I am a new member and have posted in New member area introducing myself before posting my car issues.
I did try googling before checking here, and ALWAYS will before posting a repetitive post or atleast attempt to find a similar issue with a resolution.

Just bought my 1st 1996 xj6 and so far one problem after another. Car was clearly never taken care of, although cant be known until actually buying it and diving into it in depth.

A concern is when I went through checking plugs, which were missed gaped, I got to #5 pulled the coil out and was stunned to see water/ice up the coil hole. Pretty full too, is this common to find?
It idles and sounds like a miss, thats way I went through the plugs making sure they're correct. After gaping and cleaning, the car started and ran smoothly for about a minute then the miss came back. I have pulled codes and all but one shows misfire along with other codes, I'll save that for another separate issue thread. I am wondering if finding water in a coil hole is known occurrence.

 

The valve cover only has oil splash and vapor inside , no connection with coolant path , not even the O - ring on the bottom of the coil well as that seals the oil vapor

But then you have ........

Water vaper could be coming up from the very bottom of the head surface ( head gasket ) and going up the spark plug well to the top surface plain in the head , this would be inside the radius of the coil well O - ring

But I don't see the curved upper combustion chamber point where the spark plug enters has a seal / water path

The top head machined surface has the hole going further for the plug and outside of that is the sealing surface of the coil well O - rings

The Aft # 6 and 5 coil wires can be mixed easily

The coils have power " sitting " on them from the common White / Pink wire

The second wire is the timed ground provided by the ECU

# 6 Light Green / Purple , I see that in your pic

# 5 Light Green / Orange

The engine regulation will change to the O2 sensors ( close loop mode ) after the engine coolant gets to 88 C

The rear O2 sensors connectors on top can get cross connected , there is a map , the fwd O2 sensors are only for Cat efficiency code 420 and 430 but are a swapping option to to the rear

The spark plugs are a cheap Champian copper , no exotics

You are not at a head gasket change but this will tour you around the area that someone made

See minute 2 : 40 exactly for the coil well O - ring seal surface on the head

There are some precautions to reinstalling the valve cover

Interesting seal at minute 15 : 14 as this is the rear of the engine head I have not ventured

A engine mechanical manual is the file attached to the very very bottom

Your engine codes are on page 121 for the 96 - 97 AJ16 engine as this also covers the V- 12 and earlier AJ6 inline 6

The AJ16 starts on page 51

jagrepair.com/images/Training Guides/801S - 2000.pdf

 

Much appreciated Parker, you gave me alot of info. I should mention left side exhaust is riddled with gaping holes from the engine Y pipe back. And a missing tail pipe muffler.
Thankfully you guys have covered exhaust on this forum pretty good.
So my guess o2s will need replaced, and won't stress about the miss until I repair and replace the o2/exhaust.

But in the meanwhile waiting on mail order parts, your information gives me things to go over and make sure they're in order. Previous owner did put in RC12YC and I can see they're pretty new, probably before the for sale sign. Don't understand why he would replace 3 coils and not all but I have a full set on its way. THANKS AGAIN Parker I'll keep my progress posted on this thread.

 

Sorry, btw I also appreciate the manual link! If any pictures are needed I have many documenting the mess (including the worst exhaust welds I've ever seen), I didn't want to presume and keep posting pictures unless asked for them when needed.

 

The O2 sensors will get uncorrupted gasses as long as intact exhaust upstream of the rear sensors

A clogged / collapsed Cat is a different story

the most common leak is the manifold castings and loose donut gaskets on the downside pipe joint .

You can also have a crack at the 2 pipes coming together seams

The O2 sensors are the different titania based technology , they change resistance with O2 concentration

They will read about 3.5 volts DC on the return wire to the ECU when they are properly heated up

Expect 1 of the 6 new coils to be bad out of the box


Genuine Cylinder Head Less Valves-3.2/4.0 Litre (less 6.0 Litre) For Jaguar Xj 1995 - 1997 (from 720125 To 812255) (x300) Classic | Jaguar Land Rover Classic Parts

and

 

Parker thank you again.
Good news I rushed home after work (beating daylight) and did a compression check on all cylinders. 179-180 consistently. I ran through one at a time and then cycled back and compression checked a second time from the start.
Water could be from car wash or seller cleaning the engine. All plugs have the same burn on them, not whitish brown.
Having so many holes in the exhaust and there's 3 1in holes and 4 leaks from poor seller welds. Plus the crack in the factory weld 2 to 1 Y off the motor you mentioned.
All I can do now is wait for my exhaust pieces to show up, to see if theres a miss.
I did pull codes and every code for miss fire showed up and for every individual cylinder.

 

" I did pull codes and every code for miss fire showed up and for every individual cylinder."

Other than ensuring the face ( different then connector ) 0f the CKPS is clean of grime , would throw all cylinder's timing for ignition and fuel injection

The CKPS will read 1300 ohms as a basic meter reading between ECO connector socket Black 23 and Black 26

 

Another approach is all cylinders are mis fueling , leaks the culprit and can be vacuum leak . both of these causes over fueling or toward the - 25 range , target 0

I can't remember if the Y is before or after the Aft O2 sensors that only the Aft 2 are used for Short Term Fuel Trim ,

 

I'll check both of these out this weekend, just live to far from work to do anything in the daylight.
I'll get back with ya on results this Saturday.
Thank you for giving me directions and what to look at Parker.

 

I couldn't wait. Is it 1300om testing the ECU box correct?
pics attached. It needs to be cleaned for sure

 

Good news 1300 between 23 and 26 pins. I won't be seeing the new coils until next week
I'll have to wait for the weekend still to look for vacuum leaks.
Both upstream and downstream o2s (four total) are in the Y split before coming together into second set of catalytic converters

 

There are 2 vacuum systems on the engine with one isolated for the cruise control ( vacuum provided by an electric motor and vent control valve behind and lower from the left headlights )

On the engine system there is a line on the top of the fuel pressure regulator and what was missing on mine was a line under the intake manifold ( cylinder 3 ) to the EVAP valve

See page 60

801S TITLE (jagrepair.com)

There are 2 different versions vacuum systems on the engine and the tell is if the single large rectangle vaper canister just fwd of the left rear wheel or a 2nd vapor canister on the right including the left , no jacking required

 

Sorry for delay closure. I wanted to say Thank you again Parker, and bring this post to a end for others.

My miss was solved by replacing the coils. I check the ECU as suggested in above posts and voltage was dead on. Compression checked all cylinders and all good, water in sparkplug coil boot was from outside not motor head gasket.
​​I still checked for vacuum hose leaks and none detected. Once coils were replaced, no more check engine light, codes gone by reset, no miss in exhaust. All issues in this post have ended positively.