Use of Coupe 86 V12 to replace dead Convertible 88 V12

Found a 1988 Convertible XJS with an engine that has not ran in over a year, and does not turn over - will an engine from a 1986 be a usable replacement - no ECU for the 1986 (stolen) but all else there - would the 1988 ECU run the 1986 engine - the 1988 is in a much better shape body wise than the 1986 (which also has a bad transmission) - anyone with experience of such a change out? - Thanks, Tex.

I presume the 1988 has Lucas ignition? If so, I think you can swap them right out.

Waiting for confirmation of that (Lucas type) - I thought it might work, but not sure about the ECU from the 1988 running the 1986 correctly - Tex.

I think you could check the serial number on the 88 to make sure, because unless I’m mistaken the cutoff between Lucas and Marelli happened at 88 ½. On the other hand, I would think that it would only be a matter of swapping distributors if your car already has the Marelli ignition system.

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You’d need to swap the entire ignition system, including coils and amp. Pretty easy to do, though.

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My car is an '86 with a “Marelli” engine from a later year. Previous owner has done the swap, indeed using the complete '86 ignition. Don’t know how the timing was adjusted: there’s no timing scale on the Marelli engines… Anyone has tips on how to do that?

I believe at TDC the distributor needs to be pointed to the 1A spark plug and the ECU does the rest.

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What is the VIN on the 88? My 88 is VIN 141xxx and is Lucas. The 86 and mine would be pretty much identical. ECU would work no problem.

So if your 88 is pre-Marelli, you should be golden.

Note, if the 88 convertible IS a Lucas, then it must be a Hess & Eisenhardt convertible? If it’s a Marelli, then it’s a factory Convertible?

Greg - the VIN on the 88 is 139xxx - so according to you this should be Lucas and swap should work - thanks, Tex.

Ah, I wasn;t clear enough I guess: question was on how to set the timing on Lucas ignition with Marelli-type engine. In other words; how to set timing with lucas ignition without having timing marks. scale?

There is no such thing as a Marelli type engine. The only difference between the two is the ignition setup. On either engine there has to be timing marks that shows you where TDC is, and even it there isn’t, just bring 1A up to TDC

ok, … not a different engine type then. is it OK to say that configuration of engines for Lucas and Marelli is different? becaus it is:

  • engines-configured for Lucas ignition have timing mark + scale
  • engines-configured for Marelli ignition do not have a scale but have sensors for electronic ignition timing instead.

Sure you can find TDC , e.g from removing 1a sparkplug etc, but then still: setting timing advance to whatever degrees are necessary will not be straightforward.

I was hoping for tips on this topic

Over think in progress!

Find TDC. Point the rotor at that cylinder. that will enable the engine to run/ Set advance by ear. Just before ping on load. Done

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Ye gads nobody gets what he’s asking? He has Lucas ignition and needs to set his timing!

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Well, the method described bij Carl is kind-of the tip that i was asking for… Engine seems to runf fine, but i would like to really tune it well.
:slight_smile: Overthinking this more: I COULD use the timing sensors that are still on the engine to set the timing. “just” would need to know what time the TDC sensor is set (0 TDC?) and how many pulses per rotation from the flywheel sensor. Woud be fun to connect all this to some computer and use it to set timing. Probably no-onre tried this as there’s probably not a lot of pre marreli cars with engine swapped with marelli etc…–> i;ll go for Carl’s suggestion

IIRC, the timing scale on the Lucas cars is a bolt-on item. So can’t you take the one off the 86 and bolt it onto the 88?


Just a follow-up here - unfortunately, I was not able to acquire the 1988 XJS convertible - so I will not be doing the conversion yet - hopefully I will find another 88 - want to say thank you to all who provided the information on the possibility of doing the engine swap - taking out the dead V12 from the 1988 and installing the known good V12 from my 1986 in to the 1988 convertible - again, thank you - Tex.

Good point!. In my case, however, previous owner didn’t fit the timing scale during the swap (>10 years agoo). If i’m not satisfied with the “tuning by ear” method, I will search for one.

Ask here. I’ll bet someone has a spare. And it’s tiny enough to easily drop in the mail.

I would definitely not trust the timing by ear method. That suggestion came from Carl who has a lump in his car. On the V12, knocking can be so faint as to be difficult to hear – but it can do some very expensive damage to your pistons.