Jaguar V12 w/ Marelli Ignition
Timing Map Jumper
The jumper is generally in the left rear area of the engine compartment. Here's a picture of the jumper on Tom Hollingsworth's '90:
Yes, there are two connectors. The bright orange one has a pair of wires going to an idle microswitch. The black one has a short loop of black wire. It's the black one with the short loop of black wire; the key is reportedly to look for yellow wire, and on this car there is a yellow wire on the other side of that connector (not clearly visible in this pic).
Here's what the same jumper looks like on David Buchner's '94:
Notice that there's only the one connector here -- and the loop is yellow on this one. The connector itself is different as well.
Regardless of what the jumper itself looks like, they all do the same thing. With the jumper in place, the Marelli uses an advanced timing map requiring premium octane fuel. With the jumper removed, the Marelli system switches to a more retarded map that allows the engine to run safely on lower octane fuel. Buchner reports that the performance drops way off, as would be expected from retarded timing. Hence, most people will find it best to leave the jumper in and seek fuel with sufficient octane, and only remove this jumper when they accidentally get a tankful of lousy gas.
Note that these engines tend to knock lightly even with good
if they've been driven too gently for too long. If your car is
it is suggested that you perform an Italian Tune-Up on it before
other corrective measures including removing this jumper. There
two steps to an Italian Tune-Up: First, check everything else on
the car to make sure it is in good operating condition, including the
system, fuel system, brakes, and tires. Then, take the car out on
the road and allow it to fully warm up. At about 60 mph, put it
in second gear
and hammer it. Somewhere around 5500 - 6000 rpm, let off the
throttle and allow it to coast back to sixty. Repeat several
People who perform the Italian Tune-Up universally report that the car
runs much better afterward -- even if it wasn't knocking beforehand.
Some claim the first tromp on the throttle results in large clouds of black
smoke out the rear as the crud clears out, but after a few tromps it's
clean and the throttle response is much improved.
Improve your Jag-lovers experience with the Mozilla FireFox Browser!
View the latest posts from our Forums via an RSS Feed!
©Jag-loversTM Ltd / JagWEBTM 1993 - 2024
All rights reserved. Jag-lovers is supported by JagWEBTM
Use of the Jag-lovers logo or trademark name on sites other than Jag-lovers itself in a manner implying endorsement of commercial activities whatsoever is prohibited. Sections of this Web Site may publish members and visitors comments, opinion and photographs/images - Jag-lovers Ltd does not assume or have any responsibility or any liability for members comments or opinions, nor does it claim ownership or copyright of any material that belongs to the original poster including images. The word 'Jaguar' and the leaping cat device, whether used separately or in combination, are registered trademarks and are the property of Jaguar Cars, England. Some images may also be © Jaguar Cars. Mirroring or downloading of this site or the publication of material or any extracts therefrom in original or altered form from these pages onto other sites (including reproduction by any other Jaguar enthusiast sites) without express permission violates Jag-lovers Ltd copyright and is prohibited