Here's why the EGR valve is less likely and other possibilities to investigate:
* EGR Valve Function: The EGR valve recirculates exhaust gases back into the intake manifold. This lowers combustion temperatures, reducing NOx emissions. A faulty EGR valve usually leads to rough idling, poor fuel economy, and possibly a check engine light, but it's less likely to cause a consistent misfire across multiple cylinders like a bad ignition system would.
* More Likely Culprits After Replacing Ignition Components:
* Worn or damaged fuel injectors: A clogged or leaking injector can prevent proper fuel delivery to one or more cylinders.
* Crank position sensor (CKP): This sensor tells the computer the position of the crankshaft, crucial for proper timing of ignition. A faulty CKP can lead to misfires.
* Mass airflow sensor (MAF): This sensor measures the amount of air entering the engine. A faulty MAF can cause a lean or rich fuel mixture, leading to misfires.
* Ignition coil(s) (if it uses individual coils): Even though you replaced the distributor cap and rotor, if your 1995 5.7L uses individual coils for each spark plug, one of those coils could be faulty.
* Vacuum leaks: Leaks in the intake manifold or vacuum lines can disrupt the air/fuel mixture.
* Computer/ECM issues: While less common, a problem with the engine control module can cause misfires.
Troubleshooting Steps:
1. Check for error codes: Use an OBD-II scanner to read any trouble codes stored in the computer's memory. This is the most important first step. Codes will give you a strong clue about where to focus.
2. Inspect the fuel injectors: If you have the tools and knowledge, check for leaks or clogs in the fuel injectors. This often requires specialized equipment.
3. Check the crank position sensor: This usually involves using a multimeter to check its resistance and/or signal.
4. Inspect the mass airflow sensor: Clean it with MAF sensor cleaner (follow instructions carefully). A severely dirty MAF is a frequent source of problems.
5. Check for vacuum leaks: Carefully inspect all vacuum hoses and the intake manifold for cracks or leaks. Use a vacuum gauge to verify manifold pressure.
6. If it has individual coils, check those: These are more prone to failure than a distributor.
If you're not comfortable performing these checks yourself, take it to a qualified mechanic. It's safer and more efficient to let someone with the right tools and experience diagnose the problem. Simply throwing parts at it can be expensive and might not fix the underlying issue.
