Tier 4, EPA emissions & your chipper's cat

The catalytic converter on your chipper isn't just there to quiet the exhaust — it's part of how the engine meets federal emissions standards. Here's the plain-English version of how it all ties together, and what a rebuild does about it.

Why chippers have catalytic converters

Wood chippers run off-road (nonroad) engines, and those engines are held to EPA emissions standards — the same push that brought "Tier 4" to diesels. The catalytic converter is a key emissions component: it converts the nastier products of combustion into cleaner gases before they leave the exhaust. When it's healthy, you never think about it. When it fails, it can affect both how the machine runs and how it reports emissions.

Why a plugged cat triggers a derate

On newer Tier 4 machines the engine watches exhaust backpressure and catalyst performance. As the converter loads up with carbon and restricts flow, the machine sees it — and to protect the engine and stay within emissions limits, it can throw a fault code or drop into a reduced-power "derate." Owners often feel the derate before they'd ever notice a performance change: the machine simply won't make full power until the restriction is cleared.

What a rebuild restores

A D&S rebuild puts a fresh catalyst substrate into your original housing, so the converter flows and functions the way it should again — built to meet EPA emissions standards. You get the emissions performance back and the derate cleared, without paying for a whole new OEM unit. Every rebuild is backed by a warranty against manufacturing defects.

Rebuild vs. replace, side by side →

Why not just delete it?

It's tempting to think pulling the converter off is the easy fix — in practice it usually backfires. Running the engine without its converter can push it out of spec and cause running problems over time, and on the newer Tier 4 machines it often doesn't even work: the engine watches the converter, so with it gone it can throw a fault or drop straight into a reduced-power derate. (There are warranty and compliance downsides as well.) A rebuild avoids all of that — you get the power back with the cat still doing its job.