Of late I've been boasting at how reliable my V12 Series III has been as a daily driver. I obviously over-stepped my bounds. A problem developed.

On a short trip the engine starting bucking and carrying-on. Tach needle bouncing crazily so I suspected an issue in the primary ignition system. Nursed it home; conked out entirely 10 feet from the shop door. No start. Pushed it in.

Immediately set to work. No spark. Had "+" voltage to the coil. Coil primary and secondary resistance good. Check resistance of pick-up coil inside the distributor; within spec (barely). Replace the ignition module. Engine started right up and ran well.

It doesn't get any easier than that.

I thought.

Immediately following this episode a new problem developed: Poor running after warm soak. That is, it runs poorly after being driven and then allowed to sit for a few minutes. On restarting it runs poorly, ranging from a mild roughness to severe bucking. Problem goes away after 15-20 seconds. All's well until the next "warm soak" event.

Might be a day or two before I have time to check anything. I'll keep everyone posted.

In the meantime.....any bets on what it might be ?

BTW, I mentioned above the the pick-up coil was barely in spec. The spec is 2.2K to 4.8K ohm. Mine is right at 2.2K ! Not exactly comforting, but....within spec is within spec, right?

Cheers
DD

 

Fuel vaporisation in the fuel rail ? Does the V12 have anything to prevent this ? I believe the sixes had something added at some point to deal with this problem.

 

I am with Fraser.

Why now, after so long??, you started the problem, HAHA.

On all the XJS cars, I moved the fuel filter into the engine bay, on the chassis rail, just outboard of the A/C idler pulley.
That made a HUGE difference to ALL those cars, especially in our Summers.

Might be worth a look see.

On the Coupes, you obviously got rid of about 6ft of fuel hose from behind the spare wheel, and I reckon that short blast up the fuel hose, Pump to Brass Outlet fitting in the boot floor corner, gives the whole system a better blast of fresh fuel a lot quicker.

Greg in France, has recently done the same, and reports exactly the same result. He also runs a "smaller" fuel filter, which I reckon is a top move.

 

My car takes a time to fire if the fuel rail has vapourised fuel in it; but once firing it runs perfectly.
As Doug's original symptoms were present when the car was running, I think fuel vapourisation as the sole cause unlikely. My bet is either fuel pressure (as in the pump playing up or some fuel feed cause) which is not that likely; or much more likely, some sort of coil or amplifier problem.
Doug will doubtless enlighten us all in a day or two.

 

Yes, I have the fuel temp switch on the fuel rail that allows full fuel pressure at xxx-temp to counter fuel vaporization.

I should've mentioned that the problem occurs even after just 15 minutes of driving. I doubt that's long enough to create much heat in the engine bay.

Not that the idea is entirely off the table, mind you.

Given the sequence of events I'm gonna assume, at least initially, that the problem is something I created.

Cheers
DD

 

I *Love* it when my first guess is verified by all these experienced gentlemen!
On the farm we used to call that Vapor Lock. Happened quite a lot in summer.
(';')

 

I think I've already fixed it. And it was my fault, as I expected.

I didn't properly attached the white "+" voltage wire to the coil terminal. Rather than slide the connector onto the coil terminal I managed to get the terminal in between the protective boot and the wire connector. So the wire was wasn't connected to the coil terminal. The boot was just sorta holding it alongside the coil terminal.

Haven't had time to drive it, though. We'll know more tomorrow!

Cheers
DD

 

You are NOT alone with that, I have lost count over the years.

Well found all the same.

 

All is well that ends well....

Carl

 

Not fixed !

Haven't had time to investigate; maybe next week.

The only thing I can add at this point is that the symptom feels like it is over-fueling.Soggy and boggy, if you know what I mean. And good shove on the throttle will clear the pipes, so to speak.

Other than that the engine has never run better !

Cheers
DD

 

Check the fuel pressure during hot soak restart. The fuel pump has a check valve to keep fuel from flowing back to the tank and may be faulty. Cure is to replace the fuel pump.

 

Fuel Pressure Regulator? Just a thought.

Jack

 

Defective replacement ignition module? In that, I mean a defect in the electronics of the module that appears only after heat soak and then disappears after the under hood temperature drops again. That's the type of issue I seem to run into.

 

I agree with this, Doug. Whack on a new amp!.

 

Replacement module failed.

Moral to the story: use AC Delco ignition modules only.

But.....there's a lot more to the story. I'll post more in a couple days. Stay tuned.

Cheers
DD

 

We'll be interested in the rest of the story but my first thought was that you replaced the GM module with an aftermarket non-GM/Delco module. The aftermarket modules seem to be unable to handle the demands of the V12 and very often fail "out of the box" . On the other hand, thought I, my friend Doug surely would have used a correct OEM module, right!....or...?
Doug, on one of my V12 VDP cars (#92/100) the cuprit in a similar scenario turned out to be the pick-up in the distributor - rare, but it does happen...

 

Fewer and fewer outlets keep the genuine AC Delco module "on the shelf" so I somewhat reluctantly used an Echlin (NAPA) replacement....which was available to me in ten minutes.

Hopefully I'm near the end of a period of cascading misadventures which have been complicated by the quality of replacement parts....even Jaguar branded/boxed items.

More later !

Cheers
DD

PS- I've never concluded the poor-running-after-warm-soak problem. Frankly, I had forgotten about it. The nature of my daily driving routine is such that the problem doesn't present itself very often. Meanwhile, other problems developed.

 

The pick-up failed on mine a couple years ago. The replacement is apparently still OK but, when tested, is just on the edge of being within specification.

Cheers
DD

 

My experience with electronic components. Is when they get to the edge of spec, they are unreliable at best. I have found when something checks on the edge of spec, replacing it eliminates the hassle of being on the side of the road waiting on help. I got caught on the south side of Memphis Tn. once due to a Echlin (Napa) Ignition Module on my 1987 Ford Ranger. I had replaced it earlier that morning, 300 Miles later it dumped me, in an area where white people don't want to be when the sun goes down. No more cheapies for me.

Jack

 

This may not help, but I had an intermittent misfire/rough running/engine totally stop problem with my V12 that went on for years. It was worse in hot weather, notably on Italian autostrada - not a good place to stop, especially in a tunnel. In the end, it turned out to be the engine ground strap.