Jag V12 woes

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Tierfreund

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Hi guys

I know, this is BMW, but I also know that some of the nicest AND most knowledgeable people I´ve ever encountered online in one of the best message boards (great constructive athmosphere) hang out here with lot´s of general automotive knowledge.

So maybe someone here can help me, I´m a bit out of ideas:

I have an 88 Jag XJS V12. Had it for three years. When I bought it it was pretty neglected and on a Jag that spells a lot of trouble. Except for body and paint (body is in good condition, paint is not but I don´t care...) I´ve done basically a full restauration of everything. All chassis rubbers, springs, dampers, ALL electrics, all the cooling system, igntion, Injection, camshafts, valve clearances, Gearbox. EVERYTHING has been gone through by me personally, overhauled, replaced, optimized...About 1500-2000 hours and 3x current market price of a good XJS in replacement parts alone...

By the mid of last year I brought the car back on the road. Ran quite well, went though official inspection ((mandatory here)), sorted some more niggles, I was finally getting there...

Then I used the car for about a 1500miles building confidence, going well. So finally I started running it really fast as well (I´m in Germany so that means VMax (256.9kp/h according to GPS) sometimes for a couple of minutes at a time).

The car took even that in a stride, at least for a few times.

But then in November last year after an extended high speed run I noticed that it ran "rough" at idle. Actually it was shaking and idling too low in "D" and still shaking a bit in "N". As if it was not igniting or injecting in a couple of cylinders. It also started sound like an american V8 (which has a nice but slightly offbeat sound of course).

BUT, I know how it runs with 11 or 10 cylinders (not that noticeably different actually) and it doesn´t sound like that and shakes a lot more.

So I took it off the road and had to let it hide in the garage for a couple of month (I couldn´t stand the sight of it anymore after all that work and trouble)

Around Christmas I went back into the garage and took it all apart again. Ingnition, Injection, Fuel tank(s), coil, ignition amp, dizzy, cap, ht leads, fuel pump, filter etc. all cleaned, checked replaced etc.
Took me till a couple of days ago to go through everything (had the fuel tanks professionaly cleaned and coated, thus another 8 weeks of waiting).

Car still runs poorly in idle and at low revs. Shakey. Sounds "funny"
I´m as confident as anyone with a Jag can be that there is nothing wrong mechanically with the engine (compression is even and good on all 12), and that there is nothing wrong with the ignition and injection. The exhaust is good (1,5% Co on bank A, 1.1% Co on bank B - the car has no cats so this is bang on).

I´ve been through all diagnostics (Pull the injectors, have them fire into a glass, listen to the injectors with a sthetoscope, all is well, pulled individual HT leads, all as it should be.

I also got desperate so I started driving the car for a while including some VMax running (to test power output) it still reaches full VMax, it must be firing on all 12 at least at high revs.

Then I presented the car to my father who´s an old mariner and who diagnosed: the car is injecting and firing on all 12 but it runs as if it had an imbalance in the engine. "Like a boat where the propeller has thrown a blade". He asked about the flywheel, but beeing an auto it doesn´t have one.

So we got to: maybe the torque converter. Or the harmonic balancer on the front of the crankshaft. Both are known to be a bit fragile (the TQ is a GM unit built for american V8s and thus not meant to see more than 4000 rpm for a longer period, the Jag revs 6000 at VMax), The (harmonic) crankshaft damper sits beneath the waterpump that had seized and was leaking for years before I bought the car.

Also the car startet sometimes making a knocking/rattling noise when in D (unfortunately it doesn´t once a friend is around to listen while I´m in D and on the brake) and I can currently provoke it to have a high pitched rattling sound at 4200 rpm when driving seeming to come from the area behind the engine (hard to tell of course because to provoke it you have to be driving ond from the inside all noise comes from the engine department)

So my question is:
Who has experience whith a failing Torque converter and/or a failing crankshaft damper. What are the potential symptoms?

Any other creative ideas, anyone with experience with the JAG V12 and the GM THM400 3 speed trans?

Any help is deeply appreciated. I refuse to be beaten by the english beast!
 
This may not be kind...

But in the US there is a company called "inter-Jag", they routinely drop small block 350's in all types of Jags- That's one way to beat the Brits :)

Sorry-
 
We used to drop 283 Chevy V8s in. Solved all the mechanical problems. Not so for the electrical. Headlights, entire electrical system would still disappear at speed.
 
Sure, I drop in an SBC and then that runs poorly because it turns out it was the torque converter? :)

If there is any other engine I´d be prepared to swap in it´d be the BMW V12!...
 
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My dad had Jags and a XJ12L (late 70s) back in the 80s. Fond memories of long interstate road trips. The Jag V12s are like freight trains, effortless highspeed luxury cruising. I remember a company doing the Chevy conversions back then, IIRC, they were referred to as 'Mundorf' conversions.

