When cranking cold, tensioner rattles for about 2 to 3 seconds. Should I go ahead and have it repaired now or wait until it get worse. Also should I replace with a kit or parts? This vehicle has 70,000 miles on it. When running at a average speed sometimes it has a very,very slight miss in it. Thanks, Mike.

 

Belt tensioner? Have you checked, as it may be...

 

Welcome to the forum fmmsr45,

I've moved your question from General Tech Help to X350 forum. This is the place to post tech questions about your model.

Please follow this link New Member Area - Intro a MUST - Jaguar Forums - Jaguar Enthusiasts Forum to the New Member Area - Intro a MUST forum and post some info about yourself and your vehicle for all members to see. In return you'll get a proper welcome and some useful advice about posting to the forum.

Graham

 

There an SSM (dealer service message) regarding this, and it typically condemns the VVTs. I have had this on several client's XJs, and it is REALLY expensive to repair if you can't do it yourself as it involves replacing the VVTs.
Here is the meat/potatoes of the SSM:

• If the customer complains of a start up rattle lasting up to 3 seconds after a cold start only, one or both VVT units may be the cause. Follow the diagnostic process below:
• Verify the noise by running the engine so it is warm. After verifying noise, and once the engine is warm, turn off engine and allowing the vehicle to sit for a minimum of four hours, preferably overnight, before continuing.
• Raise the bonnet and remove the coil covers from both banks. One technician should then place one hand on each of the two VVT solenoids while another starts the engine taking care to keep clear of all moving parts.
• Listen for a rattle immediately after the engine fires and note whether a vibration is felt through either of the solenoids. If there is a rattle / vibration that occurs after the engine fires but stops after a few seconds then remove the cam covers from the engine.
• Examination of the VVTs will confirm a failure if the central portion of the VVT unit is not concentric with the sprocket leading to an uneven gap.
• It is possible to view any variation in the gap statically or by using a dial gauge on the outer diameter of the VVT housing. In this case runout in excess of 0.24mm indicates a failure.
• Or, alternatively, disconnect the crank sensor and crank the engine over for a few seconds to visually look for runout. The gap should be an even 2mm. Refer to attached picture for clarification (arrow indicates area to examine unit for uneven gap).
• If a VVT unit is deformed then only replace the affected VVT unit, do not replace both VVT unless there is a problem with each part. It is not necessary to replace the spider bracket, solenoid valve or chain tensioners unless a fault is found with them.
• Rebuild the engine and, if possible, run the engine to get it warm. Allow it to sit for a minimum of four hours and re-start the engine listening for any trace of recurrence of the start up rattle.

It is not an engine-damaging issue, so you don't have to address it immediately.