No time for testing this morning as I was recruited to move a 1942 couch. Before I had to leave I replaced the dual coils with the new Jaguar DAC6093. This made a significant improvement that was immediately noticeable and combined with all the aforementioned changes has almost gotten rid of the missing. But it is still there. Very steady and much smoother. Power up a bit perhaps.

I assume my cat meltdown a while back also damaged the O2 sensors. So I popped 2 new Bosch OEM O2 sensors in. Well, that certainly did something. At least when they're active. When I pull the link in the trunk I can hear the car seeking a good mixture. Idle up, down, up, down. Just slightly, not like it's revving up or anything. It wasn't doing anything like that before. Does this take time for the ECU to determine, or is this normal?

EDIT: re-read the book on this. One wire sensors on this car do this because the o2 sensors cool and stop functioning properly at idle.

Metering the monitoring link is confusing me. Does anyone have a clear set of instructions for how I should do this check?

EDIT: Apparently I'm doing this correctly, but I'm getting significantly different readings from the two sides.

Thanks for all the help so far everyone! This is sooo much better than it was! Mileage is up, idle is smooth with only an occasional blip.

EDIT: I also found this frustratingly pointed paragraph in Kirbys book.

 

I have this operation on my task list, and the coil is already in my garage.
I have looked for the bracket for the new coil, would you happen to know the part no. ?

It's impressing to follow how much you get done to your car in short time. It must be quite annoying not to have nailed the problem yet, but now the goal is even more tempting: You will get in the Kirby book with the solution...

 

This is not a feature of mid 1980s UK spec cars, that is for sure. No cats, oxygen sensors, higher comp ratio, etc etc in the UK at that time. Maybe an ECU difference too?
Greg

 

Its possible the part you're looking for is CO-18525. You'd need 2. I haven't tried them as my coil doesn't live there any more. The single coil will fit where the Primary coil was mounted on the throttle capstan if you want.

 

I believe what I need is what Daim shows on this picture, lower right corner:

 

If you send that photo to Just XJS in the UK I would be amazed if they did not have the bracket you need.
Greg

 

You're right Greg, didn't think of that option. Andy to the rescue !

 

I don't believe that is an actual part. I believe that is a Daimco custom job.

The Jag version is an EAC5044.




If it's not available, I believe that 2 of the parts I linked earlier can replace that entire part.



If you went this route, you'd want to use two washers of equal thickness on the other two capstan bolts to keep the capstan level.

 

Here's a clip of the current idle, and revving.

https://clyp.it/2seagppw

My conclusion: Improper centrifugal advance performance was the root cause of this problem. Drive timing the car masked the issue as I added static advance that compensating for the lack of Centrifugal advance but making a smooth idle impossible. Fully advanced timing at idle is bad.

Timing it with a light to 18 degrees at 3000 w/o vac adv. would probably have made it obvious that I was missing some cent. advance, but perhaps not. Dizzy rebuild coming up...

 

So, JJ, are you saying that with a decent dizzy lube and new vac capsule connected to the port directly, you think all will be well?
Greg

 

I don't know. I have learned not to have expectations.

I'm pretty confident in my assessment of the C.Adv. not operating properly. I'll rebuild it regardless to be sure. Re-lubrication and a lot of exercise has changed it's behavior. It was not seized by any means. I have checked it numerous times. But it's action is smoother and easier now than it was.

I won't be running the V.Adv. direct from the manifold, as I want to use the dump valve. I will be checking all the components in the V.Adv. system again, Regulator and Dump ( edit: and WOT enrichment vacuum sw. ) valve are all that I am using.

EDIT: V.Adv. capsule is testing fine. Holds vac and smooth movement. I understand at some point Jag went to a "leaky" V.Adv. unit ( tiny hole ) to help the vacuum regulator function properly. Mine does not have this style. It is OE as far as I can tell.

The idle is beautiful now by comparison with before. If I can get the power and economy back to where it was with the timing too high I'll be very happy with it!

 

Greg,

Well, I can finally put this topic to rest. The answer to your query is Yes. Direct port connection and all is well! No new vac advance capsule needed.

In the "Comedy is all about the..." thread I discussed correcting my ridiculously high advanced timing. After testing for actual TDC, it turns out that my timing gauge on the motor is reporting 10 degrees higher than the actual timing. I assume my pully has rotated on the rubber inner hub.

Correctly resetting the dizzy to 10 BTDC and testing her made it clear my timing was the issue. It was timed too high to possibly idle well! But, even following Grant's instruction ( dizzy eccentric screw at full retard and reluctor and pickup alligned with 1A at 10 BTDC ) I was getting a little detonation under heavy loading. I contemplated pulling the dizzy back 3.5 degrees on it's mounting screws and moving the eccentric screw to 3.5 forward on it's scale to give me room to adjust it. Fortunately I was reading elsewhere and found a suggestion to run the Vac Adv straight off the top ports on the RH Throttle body. I hooked up my vac gauges to check it out.

The top throttle body port provides NO vac at idle, and slowly climbs on throttle opening. I connected this port directly to my vacuum advance capsule.

The result is perfection.

Buttery smooth idle like a kitten full of milk. Good power under load, no detonation, better throttle response! ( IMO ) I wish I had tried this when I first got the car and went through the vacuum advance system! It has literally transformed my experience driving this vehicle!

Future tinkering will include determining the max vac this setup provides and possibly adding the vac regulator if it is >10, drive-timing the static advancement to just below detonation levels, and possibly adjusting the response of the vacuum advance module ( mine is the adjustable variety ).

My summary, ported vacuum for the vac advance module is awesome!

 

So pleased, it is wonderful when they come right, isn't it. Have you please got a photo of where you attached the vac pipe to the throttle body?
Greg

 

Well done.

Good to have another SIMPLE fix on a SIMPLE engine.

Never did get the complications some have with the V12.

 

Poor injector spray patterns can cause uneven idle when warm. Worth using injector cleaner on your v12's.

 

I just dropped some Sea Foam in her. This weekend I'll pull the rail again. There a injector somewhere not pulling its weight. Sooooo close though!