Hi I have been fighting misfires on my XJ6 always on bank 2:
I have replaced IMT o rings all intake upper and lower seals, PCV valve and Plugs.

Still had misfires all on bank 2 so have now done compresion test on that bank and get following readings:
Dry on cold engine
Cyl 2--50PSI
Cyl 4--50PSI
Cyl 6--100PSI
Wet on cold engine gives same readings?

I this a sign of Cylinder Head Gasket failure on 2 and 4?

Any other tests I should do?

 

If you are having the same readings both dry and wet, you may have an issue with one of the valves or the head gasket.

Has the engine ever been overheated, or driven whilst low on coolant?

 

Thanks NBCAT
Not sure only had it since June, No overheating in my days with it but?
But a little more background: bought it with LPG install had misfire/rough idle issues.
So ripped the LPG out to focus on Petrol running and now wishing I had done compression checks first!!
I have had low vacuum readings since getting it and chased the usual vac leak areas.

Could it be VSR caused by the LPG?
or both gasket and valves? given identical readings on 2 and 4?

 

Just checked and it seems that you have adjustable shims on this engine so might be worth checking the clearance on these cylinders first

 

yes good shout will try a valve clearance check tomorrow the engine will certainly cold enough!! hasnt ran since yesterday with plugs and coils off.

 

If there is excessive tappet clearance against a camshaft, a valve may be bent or there are carbon deposits along the valve stem preventing it from fully closing.

It is also possible that there is a burned valve face or seat causing a loss of compression.

Download the JTIS Workshop Manual prior to proceeding with any engine disassembly so you can have the correct tools on hand and follow the procedure as outlined. The Workshop Manual can be downloaded from this forum, or purchased from a vendor via the Internet.

 

Hi
Done the valve clearance check and got following:

Inlet 1-6 all reading less than 0.05mm

Exhaust 1-0.13,
2-0.12,
3-0.13,
4-less than 0.05
5-0.12
6-less than 0.05

0.05 was smallest feeler I had at 0.002"
Jtis Gives:
Valve Clearances (cold)
Intake Exhaust
V8 Gasoline 0.18 – 0.22 mm 0.23 – 0.27 mm
V6 Gasoline 0.175 – 0.225 mm 0.325 – 0.375 mm

I guess this was caused by LPG?
Will check A bank and do full shim set up and see how it runs

Thank you all for help

 

Do a cylinder leakage test. You can then chase down leakage from the intake or exhaust valves, and short of disassembly, which you will need to do to see if the valves or seats are burnt. I'm not sure Jaguar ever intended or designed into the gas engines the properly hardened seats and valves, or the correct ignition timing mapping that are required to live under LPG use.

 

Have ordered up Gaskets and seals to do Cylinder head swap on both heads, assuming the other head has VSR also.

Waiting for ebay auction for pair of heads intact and will do static valve clearance check before fitting.

Will try to upload pictures of old heads when off.