Hello! Had a question about the Jaguar 1988 XJS v12 - the car keeps going after the key is pulled from the ignition! Is this an electrical problem?

It likely needs a new ignition switch.

Does it keep running like normal, or does it chugga chugga (poot) chugga shudder shudder? That’s dieseling. It’s almost unknown these days, but back in the dark ages big American V8’s were prone to do this when they got older. A 20 year old V12 might have a similar problem.

The cure is expensive. You have to pull the heads and clean the carbon deposits that have turned themselves into diesel glowplugs.

Or if it’s a standard, step on the brake and let out the clutch if it does it.

Andrew, if the engine is just running on as Revill queried, this may be related to your exhaust leakage problems.

If your V12 engine has a near manifold exhaust leak as badly as you described in your other post (and it sounds bad), the exhaust system can’t correctly extract the hot gases from the exhaust ports as it’s designed to do and the carbon deposits on the exhaust valves can glow red hot, this will cause engine run on.

This is very bad for a V12 and can cause the steel valve seats to fall out of the alloy head, a common and very expensive V12 problem to rectify. You can also damage the heads beyond repair.

However if the engine isn’t just running on for a few seconds but just continues running as normal, I’d suspect the engine ignition / fuel pump relay first.

IF it IS dieseling, there are better cheaper ways to remove carbon from combustion chambers than removing the heads. The first thing I’d try if I thought that was my problem is a can of BG-44K added to my next tank of gas. IF that didn’t fix it, I’d enlist the aide of a shop with a “motorvac” unit to literally suck the crud out of the engine.

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