UK Car Repair: Misfire on 1997 Jag XJ6, ceramic catalytic converter, fuel pressure regulator

Question
QUESTION: I am recieving codes P1138, P0300, and P1313. The vehicle runs OK but I get a misfire going up hill and the check engine light illuminates. Sometimes the accelaration surges but it is intermittent. The mechanic changed the spark plugs, head gaskets, fuel pressure regulator, and tested the coils which checked OK. The mechanic is now lost!! I would appreciate any advice.

ANSWER: Hello Vidal, I have looked up your codes and they are;

P1313 Misfire Rate Catalyst Damage Fault - Bank 1.

P1138 Lack Of HO2S12 Switches- Sensor Indicates Rich.

P0300 Random/Multiple Cylinder Misfire Detected.

Firstly it would seem that your Catalytic converter is damaged, REPLACE IT. A cat removes HC (Hydrocarbons) by burning them up, If there is a misfire the HC goes through the roof and causes emense heat conditions inside the cat because HC is the unburnt fuel that is pouring into the exhaust system. This unburnt fuels causes massive damage to a ceramic catalytic converter monolith, This is a direct result of code p0300.
It would also seem that you also have a defective O2 sensor p1138 REPLACE IT. If your sensor constantly indicates rich, the ECU will alter the mixture to it's weakest point and you will get what is known as a lean misfire (not enough fuel in the fuel air mixture to burn up in the cylinder, but enough to burn up the cat).  

Here are some links for you which you may find useful

http://www.bba-reman.com/content.aspx?content=jaguar_xj_range_9697_engine_manage

http://www.jaguar-kat.de/obdii_fault_codes.0.html

http://www.engine-light-help.com/jaguar-check-engine-light.html


Hope it helps you Mark - GOOD LUCK

---------- FOLLOW-UP ----------

QUESTION: Also, just to let you know that you are probably right. Sometimes when I start my car, it sounds like coins a rattling underneath.

Answer
Hi Vidal, thanks or letting me know, I appreciate it. The noise you hear is a broken up monolith, DO NOT CHANGE THE CAT UNTIL YOU HAVE RECTIFIED THE MISFIRE. If you change it, the new one will go exactly the same way and it will be a waste of alot of money.