I did some research about the PetronixD72000 aand have a theoretical question, since im not going to order it yet - not befor i have sorted out the head gasket topic.

The manual the PetronixD72000 says its for V8 engines only and its a multi spark system. The for V8 only should be no bigger problem, you just have to keep it in mind when setting the rev limiter - 9000rpm on a V8 would be the same as 6000rpm on a V12.
But the multi spark system got me thinking - doesnt the ECU get the signal from the ignition amplifyer switching to ground (spark). Wouldnt the ecu read a false rpm if the amplifyer creates multiple sparks?
The manual of the PetronixD72000 even says its not to be used to trigger ecu's.
Anyone ever had a thought on this? I think some people do run the PetronixD72000 pretty successful.



For my head gasket problem:
There are two signs for a blown gasket: the pressure loss and hissing in the next cylinder and the rough idle.
many against: clean plugs, no smoke, no water or oil where it not belongs etc...
Is there a way to surely tell its blown. I dont want to change it and then find out its not blown at all.

 

Not aware of anyone reporting on V-12 installation. I have had excellent result on XJ6 S3 with the D72000. Even though Pertronix does not recommend for for ECUs using ignition coil as source for trigger, The Jaguar wave filters to get final batch injector fire timing (not required to be accurate) and time for injector to be open (very accurate) seems to work fine.
If you look at ECU WAVE input A, it appears that a rapid second spark would not upset the final wave for fuel delivery. I think there are too many EFI systems for Pertronix to verify. Most new systems use a tooth wheel on the crank for signaling.
I Agree on your having to adjust RPM limiter for V-12 vs. V-8. I did not set RPM limiter lower for six cylinder.
Rgds
David

 

Thank you that is interesting and good to know

For my head gasket problem: I read through hours of workshop manuals now and came to one conclusion:
The engine has wet liners with a open top end. So a head gasket failure between to cylinders without a connection to the cooant is basicly not possible.
Is this thought right?

BUT if the head gasket is blown between two cylinders there is a bigger connection between the two cylinders than to the coolant system (because of the touching liners) - hence the hissing in the next cylinder and not in the cooling system.
But if i pressurize the cooling system, i should see if i have a loss to the two cylinders by listening. I will try that now since the coolant system is empty at the moment.

 

It is certainly theoretically possible to have a blow between two adjacent V12 cylinders with no leaks of coolant or oil. For a while....

As shown in this video, the cylinder liners butt up to each other, even though there are wet liners there is the slight possibility of a cylinder to cylinder leak across the butted up joint. However it would not take long for such a leak to expand!

 

ok, so the butt up and seal pretty well. But the chance that this happens at both banks in the same way is pretty small.

another explanation would be a dirty intake valve blowing to the next cylinder over the intake manifold.

What would you guys suggest? have a eye on it if it expands?

 

I suggest you do a leak-down test on each cylinder.

 

ok, i almost thought **** it, i build it up again and give it a try but then i changed my mind and followed your advice.

BUT befor i did all cylinders with a leak down test again i did a compression test on all cylinders. First i thought its a good cross check and second i thought its good for the leak down test when the engine had some movement from cranking befor.

So the compression test resulted in 10.5-11 bar on all cylinders, no significant differences at the cylibders.

so i did a leak down test again, this time for all clyinders and wow - now 6B suddenly is at 15% - slightly hissing, but its also noticeable in the inlet manifold. all other cylinders are in the same range, none above 20% loss.

So i think i spent some sleepless nights for nothing, i would not assume a bad head gasket from this result.

I also tested the Vacuum advance labyrinth and it works in the 'no voltage' state. Have to see if it changes state after 15min as it should.

Now one thing came up while cranking for the compression test: The earth cable from the battery started smoking on the screw to the chassis. I cleaned that connection befor but did it again and still smoke. I think its the crimping of the cable shoe that gone bad.

So, my to do list for now:
- Change the earth cable
- build it back up and see how it runs
- check ignition timing
- if it still runs bad, measure the fuel pressure
- if fuel pressure is fine change ingnition amilfyer

 

Well done.

 

short update:
Changed the earth cable from the battery, also changed the ignition amplifyer since i had everything disassambled.

Started it up shortly to bleed the cooling system and it still had a somewhat hard start and runs rough.

So next i will measure the fuel pressure. what pressure do i look for with vacuum disconnected?

 

still waiting for my pressure gauge.
But i have good news on the temperature. It gets up to 90° now and stays there spot on. maybe a bit higher after high load and then back agaib at 90. no flickering or whatsoever.
I changed the tenp sensor and the filler cap at the side reservour. one of the two did the trick.

when hot it idle at 1000rpm, thats a bit too high.

i also did some looking for vacuum leaks. didnt find any.
- unplugging the fuel pressure regulate from vacuum changes absolutly nothing
- unplugging vacuum advance drops rpm rapidly and it runs a bit smoother, so i will check the general advance next.
- i then reduced the idle to 750rpm via the adjustment screw at the AAV. it runs a bit smoother but not perfect. I also noticed that the screw is almost all in at 750rpm. maybe the AAV does not fully close or there is a small vacuum leak somewhere else.

