* Fuel Delivery: This is the most probable cause. Even without spark, a flooded engine or a complete lack of fuel will prevent starting. Check these:
* Fuel pump: Is it running? You might need to listen near the fuel tank (carefully!) while someone tries to crank the engine. A fuel pressure gauge would give definitive proof.
* Fuel filter: A clogged filter restricts fuel flow.
* Fuel injectors: Are they delivering fuel? This requires more advanced diagnostic tools.
* Fuel pressure regulator: Could be faulty, preventing proper fuel pressure.
* Compression: With the spark plugs out, the engine should crank more easily. If it's unusually difficult to crank, you might have low compression in one or more cylinders. This could be due to:
* Worn piston rings: Allowing compression leakage.
* Burnt or damaged valves: Preventing proper sealing.
* Head gasket failure: Allowing compression to leak into the coolant system or elsewhere.
* Timing chain/belt: If the timing is significantly off, the engine won't fire even with fuel and spark. This is a more serious issue and requires experienced mechanical knowledge to diagnose.
* Engine Sensors: Although less likely, various sensors (crankshaft position sensor, camshaft position sensor, etc.) are essential for starting. A faulty sensor can prevent the engine from receiving the signal to start, even if it has fuel and compression.
What you should do:
1. Check for fuel: Listen for the fuel pump. If you have a friend, have them try to crank the engine while you listen near the fuel tank. If you hear nothing, the fuel pump is the most likely suspect.
2. Check the fuel filter (if easily accessible).
3. Have a compression test performed. This will tell you if you have adequate compression in all cylinders.
4. (Advanced) Check fuel pressure: Requires a fuel pressure gauge and understanding of how to use it safely. This is the best way to diagnose fuel delivery problems.
Before you go further:
* Don't keep cranking the engine repeatedly without spark plugs. This can damage the starter motor. Only crank for a few seconds at a time, with pauses in between.
* Consider professional help. If you're not comfortable with automotive diagnostics, it's best to take the van to a mechanic. Multiple issues could be at play, and some require specialized tools and knowledge to diagnose and repair.
The fact that it cranks but doesn't start without spark plugs strongly suggests a fuel delivery or compression issue is the primary culprit. Start with the easier checks (fuel pump, fuel filter, listen for the fuel pump) before tackling more complex diagnostics.
