1. Weak or Failing Relays: This is the most likely suspect given your description. While pushing on the relays might temporarily restore contact, the relays themselves are failing. Replace the following relays:
* Ignition Relay: This is crucial for the engine's operation. A weak ignition relay can cause intermittent stalling.
* Fuel Pump Relay: A failing fuel pump relay prevents fuel delivery, leading to immediate stalling.
* Main Power Relay (sometimes called the Powertrain Control Module (PCM) relay): This relay controls power to the PCM and other essential systems. A faulty one can cause widespread problems including stalling.
Important Note: Don't just replace the relays you suspect. It's best practice to replace *all* three relays mentioned above as a set. They often fail around the same time due to age and heat.
2. Corroded Relay Connections: Even if the relays themselves aren't completely failed, corrosion on their sockets or wiring can cause intermittent power loss. Carefully inspect the relay sockets for corrosion. Clean them thoroughly with a wire brush and electrical contact cleaner. Pay attention to the ground connections as well.
3. Wiring Problems: Worn, frayed, or loose wiring in the power supply circuit to the relays can also cause intermittent contact. Inspect all wiring leading to and from the relays. Look for any breaks, chafing, or loose connections. Repair or replace any damaged wiring.
4. Crankshaft Position Sensor (CKP Sensor): A faulty CKP sensor prevents the engine from knowing its rotational position, leading to stalling. This sensor is a common culprit in stalling issues. You might not be able to fix this by pushing on relays, but it's worth testing if the relay replacement doesn't fix the problem.
5. Mass Airflow Sensor (MAF Sensor): A dirty or faulty MAF sensor can provide incorrect air/fuel mixture data, leading to erratic operation and stalling. Cleaning the MAF sensor (with MAF sensor cleaner – *not* general purpose cleaner) might help, but replacement might be necessary.
6. Battery and Cables: While less likely given the relay behavior, a weak battery or corroded battery cables can cause voltage drops leading to stalling. Check the battery voltage and cable connections for corrosion.
Troubleshooting Steps:
1. Visual Inspection: Carefully inspect all relays and their sockets for corrosion and damage.
2. Relay Replacement: Replace all three mentioned relays (Ignition, Fuel Pump, Main Power).
3. Wiring Inspection: Carefully inspect the wiring harness leading to and from the relays and other components mentioned above.
4. Battery and Cable Check: Inspect the battery and its connections for corrosion. Check battery voltage with a multimeter.
5. Diagnostic Scan: Take your Blazer to an auto parts store (many offer free diagnostics) or a mechanic to get a diagnostic scan. This can reveal fault codes stored in the PCM which will point directly to the problem. This is the most efficient way to diagnose the issue.
Important Safety Note: Working with automotive electrical systems can be dangerous. If you are not comfortable working with car electrical systems, take your Blazer to a qualified mechanic. Improper repairs could lead to further damage or injury.