FYI-,the current issues of Octane magazine #130 features the racing V12s including the awesome Broadspeed (who created one of the most awesome CS racers prior, of course it was in BRG) '77 XJC coupe that would walk away from the CSLs until it broke or blew up...

The 70s Jag Coupe (not many)......hhhhmmmmm.

Octane article/issue might help point a direction.

HTH
-shanon
 
The direction towards blowing up? :)

That´s a thought.


I know all about the Broadspeed XJ12C. Magnificent. Also capable of chewing up its tires in less than two laps...

They also built a few (very few) street cars. One of the featured prominently in "the new avengers" (cult english TV series in the 70s)

http://4.bp.blogspot.com/-rI5CgbyUi...Ls/paFslJbmjMU/s1600/Steed+&+Big+Cat+copy.jpg

http://fabwheelsdigest.blogspot.de/2013/02/jaguar-xj12c-by-broadspeed-1976-77.html

and as far as the Jag racing V12s goes: Nothing beats Tom Walkinshaw at Bathurst in his XJ-S:

http://www.youtube.com/watch?v=M9I7GWllPFY

about the only thing aurally more sexy than a Jag V12 driven in anger is a Matra V12...
 
Thx for the links Tierfreund!

Re:the New Avengers -I am waiting for the 'Femm-bots' to come after me.

;-)
 
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I add my name to the list of well wisher than cannot help.

Sounds like one experiment would be to see how it idles without a torque converter in place, though that is a lot of work for an experiment.
 
Well I took all the belts off today and started the engine. No change so the crankshaft damper is probably not to blame (Without the load of the alternator it would not have slipped).
So then I took the pulleys off and pulled the crankshaft damper. As usual on the Jag, somthing is amiss but something unrelated and unexpected. I found the front crankshaft seal leaking so I´ll be replacing that as well
And then I found that I had marked OT wrongly with white paint on the damper so I may have misadjusted the timing. But as my mark was at least 60deg off I probably didn´t actually adjust to it (very unlikely it would have run at all).

>Sounds like one experiment would be to see how it idles without a torque converter in place, though that is a lot of work for an experiment.<

Since the torque converter still seems the most likely culprit I probably will be running that experiment some time soon. If I have to take the gearbox out to replace the TC I might as well run the engine without the TC to make sure it´s actually the cause before I replace it.

My biggest hesitation though is spending money and time to fix the biggest shortcoming of the Jag: the old 3speed GM THM400 auto box.
I´ve been thinking a lot about a 6speed manual for the Jag lately.... :)

Thanks for the help (or at least wellwhises)
 
The timing in that car is always suspect. Started with the nasty dizzy grease that solidified and locked the advance all the way even when you are at WOT.
Running at WOT at full load with too much advance wrecked engines. Lucky you are Lucas , marelli was madness .
Check for vacuum leak swap out dizzy, cap rotor.
You can use a timing light on each wire to see if you are missing a spark and check your vacuum.
Do another compression test- valve seats are notorious.
 
True, the centrifugal advance mech on the Lucas Dist is a well known trouble spot. But I did overhaul it completely and am now lubing it with oil on a felt instead of the notorious grease. After the problems started the first thing I did was check the advance (es), replaced the dizzy and cap...

Good idea about using the timing light to check wether I have spark on all plugs.

I did seek for vac leaks, found none. Also a vacuum leak on this engine raises the idle significantly (ask me how I know).

And I´ve had it running on 12,11,10 and even 9 cylinders and it currently idles rougher than even on 9 while having full power available why I´m thinking more along the lines of a mechanical imbalance. Since the crankshaft damper seems OK, the most likely culprit is the torque converter.
Especially as there was that nasty rattling sound at 4200rpm on the last drive. A vac leak or misfiring/ unfiring cylinders would not be able to produce that.

But, beeing a Jaguar, I´m never surprised to find I have more than one fault. So I´ll be checking everything suggested!

Thanks e9ers!
 
Like your thinking...!
I will recheck the timing after I´ve changed the front crankshaft seal.
But unfortunately the rattling was too loud, in too narrow a revband and independent of load to be pinging.
Sounded very mechanical....
 
Check that front dampener at 3-9 and 12-6 for looseness just like a front wheel.
 
sfdon said:
Check that front dampener at 3-9 and 12-6 for looseness just like a front wheel.
Click to expand...

You mean like checking a wheel bearing?

I´ve got it off the crank right now and while the rubber between the two parts does look like the 25years old that it is, it all still seems tight. No slipping, no movement that I could induce by hand.
I will try to move it though once back on the crank (more leverage)
 
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