My car is '92 V12, facelift 5.3.

I am wondering if I can advance the ignition timing a bit by loosening the bolt hole of the 3 arm timing disc on the crank damper and adjusting it.

I experienced advancing the timing gave me a nicer feeling and a bit more power on my previous X300. On AJ6/AJ16 the timing can be adjusted by replacing the crank position sensor bracket with the revised one (if you see X300 thread you will find a lot of reputation)
So if possible I want to adjust the timing disc to advance the timing around 5 degree.
In Japan premium is at least 96RON so I believe there would be no problem.

Any advice would be appreciated.
Thank you in advance.

 

no its not possible with the Marelli system,

the system is locked in , the only adjustment is the red fuel selector plug for different fuel ratings by the brake system pump, or get the ecu reprogrammed


BB

 

After reading up on Andy's bracket for the 6 cylinder, it makes sense that something could be done. I have a Marelli car, and feel very comfortable with it. I still wonder why you couldn't adjust the distributor for timing advance. The system has no way of measuring where spark is occuring in the cycle, so seems if you adjusted the distributor, you could accomplish this. It appears to have a great deal of adjustment in the base of the distributor.

 

Thank you for the comment BB.
I thought the crank sensor signal is the trigger for the ignition and flywheel sensor signal=engine speed signal is for the advance/retard, that's why I thought it might possible.
Is my understanding correct?

 

Hi superchargedtr6, I believe I can't adjust the ignition timing by rotating the distributor, for the timing is detected from the crank position sensor and unless I reposition the sensor or the timing disc I don't think I can do it. I think the shape of the rotor is also the proof... It has a wide terminal, which I believe means when the spark come sooner or later(advanced/retarded) than the base timing, it can still lead the spark to the distributor cap. This is why I am considering of this possibility.

 

don't forget the crank position sensor on the fly wheel as well, only the marelli system has this i think ??


if this isn't within 2 thou then you may be experiencing some ' poor ' running ??


BB

 

Yes I do remember the flywheel sensor, but does the flywheel ring gear have lacking of the tooth to show the A1 cylinder TDC? If not it only represents the engine speed, I guess... I'm not sure though.
This is also the point I want to know, what is the purpose of the flywheel sensor...

 

i'm sure the flywheel doesn't have a missing tooth , it detects the gaps in the teeth all the way round , and shows engine speed in relation to timing

BB

 

From what I have read, understand, the flywheel "sensor" only gives the marelli ecu the engine speed. Period. The front "sensor" is the timing. Says so in the factory manual if nothing else, lol. I agre with the idea that the rotor is wide, and it may not make a difference. What I learned about Marelli is how far these little magnetic generators need to be from their point of trigger. As the iron in the magnet weakens, so does the signal. Couple that with the magnet being too far away from its trigger source, and the car is going to have weakened ignition. I'm in no way familiar with aviation electronics, but from what I think I know, a lot of ignition systems to this day are magneto powered. And that the magnetos must be replaced every 2000?? hours of sevice, for the same reasons I describe above. I honestly believe that if your "sensor"s are more than .030 away from either the flywheel, or the crank fingers, you need to break out your file, and get them there. I first hand figured out that was what was wrong with my Marelli car that I bought on eBay as a non-running project. I corrected a reversed polarity on the crank signal, and adjusted the didtance of the "sensors" to their trigger points, and the car literally fired right up after 2 years of sitting, and untold money and hours of others trying to get it to run.

 

Supercharged, the only thing rotating the distributor will do is make the spark jump more or less from the rotor to the cylinder terminal post, it will not alter when that spark occurs. Make it jump too far and you create a whole lot of trouble.

 

