* Clogged or Faulty Fuel Injectors: This is the most likely culprit. Fuel injectors can become clogged with debris or varnish over time, preventing fuel from spraying into the cylinders. They can also fail internally, even with pressure at the rail. Testing the injectors is crucial – you need to verify each injector is actually pulsing and delivering fuel. This often requires specialized tools or a mechanic.
* Injector Wiring or Electrical Connections: Even with fuel pressure, the injectors won't work if they don't receive the correct electrical signal. Check the wiring harness for damage, corrosion, or loose connections at the injectors themselves and the engine control module (ECM). A faulty ECM could also be preventing the signal.
* Low Fuel Injector Pulse Width: The ECM controls how long the injectors stay open (pulse width). If this is too short, insufficient fuel will be delivered. A diagnostic scan tool can check this parameter.
* Vacuum Leaks in the Intake Manifold: A significant vacuum leak can disrupt the air/fuel mixture, preventing proper combustion even if fuel and spark are present. Inspect the intake manifold, gaskets, and vacuum hoses for cracks or leaks.
* Faulty Fuel Pressure Regulator: While you have pressure at the rail, a faulty regulator might not be maintaining the correct pressure during the injection cycle.
* Blocked or Restricted Fuel Injectors (Internal): The fuel injectors might not be fully blocked but could have internal restrictions hindering fuel flow. This is difficult to diagnose without specialized equipment.
* Incorrect Timing: While less likely given you have spark, significantly off timing could prevent proper combustion even with fuel present.
Troubleshooting Steps:
1. Verify Fuel Injector Operation: This is the most important step. You need to confirm that fuel is actually being sprayed into the cylinders. This may involve using a noid light (to check for electrical pulse) and possibly removing the injectors and visually inspecting them for spray pattern while they are energized.
2. Inspect Wiring and Connections: Carefully examine all wiring related to the fuel injectors and the ECM. Look for any signs of damage, corrosion, or loose connections.
3. Check for Vacuum Leaks: Use a vacuum gauge or listen for hissing sounds around the intake manifold and vacuum hoses.
4. Check Fuel Pressure During Cranking: Use a fuel pressure gauge to monitor fuel pressure while the engine is cranking to ensure the pressure remains consistent.
5. Diagnostic Scan Tool: If you have access to a scan tool compatible with your 1989 Jaguar XJ6, it can help diagnose issues with the ECM, fuel injectors, and other sensors. This is often the most effective way to identify the problem.
Without specialized tools and knowledge, diagnosing this problem can be challenging. It's highly recommended to consult a mechanic specializing in classic Jaguars or vehicles with fuel injection systems. They'll have the tools and expertise to properly diagnose and repair the issue.
