Hey guys, I own an 82 xjs v12 and today while driving, it just shut off. Plenty of oil, plenty of fuel, turns over but just won't start. It was very warm today, probably mid 80's. It didn't overheat looking at the gauge but felt alot of engine heat next to the car just before driving off. 5 min later, it just stopped running. Is it possible that 1 of the 2 coils overheated and cooked? Where should I begin?

 

Where should you begin, HAHA.

This will be long, and a drink or 2 will be required.

I gather that after 5 minutes or so you drove off in that car???, right??.

If so the basics of a very loooooong list are:

Ignition module INSIDE the amp (magic black box) on the LH inlet manifold. Quite a common failure item, and heat is not its friend, and once cooled, engine starts and runs just fine.

The coolant temp sensor and/or its wiring are getting hissy. With the engine running, and by unplugging that sensor will stop that engine with conviction. It is located on the backside of the LH thermostat housing, and has a 2 pin injector type plug on it.

The fuel pump got HOT and simply died, cooled down, and worked again, sort of common.

Coil/s, yes, mainly the one in the "V".

Heat exiting after shut down is NOT uncommon, that is a monster engine in a tight space, and radiant heat is normal.

The list will go on, but that is a starting point for now.

My advice is to take your time, systematically checking things, and above all keep calm. Dont simply throw bits at it, that will not really solve what happened.

 

Ok. My mechanic tried cranking it over and said it sounded like no compression. He hasn't checked for spark or anything yet, but wanted to give it a chance to start now that the coils, module, and fuel pump have cooled. Would any of the advice you gave me make it sound like an internal issue such as a timing chain?. It has 60,000 orig miles. I would have thoght it would go alot longer than that before running into any internal problems. I would expect a coil or 2 by now or any onther routine ignition maintenance but not anything major.

 

My 1990 XJS did that - it was the crank speed sensors.

 

Is your mechanic familiar with Jag V12s? The sound when cranking the engine is a bit unusual and might be mistaken for "no compression"

Timing chain failures are rare on these engines

Cheers
DD

 

Crank sensors are a common failure point....but the car in question doesn't have them


Cheers
DD

 

I'm really hoping it's 1 of the coils. I bought this car not too long ago, I'm the 2nd owner and it was a "summer toy" I think. Everything is still original right down to the distributor cap and it's hopefully just in need of a full tune up. It seemed to me to be lack of spark.

 

OK,

Lack of spark is 2 basic things, on the more common list.

The coil in the "V", primarily.

The GM module "inside" the ign amp (that magic black box I mentioned before).

60k miles is NOT going to have any real internal failure issues. Maybe lack of use issues, but certainly not chain/rings/valves etc. One of my V12's is nudging 550000kms, still as made.

Overheating these V12's is a death knock, so please be real aware of what is going on temp wise of this engine, and the gauges are only a GUIDE, they will never be accurate, no matter what you throw at them.

 

Had another thought whilst dining with the spouse. I really do need to get out more HAHA.

Coming out of that "magic box" on the inlet manifold is a coaxial cable that travels to pin #18 of the ECU. Now this wire is responsible for communicating ignition pulse to the ECU, and keeping the system alive. It has a bad habit of breaking, and/or, shorting internally.

Sooooo, with the engine running, do the "fiddle factor" as Doug says. Basically fiddly/jiggle with that wire and see if the engine cuts out. If it does, there is ONE of your problems and easily fixed.

Please bear in mind this wire issue has NOTHING to do with the engine stopping when at operating temp, then running again when cooled down, as you described happened, other than the signal TO this wire comes FROM the ign module inside that "magic box" as mentioned a few times before.

 

Grant - have you REALLY got an engine that's done half a million kilometres ?
If so that's amazing.

 

YES.

It is "her" XJ12 1976 S2 D Jetronic, BW12 transmission, 3.31 LSD rear end.

The S2 in my garage is the one in question. Those snaps were taken about 4 years ago prior to it going to its new owner, who still uses it daily.

The trans went AWOL on 2nd gear 15 years ago, so a s/hand fitted.

The diff ratted an output shaft bearing, so cradle out, and new bearings both sides, new rotors, pads, etc, back in, about 13 years ago.

