Jaguar Repair: series III xj6, coolant temp, vacuum hose

Question
The car runs, not well though.  The Catalytic converter, will be glowing red after 5 to 8 minutes.  I have changed everything I possibly could.  I wonder if the after market fuel injectors are the problem.  I have two different ECU and the results are the same.  cold start sensor, O2 sensor etc. all new.  I don't know where to go from here?  Your thoughts.

Answer
Hi Jim,
A glowing CAT means it is receiving raw fuel. You may run out of money replacing parts before you find the problem unless you test to find the problem and only replace the part that is bad.

There are many things that can cause excess fuel to go into the exhaust so you need to start from scratch.

1. Do a compression test FIRST. Throttle open, wires off of one side of the coil, at least 4 or 5 revolutions on each cylinder tested and the results MUST be 135 to 165 PSI on each cylinder and little difference between all cylinders.

2. Run a fuel pressure test. 32 PSI with vacuum applied to the pressure regulator and about 42 PSI with no vacuum.

3. Test all outside ways for fuel to enter the combustion chamber other than the injectors. Ie, vacuum hose on the pressure regulator, cold start injector. (replacing a part is NOT a test) Warm the engine first and then remove the fuel line from the cold start valve (injector) and plug the line and clamp it.

4. If you don't have access to a scope, you need to check each plug wire with an ohm meter and clean and check each spark plug. Carefully examine the inside and outside of the cap for carbon tracking.

5. Test the injection system coolant temp censor.
0 deg C. =  5.9 Kilohms
+20 deg C. = 2.5 Kilohms
+40 deg C. = 1.18 Kilohms
+60 deg C. = .60 Kilohms
+80 deg C. = .325 Kilohms
Note the progression in readings so you only need to test at a couple of temp settings to see that it is close to these figures.

6. Set ignition timing to specs.

7. Check that the throttle position switch ONLY connects pin #3 and #18 at close to full throttle.

8. The airflow meter is a major factor in fuel mixture however it is not easily tested other than to check that the flap is not stuck open or that the return spring on the flap door is not broken. This is a carbon variable resistor that feeds info to the ECU as to what volume of air is entering the engine plus a switch to activate the fuel pump.

Don't skip any of these tests. Let me know the results of each test.
Howard