While doing a leak down test I found out a coil pack has a huge crack on top and that the previous owner had mixed NKG plugs with Bosch plugs with the 4 prongs. What kinda damage can come from that?

 

It's too late now. Just change the coil and plugs and see what happens. Probably nothing.

The bigger problem is what else did the yutz do to the rest of the car? If he did one repair half assed you can bet he did more.

One problem with Jaguars are people who can't afford them buy them and then poor boy all the repairs and maintenance. We see on this list day in and day out.
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None. The individual cylinders don't know or care about their neighbours ignition system.

 

+1

 

Amen! One thing Ford-designed engines cannot tolerate are "hot" plugs. Notorious on F-150 and Crown Victoria 4.6 and 5.4 liter engines, platinum plugs cause heat related stress on the threads on the head. Failure mode is the plug popping out of the stripped socket, requiring an expensive insert being installed in the head.

There is little aftermarket for these cars. Spark plugs aren't a place to start. Who knows what fluids were put in? Or what other bailing wire and duct tape fixes were performed?

 

What brand of plug was the cracked COP attached to?

The problem with Bosch is that the plug they list for Jaguar V8
applications has a longer reach than the original NGK.

 

He doesn't have a Ford-designed engine or an engine like the ones you mention.

 

Whew! He dodged THAT bullet! So, the 4.0 is actually 100% Jaguar designed and produced? Even with the dreaded plastic timing chain tensioners?

 

100%? No idea, there may be some bolts from a parts bin? How would we know why would we care?

I don't see how it was Ford who chose the tensioners on the 4.0.

 

Nothing else on the car that I noticed was jimmy-rigged thank god but I can tell the oil wasn't replaced as often as it should have been and they used cheap oil....The plug that was on the cracked COP was the bosch.

 

The AJ series of engines are designed entirely by Jaguar. I do not know where the perception came from that Ford had any input, let alone the design. Jaguar tested many valve formations to arrive at the four valves per cylinder layout. The engineers also considered five valves per cylinder since Yamaha were successful with that layout.

Whether you think of them as good or bad, the AJ engines are of Jaguar design origin.

 

The impression is that the 4.0 is the very same design that was in like-year Thunderbirds (I never owned one) which were 32-Valve engines. These same engines were also in the Lincoln LS, and there was a posting on this forum about plastic tensioners failing on a LS engine....so the impression may be guilt by association?

 

The Lincoln LS and Thunderbird used the 4.0 S-type Jaguar engine, not something from Ford.

 

To add a bit more info. The story I heard was Jaguar had the V-8 designed but no money to put it in production until Ford got involved. To help with the initial cost Ford piggy backed the LS and thunderbird on top of the S Type engine production so in the begining quite a lot of V-8's were produced. Espcially compared to the newer Jaguar V-8 5.0L version.

It would be intersting if we could see what the production numbers were for the different Jaguar V-8 engines. Well there are some numbers here;

Jaguar AJ-V8 engine - Wikipedia, the free encyclopedia

and it looks like the 4.0/3.9 version production was about 250K units.

This is kind of interesting too.
THE JAGUAR AJ-V8 ENGINE / AJ6 Engineering
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