Not an XJS but as S3 XJ V12's are rare, I figured that this is the better place to post for mechanical issues. My car is a 1990 Canadian XJ12 that I bought back to Texas from Vancouver a couple of years back. When I bought the car, it had a slight miss when warmed up but was glass smooth at idle. I had to replace the injector hoses and cleaned the injectors at the same time which seemed to have created serious running issues.

While the car is a 1990, it has the lucas ignition system with the little ignition box on top of the engine.

Symptoms:
Misfire on both banks but very badly on the right bank. It's hard to tell from inside the car, but you can feel the misfire in the back pressure at the exhaust
Of course, the car has reduced performance

Possible issues and planned steps:
Electrical:

1. I'm planning to use noid lights to check the electrical connection to each injector to see if it's firing
2. I'm planning to use a stethoscope to listen to each injector to hear if it's clicking
3. Check firing order of plugs
4. There's a couple of electrical spade connectors below where the accelerator cable connects to the top of the engine that look flimsy. I need to figure out what they do and if they're connected right (two same size connectors)

Vacuum: - If I can find a vacuum diagram, I'd like to check the vacuum lines and make sure I put everything back as it was

At this point, what else can I check?

 

Post a photo to be sure, but the connectors sound like they are the kickdown loom.
Have you renewed the dizzy cap and rotor, plugs and HT leads?
Have you checked the dizzy rotor is free to turn and snap back?
What shape is the injector loom in?
Have you cleaned the injector resistor pack connectors?
Is the vacuum advance capsule intact and not cooked?

 

I think you might be right.

1. Have you renewed the dizzy cap and rotor, plugs and HT leads? - Not yet, but it's an action item. As there was no issue before I took the fuel rail and injectors out, I don't want to throw these parts at it first
2. Have you checked the dizzy rotor is free to turn and snap back? - Not opened the cap yet, again because the running issues got worse after I removed the fuel rail
3. What shape is the injector loom in? - Meh the noid lights will tell me. It could use new connectors for sure.
4. Have you cleaned the injector resistor pack connectors? - I have no idea what they are or where they are
5. Is the vacuum advance capsule intact and not cooked? - Again,not sure what these are or where

 

I suggest that you download and study Kirbert Palm's book on the XJS from the Jag Lovers website. THis explains in detail all the matters I refered to.
https://www.jag-lovers.org/xj-s/book/XJS_help.pdf

This link explains about the resistor, pack connector:

https://www.jaguarforums.com/forum/x...sistor-134745/

 

Greg is on it as expected.

Also, inside that Amp is a Condensor looking item, tucked away in the corner. Remove it and bin it. It"was" a noise suppressor, and old age has them leaking to earth and reeking havoc with the Ignition system.

You are CORRECT, the Series cars never got the infamouus Marelli nightmare, that was purely the XJS, until the 6ltr arrived in the late XJ40 body style.

Also, check the main engine earth strap fiasco at the LH engine mount, OR, run a dedicated earth strap, engine to chassis.

 

Gentlemen, thank you for your response. I'll have some stuff to check this weekend and will report back. I suspect that the injectors are not firing correctly as sometimes cleaning them can also create problems with different voltages coming out of the injector machine vs what the injector requires. Are there any sources for new or rebuilt injectors? I was fortunate with my BMW E28 M5 in that the injectors cross referenced to some 80's GM cars and am hoping the same in this instance.

 

Injectors are easy to rebuild yourself, if you want to, there are lots of injector rebuild companies about too. The injector loom is FAR more likely to be the problem, new ones are available or you can also build your own.

 

Yep, I have a full kit of pintle caps, filters and o-rings. I also have an injector flow tester and ultra sonic cleaner. The injectors all tested out well and balanced. However, there could be a problem when the voltages between the flow tester and the injectors themselves are different in that it can create problems

 

It is the loom!

