V12 stalling ... in the afternoon!

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V12 stalling ... in the afternoon!

Postby 53v12 » Wed Jul 10, 2019 11:47 am

Over the past few months I've experienced a problem with the car stalling. It only seems to do this when coming back home and not on an outbound journey. All I can deduce from this is that it may have something to do with the car being started from warm.

A great example was at the Blenheim event a couple of months ago. Completely trouble-free journey of 60 miles getting there, but a nail biting series of stalls on the way home.

Once the car stalls, it is generally pretty easy to restart.

Would love to hear clues or ideas as to what to start investigating first. I've recently replaced the fuel filter but this seems to have made no difference.

I have been running the Barratt's replacement OPUS kit successfully for 10+ years.

1977 XJ5.3C

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Re: V12 stalling ... in the afternoon!

Postby PaulGover » Wed Jul 10, 2019 12:47 pm

Could you expand a bit on the symptoms please? I presume you mean that when stationary, opening the throttle causes the engine to die. But it could be something else!

You say that on the outward journey there was no stalling - did you move off from stationary several times? If not, it might have been just luck.

I wonder if it's the cold start device - the tall aluminium beast on the LH inlet manifold that lets extra air in when cold. It contains a wax cylinder that's sensitive to the cooling water temperature. It's notorious for failing; I wonder if yours is gummed up, and seizing in an incorrect posture after a warm restart. AFAIR it's moderately easy to test. Drain a gallon of coolant to get the level below the device, remove it and see if the piston move up and down when you put it in a bath of hot water on the cooker. You'll find other discussions of it on the forums.
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Re: V12 stalling ... in the afternoon!

Postby RichardSEL » Wed Jul 10, 2019 5:00 pm

Change the coil
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Re: V12 stalling ... in the afternoon!

Postby 53v12 » Wed Jul 10, 2019 5:12 pm

Thank you both for speedy replies.

A bit more detail about what happens: the stalling happens when driving along, which can be unnerving when on the motorway! All that seems to happen is that Engine revs die away completely, assistance from power steering is lost and by the time I get to pull over by the hard shoulder, the ignition warning light is on.
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Re: V12 stalling ... in the afternoon!

Postby mike020150 » Thu Jul 11, 2019 10:22 am

With faults like this which you can't replicate in the safety of your garage you will need to be logical and work through all the possibilities. If the failures occur suddenly with no other symptoms, the chances are that the issue is electrical, cutting off either sparks or the electrics to the fuel supply.

If the engine restarts instantly, the problem is unlikely to be the fuel pump itself (they tend to go or stop without recovery) but it could still leave the fuel pump relay/wiring as suspects. Substitution of the relay would rule it out.

On the ignition side, again there are main and ignition relays to check (by substitution) as well as operation of the coil, ballast resistor and ignition amplifier to consider. Work through them one by one. Testing appropriate components with a multimeter, by a process of elimination of those components you can test, should get you closer to the source of the problem. A faulty ignition amplifier can be difficult to diagnose since they can develop intermittent faults. However, in these circumstances, restarting is usually only possible after the unit has cooled a little rather than immediately after an involuntary stoppage. Mike.

Ps One further thought occurs - don't rule out a worn, faulty ignition switch when you are checking wiring continuity.
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