Okay... The front is still for the ignition

 

My handbook states both are for the ignition (sorry for that) BUT the front is for general ignition trigger. The rear for engine position (TDC on 1a). A combination of both would present the engine with a full setup.

If the front or rear are problematical, then all the cylinders would be affected, not only one side.

To be a bank on it's own, would mean it is something between the ICU and the coil. The ICU does both banks. As it fires normally on A and not on B (or vice versa) it can't be the ICU as such. But behind the ICU are two ignition modules (on radiator support), followed by two coils, followed by two distributor rotors merged into one... Then the HT leads.

I still think it is rotor related. Everything else has been checked or would do the same on the other side...

 

Thanks. To be sure. Do you think it's possible to switch all HT leads => A to B and B to A and adjust the position of the distributor. You put Coil B on A position on Cap and vice verse and move all HT leads. On 6 cylinders it's easy but on V12 I'll check if it's possible.
DO you have détails concerning magnetti Marelli Ignition?
And for remember, when I start the engine (when it's cold) during 45 s all it's OK.

Nicolas

 

Hi Nicolas

That does not sound like a good idea to me!

The Lower Coil the Red One goes to 'A' Bank

The Upper Coil the Yellow One goes to 'B' Bank

Get those the wrong way round and She won't Start

As for the Marelli Ignition, inside the Distributor is a 'Stepped Rotor' (Like half a Rotor on top of another half Rotor) if you see what I mean

The 'Top' of the Stepped Rotor operates 'A' Bank

The 'Bottom' of the Stepped Rotor operates 'B' Bank

Like 2 X 6 Cylinder Engines Joined Together

If the 'Stepped Rotor' ever gets burned by shorting through the 'Cap' more often than not its the 'Top Step' which then Shuts down 'A' Bank and leaving 'B' Bank Running, while the Exhaust Box on 'A' Bank can then fill up with about a Gallon of Petrol, already to burn the Car to the ground

If somehow 'A' Bank should attempt to Start, which could be very Bad News!

Anyway we haven't run out of 'Tricks' Yet!

Next thing to try is Cleaning 'The Resistor Pack' which very often gets overlooked because it really doesn't look like it does anything, except this is a Vital Component
That can really play havoc with the Firing of the Injectors if the Pins inside it get corroded or dirty

This is a little Silver Box about the size of a Cigarette Packet, which is located down by the Headlight Nacelle drivers side on a RHD Car, its only held on by a couple of Bolts which can make it awkward to get out

Though it needs to at least be turned upside down so that you are able to give the Pins a good Clean and also the same with the Plug, that Plugs into it 'Lemon Juice' and something like an old Tooth Brush, would be ideal, as the Pins need to be 'Shiny Bright' just like I did mine (See Link Below)

Then when it is nice and Clean and Dry put the Plug back in, then bolt it back into position and then give the Engine a try

Cleaning the Resistor Pack on an XJS V12 as a dirty Plug and Socket can Play Havoc with the Firing of the Injectors 'Cherry Blossom' Restoration Thread Page:11

 

I have the official Jaguar diagnostic book in paperform and no scanner, so it is hard to do anything.

Do NOT simply try to replace the firing order of the HT leads... That will cause havoc, as said by OB.

Question right now is: is it ignition or is it fuel?

You can put some little light bulbs in between the connection of the injectors and see if all fire after 45 seconds or not. No fuel might be simply a broken wire which, when warm, expands and causes a short or so. I would give that a check to make sure WHAT part of the combustion process is missing.

Missing sparks are a common thing on the Marelli ignitions, but so are issues with other things...

 

Hi Nicolas

Forgot to ask, did you fit the New Flywheel Sensor?

As any possible causes of the problems you are having need to be eliminated one step at a time

 

You mentioned that you changed the spark plugs. Pull one and verify the gap. The Marelli cars are very sensitive to spark plug gap. The wrong gap also has been responsible for the rotor failure with the Marelli ignition.

 

Hi Nicolas

Even if you haven't fitted a new Flywheel Sensor yet, there is something else that we can try so please get back and then we can hopefully get your Car running again

 

Yesterday I checked resistor pack, ECU contact (cleanning) and potentiometer.

ECU potentiometer => NOK
ECU and Resitor pack cleaning => Good, not perfect but a marked improvement
But I don't know if it's ECU or resistor pack the root cause

In the past I had cleaned several times.

I'll test for more time.

Thank you for your help. Nicolas

 

Hi Nicolas

Going by what you have mentioned 'A' Bank seems to be running ok

And 'B' seems to run ok but not for very long!

