1. Fuel Delivery Beyond the Pump:
* Fuel Filter: A clogged fuel filter will prevent fuel from reaching the engine even with a new pump. Replace or clean this.
* Fuel Injectors (if fuel injected): If your Suburban is fuel-injected, the injectors might be clogged or faulty. This requires more advanced diagnostics, possibly needing injector cleaning or replacement.
* Fuel Pressure Regulator: This regulates fuel pressure; a faulty one could lead to low or no fuel pressure. It needs testing.
* Fuel Lines: Check for cracks or blockages in the fuel lines themselves. A visual inspection is crucial.
2. Ignition System Issues (Beyond what you've replaced):
* Distributor Cap: While you replaced the rotor, the distributor cap itself could be cracked or worn, leading to poor spark distribution.
* Ignition Module (or Electronic Ignition Control Unit): This component controls the spark; a faulty module prevents the coil from firing properly. This requires testing with a multimeter or a dedicated diagnostic tool.
* Cranking System: Ensure your battery is adequately charged, and the starter motor is engaging properly. A weak battery or faulty starter will prevent sufficient cranking speed to ignite the fuel-air mixture. Check battery voltage and starter operation.
* Timing: If the distributor is out of timing, you won't have proper ignition. This is more complex and usually requires specialized tools and knowledge.
* Pick-up Coil (in the distributor): This component sends signals to the ignition module; a faulty pickup coil can prevent spark. This also requires testing with a multimeter.
3. Other Potential Problems:
* Computer/ECM Issues (if applicable): If your Suburban has a computer-controlled ignition system, a faulty computer can cause numerous starting problems. This requires specialized diagnostics.
* Security System (if equipped): An aftermarket security system could be preventing the engine from starting.
* Sensor Issues: Various sensors (crankshaft position sensor, etc.) communicate with the computer to control engine operation. A faulty sensor can prevent starting. These require testing with a multimeter or a scan tool.
* Air Intake System: Blocked air filter, vacuum leaks, etc. will prevent proper combustion. Check for any restrictions or leaks.
Troubleshooting Steps:
1. Check for Spark: Remove a spark plug, connect it to a wire with the metal end grounded, and crank the engine. You should see a spark. If not, the problem lies in the ignition system (beyond the parts you've already replaced).
2. Check for Fuel: If you have spark, check if fuel is reaching the engine. Remove a fuel line (carefully!) and crank the engine to see if fuel comes out.
3. Check Battery Voltage: Use a multimeter to measure the battery voltage. It should be around 12.6V when fully charged.
4. Listen Carefully During Cranking: Listen for unusual noises from the engine, which might indicate a specific problem (e.g., a grinding starter).
5. Consult a Repair Manual: A factory service manual for your 1988 Suburban is invaluable. It will provide detailed diagrams, specifications, and troubleshooting guides.
If you're not comfortable performing these tests yourself, take it to a qualified mechanic. They have the tools and experience to diagnose the problem accurately and efficiently. Throwing parts at a problem without proper diagnosis is inefficient and expensive.
