Hi Guys,


Probably a stupid question but how do you get too and remove the cap on a Marelli distributor cap? I looked at it and it seems like you need to remove a bunch of stuff. I'm afraid to mess things up and am asking for help. Any steps?


I want to do this so that I can do the silicone squirt under the rotor. Have any of you done this?


My XJS is running great and I want to keep it that way. I usually hate messing with something that is running good but I read that this is an important step to take. Thanks for your help...

 

Anyone? Thanks...

 

I don't have the Marelli ignition but on the earlier Ptronic with the big Lucas distributor you (pretty much) have to at least remove the spark plug wires. If you label the wires with nice big numbers (I use masking tape and a Sharpie) its a pretty simple process.

 

There are 2 screws that hold the cap on. I would make sure your plugs and wires are in good working condition THIS IS THE CAUSE of the so called Marelli failure which I have never experienced.

The reason for the failure is the high voltage of the ignition HAS to find a path to ground if a couple of plugs are not firing it will spark on the manifold until the plug lead breaks down, once this is suitably stuffed the only other place is the rotor and plastic does not hold up well to burning.

So if you change your spark plugs at regular intervals you will not experience this phenomenon. BTW on the 5.3 engine the front 4 plugs rarely get changed because the AC compressor is in the way.

 

my 10mm diameter wires looks like a spaghetti mess.

but i have no problem with anything related to ignition trouble.

of course dist. and cap are early Lucas, cap removal takes about 5 minutes, three screws, tilt the cap and wires are long enough for moving it out of way, and getting into dist., a little redundant , only had the cap off 2-3 times in 18yrs!

notice my fix for early fuel rails, custom aluminum extruded with O-rings top and bottom.

 

Mine is a Marelli system and it has a electrical harness and bracket over the top of the cap. It's hard to get at it and I was wondering if this is the norm to have to remove all of this crap just to remove the distributor cap.

 

well jaguar engineers of the era, thought that there systems were so good , that the cap would never need to be removed,(English thinking).

 

The Marelli cap is difficult (almost impossible) to remove without removing all of the ignition leads. the diameter of the cap is much smaller than the Lucas cap.

 

Yup, pretty much


If you're in the mood to do yourself a big favor.......

Remove the cruise control servo, coils, and throttle pedestal. It really isn't all that bad. Then remove the cap and wires. Then you'll have easy access to (most of) the spark plugs and can properly clean the spark plug wells, replace plugs and wires, repair any brittle wires and vacuum hoses, etc. Clean your throttle bodies and adjust the linkages, and replace the throttle bushings.

The front two plugs are easy if you tilt the a/c compressor forward....just 4 bolts to release it.

If you *really* want to do yourself a favor go ahead an replace the fuel hoses while you're at it.

Do it all and be done with it ! Bite the bullet. Order everything you need and make a weekend of it. Work slowly and gently. The car *will* fight you if you rush.

I've been down this road a couple times. Virtually all old V12s need the full treatment. Easier to do it all at once than going alá carte.

Cheers
DD

 

Thanks guys.


The fuel hoses are in good condition and the spark plugs only have 5K miles on them. My main reason to remove the cap is to do the rotor silicone squirt... Is that something you would not recommend to do? The weather is turning for the worse here in Wisconsin so I may put the XJS to sleep until Spring.


I was just thinking of preventive maintenance. Is it true that the rotor burn thru is because of older/high mileage spark plugs? Thanks.

 

This is my theory, based on 35 years of electronics experience. My XJS has 250,000km on it and the rotor has around 100,000 with no scorching and no silicone just replace the plugs every 20-30K or so.

BTW my car still has the Original Magnetti cap and an aftermarket rotor.

 

Keep me posted on your progress. I also have a 1990 and the ignition is next on my project, as I don't know when the spark plug, wires etc. were last changed.
I have read about the silicone fix. Anybody has any pros or con of doing the upgrade.
Thanks

 

My car does not have the silicone in the rotor and I do not plan on doing it, but it will not hurt if you decide to go ahead and do it. The idea behind it is it increases the insulation between the rotor and rotor mount. IMO this will only work if the ignition is in good condition, if the plugs are neglected there is nothing short of removing the rotor altogether that will save it. 20,000 volts or so is capable of arcing a fair way in open air, this is what destroys the rotor IMO.

 

Sounds good. I would rather just leave everything alone considering the spark plugs were replaced only 5K miles ago. The current cap is a Marelli as is the rotor... Thanks...