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Oxygen Sensors and check engine light


Old 12-28-2017, 09:17 AM
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Oxygen Sensors and check engine light

So hopefully the smog test is going to be over where I live with the next election...or I could just move across the road...or even better out west! Anyhow...and a lot of ifs here...if the Cats go and I elect not to replace them and just straight pipe them, or if I put on a header which doesn't have the port for the one sensor, what do I do with the disconnected sensors? Likely disconnecting them or leaving them connected but not in the exhaust will trigger a ' Check Engine' light and that light is very annoying to say the least! How will this affect engine operation (performance/milage, etc)

What do guys do that swap newer fuel injected engines into first gens? (Yah I know wrong forum!)
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Old 12-28-2017, 09:39 AM
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You can't do without a functioning upper o2 sensor. The ECU absolutely requires it for fuel management. (This is the one that would require a bung in the header.)

The second O2 sensor that is behind the cat is only there to monitor cat efficiency for emissions requirements and it does NOT contribute to engine management.

You CAN do without that one, but I don't know how to turn the 'check engine' light out in its absence.
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Old 12-28-2017, 10:07 AM
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"I know it's the wrong forum, but I'll post anyway"

The above info is correct all the way. However, I highly recommend just putting in an aftermarket cat. They are generally smaller and more efficient, so the fumes will be cleaner. They also help with sound and backpressure.

The second O2 sensor isn't required, but it's nice to have. There are ways to emulate it.

If you're doing an engine swap, you should have some experience working with welding. If the exhaust doesn't have an O2 flange, add one. I re-used the old pipe just fine, with new hardware.

If you're going through all this trouble anyway, you can always just pull the light out of the socket if it's annoying
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