3.6 Transplant issue with the o2 sensors.

[ike84]

You are correct, the precat sensors adjust the fuel mixture. As blue said, it is related to emissions. Performance is a big factor too though. If you lean out beyond 14.7, you get a more complete burn of the fuel (14.7:1 is stoichiometric but in the real world, especially with our style injectors, it does not result in a complete burn) which will result in more power but also MUCH more heat. This will damage cats, but it can also damage the motor. On the other hand, while you start to lose caloric efficiency as the mixture becomes more rich, you gain the cooling effect from unburned fuel and this helps the motor perform better at sustained high loads. That is why open loop should run a bit on the rich side. The excess fuel will damage cats though, so there's another tradeoff.

You said youre stuck in open loop? I don't see how that's possible if you're not getting a CEL. That's just not how the dme is configured to operate. Additionally, even if you have a ROW tune, the dme is still looking for the precat sensors. If they're not there, the dme will throw a CEL.

If you're really concerned about this, get an aftermarket AFR guage wide wide band sensor. Bosch makes an excellent sensor and the kits are not expensive or difficult to install. They mount into standard sensor bung (m18x1.5) and easy to install. I ran mine up the back side of the engine bay, under the intake plenum, and through the center console tunnel up to the dash, less than an hour start to finish. It will give you a much more meaningful number to use.

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[Kroggers]

Originally Posted by ike84

You are correct, the precat sensors adjust the fuel mixture. As blue said, it is related to emissions. Performance is a big factor too though. If you lean out beyond 14.7, you get a more complete burn of the fuel (14.7:1 is stoichiometric but in the real world, especially with our style injectors, it does not result in a complete burn) which will result in more power but also MUCH more heat. This will damage cats, but it can also damage the motor. On the other hand, while you start to lose caloric efficiency as the mixture becomes more rich, you gain the cooling effect from unburned fuel and this helps the motor perform better at sustained high loads. That is why open loop should run a bit on the rich side. The excess fuel will damage cats though, so there's another tradeoff.

You said youre stuck in open loop? I don't see how that's possible if you're not getting a CEL. That's just not how the dme is configured to operate. Additionally, even if you have a ROW tune, the dme is still looking for the precat sensors. If they're not there, the dme will throw a CEL.

If you're really concerned about this, get an aftermarket AFR guage wide wide band sensor. Bosch makes an excellent sensor and the kits are not expensive or difficult to install. They mount into standard sensor bung (m18x1.5) and easy to install. I ran mine up the back side of the engine bay, under the intake plenum, and through the center console tunnel up to the dash, less than an hour start to finish. It will give you a much more meaningful number to use.

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Installing an aftermarket AFR guage is a good idea. Can I install this in the bung I have for the post-cat o2 sensors, as I do not need these. Or do I need to install the AFR before the cat?

[ike84]

Originally Posted by Kroggers

Installing an aftermarket AFR guage is a good idea. Can I install this in the bung I have for the post-cat o2 sensors, as I do not need these. Or do I need to install the AFR before the cat?

The best position for a wideband sensor is in the header collector. Post cat exhaust is leaner than the gases in the header/collector. How much leaner depends on a lot of things. I know some guys will temporarily clip an afr sensor in the end of the tailpipe for reads while tuning. I don't have any direct experience with this technique by you may want to just try it and see how your reads look. If they look off, then I would install it precat if possible.

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