Change exhaust from dual cats to single?

[Mr Rush]

Ok. I have a question about o2 sensors and catalytic converters. I have a 97 5.7 1500 4x4. The exhaust is shot beyond simple repair. The previous owner did some hack job welding. It's still in the factory configuration. I have a 99 OBS 5.7 vortec with a new exhaust system the previous owner paid to have installed. This exhaust has a Y-pipe pre-cat, so its a single cat system with only one post converter o2 senser. Since mine has the two pre-cat and 2 post-cat sensors, what would be the best way to put the new system on my 97 truck? Could I just add both my post converter o2 sensers somewhere after the converter? Thanks for the help!

 

[YukonKyle]

This is exactly what I am thinking of doing. How did it work out?

 

[kennythewelder]

The rear 02 sensors, tell the ECM, that the cats are working. Without this info, the truck goes into limp mode. The sensors there selfs dont know where they are, its the connector that says sensor 2 bank 2, or whatever. IMO, you should be able to put both the rear sensors after the cat in the exhaust pipe, and that should work. as long as the rear sensors see less carbon in the exhaust gas than the front sensors are seeing, that should work. Also there are 02 simulators that can be installed to fool the ECM and give it the signal it is looking for. All of this being said, why do you want to go to a Y pipe system? A X pipe will have the same effect, and you wont have to replace the whole exhaust system, more or less.

 

[Supercharged111]

No rear O2 sensors will not put the truck into any sort of limp mode. The only way I know that they alter the engine's performance is by adding fuel when they detect a cat overtemp condition.

 

[kennythewelder]

No rear 02 sensors will trip a CEL hence limp mode, without tuning them out, or using 02 simulators.

 

[Supercharged111]

No rear 02 sensors will trip a CEL hence limp mode, without tuning them out, or using 02 simulators.

Yes, the check engine light comes on. No, there is no limp mode. You'll just fail an emissions test with the light on, and if you run it that way long enough the cat will probably plug itself and you'll have a gutless truck.

 

[kennythewelder]

With a cel light, the truck is in a diminished performance mode. You will loose power and MPGs. Dont believe me, just unplug your rear cats and see for your self. I know, I fought this when I gutted my cats, untill I made some 02 simulators.

 

[454cid]

I've always been told the rear O2's don't change tuning at all. GM eliminated them from the 2000 454's.

 

[df2x4]

I've always been under the impression that the rear O2 sensors shouldn't effect the way the truck runs under any circumstances. It's common practice to disable them in the tune (or fool them in various ways like Kenny mentioned) if you don't want to run cats. I thought that the front O2 sensors handled all of the fuel adjustments.

@Supercharged111 This is the first time I've heard anyone mention that the rear O2s are capable of detecting an overtemp situation, how'd you figure that out?

I've definitely driven my '97s a few times with CELs for the rear O2 sensors, I don't recall any noticeable loss of power or anything that resembled a limp mode.

 

[kennythewelder]

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The front 02 sensors, adjust fuel trim ratio. The rear 02 sensors read the same thing, as the front sensors but the ECM looks at the difference between what the front 02 sensors are reading, and what the rear 02 sensors are reading, and tell the ECM that the cats are working. Without the rear 02 sensors you get a CEL. Reason being, emission regulations. Without cats, you engine puts out more C0. The cats help scrub or burn off excess C0 emissions from the exhaust gases. This can be deffeted with a tune, or simulators on the rear 02 sensors. When I gutted my cats, I had a CEL. I lost ,1.5 MPGs and some performance. When I made my simulators, I gained all that back. They have been on my truck over 5 years now. Here are pics of my simulators. You can see in the first pic, there is a little piece of cat honey comb meteral that I ground down, and cut to fit inside the spark plug spacers. This way the exhaust gas passing through a piece of cat meterial before it gets to the 02 sensor.