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shovel · 01-27-2010, 05:30 PM

Starting mid-year in 2000, v6 equipped S10's began to get dual inline catalytic converters... the rear one stayed in the same location and is the same part number, but a new smaller one was added a couple feet forward, immediately after the junction of the two cylinder banks' exhaust.
This "precat" as it's called serves only one purpose: it heats up more quickly due to being closer to the engine and made of a lighter material - so it reduces HC emissions during the first few minutes of driving before the main cat gets up to temp.

"a guy I know" shattered the catalyst inside his precat after partially crushing the enclosure with a rock on a particularly rough Arizona road, removed it entirely & blew out the main cat with a leaf blower (to remove debris from the damaged precat) and filled the gap with a section of straight pipe. No driveability difference was apparent, the ECU did not report a post-cat O2 sensor failure, and the vehicle produced nearly identical #'s on its next emissions test.

YMMV.

01-27-2010, 05:30 PM	#2 (permalink)
shovel Master EcoModder Join Date: Feb 2009 Location: Phoenix Posts: 593 Thanks: 106 Thanked 114 Times in 72 Posts	Starting mid-year in 2000, v6 equipped S10's began to get dual inline catalytic converters... the rear one stayed in the same location and is the same part number, but a new smaller one was added a couple feet forward, immediately after the junction of the two cylinder banks' exhaust. This "precat" as it's called serves only one purpose: it heats up more quickly due to being closer to the engine and made of a lighter material - so it reduces HC emissions during the first few minutes of driving before the main cat gets up to temp. "a guy I know" shattered the catalyst inside his precat after partially crushing the enclosure with a rock on a particularly rough Arizona road, removed it entirely & blew out the main cat with a leaf blower (to remove debris from the damaged precat) and filled the gap with a section of straight pipe. No driveability difference was apparent, the ECU did not report a post-cat O2 sensor failure, and the vehicle produced nearly identical #'s on its next emissions test. YMMV. __________________ Work From Home mod has saved more fuel than everything else put together.