* Loose or Corroded Connections: While changing the battery, you might have inadvertently loosened other connections, or the corrosion cleaning might have been incomplete. Check all battery terminals, the ground cable connections (especially to the engine block), and any other connections near the battery for tightness and corrosion. A loose or corroded connection can cause intermittent power issues, leading to poor running.
* Damaged Computer/Sensors: A sudden power surge or dip during the battery change (e.g., if you accidentally shorted something) could have damaged a sensitive computer module (like the PCM - Powertrain Control Module) or a sensor. This is less likely but possible. You might need a diagnostic scan to check for error codes.
* Unrelated Existing Problem: The bad running could be coincidental and unrelated to the battery change. The issue might have been developing before the battery change, and the weaker battery simply made the problem more noticeable. Symptoms that were previously masked (like a misfire or fuel delivery problem) might now be more apparent.
* Alternator Issues: While not directly related to *changing* the battery, a weak or failing alternator could be exacerbated by a brand new battery. A new battery might initially mask the problem, but then the alternator's inability to keep up with the battery's demands will lead to poor running.
* Incorrect Battery Installation: Ensure you installed the correct battery for your vehicle. Incorrect polarity (positive and negative reversed) could cause significant damage.
Troubleshooting Steps:
1. Check All Connections: This is the most likely culprit. Clean all terminals thoroughly and ensure everything is securely tightened.
2. Have it Scanned: Take your Expedition to an auto parts store (like AutoZone, Advance Auto Parts) and ask them to perform a free OBD-II scan. This will read any diagnostic trouble codes (DTCs) stored in the vehicle's computer that might indicate the problem's source.
3. Check the Alternator: Have your alternator tested to make sure it's charging properly.
4. Inspect the Battery Cables: Look closely at the battery cables for any damage.
If the problem persists after checking these things, it's advisable to take your Expedition to a mechanic for professional diagnosis and repair. They have the tools and expertise to pinpoint the issue more accurately.
