Where is the engine computer in a 1989 GMC 3500 4x4 454 pickup?

The Engine Control Module (ECM), often called the engine computer, in a 1989 GMC 3500 454 is typically located under the hood, near the firewall on the passenger side. However, the exact location can vary slightly depending on specific options and modifications. It's usually mounted to the inner fender well or a nearby bracket.

Because of the variations, the best approach is to:

1. Consult your owner's manual: This is the most definitive source.

2. Look for a rectangular box with numerous wires connected: The ECM is usually a fairly sizable black box.

3. Check online forums: Search for "1989 GMC 3500 454 ECM location" on forums dedicated to classic GM trucks. Pictures posted by other owners can be incredibly helpful.

Keep in mind that working on the ECM requires caution. Avoid touching its components directly and be mindful of disconnecting and reconnecting wires properly.