1. Fuel Delivery:
* Fuel Pump: The most common culprit. Listen carefully near the fuel tank while someone cranks the engine. You should hear a whirring sound from the fuel pump for a few seconds when the key is turned to the "on" position (before cranking). If you don't hear it, the pump may be faulty or its relay is bad. You might also check the fuel pump fuse and relay.
* Fuel Filter: A clogged fuel filter restricts fuel flow. It's a relatively inexpensive and easy part to replace.
* Fuel Pressure: You'll need a fuel pressure gauge to check the pressure at the fuel rail. This requires a bit more mechanical knowledge and the right tools. A low fuel pressure reading indicates a problem with the fuel pump, filter, regulator, or lines.
* Injectors: While less likely to prevent cranking entirely (they usually cause running issues), faulty injectors could be a contributing factor if they aren't delivering fuel.
2. Ignition System:
* Distributor (if applicable): While you mentioned fuel injection, some 1990 Suburbans might still have a distributor. Check the rotor and cap for wear or damage. A bad ignition coil is also a possibility.
* Ignition Coil: This supplies high voltage to the spark plugs. A faulty coil will prevent ignition.
* Spark Plugs and Wires: Worn, fouled, or damaged spark plugs or wires can prevent a proper spark. Check for corrosion, cracks, or gaps that are too large or small.
* Crankshaft Position Sensor (CKP): This sensor tells the computer the crankshaft's position, vital for timing the ignition. A faulty CKP sensor will prevent the engine from starting.
* Camshaft Position Sensor (CMP): Similar to the CKP, a faulty CMP sensor can disrupt the engine timing and prevent starting.
3. Battery and Electrical:
* Battery: Test the battery voltage. A weak battery might crank the engine slowly, preventing it from turning over. A corroded battery terminal can also cause problems.
* Starter: A weak or faulty starter motor can crank slowly or not at all. This requires a bit more mechanical expertise to test or replace.
* Alternator: The alternator isn't directly involved in starting but if it's completely failed, the battery might be too weak to even crank.
4. Other Possibilities:
* Security System: Some vehicles have immobilizers or security systems that might prevent starting if a key isn't recognized.
* Computer Issues: A faulty PCM (Powertrain Control Module) is less likely, but possible. This requires specialized diagnostic tools.
Troubleshooting Steps:
1. Start with the basics: Check the battery, terminals, and fuses.
2. Listen for the fuel pump: Does it prime when the key is turned on?
3. Check spark: With the spark plug wires disconnected, have someone crank the engine while you check for spark at each wire using a spark tester or even just a gap between the wire and a grounded metal surface (be careful!). Observe the spark's strength.
4. Visual inspection: Look for any obvious signs of damage or loose connections under the hood.
5. Consult a repair manual: A repair manual specific to your 1990 Suburban will provide detailed diagrams and troubleshooting steps.
If you're not comfortable working on the vehicle yourself, take it to a qualified mechanic for diagnosis and repair. Providing more detail (e.g., any sounds the engine makes, warning lights on the dashboard) would help narrow down the possibilities.
