is it possible to piggyback o2 sensor signal`

My son and I recently swapped a 98 4.0 into our 01 xj. We finally got it to start and run. One of our last hurdles is the o2 sensors. The 01 motor used 4, 2 before and 2 after the 2 cats. The 98 exhaust only uses 2, 1 on the down pipe and 1 post cat.

Is it possible to run one sensor in each place and piggyback the signal to feed the 2 separate connections on the wiring harness?

I've heard some folks just ignore the post cat sensor(s). But the pre cat sensor is still important to make the beastie run right.

Not sure how much this helps but you can get a dummy o2 that sends the "correct" signal to ECU, not sure where I saw them though

But the answer to "piggy-backing" is no!

ptimhere said:

Is it possible to run one sensor in each place and piggyback the signal to feed the 2 separate connections on the wiring harness?

I've heard some folks just ignore the post cat sensor(s). But the pre cat sensor is still important to make the beastie run right.

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The 2001s are sensitive to any issues with the O2 sensor and the mini-cats.
I doubt it will ever run right without installing the mini-cats and the second set of O2 sensors. Until corrected, it will show a CEL at all times and, if your state performs emission tests, it will not pass.
If emission tests are not required, swapping to a 2000 Federal ECM should work, same engine and head but missing the mini-cats.

Getting a 2000 federal ecu is probably your best bet. I cant see a reason why splitting the signal from bank 1 sensor 1 to bank 2 sensor 1 wouldn't work. Defoulers can fool the 2000/2001 ecu successfully.

RCP Phx said:

But the answer to "piggy-backing" is no!

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Actually, it would probably work just fine. The O2 sensor is a voltage source and the ECU is essentially a high-impedance voltmeter. No different than piggybacking in a meter to diagnose it.

lawsoncl said:

Actually, it would probably work just fine. The O2 sensor is a voltage source and the ECU is essentially a high-impedance voltmeter. No different than piggybacking in a meter to diagnose it.

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Agreed. I have piggy backed a meter to an oxygen sensor used for ecu engine management, no ill effects. as ,long as you dont short it out, the voltage signal will be fine.



Now...
As for post catalyst senders, I assume they do not effect engine mixture, as that would not make sense to tune the engine mixture based on performance of a catalyst. I assume the
post catalyst senders are only used to sense catalyst health, and trigger a warning code. the pre catalyst sensors control the engine's mixture.

Is this correct? This is only based on my assumption.

Black1990jeep said:

Now...As for post catalyst senders, I assume they do not affect engine mixture, as that would not make sense to tune the engine mixture based on the performance of a catalyst. I assume the post catalyst senders are only used to sense catalyst health and trigger a warning code. The pre-catalyst sensors control the engine's mixture.
Is this correct? This is only based on my assumption.

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The ECM modifies the mixture to keep the catalytic converter(s) happy, using both the upstream and the downstream O2 sensors. All OBDII systems do this.
Using a scanner to watch the outputs of my 2001's four O2 sensors, the outputs vary from high to low, rich to lean continuously, as the ECM slightly adjusts the mixture to keep it near 14.7 AFR and the converters in range, as measured by the O2 sensors.
If the downstream O2 sensors do not respond as the ECM sees correct, a CEL will be set showing the converter(s) not working or its effectiveness is not up to standard.
If having a constant CEL is OK, fine do it. I want the OBDII system working and showing any other problems that pop up. Having a constant CEL, eliminates its usefulness.
If piggybacking is going to cause problems, it will show up quickly.

If the post catalyst sensor is used by the ecu to tune mixture, then a defective catalyst which will give a high oxygen content, so what will the ecu do to mixture. Keep in mind the upstream sensor will read the same regardless of catalyst performance. Will the ecu in the case of a dead catalyst try to tune the mixture via the down stream sensor or the up stream one? since the condition of the catalyst will alter the down stream sensors reading, i.e the catalyst condition effects the oxygen content, we cant allow that sensor to control the mixture. The mixture must be controlled by a sensor that sees the exhaust as burned, not after it has been altered by the catalyst. The down stream sensors will serve to indicate if the catalysts are performing correctly or not.