as far as the timing chain adjusters are concerned, i have the aluminum tensioners installed,,this was the first thing i checked when i purchased the car indeed both of my xk8's.
however, i do have one niggling problem i was reminded of today and as you guys were so hot at my non start problem i thought i would run it by you all.

in high gear cruising, if i floor the throttle it miss fires and i can hear a popping in the exhaust like fuel is reaching the cats and igniting every time it miss fires, if i down shift it will stop popping and miss firing and accelerate as it should.
so to recap. under heavy load in top gear at heavy throttle it miss fires and pops in the exhaust.

the fuel pressure is 45 psi running, so i think as i can hear it pop in the exhaust i would think this is not fuel related.

any help please would be wonderful, thanks John.

 

Lean misfire? Coil-on-plugs breaking down under load? Spark plug gap too wide?
MAFS fault causing lean run?

Many diagnostic scanners can read data so you can see fuel trim (STFT and LTFT).
You can watch MAFS and other parameters.

more info for diagnosis.

bob

 

i will scan it tomorrow !
it feels like it turns off and i can't see all 8 coils going down at once.
idle is stable.
most fords i have worked on will run happily on just the cam position sensors but won't start without the crank sensor, i wonder if the cam position sensor is going away?

 

This is a bit of a longshot, but there are two ignition modules under the windshield wiper area- try swapping them out and see if the issue switches sides

 

scanned the car today and as expected, no DTC's drove the car up the side of the grand canyon and found it difficult to create the fault but i did at just over 90 mph, bump bump bump.

live data from the fuel trim was almost identical from side to side fluctuating between "short term -1.6 tp +3.2" with bank 2 slightly slower to react and long term around +6.2 to +5.6 dependent on whether i was on the throttle hard or feathering it a bit.

as to the modules, if i knew which side of the engine was miss firing that would be o.k. but when it only does it at speed without setting a DTC i would say its impossible to tell, maybe someone could lend me two modules for substitution or eight coils to substitute, see without a code it is hard to diagnose.

there is no way of looking at the coil KVA's so if i have a bad coil, moving it around would have the same result, a miss fire at speed up hill under hard throttle.

my mind is back on the fuel, i will need a longer hose for my gauge so i can see what the pressure is at 90 mph when it starts to cough.

and yes i have fitted a new fuel filter.

if you never drove up steep hills on a freeway at speed, you would never know there was a fault.

keep up the good work guys, we'll get it beat i'm sure, thanks.

 

as far as the ignition goes, we could rule out things like power supply, as a fault in those would be evident at any speed, that leaves only things that could break down.

ignition module
coils
spark plugs
cam position sensor

fuel could be a flow problem as the pressure is good and with the return line capped the pump makes almost 100lbs at idle but if the flow from the pump is low it could starve the engine at speed, i need to test the pressure when the fault is occuring at speed.

 

motorcarman, i think you may by close to the problem, i ordered some coil boots and new plugs on the basis that if the coils or a coil was bad, it would set a code.

there fore i believe the spark is still being produced by the coil, it just is finding the path of least resistance when the mixture is lean and that aint across the plug gap so either the plugs are bad or there is a tracking path to ground from the business end of the coil.

i had to replace some vc seals as oil was getting to the plugs so we may have a tracking problem.

 

fitted new spark plugs and a boot kit from rockauto.
tested and all is fixed!!!!!!!!

YIPPPEEE.

again, thanks to all who posted.