Here's a breakdown of likely culprits:
* Fuel pressure regulator: This is the most likely culprit. The regulator maintains fuel pressure in the system. If it's leaking internally, pressure bleeds off after the engine is turned off, making it impossible to restart without starting fluid (which provides the initial fuel boost to get it going). A faulty regulator will often show symptoms similar to what you're experiencing. Check the vacuum line to the regulator; a leak there would show similar symptoms.
* Check valve in the fuel pump or fuel rail: A check valve (sometimes integrated into the pump itself or located within the fuel rail) prevents fuel from returning to the tank after the engine is shut off. If this valve is failing, the fuel pressure will bleed back into the tank, leading to a no-start condition.
* Fuel injector problem (less likely, but possible): While less probable given the other symptoms, a problem with the injectors could also contribute. If the injectors are leaking fuel internally, it can slowly decrease the fuel pressure over time. The starting fluid jump-starts the process. This is less likely to cause the sharp pressure drop you see.
* Ignition system (less likely): Although you say it runs fine *while* running, a weak ignition coil or other component could be failing when the engine is cold, worsening with the low fuel pressure. This would need further investigation if other tests rule out fuel issues.
Troubleshooting Steps:
1. Fuel Pressure Regulator Test: The simplest and most likely thing to address first is the fuel pressure regulator. Have a mechanic or someone experienced test the pressure with a gauge after the engine has been shut off for several minutes. Significant pressure loss indicates a bad regulator. Replacement is relatively inexpensive and easy.
2. Check Valve Test (more advanced): Testing the check valve involves measuring pressure after shutdown and seeing how quickly it drops. A slow drop points to a failing valve. This often requires specialized tools or a pressure gauge with a long-term data logging capability.
3. Inspect Fuel Lines and Connections: Look for any signs of leaks, cracks, or loose connections in the fuel lines and fittings.
4. Inspect the Fuel Pump and Filter: Although you have 50 PSI while running, ensure your fuel filter isn't clogged. This restricts fuel flow even if the pump works well. A fuel pump pressure test might reveal a weak pump struggling to maintain pressure, especially after a long period of rest.
Important Note: Starting fluid is highly flammable and can be dangerous. Use it sparingly and in a well-ventilated area. It's a temporary fix, not a solution. Get this issue diagnosed and repaired as soon as possible. Driving with a faulty fuel system could cause further damage or even a fire.
