1. Identify what the ECM B fuse powers:
Consult your owner's manual or a wiring diagram specific to your 1991 S10 Blazer. This is the *most crucial* step. The ECM B fuse doesn't power the entire ECM; it powers specific components related to the ECM's operation. Knowing precisely what circuits it protects will drastically narrow down your search. Common possibilities include:
* Specific sensors: Oxygen sensor, crankshaft position sensor, coolant temperature sensor, mass airflow sensor (MAF), etc. A shorted wire or a faulty sensor can draw excessive current.
* Ignition system components: Parts of the ignition system might be on this circuit.
* Fuel injectors (possibly): While less likely to be solely on this circuit, a problem here could contribute.
2. Visual Inspection:
* Check the fuse holder: Make sure the fuse holder itself isn't damaged or corroded. Clean the contacts if necessary.
* Inspect the wiring harness: Carefully examine the wiring connected to the components powered by the ECM B fuse. Look for:
* Chafed wires: Wires rubbing against metal parts can create shorts.
* Broken insulation: Exposed wires touching each other create shorts.
* Corrosion: Corrosion on wire connectors can increase resistance and cause overheating and shorts.
* Loose or disconnected connectors: Improper connections can lead to arcing and shorts. Pay special attention to the connectors for the components listed above (sensors, etc.).
3. Systematic Testing:
Once you know what the ECM B fuse powers, test each component individually:
* Disconnect the components one by one: Start with the easiest to access components on the ECM B circuit. Replace the fuse, connect the rest, and start the engine. If the fuse doesn't blow, the problem lies in the disconnected component or its wiring. If it still blows, continue disconnecting components until you isolate the culprit.
* Use a multimeter: Test each component's resistance and voltage to determine if it's functioning correctly. A shorted component will show a very low or zero resistance. Compare your readings to factory specifications from a repair manual or online resource.
4. Professional Help:
If you're not comfortable working with automotive electrical systems, take your Blazer to a qualified mechanic. Improperly diagnosing and fixing electrical problems can lead to further damage or even fire.
Important Considerations:
* Never replace the fuse with a higher amperage fuse. This is extremely dangerous and will likely cause more damage.
* Turn off the ignition before working on the electrical system.
* Disconnect the negative battery terminal before starting any significant work.
By systematically investigating the circuits powered by the ECM B fuse, you should be able to pinpoint the source of the short and resolve the issue. Remember safety first!