I agree. Yet I also know thats exactly how we changed the timing on our cars since the begining of the internal combustion engine. Looking at the inside of a Marelli distributor, there has to be at least 30-40 degrees of movement. I also agree with the fact that due to the width of the rotor face, moving the distributor will most likely have no effect whatsover. With all of that said, I have personally dismantled the entire Marelli system, rewired it, and feel pretty confident that as long as the ECU is good, and those "sensors" and working properly, the Marelli is pretty good as-is.
I will again reitterate the point of the "sensors" being small AC generators. If you've never tried it, simply unplug it, and put a digital voltmeter on it. On cranking, mine puts out around .2 volts AC. Again, AC, NOT DC!! The ECU uses this AC signal to convert that data to a usable DC signal to the amps. If this AC signal is out of the designed parameters, then the Marelli system is not working at its optimum design. I'm only saying all of this, because I went through trial by fire. I bought a unknown history, low mile, 89 Marelli XJS from a shop that gave up on it. Looking back, I feel a little stupid for this decision. I let price overide intellect. With that said, when I got the car, it was a absolute mess as far as wiring goes. With help from several forum members, especially Mike in Ohio, I just scratched the whole system, and started over on wiring. Once Mike determined my ECU was good, by installing it on his car, from there it was just determining what was wrond, and where. I'm not sure how critical timing really is on this system. Due to the nature of its design, it has a very long spark duration, that other systems either aren't capable of, or lack the energy to provide.

I pointed this out on another Jag forum, and it didn't seem to generate much interest, so maybe I'm the idiot here. Yet, the truth is, I'm not passing along heresay. I worked through this. Even bought an handheld oscilloscope to make sure my "sensors" matched what the Jag manual said they should be, only to find out that a digital voltmeter will get you by. Put a ohm meter on one of these "sensors" and it it reads 690-750 ohms across the two terminals, it most likely is good. Make sure it is as close to the flywheel, and fingers as practical, and you've got a system that seems pretty good. By the way, you can't read voltage on these "sensors" as the pulse moves to fast for most digital voltmeters to read it. Got to use a old fashioned analog volt meter for that. Ask me how I know.....

 

One more thing,.......when trying to get my front "sensor" as close to the figers as possible, I found that the fingers are shaped in such a way, that every finger (all 3, lol) will vary. From what I remember, there was a .011 difference from "sensor" to finger. What I did was get the distance, by filing the boss, to .020 on the one that was tightest, leaving a distance of .027, and .031 on the other two. Either way, my rear started at .047, and that was too far away, at least for a older "sensor". May have worked when the whole system was new, but due to the low miles on this particular car, my thoughts are that if I could speak to the previous owner(s), I would find out that this car was problimatic from the beginning. I may be wrong here guys, but until proven so, I still say that if you own a Marelli car, filing those mounting bosses down, to get those "sensors" to .020, and you've done about all you can to optimize its function. Sorry to seem redundant in my "sensors" discussion, but they simply don't sense anything. They generate AC voltage. Period. No magic to it.

 

Thank you supercharged for the input. OK then it seems I can make an attempt. The division of the flywheel sensor and the crank position sensor on Marreli cars was my concern, now you make it clear for me.

I actually know the sensors create AC voltage. They have a small coil in them and generate voltage by Fleming's law. Diff speed sensors, ABS sensors, they all have the same principle.

 

As far as a marelli equipped car is concerned the traditional function of the distributor in starting the sparking process is gone. The distributor is now just that, a distributor of the spark generated by another totally remote system. You can not alter the timing via the distributor regardless of how much you rotate the distributor.

 

This is spot on. You CAN NOT alter ignition timing by rotating the distributor.

The 3 tooth wheel on the front of the crank is what the Marelli controller uses to fire plugs. The 2 teeth close to each other provide index the third one is cylinder 1A TDC.

 

Many thanks for all the input guys, I will try having the hole machined and adjust the position of the 3 tooth disc to fool the ECU.
Hopefully I changed the crank damper a year ago and I have a spare disc.
I will report when I have done this.

 

Dug out an old thread.

Finally I put on a revised timing disc.
I haven't finished the task completely yet, I still haven't installed a fan unit and rad upper panel... So I will post again tomorrow. In the meantime I upload some pics.

 

I have always felt that the V12 could use a bit more timing advance so I am very interested to see how this works out.

Mark

.

 

Job done.

Eventually I made approx 5 degree advance.

I started to drive a car and gave it an acceleration... Significant difference!
The torque and the smoothness are increased. Revs up more sharply than ever. Stinky thick exhaust gas is thinned.
No placebo.

The Intake and exhaust sounds a bit louder now when running.

I have done several mods like cold air intakes, replacing viscous fan to electric fan, deleting 2 cats, but this mod makes the most noticeable change.

This is only a step away from the belt change. Undoing all the belts are the most painful part...

 

You chose difficult way. There is no possibility to adjust.
https://www.jaguarforums.com/forum/attachments/xjs-32/84878d1400616240-what-if-front.jpg