 

How long does the car need to sit before it has trouble starting? Just once it gets to ambient temperature or a bit longer? If my XJ-S has been sitting for more than about 3 days, it starts the way your XJ12 does. But if I had it running earlier in the day, or the day before, it starts right up. It seems to not be holding fuel pressure, but I haven’t really dug into fixing it yet.

 

its hard to tell when the engine really has ambient temperture but over night usually causes the problem.

holding fuel pressure seems not to be an issue since multiple priming of the fuel rail does not change a thing at mine.

 

Ok there are news from the workshop:

I tested the fuel pressure and it is fine at 36psi.

I also checked the ignition and now i have to do some research on the vacuum advance, that i hope you guys can help me with.

So the should be for the V12 H.E is 18 degree at 3000rpm with vacuum disconneted.

Here are my results:
800rpm, Vac. connected: 13°
800rpm, Vac. disconnected: 0°
3000rpm, Vac. connected: 33°
3000rpm, Vac. disconnected: 14°

Ok that would mean: First of all the overall ignition adjustment is off by 4° to late since i only have 14° and not 18° as it should.

BUT the Vacuum advance is a LOT and gets more with higher rpm? can that be right?
Does anyone know how much Vacuum advance you should get at what state of the engine.
I know vacuum advances of maybe 6° at other engines...not 13° at idle and going up to 19° at 3000rpm.

Are there any ideas how it should be and what could cause this?

 

First of all the figure prove your vac capsule is working!
Second, advance does become greater as revs rise. This because the time for the flame to propagate in the cylinder is basically fixed, and the spark at a few degrees before TDC needs the time to propagate so by the time the cylinder is just over TDC on the power stroke the flame is going good and hard. As revs rise, because this flame propagation time remains more or less constant while the actual time the cylinder travels from (say) 10° BTDC to just after TDC greatly reduces, the extra advance gives the flame enough time to propagate before the downstroke. If it did not advance, the flame "high point" would be well after TDC on the downstroke and thus the power stroke would be far less efficient and powerful.
14° advance at 3000rpm vac off is not that far out, and I doubt it is causing your misfire; but worth correcting, obviously.

The peculiar characteristics of the May fireball head in the HE engine means that plenty of advance is needed because the lean burn flame propagation system needs more time to get the mixture properly ignited. This system works by the injected mixture on the compression stroke being squeezed from directly under the intake valve through a narrow passage into a 'hole-shaped' chamber under the exhaust valve. Then the very lean mixture is just rich enough (by design of the chamber) around the spark plug, which pokes into this 'hole', to ignite. Once alight, then the flame is able to light the much leaner mixture further away from the spark plug. All this takes time, hence the greater advance on HE engines.

 

Thank you for that detailed information. So that high vacuum advance is nothing to worry about and the whole vacuum system seems to work when the engine is hot.
The vacuum advance is at 13° at idle, shortly drops to zero (to prevent detonation) when quickly opened and then rises again even higher.

It does not switch to the other mode when its cold but that should only effect the warmup.

It does not really misfire...it has some losses causibg a slightly rough idle. and the cold start problem. But i assume the cold start problem has nothing to do with ignition advance

 

i did some research and the static advance should be 0° (at 750rpm) and 18° at 3000 rpm.
That means i am nlt that far off for the mechanical timing and i will adjust that be the missing 4°.
That would maybe also solve the problem that engine feels a bit lame.

the 13° vac. advance in idle also seems to be normal.
What i did not find: whats the maximum vacuum advance? should i adjust the mechanical limit from the vacuum capsule?

What makes me worry:
if i advance the overall ignition by 4° now, the idle will rise and i am already at the limit of the adjustment screw at 800rpm.

 

You are at the adjustment limit because the AAV is sticking (very common). Deal with this, I suggest, after you have done the timing and the injectors etc.

 

i had the AAV out and tested it. it did fully close at 92° degree. maybe its a bit lame since it should fully close earlyer. Gotta have it rebuilt i think.

The injectors should be fine, i am currently running a engine cleaner with the fuel through the engine and will get some miles on it.

The cold start problem is still a mistery

 

I spent hours thinking about the markings for the ignition timing.

maybe someone can help wrap my head aeound this.
The markings look like this from the front of the car looking backwards:


isnt that switched up befor/after when the engine is running clockwise? but the reading where correct towards "befor". I am really confused and got a bit nervous that i might have turned the engine in the wrong direcrion while doing the pressure loss test.

 

forget the last question i had a brain fart from being upside down under the car. befor and after are switched and therefore correct.

i have adjusted the timing and it runs like a different engine. definatly more power an way smoother while driving and accellerating. Sounds and feels way better.

slightly rough idle and hard cold start is still there but i think i can live with that for now. I will rebuild the aav next winter, now i want to drive