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Greetings all, I’ve checked for a thread addressing this issue and have yet to find one so I’ll ask here.

I got my mr2 not long ago and immediately found out about the precats, mine were in bad condition And I just wanted them off so I installed a header and down pipe assembly, thus completely straight piping the car. The new header/downpipe has slots for all three o2 sensors, however the two upstream sensor installation points are farther downstream then the original header so the wires don’t reach, the third and final sensor went on just fine. After splicing the old o2 sensors and extending the wires I installed them and it made the engine sputter and want to die when I accelerated. I trashed those sensors and ordered new ones with proper extension harnesses, they did the exact same thing.

I’m being told to either order o2 sensor simulators or try and have the ecu remapped. Any help would be appreciated. Thank you.
 

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I don't know who is giving you advice like that - in the future just ignore anything they tell you.

You cannot run your car on O2 simulators. It will run even worse. Functioning O2 sensors are crucial to the operation of any modern electronic fuel injection (EFI) car.

Hundreds if not thousands have deleted their precats and operate their car without any problem and without any remapping of the ECU - which would not be possible anyway.

You probably have some kind of installation error. Post some pictures of your setup and the parts you've used.
 

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@MerryFrankster Thank you for the reply. I found the link below and this is most certainly the issue. it would seem I’ve gotten myself into a world of trouble unknowingly. Both o2 sensors have been placed into a single pipe downstream. I’ll have to do more research on the splice method below, I don’t have the resources to fabricate the o2 sensor bungs into the header.

 

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This is a situation where you are damned if you do and damned if you don't.

Putting the O2 sensors upstream on single runners is far less than ideal because it leaves two cylinders completely un-monitored and I think by now everyone has woke up to the fact that this is not recommended.

Splitting the signal from one O2 sensor seems to work on some cars but it does not work on others and nobody knows why. I ran the split signal successfully on my car but others have reported errors when they do. It is worth trying, the wiring is fairly straightforward and you can use a discarded O2 sensor as the "fake" resistor.

I don't know if anyone has ever tried putting one O2 sensor on a runner and the second one after the merge. This could be an interesting solution.
 

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Discussion Starter #5
This makes sense, in terms of leaving cylinders unmonitored. I will attempt the single o2 sensor split you said you are currently running in a couple days. what advice would you offer before attempting it?
 

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Use good solid butt connectors or barrel splices and a good solid crimping tool. If you want to solder be advised that O2 sensor wire is not the greatest for soldering. Many problems arise because of improper wire connections.
 

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...Splitting the signal from one O2 sensor seems to work on some cars but it does not work on others and nobody knows why....

...I don't know if anyone has ever tried putting one O2 sensor on a runner and the second one after the merge. This could be an interesting solution.
I think that it is because the two channels never read exactly the same signal. The two channels are read in sequence, and means that there will be some random difference between the two. Hence, the two channels will diverge in a random walk without any additional information. If that is the case, then resetting the fuel trims should recover basic operation.

It should be better than a single sensor. At least it is theoretically stable.
 

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@MerryFrankster Thank you for the reply. I found the link below and this is most certainly the issue. it would seem I’ve gotten myself into a world of trouble unknowingly. Both o2 sensors have been placed into a single pipe downstream. I’ll have to do more research on the splice method below, I don’t have the resources to fabricate the o2 sensor bungs into the header.

@zrretz I have an idea for you. Use a Celica 1zz ECU. This ECU uses a single O2 sensor, instead of two. You will have a very limited amount of wiring to do on the ECU connector, namely, move one O2 sensor wire and one ground wire. It is similar to doing the wiring for the 2zz swap, but without the lift OCV and pressure sensor.
 
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