So, after getting an expensive new Wizard radiator for Lady Mary, getting her transmission fully rebuilt for even more money, having her brakes go out and getting those fixed for not that much money, I pick her up from the garage and go for a test drive. Everything seems to be working well. Seems to be....

She's always vibrated a bit when waiting at the lights - you can feel it through the seat. I've not been happy with it, but it didn't seem serious. Today, however, I drop her into neutral at one set of lights to see if that changes the feel (not that much, if at all), then back into D, and after that the vibrations are much larger - the whole car seems to be affected. Back home, I pop the front while the engine's still on, and twist the throttle. The entire engine moves side to side, very very noticeably. The car feels fine when driving; it's only when stopped (idling) that the shaking is noticeable. There's no new or excess noise, mind.

I suspect the rubber engine mounts are shot. Not being remotely equipped to remove the engine myself and check, it's back to the garage tomorrow. I am seriously starting to wonder if I bought a lemon....

I could be completely wrong about what is causing it, of course.... But how major a blow is this likely to be to my wallet?

This is what it feels like at the lights, only more sideways than up-down....

 

Changing mounts is straightforward. The subframe needs to be swung down to get at the bottom of the mount fixing bolt. The top of the mount fixing is undone, then the engine supported, then shck absorbers disconnected, steering column disconnected, maybe need to undo the brake flexibles, maybe you can get away with not, undo rear subframe mounting bolt one each side, subframe can then be swung down pivoting on the front six shot bushes, just enough to get at the engine mounting bottom bolt attaching them to the subframe.


The part you need is no. 9 on this diagram (MMB7520BA)

While the garage is in there, worth renewing the rear subframe mountings too. part number 2 below:
http://www.jaguarclassicparts.com/uk/part/CBC5735
About a morning's work tops. All you are dong is debugging the car after years of neglect. It will pass, press on, we have all been there.
Greg

 

Just to understand properly, how much movement is there to the engine when reved? ie left intake rises 1" etc

The engine shaking is another matter entirely. Listen to your exhausts. Is there a chuffing from one or both? You can hold a playing card against them to make the exhaust pressure waves more distinct. Are you missing on a cylinder or two?

 

The vibrations can also be the ignition. My V12 ran (as it wasn't in pieces) on idle a little rough. The engine mounts were still fine though. I assumee it is either the ignition (Marelli) or the injectors not running 100%.

 

or your coil is starting to go bad...

 

One of his coils... Being a Marelli it has two, so my post still works

 

Thanks for all your replies and advice. Very helpful, as is usual for this forum.

When I twisted the throttle assembly, the left (looking towards the front) did appear to rise or move a good inch, though it wasn't a rise and hold, but a shaking, as if the entire engine was being rocked or pushed side to side. I also held my hand (as a quick test) as close to the exhaust pipes as I could to test for any obvious missing pulses, but didn't detect any. I'll try again with some card soon.

I've read that bad spark plugs can be an issue, but the shop selling it told me they checked the plugs, and replaced one. The ignition coil (Marelli coil) itself is an issue I hadn't considered, but will certainly suggest to the mechanic - a Marelli going bad is definitely something to avoid, as I would prefer to not have my car burn quite yet....

 

The shop checked the plugs and changed one? Who does that? Those cheap buggers

 

Well, the guy said that was the only one that needed it. Could he be trusted? Increasingly, I think the answer is no, based on amateurishness rather than active malice. The place I got it from is the biggest single source of XJSes in the country, so made a logical place to start, but I definitely think they're a bit amateurish. Was I just unlucky, or was I duped? I'm pretty sure I made my decision a bit too fast, but these things are getting very thin on the ground here - and increasingly expensive. There's currently about 22 on the market nationwide (a couple more than when I was looking), but only 3 post-facelift coupes, and these three average about twice the base cost of the one I got.

Oh well, live and learn - as I told my wife last night, at least once these things get fixed I won't need to worry about them going wrong next year - at least I hope not.
And as I also told her, if I'd got something else, such as a Daimler Super V8 or a Jag Sov, I would still be wondering if I'd been a chicken and I shouldn't have got the dream machine instead. At least this way I'll have that out of my system....

 

Well....
I started her up this afternoon, with the bonnet open to see how much the engine moved. It didn't seem as bad as last night. However, the ABS and brake lights didn't go out, and, as I was to find, the brakes were pretty stiff - having just had that very problem supposedly corrected, I wasn't happy (and it was fine yesterday). I used a card to check the smoothness of the burbles from the exhaust pipes - the right hand one definitely seemed to miss every so often. Hmm.
As the brakes were working sort of, I decided to see if it would be sensible to take her to the garage, so did a couple of loops around the block (no cars to worry about) to test stopping ability. The brakes weren't great but worked after a fashion.

What suddenly stopped working after a fashion was the accelerator pedal - a sudden loss of response - well, you all know what this means. Being just a few dozen metres from home, I managed to get her there just as the "hot exhaust" warning light (a Japan-only warning) came on, the engine quit on me, wouldn't fire up again, and I noticed smoke coming out from the bonnet. (The engine did fire up when the mechanic tried it once it was at the garage, after it had cooled, but it's definitely lumpy.)

