Good evening everyone, I’m brand new to the forum. Have had several vintage Jags. Just picked up an XJ12 and was told by the previous owner he took apart the distributor and air filter housing and it will turn over but not fire.

I noticed the disc shaped item with the cable connected to it being loose on top of the motor (see pic) and wonder what it is, and if it could be the culprit.

any help would be greatly appreciated!

 

It's the cruise control bellows. The plastic heat shield should be under the bellows, not over it, by the way. In any case it shouldn't have any bearing on your no-start issue

Cheers
DD

 

Thank you!
im wondering how where to begin in diagnosing the no start issue.
spark or fuel?
if anyone can please point me to any sources.
I know the V12 is rather finicky.

 

The first post in this thread.....

https://www.jaguarforums.com/forum/x...he-v12-178286/

....has a link that you'll find helpful

Cheers
DD

 

thank you so much!
I remember my old XJS having fuel rail issues.

 

Failure to start on the V12:

1) failed GM Delco 1906 module in the ignition amplifier
2) failed fuel pump relay OR failed “main” relay beside it. The main relay powers the fuel pump relay. A failure in either (or both) will prevent fuel flow
3) broken wire under the cruise control bellows leading to the distributor (and please turn the heat shield so it actually shields the bellows rather than cooking it!)
4) failed pickup in the distributor (rare)
5) broken wire in the shielded wire sheath to the ignition amplifier.

And the V12 is not “finicky”. It is a superb engine. But proper maintenance is necessary.
Check that the fuel hoses are not hard. If they are, replace them!

 

Thank you so much. May I DM you if possible?
the previous owner said when he drove the car home it was running rough so he said that he opened the distributor cap and there was something stiff in there that he hit with WD40. Then it loosened up and then it would never start again. I do have a replacement disstributor that he gave me along with a few other parts.

I live in Toronto. So many of the old and veteran mechanics are gone, replaced by kids, computers and obd2 scanners.
Is there anyone here who lives around the GTA who can help and assist or recommend anyone if I need it?

 

Yes, send me a private message, but first try this: turn on the ignition, but not to Start. You should hear the fuel pump run for several seconds, then stop. If you do NOT hear the pump run then the issue is likely in one or both of the relays I mentioned. They are found on the radiator rail beside the red cylindrical fan relay. Very rarely, the ignition switch itself can be at fault. These are the relays in question; the red is the fan relay but the two square ones are the fuel pump relay (the middle one) and the "main" relay - it has a red diagonal stripe on the top - in the photo there is a sticker masking the stripe:




If the fuel pump DOES run, you are looking at an electrical issue, and this can be the wires - the single pinkish wire leading to the distributor, a favourite of rodents, or the shielded wire to the ignition amplifier on top of the manifold, or the pickup in the distributor OR the Delco 1906 module in the ignition amplifier - this is the most frequent failure point.
This is the distributor advance, which can provide rough running:


and this is the shielded wire leading to the amplifier - it is a white wire inside the shielding which can short out if its covvering has been damaged:


Note the uncovered bellows - the plastic shield sits below it, not above:
This photo shows the entire engine - the amplifier is the black square box with a red label, below the fender brace - the module inside the box is the Delco 1906 - it is the most failure-prone item and responsible for most non-start issues:



Another possible cause might be the coil. Your car is an 86 models so it will have the dual coil system (one of them being mounted to the radiator rail) (Your car, and every V12 sedan, has the Lucas Bosch ignition system…NOT the Marelli system which was used only in the XJS model 89 onward).

 

I turned the key to second position and heard what I believe to be the fuel pump power up for a few seconds. I did it again twice and the same whirring sound.
so it seems the fuel pump is working.
now onto the next in trouble shooting ….
i sent you a PM btw.

 

I thought there was a faint chance that she was just out of fuel and she would start…. So I put 5l into each tank.
on to find out that the right side tank immediately began leaking it out….

I tried using the fuel switch to jockey from one tank to the other and she still wouldn’t start.
but now I know she leaks on one side…..

 

So far you report that you can hear the fuel pump run. That indicates that the two relays, the “main” relay and the fuel pump relay are operative, as is the pump itself.
Now you must address a possible electrical issue by assessing the items I have mentioned in my earlier responses.

 

I just moved the bellows and put the heat shield back to where it should be. Found a few of the connectors unplugged and bolts missing where the heatshield bolts onto.
I’ll send some pics of what I found later on.

oh and the right side tank leaks!

 

Connectors unplugged?…what could go wrong?

 

Found these connectors off…..
and reconnected one vacuum hose on the left side of the cruise control bellows drivers side….

 

Yikes….no wonder it won’t start.

 

Looks like he pulled out a lot already trying to think where to start…. Any help and tips would be greatly appreciated

 

Start with the ignition amplifier. That is the black box bolted to the B bank (LHS) inlet manifold.

It should have four wires coming out of it towards the distributor. One goes to the coil positive, one to the negative, one to the tacho (the thin white with a blue spiral) and one, VERY important white wire goes rearwards via a connector to the engine loom with a shielded wire. This is the connection to the ECU.
This is the coil, current ly not connected:


See if you can find these and post a photo of them close up and people can tell you where to connect them.

Secondly, there should be a flat black plug with two wires connected to the rear side of the amplifier and an earth strap going to one of the fixing bolts. The twin wire with the black plug comes up from the base of the distributor down in the bottom of the V. Ensure this wire is there and connected (it has another connector half way down the wires) and the wires exiting the base of the dizzy are good.

Once these are identified and connected as they should be, then I can suggest the next steps. This needs to be done methodically and carefully, and the car will get started, but it can not be rushed. Do not hurry it, just get each step done correctly.

This link will help you understand the system:
https://www.jaguarforums.com/forum/x...he-v12-178286/

 

It appears the previous owner replaced the original dual coil set up with the solid DAC6093 coil which is fine. I did the same on my '87 VDP V12. You can also see this coil in Post #8 from Sov211. I can take some photos of the connections on mine or draw a small diagram of the same when I get a chance, if no one else is able to detail the connections for you. From memory there is a miniscule "+" sign on the coil that helps.

 

If one tank has rusted to the point that it's leaking, it's likely that there are a lot of rust particles in the fuel system. That is unlikely to be the cause of the failure to start but might well be why the PO suffered rough running. Look there after you've resolved the electrical issues.

 

I would love to help further in sorting this out but I no longer have a V12 in the garage (to my very great regret) to use as a model.

Getting this car back in shape will mean careful attention to the wiring and vacuum line details at the very least, so having a proper engine model would be very helpful.

It will be rewarding work, but time consuming and character-building!