The fan hub froze, so a Ford Falcon twin thermo fan pack took the place of the nonsense in there, about 16 years ago.

Lots of other little odds and ends over the 22 years were have owned it, but the engine is untouched. OK, it leaks oil (camblocks), luvs the fuel (its a PreHE so what), goes forward in "D", and backward in "R", and only stops when the ignition is switched off, what more do you want.

The kms is really nothing to these engines, or any Jag engine for that matter. Clean oil, clean air, good fuel (no Ethanol down here), and DO NOT let it overheat is my recipe for this. Of course the "nut behind the wheel" has a lot to do with it HAHA.

I know of a few AJ16 (X300) here over 300K kms, and X308's well into the 300K km range also, and still thundering down our roads daily.

Trouble is, as I see it, some owners are just paranoid about using the thing, and breaking down somewhere.

We took the '85 XJ-S from Adelaide to Port Douglas in Far North Queensland twice, via the coast road, about 10000kms return, and never ever had issues. Lots of weird looks and comments, for sure. "Fear NOT its a Jaguar, built to run", was my usual polite reply. Lots of other unprintable replies were more common.

 

Extraordinary, apologies for post hijack !

 

Ok, My mech says "when I try to start it, there's power going to the spark amplifier but not coming out of it" He thinks it's the amp that's failing. Would there be power to the amp if the module in the " black box" was junk? And would there be power to the amp if the coolant temp sensor was not working? Or, power in but not coming out indicate that it is, in fact, the amp thats failing?

 

That confused me, so a drink appeared out of nowhere, damn.

The amp will see 12v as soon as the ign is ON, NORMAL.

The "no out" is classic amp module gone AWOL.

I use Echlin brand, the part number is EP45, never had an issue, and since they are "Made is the USA", you should be able to source one a lot easier than I can.

The CTS unplugged, fritzed, whatever, will have NO affect on the module's behaviour.

If this guy is NOT real familiar with the V12 system, he will possibly damage that shielded wire I mentioned previously. That I have seen tooooooo many times in all my years, and then it still wont start, and/or stay running, and the module will get blamed again, and so around in circles we all go again.

That shielded wire is one very fragile item, so PLEASE be aware of its existence.

 

I'm confident enough now to reach deep into my wallet and go for the module. From what I'm seeing and hearing from my vehicle, and what I'm seeing here in your replies, I'm going to give it a shot. I'm ASE P2,(parts specialist) certified, and can order my module @ my job, but there's nothing worse than a Jaguar that's not running and not knowing where to begin. I'll let you know how it turns out.

 

I replaced the module inside the box, still no spark. Next, since I had the temp sensor in stock where I work, it would make sense to try that. Still no spark. So after the rain stops, I'm going for the coil in the "V" of the engine. I'll pick that up tomorrow. As of now, still under $50.00 and the ol' girl probably needed em anyway.

 

the "echlin" ignition amp I bought last month from NAPA would not fire the car as well as the "newer" A/C delco....had to resort to a NOS Delco circa 1980's on e-bay and it worked great. The grounding lugs on the newer ones were not the same as the original or the NOS one I got...the parts guy said A/C Delco had changed suppliers and most availible to fit my XJS were of the "new" supplier, the three new ones I got Echlin, Delco and Wells all looked the same BUT didn't have the same grounding lug as my original or the NOS one I got plus none of the 3 new ones would fire the car..

 

Very interesting. I used my original grounding lugs. I didn't think that would make a big difference. I didn't replace the entire amp. I opened it up and replaced just the module on the inside with a Standard Motor parts G.M. module (part #) lx301. The lx301 was an exact interchange from the G.M. module that came out.

 

Here's a pic of the NOS one...it looks just like my old one...all 3 new one's including the 'echlin" did not have the same lug set up on the top hole and while my old one worked I just wanted to replace it since it had 70K on it....I tried all 3 new ones and no joy as soon as I'd pull them off and put the old one on, VEROOOM fired right up, put in the NOS, same result, put in the echlin, wells or new delco, no joy. The new versions top hole looks similar to the bottom mount hole...I think the solid groud lug is imparative to it's working properly in our cars system....I can say I'm convinced after going to 3 new ones and then finding the NOS one that works.