 

Could well be. The noid light will test it. I also bought a set of end connectors which are on their way. You never know when you need them

 

So I wanted to give you an update on this. Using an automotive stethoscope, I was able to verify that one of the injectors was not firing unless I pushed the connector in. I bought replacement pig tails but they don't clamp well so I used a zip tie to hold the connector on the injector until I have a permanent solution (I'm guessing these are BOSCH EV1 style connectors). The car runs better but is still misfiring and I was able to hear all injectors firing. You don't notice so much at the engine side but at the exhaust, you can clearly hear a misfire. It also smells pretty fowl which I assume is the cat.

Also what are these two connectors for?




Here's a quick video so that you can see what what I'm talking about. Let me know your thoughts.

 

The wiring harnesses do get crispy, you've verified that all the injectors are firing? The next step I would do is put an inductive timing light on each spark plug wire and make sure they are all firing. The exhaust sounds like you have a dead cylinder.


The two connectors are for the kickdown switch.

 

Thanks for responding. I did verify that the injectors were firing with a stethoscope (I could hear a solid click from each of them). I think my timing light is at the hobby shop but I will check the exhaust manifold with an infra red thermometer to see if I can narrow down the cylinder

 

OK, Some observation to take into the brain.

Just because the Injectors are "clicking: does NOT mean they are passing fuel. FACT.

Spark plugs on a HE that has been running "odd" are at best, knackered. New plugs, gapped to to 0.025" is more important than beer, and I luv beer.

The bare bones basics is all these engines need to run as designed. All this fancy stuff is justthat (NO disrespect intended), but after many, too many, hours with these beasts, its a;ways the simple stuff.

 

I appreciate your feedback. but I'm not sure what you're talking about WRT fancy stuff. The injectors were cleaned by me on my injector cleaning machine and flow tested. I'm now moving to ignition and checking temps at the exhaust manifold is a whole lot easier than pulling plugs which I don't mind doing, but not in the next day or so.

 

OK.

Plugs are easy enough, and on an unknown when last changed, are always 1st on my lists, but its your beast, do what fits best for you.

 

So I was trying to figure out the running issues and saw flames coming from the transmission tunnel so I assume the cats got so hot, they lit the insulation up. I was able to put it out pretty quickly but now I have a match lit under me to figure it out. I'm wondering if there's a problem with my vacuum wiring. Some vacuum lines are not connected and I'm not sure where they go. I put a video together and I'm wondering if anyone can guide me in the right direction.

 

Vacuum leaks will cause idle problems, but not misfires. Its important for the long term health of the engine that the vacuum advance module is working, but that shouldn't affect how it runs at idle. Its sticking out the side of the distributor. You really need to go through the whole ignition system.

Plugs
Leads
Cap & Rotor
Rebuild distributor to ensure mechanical advance is working
Rebuild/replace vacuum advance
Replace injector loom. I made a new one over the course of a weekend and could have done it in a day if I'd felt like it. As automotive wiring goes its really easy.

Here are a couple of the vacuum lines you were asking about, from my '87 XJ-S. But I really don't think that's your problem.

 

Brown switch on fuel rail is the fuel temp switch. Ok that it is bypassed; isn't causing your problem. Can be discussed later.

Make sure both fuel pressure regulator vacuum hoses are attached to a source of manifold vacuum. If not your fuel pressure will be too high....but on both banks.

Cat converter fire suggests over-fueling mixture on that bank

A shorting injector harness can cause injectors to stay open, over-fueling the cylinder(s)

Browsing the parts catalog can be helpful on vacuum hoses...but make sure you're looking at the correct illustration as there are sub-variations

Examples:
https://parts.jaguarlandroverclassic.../brand/jaguar/
https://parts.jaguarlandroverclassic.../brand/jaguar/

Cheers
DD

 

Thank you both, from the image, I see an immediate issue with one of the vacuum routing which I will address. I will order replacement ignition parts and go through the system. First the injector hoses and now the cats. This car seems pretty determined to burn itself down.