Which is now leading me to think that it could be the AAV (Auxiliary Air Valve) that is causing the problem, which is on the 'B' Bank side of the Car just to the rear of the Airbox: So have a look at this Photo first, just so you know what it looks like and where you can find it (there is only one of these as 'A' Bank doesn't have one)



The Auxiliary Air Valve (AAV) on the 'B' Bank Side of the Car to the rear of the AIRBOX Note the Adjusting Bolt that's on the Side

Inside the Alloy Body of the AAV (with the adjusting screw on the side) is a Piston which can sometimes get stuck during a layup or through lack of use of the Car

So if the Piston in the AAV is 'Stuck Open' as is very often the case with that fault, then as soon as you Start the Car the Engine will Roar away where you would notice a very high RPM But not for long, as this sends a Signal to the ECU to cut off the Fuel to the Injectors on 'B' Bank, at which point 'B' Bank starts to die!

But once again not for long, because as soon as those Revs go down, those same Injectors get more Fuel and the Revs go up again!

Which then creates a phenomena which is called 'Hunting' as the Revs of the Engine just keep going up and down in and endless cycle, which of course is not supposed to happen, as the function of the AAV is to Increase the Revs on Start Up to about 1000 RPM (High Idle)

Then as the Engine Starts to 'Warm Up' the Valve in the AAV starts to close and then the Revs should go down to around 750 RPM (Hot Idle) which can also be fine tuned with the Adjusting Nut that is on the Side (unscrew the Bolt to increase the Revs or screw the Bolt in to reduce the Revs)

So how would you know if that is the problem?

How would you know if the Piston was Stuck or why the Engine was 'Hunting' Up and Down

There is a very Simple Test in order to find out

Open the 'Air Box Cover' on 'B' Bank (only) and have a look inside, where you will see the 'B' Bank Throttle Opening and just forward of that is a Hole and on the back of that hole as it exits the Air Box is a Rubber Tube that Connects it to the AAV (See Photo)



'B' Bank Airbox with the Air Filter Removed



Just to the Left of the Throttle Body is a Bolt (don't touch that) and to the left of that Bolt is a Hole which is an Air Inlet for the AAV which goes right through the Airbox and exits at the rear of the Airbox at which point it is joined to the AAV with a Big Rubber Tube



You can see that Big Rubber Tube in that Photo that takes Air from the Air Box into the AAV

And so in order to find out if the Piston in the AAV is Stuck open and wont close, what you need to do is to Block that Airway to the AAV

Not permanently Block it but just for a couple of Seconds, which should then be long enough to 'Fool the ECU' that the Piston in the AAV is closing like it should do, as the Engine Warms up

Just a little 'Spot Test' Block the Air to the AAV for just a couple of Seconds, at which point if the Revs go down then that is all you really need to know, as then you will know that the Piston in the AAV is Stuck Open

Also a word of Caution Block the Air off to the AAV with a very tight bundle of Rag or something like that as you do not want any rag to get sucked down that Tube

And also be VERY CAREFUL Not to let anything get sucked in to the Throttle Body Opening, as the Suction from this is so extreme, it can take you by surprise if you're not Careful, so keep everything out of the way of the Throttle Body Opening

Assuming that the Revs dies down with that very quick Test, you should be able to tell from this, that the Valve in the AAV is Stuck

At which point you have a few options:

You could remove the AAV and have a look and Test it by putting the Brass Probe on the end in Hot (but NOT boiling Water) and maybe trying to free the Valve and giving it a squirt of WD40

Or you could Screw in the Adjusting Bolt with the AAV still on the Car, so that you can get the Revs down to 750 Rpm or whatever your Engine feels comfortable with, as its not unknown for the Piston in the AAV to free itself off after a bit of use as it did in my own Car

Though once you know the AAV is the cause of the Problem, then you could always treat your Car to a New One, although they are a little bit expensive or 'Grant' 'The Wizard of Oz' does have a fix, which I'm sure he will jump in and tell you all about

So once you know that the AAV is the problem, which way you go on that is up to you

Though in the event that it's not the AAV there is other Stuff that we can try

Hope that helps

Good luck

Alex

 

Hello

Thank you for your answer.

During the weekend i made few tests

Resistor pack => OK => the problem is still here.
Engine speed sensor => New part => Problem is still here

So I tested to switch ignition bank A on B bank and Vice versa.
I turned the ignition finger holder 180 degrees
And i put
1A on4B 6B on6A
5A on1B 2B on2A
3A on5B 4B on4A
6A on3B 1B on1A
2A on6B 5B on5A
4A on2B 3B on3A

I put Coil B => A on cap
and coil A => B on cap

And I adjusted position of distributor in the good direction 20 to 30 ° approximatly

And I tested

Bank B => OK
Bank A => NOk same issue but now on A Bank

So for me the issue is due to the Cap or finger for B Bank
I ordered a new one (after market) and I'll test them as soon as possible

Thank you

 

Hi Nicolas

Looks like you've found the problem out of all the things it could have been

Well done

Alex