I think the exhaust set-up might have been changed due to technology changes between 1997 and 2001. The way mine is, I should be able to just take the cat off from the front flange and the back flange (before muffler) and put a pipe in with appropriate flange on either side.

It is indeed bizzare that a manufacturer would have so many changes within the same model lifecycle, yet aftermarket parts are interchangeable from 1997 to 2006 (heck, Dana 44 gears can go back to the 1948 model!!)

[BIG_BOY]

soak it in vinagar the plane stuff then hold it in a vice put a muilty meter set on DC volts .01-2V (or lowest setting) the -ve to the sensour & +ve to the wire off it & heat the sensour jentley with a beutain propain flame once the sentre is warm wave the torch past it slowley & see if the readings on the meter change

it might be dead

if its a 2 wire one muilty meter clip on each pin
if its 3 2 wires will be for a heater & will measure a restince of about 15ohms accross them the other one wont conect to anything use that one & the sensour for groung

if its a 4 pin plug post a pic of it il check witch pins to use

[TJ]

if its a 4 pin plug post a pic of it il check witch pins to use

On my 01 TJ, it was 4 pin plug. Two white wires are for ground, so should make no difference if you switch them. The other wires are for the sensor and the heater. Can't remember the colour.

[TJ]

Factory Manual says:

An O2 sensor is a galvanic battery that provides
the PCM with a voltage signal (0-1 volt) inversely
proportional to the amount of oxygen in the exhaust.
In other words, if the oxygen content is low, the voltage
output is high; if the oxygen content is high the
output voltage is low. The PCM uses this information
to adjust injector pulse-width to achieve the
14.7–to–1 air/fuel ratio necessary for proper engine
operation and to control emissions.
An O2 sensor must have a source of oxygen from
outside of the exhaust stream for comparison. Current
O2 sensors receive their fresh oxygen (outside
air) supply through the wire harness. This is why it
is important to never solder an O2 sensor connector,
or pack the connector with grease.
Four wires (circuits) are used on each O2 sensor: a
12–volt feed circuit for the sensor heating element; a
ground circuit for the heater element; a low-noise
sensor return circuit to the PCM, and an input circuit
from the sensor back to the PCM to detect sensor
operation.

NZ models only had one sensor (California models had two sensors, which the manual refers to).

[Steve_t647]

You should be able to remove the cat the amount of unburnt fuel (and this is what it is looking for) won't change before in or after the cat. To me it sounds like the Oxygen sensor stuck at lean position so have a look and see if you can find something there

I also found this (O2 sensor lean) may be tripped by a bad EGR system causing a rich condition, and the O2 sensor trying to compensate. The O2 sensor may still be good. The EGR assembly consists of two pieces, the valve and the vacuum transducer (round plastic unit with cylinder on top and both electrical and vacuum connections)

as to how to test the EGR I have no idea, in NZ we may not even have it as it is part of the smog control.

Anyway the O2 sensor controls the fuel mixture and will make it as rich as possible this may affect spark if you have a more open plug or slightly fouled one in one cylinder (explains the rich and the miss)

Good luck

[xj]

well the good news is that im doing some work on a friends commodore tomorrow, and at the same time the company auto sparkie is working on another staff members car..... so i'll waylay him and get him to have a shuftie for me.

Cheers for the advise and options chaps.