Hello to all,
For the second time in the last 10,000 or less miles the distributor in my 92 XJS V12 has caught fire. I have owned this car since 1997 when I purchased it from Moore Jaguar in St. Louis, Mo. It currently has about 125,000 miles on it and it has been maintained to perfection. The only modification is a re-engineered fuel system including an external fuel pump.

Any suggestions concerning the burning distributor cap? A fire this close to the fuel rails does create excitement in this old man. The first time I replaced all the plug wires, distributor cap, rotor and coil wires. This time I had the car hauled to John's Cars in Dallas, whom I have done business with since about 1978 or 79.

 

There must be a reason why the cap catches... Is there a fuel leak in the near? I mean, how old are the hoses around the cap? Or all hoses to be correct...

 

There is a vent on the V12 cars, on the distributor. It has two hoses. One has a small filter on it, and the other goes to the air valve hose on the left bank. There is a plastic 90 degree elbow up under the intake. The plastic gets old, brittle, and falls apart. Ask me how I know. Anyway, bought a brass vacuum 90 at my local parts store, problem solved. I think vapors build up inside the V, get inside the distributor cap, and without proper venting, well, you know. Just look at your distributor really closely, and follow the hoses. Clear as mud, lol.

 

His would be a Marelli cap, no vents. Lucas dist caps had vents.

 

My car is a Marelli car, and has the vents

 

Interesting I ordered one and they sent a marelli by mistake and it had no vents, all pictures I find on line of Marelli caps show no vents. Go figure?

 

Fumes are getting into the inside of the dizzy and being ignited by the HT spark. They may be coming up from below because of a failing seal of some sort from the drive. There may be a flash shield that has been left out. The Lucas cars have a flash shield immediately below the rotor arm/cap contacts AND a fresh air vent system as someone mentioned above.

Someone with knowledge of a Marelli car should be able to confirm? Also, it would not be that hard to rig up a fresh air vent system. If Supercharged 6 would post some photos of his Marelli vent setup, it is essentially just a matter of a filtered inlet low down into the dizzy and plumbing an outlet at the top into one of the airboxes. A 5 millimetre diameter hole would be quite enough. Well worth the effort I would think !

Greg

 

I can take pictures, but the vent isn't in the cap at all. Its the distributor body that has the vents. As I say, it draws air from the same hose that feeds the auxiliary air valve, then has another line that goes to a small filter near the master cylinder

 

no need to "rig" up a vent system on the marelli, it already exists. Hoses are not shown in the pic but the fittings are obvious.

 

Makes sense! I stand dejected.

 

We are all in this together, lol. Birds of a feather flock together, and all that talk. All I know, is that mine was inoperative due to that cracked elbow. You can't see it, but reaching under the manifold, it can be felt easily enough. I understand they all fail due to the heat. Anyway, I put that brass one on it, and I seriously doubt that will ever be a issue again. Again, its plumbed into the hose that goes from the left side breather, to the AAV. It goes from there, to one of those fittings on the distributor, and then from the other fitting on the distributor, to a filter out near the brake master cylinder (on a LH drive car)

 

Thanks to all who responded. If fuel vapors were getting inside the distributor and ignited wouldn't there be some sort of a small explosion?

 

I would think so, yes.

In your first post you mentioned 'caught fire'. Do you mean it actually ignited, with actual flames spewing?

Or did it somehow get very hot and meltdown ?

Or did it explode?


Caught fire and meltdown might be confused ig you were looking only and the end result. Explosion would be self-evident, though.


Correctly identifying what actually happened might help us figure out a possible cause.

Cheers
DD

 

The spinning rotor and the 12 electrodes at speed can kill the motor. The vents allow fresh air in to help slow the progress of the static build up from this action. The fuel will probably just ignite as there is a lot of ignition sources and not blow. Kind of like throwing a lit match into a raw bucket of fuel. Won't ignite fast because match will loose oxygen too fast to stay lit. But, throw a match unto a bunch of fumes and bye, bye. Reroute fresh air tubes to a fresh area and make sure intake tube has filter on it.

 

In both instances the car started misfiring and when I started pulling off to stop there was smoke coming from under the bonnet. When I opened the bonnet the distr. cap was in full flame. Engine bay is kept very clean so both time I was able to extinguish fire with no additional damage. Both cases a hole was already burned in the distr. cap.

 

Classic Marelli failure mode. There really needs to be a sticky post for every new member to read.

 

Rotor on the marelli is a must do from what I understand although I don't have one myself. Lots of details about on here I am sure. Should you get another fire try not to open the bonnet, just squeeze the extinguisher in and squirt as a habit you will save yourself an engine or two in a lifetime of Jag ownership


As for vapour in the cap, they normally shatter spectacularly on American lumps so not sure why yours is burning so well. Good luck

 

Twice in 10k miles? That doesn't seem like a classic Marelli issue to me....although I'll admit that I'm having a hard time coming up with any ideas of my own in this case

Cheers
DD

 

Yeah, if there was a vapor build up problem I would expect to see a cap blown apart, not a cap in flames. Still, on GP, make sure your dist vents are intact.

When this happened 10k miles ago what repairs were done; what parts replaced?

Are your spark plugs and spark plug wires in good condition?

Cheers
DD

 

I may just be gun shy Doug, happened to my twins. Didn't have the third one long enough, but I did the fix 2 days after I brought her home.