Not quite a Marelli fire as such, more a Marelli smoke, but seems pretty clear that the ignition coils, as Daim and Jonathan wisely suggested, are toast - or certainly well toasted. So she's back in the shop, partially as I don't have the time or expertise right now to change the ignition, and also as the ABS/Brake lights shouldn't be back on and I want the brakes to actually work....

It's strange how sitting for a night can create new faults. I think the Fault Fairy swoops down once I'm in bed and waves her magic wont (as in "won't start") to create new and hungry gremlins....

 

Firstly, to get your XJS working the way it should, you need to work on ONE problem at a time, get it fixed properly and then move on the next issue.

I would get the engine running as my first priority.

My experience is the front plugs never get checked let alone replaced, as it requires removing the AC compressor. My engine can be reved hard and there is hardly any movement, it wouldn't spill a full glass of water.

You only need a couple of cylinders to go down and the V12 will idle with a hiccup. I can tell you from experience if you lose one cylinder it will destroy the catalytic converter.

This is how I would approach the problem.
Change all 12 spark plugs.
Pull the cats and check to see if they are damaged or blocked.
Pull the dissy cap and rotor to see if its been damaged by misfiring spark plugs.
Check the primary and secondary resistance of the coils.

 

Also check the routing of the HT leads. There was a TSB regarding this.

 

A glass of water would definitely fall off my engine right now. I've seen a video of someone balancing a large coin on its side on the engine, and definitely wouldn't be able to do that. Generally, one issue at a time has surfaced, though this concurrent brake issue is a bit of an exception.

I've made a note of those points to check, and will pass them on to the garage. Wish I could do it myself, but have neither the time nor place. Makes me feel like a bit of a wannabe or a fraud, or at least someone who shouldn't be entrusted with an XJS. At least if I can't look after her myself, I can pay for her to be looked after, so it's better than nothing, I guess.

Daim - I looked at the list of TSBs in the sticky, but am not sure which one you mean. Is it "Rough Idle/Engine Misfire – New Spark Plug Wires and Routing"? Sounds right. My VIN starts with 182, so definitely before 195. I'll translate that into Japanese and deliver it to the mechanic asap.

 

It could just as easily be an ignition amplifier failing, so these need checking too, and their associated wiring.

As to the brakes, the garage is most unlikely to have rebuilt the ABS unit, and this could be part of your brake trouble. There is a thread about this by Orangeblossom that this is the link to. Whetehr you have the TEVES ABS system or a later type, I do not know.
https://www.jaguarforums.com/forum/x...photos-140828/
Greg

 

Yes, they just replaced a broken hose. It worked fine yesterday, however.

Greg - would the ignition amplifier failing cause smoke? That's the main thing which makes me think Marelli, though again, that's just guessing based on what I've read about them failing.

I found this thread by OrangeBlossom, which seems like it might be the one.
https://www.jaguarforums.com/forum/x...js-v12-146672/

 

Was it electrical smoke or engine smoke?

 

I honestly don't know. How would I tell the difference? It smelled, for what it's worth, much like the oil smoke earlier. I didn't detect any ozone. It didn't smell like burning rubber either. It could have been brake fluid that somehow leaked and spilled somewhere in the engine.

 

my whole left side went out
bank B
smelly smoke cooled it with a super soaker on the cats from above...
through engine compartment

lost the outer heat shield covering on the ABS sensor wire on that side
(from the heat) wires still good and ABS works ok (it did not melt... the heat made it break down and fall to pieces)


I changed the CAP and the rotor (I keep them in stock...)
no change... then had a coil on the shelf too... ( I now keep two on the shelf)
changed it (the coil) everything became better than when I bought the car...
I also have a full set of plugs on the shelf and a new set of magnicore 1508 wires ready to go...
so I keep wires plugs rotors and caps ready to be used when needed....
I figure it is a worth while investment...
and will be changing them on a 5k mile bases smooth running or not
and yes my cat melted and clogged up the left bank...
Oddly it is better NOW.... and not clogged....

mental simulations of the system lead me to ....
the inserts in the down pipes... are not what everyone thinks...
they remind me of the BRM 1.5 liter supercharged V16 spark arrestors
and on the cat melt down and subsequent back fires caught cat melt/pieces and saved my engine from real damage...

and have now passed the debris on out the exhaust...
so now I have it flowing freely again...

WIERD

I will not be able to confirm this theory until I do my exhaust upgrade... (it would be funny if they are not on the 1992 being that it has front and rear cats) (then my mind would just be spinning its wheels)

 

For the moment lets assume it was oil smoke, quite possible if the shop spilled oil and it dripped on the hot exhaust.

You need to do this in this order.

Change all 12 spark plugs.
Pull the dissy cap and rotor to see if its been damaged by misfiring spark plugs.
Pull the cats and check to see if they are damaged or blocked.
Check the primary and secondary resistance of the coils.

 

Regarding the rough idle, mine didn't sound a bad as what you described but, going through the ignition didn't help me, still well worth doing though.

My problem turned out to be in the injector wiring harness. After some advice from this forum I went through and pulled the injector plugs one at a time, I'd you pulled a bad one it wouldn't change how the engine is running. I found one that, when I tried too remove it, the engine smoothed out - it was either a bad plug connection or a fault in the harness itself that reconnected when it was wiggled around. In any case the problem hasn't returned yet. Replacing the harness is still on my list though, it seemed kind of "brittle" from the heat under the hood plus age I'm sure.

Hope this helps, Eric