Timing issues and next step?


I have finally discovered why the v12 is so gutless and angry in the cold. The timing is waaayyyy off. Through the use of a timing light I have discovered that the spark on cylinder 1 is 50 degrees after top dead center. Does anyone know how to remedy this?

What year etc. since several ignition systems were used any help will need that info. May be as simple as the distributor body has moved but may also be more involved.
Edit. Just checked your profile. If it is the 84 HE you could start by checking the security and static timing of the distributor and the condition of the advance mechanism within.

It’s an 84 with the Lucas system

Kirby Palm’s book has a good writeup on the distributor and timing. The Jaguar XJ-S Repair Operations Manual (ROM) also has a lot of helpful information. There are both vacuum and centrifugal advance mechanisms in the distributor that need to operate properly. Often one or the other is bad, I just experienced and fixed a bad vacuum advance. BTW, timing is checked at 3,000 RPMs with the hose removed from the vacuum advance and plugged. The 3,000 RPM part was a surprise to me when I first learned about it. That is not intuitive. :wink:


I think that means it’s one cylinder off. Are you sure you’re looking at cylinder 1A? If so, check that the spark plug wires are correctly located on the cap.

Yeah, each rotor turn from one plug terminal to another is 30 degrees (360/12=30). And if I remember, that equals 15 degrees of timing? So “hopefully” your plug wires are just one or two off.

If not, then your distributor is several teeth off, and you’ll have to pull it and put it back in. I would get the engine to #1 TDC, and static time it. Been there, done that. A lot of work, but good to get car to square 1.

Or as a hack, you can put your plug wires one off to compensate until you get the right timing.

Sounds like previous owner didn’t get distributor in right. I understand, took me a couple tries. MUCH more difficult than a 4 cylinder engine!

Also, if your engine is truly 30degrees too advanced, I would think the thing would be pinging pretty badly.

Yeah the car is running pretty poorly
Can’t hear any pinging though.

I’ll go ahead and move the plug wires and see if that affects anything.

Then do it properly if the test goes well
Thanks again for the input

Yeah, but that’s half of crank degrees. This engine has a fire every 60 crank degrees. Since it’s normally timed at 10 degrees BTDC and this guy claims his is 50 degrees ATDC, it’s one cylinder off.

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Oh, I misread it as 50 degrees BTDC! So yeah, no pinging. Car must run terrible if it’s 50 ATDC! Supposed to be 18 BTDC, so it’s 68 degrees off? IMO, it shouldn’t even start! Maybe he tested it at idle, which could be about 0 BTDC. So that’s 50 degrees off.

Idle was the best the engine could manage at the time.
Probably should have mentioned that sooner.
Also, the engine has been “backfiring” out of the intakes a lot recently, (it almost looks like flame coming out In Low light) and it will start if you try hard enough.


We also don’t know what RPM he tested the timing at or if he disconnected the hose to the vacuum advance. So I am not sure what his timing reading of 50 degrees ATDC really means.


Yeah, best thing you can do for this engine, static time it to #1 TDC and go from there.

Sorry I should have out right said those numbers at the beginning of the thread

Rpm was somewhere around 1500 (fluctuating)
Vacuum advance was disconnected
And the centrifugal advance system was working

Check what the decal on the underside of your hood says about the timing, start there, and then make your adjustments. I have no idea what the timing should be at 1,500 RPMs or what using that value means.