* Increased Fuel Vaporization: Heat causes fuel to vaporize more readily. If your fuel system has any leaks, loose connections, or a failing fuel pressure regulator, warmer temperatures can lead to increased vapor in the fuel lines. This vapor can disrupt the proper fuel/air mixture, causing a lean or rich condition, leading to rough running and potentially misfires, similar to a cylinder dropping out.
* Mass Airflow Sensor (MAF) Issues: The MAF sensor measures the amount of air entering the engine. Heat can affect its accuracy. An inaccurate reading can cause the computer to inject the wrong amount of fuel, leading to a rich condition (too much fuel) or lean condition (too little fuel). A rich condition is more likely to cause rough running, stalling, or the symptoms you describe.
* Ignition System Problems: Heat can stress components in your ignition system. Worn spark plug wires, a failing ignition coil, or even a weak spark plug may perform poorly under higher temperatures. A misfire in one cylinder will certainly feel like it's running on 5. This is particularly likely if the problem only surfaces in warmer weather.
* Coolant Temperature Sensor: The coolant temperature sensor informs the engine control module (ECM) about engine temperature. An inaccurate reading due to age or heat damage can cause the ECM to deliver incorrect fuel and ignition timing.
* Throttle Position Sensor (TPS): A faulty TPS can give inaccurate readings to the ECM, leading to improper fuel delivery, particularly noticeable under varied engine loads and temperatures.
In short: The heat doesn't directly *cause* the problem, but it exacerbates underlying issues in your fuel delivery, ignition system, or sensors. The symptoms you describe strongly point towards a fuel delivery problem (loading up/rich mixture) but a faulty ignition system could also manifest in a similar way.
Troubleshooting Steps:
1. Check for Vacuum Leaks: Inspect all vacuum lines for cracks or leaks. Heat makes leaks worse.
2. Inspect Spark Plugs and Wires: Check for wear, cracks, or corrosion. Replace as needed.
3. Test the Mass Airflow Sensor (MAF): This may require a professional scanner to check its readings against the expected values. Cleaning it with MAF sensor cleaner (following instructions carefully) is a cheap first step.
4. Check Fuel Pressure: Have a mechanic test the fuel pressure at the rail.
5. Inspect Fuel Pressure Regulator: A failing regulator can cause excessive fuel pressure, leading to a rich condition.
6. Check Coolant Temperature Sensor: This is often a fairly inexpensive part to replace if testing shows it's faulty.
7. Scan for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to read any stored codes. These codes will offer valuable clues about the potential cause.
It's best to take your Blazer to a qualified mechanic for diagnosis if you're not comfortable with these checks. They have the tools and expertise to pinpoint the problem quickly and accurately.
