Jaguar Repair: XJ6 Vanden Plas hard cold starting, vanden plas, intake horn

Question
Howard,

  It takes many tries to start my 84 Vanden plas when the engine is cold, especially when it's cold outside, close to freezing.  I replaced the usual maintenance items like coil (old one was leaking oil), air filter, spark plugs & wires, dist cap and rotor and Oxygen sensor.  Could it be something like the thermo time switch or cold start valve or temp sensor and how could I test it ?

Many thanks,

Steve.

Answer
Hi Steve,

The first test is to take a can of starting fluid and when you know it is going to be difficult to start, spray starting fluid into the intake horn to the air filter. If it starts up then you have ruled out Ignition problems.

Next test is to check for power on one of the two wires going to the cold start valve while in the "Start" key position. Next test the other wire for a good ground (stone cold engine)

If you have a power in the "Start" position and a good ground, remove the cold start valve and connect it back up to the fuel supply and the wires plugged in and point the valve into a bottle or can and note if it sprays fuel in a fan pattern. If it just dribbles or produces a straight stream test fuel pressure. (aprox 42 PSI not running) If fuel pressure is correct replace the valve.

If you have no power or a good ground you must refer to your wiring diagram and trace the wiring problem to it's source problem.

If you had no ground, test the thermo-time switch. (usually the front one in the coolant rail.)

The thermo-time switch receives power from the "Start" position from the starter relay which starts an electric heater in the switch which when warm will break the ground of the cold start valve. The coolant heat will also brake the ground of the cold start valve. Thus the switch is a temperature and time breaking ground of the cold start valve.

If you don't have a good diagram of the system, go to my web site and copy the one I have posted for the XJ-6.  http://mg-tri-jag.net/XJ-6InJect1.jpg

Any problem with the engine, Ignition or injection can make it difficult to start, especially when cold. This is made more of a problem when several failed attempts are made to start the engine due to the "Time" factor built into the switch. I have received cars that the customer had bypassed the switch and grounded the cold start valve, but this can be very dangerous to the engine and the exhaust CATs and possible ring damage to the engine. The system works very well when each part is operating so it is always best to just correct the system.

Let me know if you still have a problem.

Howard