Coil Failure
Posted: Thu Jul 13, 2006 6:56 pm
In case it may help others, I thought I would put down the details of a coil failure episode.
My '89 XJRS 6 litre died on the motorway last week. I had literally just got it MOT'd the day before after 2 years off the road, so I was probably asking for it... There were no warning signs, just a sudden loss of power as if I had just taken my foot off the pedal. The engine cut and I came to a halt fortunately well off the motorway. I could not get it to fire, but could smell fuel, so suspected ignition.
After getting home via Britannia Rescue (top firm, cannot recommend them enough - PM me if you want more detail) I checked the ignition as per the manual. No spark from an HT lead selected at random, no spark from king lead. Checked coil - 12V at +ve terminal with ign on, but nothing from the -ve terminal (note you have to remove the wires from the -ve terminal to test it as the amplifier is supplying 12 V). Took coil off, case badly cracked, so definitely U/S.
So far, so good, but now it got interesting. Which system is it, and which coil is the right one to replace it with? Jaguar fitted HE models with twin coils, then (according to the books) went to a twin Marelli set up with the face lift cars. But they also found that as better coils became available, the original twin Lucas system could be replaced with a single coil, and later cars, but still pre facelift, were so fitted. However, there is nothing listed in the parts manual. Further confusion arises from Nigel Thorley's excellent 'You and your XJS' book which mentions this mod but which suggests the single coil is a Marelli unit, and that all XJRS' have this system fitted. After much checking and cross checking, I eventually found that the right replacement is part number DAC6093, made by Ducellier. The KWE website has a very helpful picture against which you can select the right coil, see
www.kwengineering.org/acatalog/ELECTRICALXJS5_3.html
From what I read in Kirby Palm's book, and on the AJ6 site (what would we do without either of these sites?) I think these coils are prone to failure.
So, as far as I can tell, the situation on coils for V12s is:
Pre - HE single Lucas coil
HE up to 89 (ish) twin Lucas coils, but can be, and might have been, replaced with the single Ducellier coil
facelift (and very late pre facelift?) Marelli system with twin coils, and twin ign amp units fitted on radiator top cross member (esentially a coil and amp per bank).
Apologies for a long ramble, but if you are reading this with a dead V12 outside, I hope it helps!
HM
My '89 XJRS 6 litre died on the motorway last week. I had literally just got it MOT'd the day before after 2 years off the road, so I was probably asking for it... There were no warning signs, just a sudden loss of power as if I had just taken my foot off the pedal. The engine cut and I came to a halt fortunately well off the motorway. I could not get it to fire, but could smell fuel, so suspected ignition.
After getting home via Britannia Rescue (top firm, cannot recommend them enough - PM me if you want more detail) I checked the ignition as per the manual. No spark from an HT lead selected at random, no spark from king lead. Checked coil - 12V at +ve terminal with ign on, but nothing from the -ve terminal (note you have to remove the wires from the -ve terminal to test it as the amplifier is supplying 12 V). Took coil off, case badly cracked, so definitely U/S.
So far, so good, but now it got interesting. Which system is it, and which coil is the right one to replace it with? Jaguar fitted HE models with twin coils, then (according to the books) went to a twin Marelli set up with the face lift cars. But they also found that as better coils became available, the original twin Lucas system could be replaced with a single coil, and later cars, but still pre facelift, were so fitted. However, there is nothing listed in the parts manual. Further confusion arises from Nigel Thorley's excellent 'You and your XJS' book which mentions this mod but which suggests the single coil is a Marelli unit, and that all XJRS' have this system fitted. After much checking and cross checking, I eventually found that the right replacement is part number DAC6093, made by Ducellier. The KWE website has a very helpful picture against which you can select the right coil, see
www.kwengineering.org/acatalog/ELECTRICALXJS5_3.html
From what I read in Kirby Palm's book, and on the AJ6 site (what would we do without either of these sites?) I think these coils are prone to failure.
So, as far as I can tell, the situation on coils for V12s is:
Pre - HE single Lucas coil
HE up to 89 (ish) twin Lucas coils, but can be, and might have been, replaced with the single Ducellier coil
facelift (and very late pre facelift?) Marelli system with twin coils, and twin ign amp units fitted on radiator top cross member (esentially a coil and amp per bank).
Apologies for a long ramble, but if you are reading this with a dead V12 outside, I hope it helps!
HM
and the drive is noticably more lively.