V12 engine cutting out

[leodistiger]

I am having a problem with my 1986 XJ-S V12 and I wonder if you can help.

The problem is that the car will start from cold with no problem, but almost as soon as I set off the engine cuts out and I come to a stop, the engine will then start after a bit of churning only to cut out almost straight away. After the 3rd time of starting it will usually run indefinitely without a problem.

This has occurred ever since I had new calipers, disks and pads installed.

The problem came to a head yesterday when the car cut out as soon as I left my drive and it refused to start despite lots of turning the engine over. I gave it a while to rest (about 15 minutes) when it started and I managed to get it back into my drive and garage before cutting out again.

I have had the car for nearly two years, I bought it from a gentleman who had had the car stored for many years. For the first 18 months of my ownership it was outside under a cover and it started and ran without a problem.

I must admit the car has always idled around 1000rpm and sometimes it seemed a bit short of breath, but I sort of accepted this as normal for a 20 year old car. I recently went to the Jaguar Northern Day at Harewood and was very envious of a V12 E-type with an engine which just purred silently instead of running lumpily like my own.

Please can you offer me some advice as I love driving my XJ-S and I hate to see it in it's current state.

[HerefordMark]

It sounds like a fuel problem to me - when you sit churning it over, is there a strong smell of petrol? If not, fuel is not getting through. I have heard that cars can show this symptom when they have a blocked fuel filter - fuel in the system gets it going, but suction on the fuel line draws up muck which blocks the filter, causing it to stall. Once it's not running, the muck falls away, allowing you to start it again. The recent work you had done might have stirred up some muck in the tank, perhaps?

If this sounds about right, the fuel filter is easy enough to change (make sure you depressurise first). I would also check the air filters if it seems breathless - they might be blocked as well.

Hope this is useful

HM

[leodistiger]

Thanks for your response Mark. I will look at this.

The mechanic(!) at the garage where it went for the new brakes said it had run out of fuel while he had it, so sounds like some dirt from the tank has got into the fuel pipes and is causing a blockage.

Could the Auxiliary Air Valve (AAV) be contributing to the symptoms? I have read that it causes similar symptoms to those I have been getting.

[Telsmoneypit]

Thanks for your response Mark. I will look at this.

The mechanic(!) at the garage where it went for the new brakes said it had run out of fuel while he had it, so sounds like some dirt from the tank has got into the fuel pipes and is causing a blockage.

Could the Auxiliary Air Valve (AAV) be contributing to the symptoms? I have read that it causes similar symptoms to those I have been getting.

If that is the case (running out of fuel) I suggest you change the fuel filter located behind the spare wheel in the boot. Don't forget to depressurise the fuel system first and clamp the hoses with brake hose clamps.

Terry

[leodistiger]

hi there

i know the theory, but not the practice. Can I ask dumbly how I de-pressurise and then re-pressurise the fuel system?

The mechanic said he had changed the fuel filter before he returned the car to me, but I'm not so sure!

[HerefordMark]

In the boot, remove the right hand trim bits to reveal the fuel pump relay, and disconnect it. Then crank over for a few seconds. As Tel says, you can then clamp up the fuel filter lines either side of the filter, which is behind the spare wheel cover, and disconnect it. I'd have some cloth ready in case of spillage/incomplete depressurisation. Replace filter, then refitting is a reversal of removal, as they say.

If your mechanic says he has replaced it, I'd have word with him to see what he has actually done. If he's not used to V12s he might have mucked about with one of the fuel pressure regulators in the mistaken belief that it was the filter - I would think a few non Jaguar mechanics would be unaware that the fuel filter is in the boot, not the engine bay.

Regarding the AAV, I don't think it would give the cutting out symptoms (but I might be wrong). However the idle control nut is on it so this is where you can bring down the 1000rpm idle. There isn't much you can do with an AAV as it's pretty much like a thermostat - if it's broke, you need a new one. And it's a faff taking it off as you are opening up the cooling system. However, on my car I disconnecetd the air hose and squirted a ton of WD40 into the valve. It did seem to make a significant difference to the smoothness, so you might want to try that.

Once it's all going again I would also put some fuel cleaner/conditioner through the system - a full can in half a tank of gas, plus a good run will clean up a lot of problems, in my experience.

Let us know how you get on!

HM

[leodistiger]

Hi Mark

Many thanks for this information, I will have a look at the weekend! It's a pity there are not more helpful people like you in West Yorkshire - they could come and have a look at things for me (I'm not yet practiced with this car).

Anyway, will let you know what happens.

[poprivet]

I think Im correct in saying that lifting the inertia button (footwell) will disable the fuel pump to allow depressurisation. If correct, it would be easier then locating and disabling the fuel relay. I'm sure someone else will confirm/dismiss the idea.
Pop

[Hosier77]

The inertia switch will stop the fuel pump but unfortunately it will also stop the injectors so it wont let the pressure out.
Sorry.
I am sure if you ask the local JEC they can find someone to have a quick look at it (of course its best if you are a club member!). If you are not sure then its best to leave it to someone else, the V12's are unfortunately complicated and unconventional cars, but definately worth the effort
It sounds like there may be more than one thing that needs sorting, it maybe that someone raisd the idle speed to cover up the poor performance. I am sure with an expert eye cast over it then it can be restored to its former glory.