About 3 months ago I had the Cylinder head gaskets replaced at cost of £2000 on my Jaguars S Type 2004 2.5 ltr V 6 car I am getting multiple misfires code P0300 P0306 P1314 P1316 I know cylinder 6 is misfiring and probably cylinder 2. It could just be the coil packs as the spark plugs were replaced as part of changing the Cylinder head gaskets. The problem could also be the Valve Cover gaskets (pray to god it isn't them) letting oil into the spark plugs. My question is would the valve cover gaskets have been replaced as well, during the process of having the Cylinder head gaskets changed. If not how long does it take to change the valve cover gaskets and what would be a rough price. Thanks.

 

Don't panic! Step back from the ledge.

P0306 means reduced power output (not necessarily an ignition misfire) from cylinder #6. Codes P1314 and P1316 are related to P0306, indicating possible catalyst overheat and excessive emissions, respectively. What makes you think you've also got problems with cylinder #2?

Before worrying about the valve cover gaskets, I'd investigate if they are really needed. Most likely they should be new after cylinder head work, but who knows. More importantly, it may not matter. Pull the coil on #6 cylinder and look for oil contamination. If oil is present, yep, the valve cover seal around the spark plug well has failed. If not, your valve cover gaskets are not at fault.

If you need to replace the seal around the spark plug well, it's not fun but certainly not impossible. Are you doing the work yourself or having it done? I had one of these seals fail about 2 years ago and oil collected in the plug well and gave a misfire code and flashing Check Engine light. I think it took me about 3 or 4 hours to replace the gasket, but I work at a leisurely pace. On my '02 V6, naturally it was the difficult side that required removing the big intake plenum. No idea what a shop would charge.

If you do find oil caused the misfire, definitely replace the spark plugs. Once oil bakes onto the porcelain, it provides an electrical path to ground even after cleaning. In my case, the coil was just fine after a cleaning with electronic cleaner spray. I swapped in a known-good coil from the other side and moved the freshly cleaned one to the side with easy access in case the fault followed, but it never returned.

And just curious, but why were the cylinder head gaskets replaced? Has the car run okay since then? Is this a new problem? Or did it predate the new head gaskets?

 

Thanks for a great reply. I found the problem which was water in the spark plug well's all on the one side cylinders 2,4,& 6. I had this problem on my last Jag as well. It is caused by heavy rain and the water runs under the cowling and gets into the engine compartment then it drips down on the bank and runs into the well's. All sucked out and cleaned purrs like a kitten now. Having a sensor changed on Tuesday garage can have a look.

Head Gaskets were changed because i was losing coolant and the cylinder head gaskets had failed and you could smell the gases in the expansion tank hence having to replace them.

 

Water's not meant to get into the plug wells so something is not sealed to prevent it. Not sure what on the V6...

 

it is the windshield scuttle cowl which the rubber bit sits flush on the windscreen but mine has lifted on the UK Passenger side meaning water is leaking behind it. It then drips down onto bank 2 where cylinders 2,4 & 6. It then drips into the spark plug wells. Posted another thread asking for advice

 

I replied to other thread.

Remove scuttle cover, apply 2 beads black caulking along length of windscreen, reattach cover. Bob's yer Uncle!