Engine swapping and exhaust

[Ronald Cookson]

I'm swapping my 5.7 vortec from my now wrecked 98 Sierra to a 97 Sierra body.the wrecked truck has a 3" exhaust with a new cat.the 97 had true duals with what are probably clogged or burnt out cats.if I swap the exhaust system what do I do about the extra O2 sensor?I could also swap out the ECM but again,what do I do about the extra sensor? Does it have to be deleted at a shop or will it be a non issue?

[richard wysong]

the 98 exhaust has 2 cats and 4 oxygen sensors if it's factory exhaust. if it doesn't have  that system drill a hole downstream and weld a bung to the pipe for the sensor

[Ronald Cookson]

The 98 Sierra is an SL with a single 3" exhaust pipe.this is what is actually in the truck.one cat,3 sensors.the truck I want to put into is a 97 GMC Sierra SLE with true duals,2 cats and 4 sensors but the cats are dead and most of it is rusted out.im just wondering what to do about that pesky extra O2 sensor connection that going to be left when I swap the exhaust out.short of swapping the ECM (which is an option)or even if I do,what will I have to do to make it run normally?

 

[KARNUT]

On the cheap I would use as much of the exhaust as I could. As well as anything else that matters from the wrecked vehicle to make a smooth transition. Once up an running modify to your taste. 

[richard wysong]

Weld a bung in the pipe downstream of the cat and use all 4 sensors is probably the easiest solution. An 18mm nut works as a bung. Not sure how that will affect fuel trims if at all because downstream sensors monitor cat efficiency. it may be possible to reflash the ECM to the 3 sensor system

[CamGTP]

If the 97 uses 4 o2 sensors, you need to keep using 4 o2 sensors. Also means you need to have two cats otherwise the check engine light will always be on and fuel mileage can decrease.

 

Only way around that is with tuning but the 96-97's aren't supported by much of anything for tuning.