Okay sooo bottom line is there is a 1989 xjs for sale in my area for $800 in beautiful condition except the engine is locked up from a dropped valve or who knows. I have an '86 engine laying around that's a real strong low mileage engine and I've been looking for a car to put it into. This 1989 has marelli ignition.

My question is can I swap electronics over to the '86 without any problems? Were there changes made to the block or cylinder heads between '86 and '89? I heard there was a crank sensor added in '89. Is this swap possible?

Thanks!

P.s My 1988 xjs is running great and I've been using it as my DD for the past week or so

 

I set up an 87 engine to use my existing Marelli ignition. Make sure to use your existing engine wiring harness. You also have to use the harmonic balancer from the 89 engine as well. and the timing cover. The 89 cover has a mount for the front magnetic sensor that reads the three fingers on the harmonic balancer to tell crank position. You will have to drill and install a couple of roll pins to mount the rear panel that closes the front bottom of the bell housing. The Marelli counts teeth on the ring gear for engine starting and uses another magnetic pickup. That is why you have to use the 89 engine harness so that you can connect the two pickups.

 

The pickup for the ring gear mounts on that plate. There is a small amount of play in the two bolt holes and the clearance for the pickup is important. Get your dimensions from the 89 engine when you pull it. Pull the three studs from the cover that the front of each head secures to so that you can remove the timing cover without pulling the heads.

 

Those sensors need to be within .045 of the flywheel, and the fingers on the front pulley. From what I can figure, .020 is even better.

 

mikebaker3, is there a thread or website journaling your XJS swap? I'd love to read it.

 

Wow. That sounds daunting. Forgive me if I'm misunderstanding but (Mike) you are saying there are two sensors, plus the harmonic balancer that will have to be transferred- one sensor in the front of the engine and one on the flywheel. What is it that I'll have to drill?

Mike, how difficult did you find it adapting your '87 motor?

I guess if I had both engines sitting next to each other I could do this. All the money this would cost should really go into my '88 xj-s if I had any common sense but I just hate to see another xj-s go to the crusher.

 

I hear you brother. If it were in Houston, I'd buy it. Mothball it in storage for a year till you're ready to start working on it.

XJS prices can't go anywhere but up!

 

If you are brave enough to tackle a engine change in a V12 Jag, I assure you, switching over the parts to mount the Marelli sensors will be the least of your worries. As Mike says, one mounts at the bottom rear of the engine, and the other is at the front bottom of the timing chain cover. I bought a non-running 89 Marelli car, and after being given up on by a shop, it wound up on eBay. After much help from forums, and the dedicated folks that frequent them, I now have a pretty good grip on Marelli. The sensors are actually small magnetos. On my car, the rear one was too far away from the flywheel, and gave the Marelli ECU a poor signal. These "sensors" send a AC signal to the Marelli ECU. The rear one starts out at maybe .2-.3 volts, then goes up from there, depending on engine speed. The front one controls timing. From what I learned, they are very important. But a feeler gauge, a small file, and you can get them in a perfect position in no time. I set my rear one at .020, and the car fired right up, after being given up on.

 

If I have this correctly, you are going to install the 1986 engine into the 1989 car that already has the Marelli loom, ECU etc stuff?

This should be pretty straightforward, as the Marelli looms, amplifiers etc etc are all in the car. Just make a careful note and take photos of EVERY wire that is connected to the 1989 Marelli engine. Undo them and label each with where it goes. Then pull the engine, swap over to the 1986 engine the sensors etc and the dizzy off car.

For the dizzies, get BOTH motors to TDC on the compression stroke on cylinder A1, then remove the dizzy cap and carefully note and photograph the position of the Marelli dizzy rotor. Unbolt dizzy and install it in the 1986 motor in this exact same position.

I think this will work Ok and be quite do-able for the determined enthusiastic owner.

Greg

 

I have to totally agree with Greg, this shouldn't be so hard to do, its better going forward and using newer bits and pieces than older.

Let me just throw another spanner in the works here, if your not in to much of a hurry to put this motor in, do a little reaserch and look into simply changing the Ignition and injection control system. I have said this a number on times on this forum we need to look into systems like Megasquirt, Haltech or Wolf to transform our motors to distributor less ignition and and a better injection control. Basically a better all round ECU that will dispose of 90% if not more of the gremlins in these cars, the added performance wont hurt us much either.

 

Katoh
In principle I agree with you (but this is miles off topic for the OP and does not in my mind, constitute a serious alternative for him). My problem with using the more modern stuff is twofold:

1. I believe, and am open to correction, that the only way you can set up a new ignition and injection system correctly is on a rolling road or a dyno. I cannot see how an individual can set up a system properly without these things being available for a considerable period.
2. The Lucas ignition HE system is very reliable. I have yet to be persuaded that an aftermarket system would produce any more power, any more MPG, or be MORE reliable than a re-loomed OEM system.

If an aftermarket company were to produce a bolt on ready mapped system with clear benefits, I would be all for it. Finally, any modern electronics I have put into my car (eg timer relay for the fan switching so it did not cycle too much) has had a half life of about 9 months, if that, of not that frequent use - owing to fuel poverty... The V12 is not that forgiving a place for modern electronics, I reckon.

Greg

 

Greg
I must agree and disagree with you.
Firstly I apologise for taking the thread in a different direction, but while someone has the opportunity in a motor swap and must look at what system to use why not go that bit further and look into the distributor less ignition.

Now I have researched a little and know that the new range of Megasquirt will handle spark and fuel on a V12 with no problems, I have spoken to the guys at DIYAutotune and gone through it with them. For spark to work its very similar to the way the Merralli system is using a crank angle sensor only now we use 2 at 60Deg apart, we can use either 2 banks of 6 coil packs or better is the 3 banks of 4. All settings can be programmed in to mimic standard distributor ignition settings and fuelling can be set all without a Dyno, Once your up and running then I agree go put it on the Dyno and get the most out of it.

There is plenty of information out there so I really don't need to get into specifics, Phillip has a wealth of information on this read his findings here Dual EDIS ignition.
As far as I know there is no off shelf alternative but you can make something much better with a little effort.

 

I did not do a thread about the swap, but I am working an a V-12 in a MKIX swap and have the engine sitting in a stand. I will take some photos. The only drilling was for the roll pins for the rear cover. I will post some photos in a week or so about that step.