I cannot find a simple answer out there on google…
Is taking a Marelli cap off to simply check on the condition of the rotor easy enough to do with just a philips screwdriver?
Or do I need more tools?
thanks
reason I ask, I’m considering a used XJS with the marelli ignition. PO has owned it 10 years, and never changed plugs or wires because the V12 runs so smooth. Low mileage (72,000). Before I drive it on the freeway to get it home, I want to make sure I don’t go out in a ball of fire If I can’t check the rotor, then I may have it towed to be safe. But if I can bring some tools and simply check, that would be great.
Gregma,
Attached is a picture of an OEM Marelli distributor cap. It is held on the distributor with three straight slot screws not Phillips head screws. Removing the spark plug wires and cap can be a challenge especially if they haven’t been touched in a while. If you decide to do this you may want to have a spare Marelli cap gasket on hand in case there is not one on the car already or if the one tgat is there get torn when you remove the cap. Also take lots of pictures and make notes of how the wires run because people sometimes reconnect them incorrectly and then wonder why their car isn’t running properly. I have never just removed the cap for a look and then put it back on so I don’t know how long it will take. Be sure to allow lots of time.
Looking at photos of V12s, it looks like I should be able to just remove the plugs on the rear side of the cap, remove the screws, and rotate the cap towards the front of the car to take a peak? may even bring my telescopic mirror to help.
Gregma,
Well I have never done that so I have no idea if it is possible.
BTW, if this car has an aftermarket distributor cap I have no idea what kind of screws it has. The OEM Marelli cap has “MAGNETI MARELLI” cast in the plastic. The aftermarket caps say “Made in Italy”.
Paul
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
5
You’re going to need to remove two screws to get the rotor out to look at the underside.
Those screws are allen head. If the car is running fine, I would leave well enough alone until you get the car to it’s new home. Then you can change the plugs, wires, cap and rotor. Sometimes disturbing things causes more problems than it prevents. If I was the owner of the car I wouldn’t want someone touching anything under the hood until money changed hands.
I would check to make sure the car is firing on all 12 if so drive it home. Although the Aussie car is different than the US spec I have never had an issue with the ignition. Change the plugs regularly and make sure the wires are good and mine has never hiccuped.
I do know the original owner had an ignition module fail under warranty but even that did not have the car burn.
If it has a genuine Marelli cap KEEP it if it;s in good condition, they are much better quality than the aftermarket. I have 2 caps the original Marelli that was on my car and an aftermarket spare that came on my 6.0L engine, Until recently my car ran the OEM Marelli and it had 260,000km on it and will go back on my 6.7L when that goes in. I did change the cap to the spare 2 years ago (only 5000km these days) just to see how it went.
I agree with you completely. If the car appears to be running on all 12 cylinders (relatively even exhaust and plenty of torque) then drive it home and take it apart there. If I was selling the car I wouldn’t let anyone mess with it until ownership changed hands.
There is plenty to go wrong with trying to do a quick check of the Marelli cap and rotor that haven’t been removed in over 10 years.
Speaking of cats, in my state a car older than 25 years does not need emissions testing.
So once I decide to replace the exhaust system, I’d like to get rid of the Cats to improve performance. Will I need an ECU update? Or different O2 sensors?
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
13
The good news: You won’t need to change ECU or O2 sensors. The bad news: Presuming your cats are in decent condition, you won’t gain any performance.
What? I’m pretty sure CATs restrict exhaust flow a tiny bit. Although I’m used to having Turbo cars. I guess with a N/A engine, it makes little difference?
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
15
Apparently, roughly the same restriction as a length of pipe.
I dunno what year car we’re talking about, but if you have those flow straighteners in the downpipes, those are probably worth removing. Another option is to simply replace the downpipes with the 6.0 versions, which reportedly not only don’t have flow straighteners but are also configured better for flow.
Cats, at least clean and modern ones, will not make a detectable difference in performance: in the case of an A or B bank ignition failure, however, you wont have the meltdown/ Fire hazard of a flooded cat.
Greg,
The Marelli break in point was sometime in the 1989 XJ-S Model Year. I don’t know the exact changeover VIN # but this has been discussed many times since I joined this list in 2005 so the archives will have some posts with that VIN#.
Yes our cars had cats from about 1985/86 and mine has O2 sensor April 1989 build.
What we do not have is the cats in the down pipes, this might be the cause of the fires in the USA. I have never heard of an Aussie Marelli XJS burning.
BTW Ferrari, Lambo and the dual plug Porsche used almost exactly the same Marelli system. Some of the Lambo guys modify their system to take the Jaguar rotor which is slightly different than the Lam,bo.
Yes they will just like mufflers there are good flowing cats and bad flowing cats. Cats in older cars tend to be more restrictive than newer ones.
I had a turbo VL Commodore in the late 1980’s which had 400RWHP. Replacing the restrictive OEM cats with highflow ones made a significant difference on the dyno.
What is not a good idea (except gutting the down pipes) is gutting a stock cat, this can actually increase restriction due to turbulence in the cat chamber.
If I can’t check the rotor, then I may have it towed to be safe. But if I can bring some tools and simply check, that would be great.