I think by now all of us know the X300 has an ignition coil life problem. If you have OEM coils they last about 120,000 miles. After market coils last about a year according to some members that have posted. My OEM coils that were on the car when I bought it with 65,000 miles lasted to about 110,000 miles before starting to stall the car when stopping. I was lucky enough to get a set of the Japanese made coils that were made during a second production run of the OEM company. With 145,000 miles on the car now I want these coils to last a very long time. I believe the main problem is probably heat. So I made a modification to the coils mounting and the coil aluminum cover. I removed the coils (found two with oil in the wells that didn't seem to cause a problem) and removed the paper gaskets. I remounted the coils with fiber washers under the coils where the bolts go through. This raised the coils slightly giving a gap for air circulation. With the aluminum cover I have remover the rubber seal around the edge of the cover and used fiber washers between the cover and the head where the three bolts are that hold the head in place. This also gives air circulation for cooling. At least some cooling.

The car runs fine with these modifications. I don't know if I will get more life from the coils or not. But it makes me feel better for now. I will let everyone know if I ever have problems due to these changes.

 

I do wonder why we should have a coil problem other than poor quality coils.
The coils on my 1996 XJR are all original at 175000Km's & I have never suffered problems. Many engines of all makes have their coils located in the center of the cylinder head in the same manner as the Jag. its not an unusual scenario.
I must admit my plastic coil cover (its not aluminium ) does not have the seal in place & never has. I always thought it was a good idea to have the slight air space between it & the Cam cover. Why seal in any heat generated. The seal is shown on the attached part listing.
I would just check the cover is clearing the bonnet insulation, my cover is secured directly to the attachment points ( no additional washers) & I note it does have slight rubbing marks on the front right hand corner from contact with the under hood insulation.

John Herbert
(1996 Jaguar XJR)

 

You're right. It is plastic. As far as other engines with the same coil arrangement also have problems. My 2000 XK8 recently had one of the coils go bad and put the engine in safe mode. And I mean the coil completely stopped working for short periods. You can go to those threads on the XK8 and read that episode. And that is a Ford engine. Talking to mechanics, Ford has had a coil problem for sometime. I think all engines with this coil installation have problems with failures. The X300 coil failure is not total like it was on my XK8. It just gets weak and causes the engine to stall at idle. This I believe is typical of a heat problem. Just MHO.

Come to think about it, I might do this same mod on my XK8. I don't want another coil failure on that car. With that car you get a total misfire and safe mode. At least there you get a code that tells you exactly which coil.

Thanks for responding, John

 

Well.... OTOH, if we can reliably say that the OEM coils last 100-150k miles over 10-20 years, I think that's pretty good, and likely the design life expectancy of the coils and likely just about everything else on the car. If that truly is their typical lifespan, we may not be dealing with coils that fail early per se, but just coils that wear out. So while we might be able to extend their lifespan, which is a good thing, I don't know if its a priority to really figure out if they are indeed lasting that long.

I've had a lot of cars whose coils, distributors, COP coils (yes, that's redundant ), ignition modules, etc all seem to last around 100-150k miles or 10-20 years, "whichever comes first" as they say And I think that is pretty reasonable. Would I like them to last 200 or 500k miles? Sure, but that's probably just not realistic for coils that cost $50-200.

The paper gaskets under the coils serve two primary purposes as far as I can tell, which is to keep water out of the well, and to insulate the coil from heat and electrically from the valve cover.

The rubber gasket around the plastic cover is to keep water and debris from getting on the coils and the coil wiring. It isn't water-proof, especially since it is open at the rear, but I assume is meant to control moisture.

So opening that all up to circulate air might cause more issues than it solves by allowing water ingress, plus that small amount of air-flow likely isn't going to make much difference to counteract the heat from the head in which the coils sit.

Ironically what would really likely solve this problem is to do what Aston Martin did:




They went old school and put the coil(s) away from the AJ16 engine and used wires


.

 

Do I understand you that Aston Martin went back to a distributor instead of individual coils. What year was that? I thought that a computer controlled engine required individual coils due to the need to control individual cylinders which I believe that is the case here and from this point on.

 

I'm no expert on how Aston Martin implemented the Jaguar AJ6 engine ignition on the DB7, but here's some additional information:

Aston Martin AJ16 engine (3.2, 250 kW)

https://en.wikipedia.org/wiki/Jaguar_AJ6_engine


...the topic of failed coils and that Aston Martin used wires, or "can we use the Aston Martin valve cover" comes up every so often, but the consensus on the latter I think is "no". I can't say whether one could modify the coil implementation on the Jaguar X300 to use wires, but I don't see why not if enough effort was invested. After all, my 1995 Buick Riviera (all GM 3800 engines) use a hybrid of dedicated coil packs (one coil for every two cylinders, lost spark) that are external to the head and plug wires that run from the coils to the plugs.

Simplistically, one could in theory just mount all six X300 coils in some sort of bracket, extend the coil wiring to that location, then replace the coil rubber extensions with custom wires that run to the plugs. Would that work? Not sure, but it probably would work, although there may be resistance considerations due to wire length. Testing would have to be done.

Is there an advantage to doing so? I have no idea.

.

 

 

Darn good price. I also have a set from eBay on standby. With those coils installed a hearty suggest you do the air venting process to accomplish some cooling. I believe heat is the worst enemy for coils that sit all snugged up not the cylinder head.

 

What if someone, like me, added a 1/4" tall nylon washer on each of the bolts holding the coils down? Would that help? I don't know. Right now, I run the car without the plastic coil cover, I can't imagine there's anything more significant I can do, short if opening up some holes in my hood!

 

I still have my OEM coils, just turned over 100K on my 95 X300. I also took that plastic cover off years ago. So far so good, shouldn't brag though.

 

You were smarter than I was. As I mentioned I got to 110,000 before it started to stall now and again. But I was lucky that I got in on that rerun by the OEM maker. And doing the mods I talk about the coils should last as long as I do.

I consider the 95, 96, &97 the best Jag of the modern generation. From 98 on I'm not interested. I'm keeping mine and enjoying every drive.

Keep'em running Guys and Gals.