Mk2 won't go

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Graham L - 20 Jul 2004 01:49 GMT

Got a little problem with my 3.4L Mk2. It has been running superbly until
last Friday when all of a sudden it started misfiring and losing power
almost completely. Managed to limp home and when I pulled the plugs out
they all had beards of soot. Now, compression is good on all cylinders,
spark (on clean plugs) is good on all plugs, have pulled the carbs apart and
reset them no problems so it idles nicely, revs nicely. Get the car on the
road and it runs well with the gentlest throttle pressures but a little more
throttle and no power and in minutes the plugs are fouled again and it
starts missing again. Starting carburettor is a suspect, I guess, but I have
long since disconnected the thermal switch and replaced it with a switch in
the cabin, and it is definitely not open by the solenoid anyway. It has
three mechanics at my local garage baffled (not Jag specialists but the
local centre for vintage car repairs).
Any suggestions?

GrahamL

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Ron the Barbarian - 20 Jul 2004 02:33 GMT

> Got a little problem with my 3.4L Mk2. It has been running superbly
> until last Friday when all of a sudden it started misfiring and losing
[quoted text clipped - 13 lines]
>
> GrahamL

Sounds like the coil, whack another in and see what happens.

My XJ6 usually starts missing under power when the plugs are weak.
The 420G started doing the same thing, so I replaced the coil, as the
plugs were new, it fixed the problem.

Ron

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Graham L - 20 Jul 2004 04:09 GMT

> Sounds like the coil, whack another in and see what happens.
>
[quoted text clipped - 3 lines]
>
> Ron

Thanks, Ron. It had crossed my mind but the mechanic talked me out of it.
I'll try it today.

GrahamL

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Blake Dodson - 20 Jul 2004 07:56 GMT

> Got a little problem with my 3.4L Mk2. It has been running superbly until
> last Friday when all of a sudden it started misfiring and losing power
[quoted text clipped - 12 lines]
>
> GrahamL

Besides the coil the "Barbarian" mentioned ->What brand of plugs are
you running? What is the heat range <plug number>?

Carbon fouling is typically caused by the folowing-

1.) Plug heat range too cold. <can't self clean>
2.) Extensive low speed driving. <Come on its a Jag! Hammer down!>
3.) Driving short distances. <Also creates condensation in oil>
4.) Weak ignition system- ala Ron
5.) Rich fuel mixture. <I think you cranked it up when replacing an
air filter>
6.) Vacuum leaks. <eek>
7.) Improper choke operation. <Cable in man, cable in!>
8.) Coolant Thermostat missing or not operating correctly.
9.) FUEL ADDITIVES <LEAD DOES NOT LIKE CERTAIN PLUGS>

If you have addressed the above then move up to the next plug heat
range and drive again.

Regards,
Blake

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Ron the Barbarian - 20 Jul 2004 08:35 GMT

>> Got a little problem with my 3.4L Mk2. It has been running superbly
>> until last Friday when all of a sudden it started misfiring and
[quoted text clipped - 35 lines]
> Regards,
> Blake

Heh, heh, you don't know who the "Barbarian" is, Blake :-)

http://home.iprimus.com.au/rmcgrice/

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Nick Bennett - 20 Jul 2004 09:36 GMT

Do not want to alarm you too much but I had the same problem on a Jeep CJ7
straight six, turned out to have a crack in the block

Nick

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Tin Paradise
www.tinparadise.com
Phone / Fax 01942 511912

> >> Got a little problem with my 3.4L Mk2. It has been running superbly
> >> until last Friday when all of a sudden it started misfiring and
[quoted text clipped - 39 lines]
>
> http://home.iprimus.com.au/rmcgrice/

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Blake Dodson - 20 Jul 2004 16:44 GMT

> Do not want to alarm you too much but I had the same problem on a Jeep CJ7
> straight six, turned out to have a crack in the block
>
> Nick

And a cracked block caused dry fouling?

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Blake Dodson - 20 Jul 2004 16:37 GMT

Cmon Ron, I knew it was you...but if you are projecting that to me you
are simply wrong! Hell, I am a savage. ;-)

Blake
(Nice website)

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Graham L - 21 Jul 2004 11:17 GMT

> Besides the coil the "Barbarian" mentioned ->What brand of plugs are
> you running? What is the heat range <plug number>?
[quoted text clipped - 17 lines]
> Regards,
> Blake

Blake,
Thanks for the input.
1. I'm using hot plugs, Denso W16EX-U
2. I'm in the country and therefore free of log jams and only use the Jag
for playing i.e. zoom! zoom!
4. Tested coil and condenser - no problems
5. I've driven quite a few k's since the air filter saga and with clean
burning plugs
6. Can't find any leaks, but possible
7. Have checked out starting carb. because I had this trouble before when
the thermal switch was faulty and was switching the "choke" on
intermittently. Now switched manually and definitely closed when switched
off.
8 and 9 . Maybe. But we're talking about really serious fouling here.
Clean plugs to plugs breaking down in minutes not miles! It also startes
suddenly last Friday.

To me it seems that I'm getting really, really rich fuel mixtures when the
engine is under load and throttle is opened. Have pulled the carbs off
tonight (what a begger of a job - it'll be fun putting them back!) to check
the state of the diaphragms. Yet to check them out. Someone suggested to me
that a leaking float (i.e. a sink?) could cause the problem.
Not looking promising for this weekend, however.

GrahamL

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The Three Kings - 23 Jul 2004 23:03 GMT

Did it ever go???

Can we please have the outcome.

Ta.

> > Besides the coil the "Barbarian" mentioned ->What brand of plugs are
> > you running? What is the heat range <plug number>?
[quoted text clipped - 43 lines]
>
> GrahamL

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Graham L - 23 Jul 2004 22:30 GMT

> Did it ever go???
>
> Can we please have the outcome.
>
> Ta.

Sadly, Mike, Bodecia, warrior queen is still in the garage with bits of her
carburettors spread out on the bench. I can't find any problem with the
diaphragms but I'm replacing them anyway as soon as they arrive in the post.
Still open to suggestions.

Graham

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Blake Dodson - 26 Jul 2004 23:49 GMT

> Not looking promising for this weekend, however.
>
> GrahamL

This somehow reminds me of the time my cafe racer exhaust pipe clogged....

Good Luck.

Blake

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Graham L - 30 Jul 2004 03:55 GMT

> <SNIPPY>
> > Not looking promising for this weekend, however.
[quoted text clipped - 6 lines]
>
> Blake

Yes, Blake.
That occurred to me, too. Plates can dislodge in mufflerr, for example.
However, the Mk 2 has two separate exhaust systems, 3 cylinders each. All
the plugs are fouling up at the same rate.
With several other disasters to deal with over the last week, I haven't had
time to look at it. I am going to replace the coil, condenser and spark
plug leads. If that doesn't work, at least I'll have some spares.
Graham

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