Steven,
The AJ6 and AJ16 engines were a bit more reliable than the older
v12 engines, and much less of a challenge to work on.
The AJ6 and AJ16 engines are included in the XJ40 lists,
since that covers about 99% of the XJ40 cars, and all of the
X300 cars I think…
Even if they split the engines up, half the mail on the XJ40
list would likely stay engine and trans related, as things
interact between the engine, trans, and body controls.
In the US, the 1987 to 1989 cars used the 3.6L, 1990 to
1994? used the 4.0L, and then the AJ16 came out.
The AJ16 is basically the same engine, but many small changes
were made, different cams, different intake manifold,
egr setup is different I think, another 10 or 20 HP output,
and the different cam cover…
The AJ16 is likely OBD2…
Its hard to separate the differences Jaguar made year to year
with just the engine change…
I don’t know if you would notice a difference between the
4.0 AJ6 engine, and the 4.0 AJ16 engine…maybe a little
smoother at idle with the AJ16.
I have driven both, and did not notice any real difference.
You WILL notice a difference in the 3.6L engine, partly
because its got a different transmission, and it seems
much smoother in comparison to the 4.0 engines.
Not that the 4.0 is a cement mixer, but the 3.6 must have
been designed for incredible balance, and when they increased
the size to 4.0, they lost some balance.
The Jag-lovers web page may have some info on it, maybe
in the brochures for the new models…
Brett
1990 XJ6
So the XK and V-12 engine folks have their own mailing
lists. How come there is no AJ40 mailing list? Or are the
AJ40 engine so trouble free that there is never any need to
ask questions about them? 
While we are on the topic of AJ40 engines, can anyone point
me towards a resourse (web site?) that would have info on
the differences between the various AJ40 engines? I see the
3.6 and 4.0 liter engines in the XJ40 cars had the ribbed
black/aluminum cam cover but the later 6-cyl engines had a
much more bland unribbed cover. Are there any other
significant differences between the early and late 4.0 liter
engines (assuming the later un-ribbed cam cover engines are
still 4.0 liters) ??
Steven A. DuChene - XJ6SRIIIVDP XJ6C XJ12C XK120SE 3.8S
Reston, VA, United States
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