I have cleared the codes down and they go away. However as soon as you recheck the faults they come back as pending and then on restarting the engine come back as current faults and RP is then instigated.

I am going to have to throughily trace through the wiring and check out the resistances as you say.

What I can't understand is how cylinders 2,3,5&8 can be linked, they are not even all on the same bank and I therefore assume on different looms. Do they share a common earth? With the ignition modules one of them supplies 2, 3, 5 and 8 also. Is it to do with firing order? Again you would think that there would be just one module for the right bank and one for the left, so why do the igniton modules supply two cylinders on one bank and two cylinders on the other and are the injectors linked in this way for the same reason? Or have I just got all my cylinder order mixed up?

As I say will have to print off the wiring diagrams and have a good look through and try to understand better how it is all connected as I can't really get my head around it at the moment.

 

I think you've got JTIS - the wiring diagram shows +ve coming into the injector relay then a star serving all 8 injectors. The ECM grounds the other side of the coil.
Worth testing the ECM ground with the engine running see
https://www.jaguarforums.com/forum/x...-ground-90481/

I don't know how the ECM checks the injectors, maybe voltage across a resistor, so it is possible if something like ground was borderline some would pass and some wouldn't.

I'm not very good with where connectors are but it looks as if all the injectors are fed through one dirty great big one.

If you look in JTIS under Powertrain>Fuel Charging>Diagnosis + testing>Pinpoint tests
there's a useful schema which will check the individual injectors and their 12V supply side but not the ECM ground side.

 

Can I just clarify a few points to make sure that I am singing from the correct hymn sheet.

Bank 1 is also known as bank A and bank 2 is also known as bank B. Sitting in the car bank 1 is on the RH side and number 1 cylinder is at the front of the car on that side. So from sitting in the car, cylinders 2 &3 are the the centre cylinders on the RHS and cylinders 5 & 8 are the front & rear cylinders on the LHS, number 8 cylinder being the bulkhead end. On some diagrams the cylinders are shown as 1A and 1B and 1A is then cylinder 1 and 1B is then cylinder 5. I deliberately haven't mentioned drivers and passenger sides as obviously that causes even more confusion with RHD and LHD cars and every time I read something I am never sure whether they are talking about from a UK or US point of view.

Are all my assumptions correct and are we all singing from that same hymn book?

I will check the ECM earth to see if that is OK. However if the ECM earth was bad surely that would affect all the injector circuits as they all are wired through the ECM. Conversely on the power side all the wires are again connected to the same point so again if this connection was bad all the injectors would be affected. I also can't believe that 4 seperate wires on two different sides of the engine could all be damaged at once whilst the car was just sitting in the garage. I will have to check the resistances any way just to be sure, but I am doubtful. Is there definitely no other common denominator with these 4 injectors?

So what else does that leave, the ECU itself?

 

Here is the hymn sheet, probably better if I don't sing.

 

Wow now I really am confused we have got all the first eight letters of the alphabet and even further cylinder configurations.

I presume that my 2000 ECU does read the cylinders as I have just stated in the 1 to 8 configuration.

I have heard that you have a beautiful voice Norri, perhaps you could give us a tune on You Tube!

 

You are right, yours should be the middle set on the diagram "alternate V8 cylinder numbering" for pre 2003 engines.

 

The pattern I see, is that regardless which reference diagram you use, the affected cylinders are every other cylinder in the firing order. That has to be significant.

I'll have to ponder that as time allows. I'm swamped this week preparing for vacation next week.

Cheers,

 

The only connection I see is that this group of cylinders where connected with the AJ26 to 1 ignition control module, which changed to the AJ27 engine you have now.

It may be that inside the ECU some components are shared with the same grouping which is failing.

Have you already swapped an injector? Then at least you can put a tick in the box if it could be injector related (which I doubt, but its always nice to know what works and what doesn't, especially if its so easy to do)

 

No I haven't swapped an injector yet as I wasn't sure how to get them out and have read that the seals need replacing if you remove them? But if it is easy I will certainly give it a go.
This whole incident seems to stem from when the car wasn't used for a while and the battery voltage dropped. The car is also intermittently throwing up all the ABS, NO TRAC and ASC warnings although at the moment they are all clear. My code reader does not read these faults so I suppose it may be worth putting the car on a reader that would show what has been triggering these faults to see if anything could be related.
I wish I had another ECU I could try, but I understand that they are all different and I would be lucky to find one secondhand that was the same.
Luckily this is just a fun car for me and I do not have to use it every day so there is no rush, but it would still be nice to get it right and finally solve this problem.
Thanks for your advice and have a good vacation.

 

Is the battery new or are you trying to limp around on the old battery after the battery incident?

Sometimes, once a battery has fully discharged it is not up to the job.

 

That's a good thought. I've not heard of these particular codes being thrown as a result of a bad battery but if you've been getting the ABS + NO TRAC ones the injector codes could be spurious.
Well worth, at the least, getting your battery tested.

 

Sadly he mentioned fitting a new battery in post #1.

 

Thanks, Norri.
This thread's too long !!

 

Sorry, I know this has been going on for ages and even I sometimes cant remember what has or hasn't been done.

As Norri says I did fit a battery right back at the beginning.

I really am not sure what else to try now and am wondering if it would be worth trying a secondhand ECU.

If I find a replacement ECU with the same part number will it need reprogramming to my vehicle, or will it just work as fitted?

 

The battery question was preliminary to dealing with ...

Drawing from the information given in JTIS for the AJ26 as used in the 1998 XJ ...

that year also uses the twin ignition modules and the two wire coils.

The coil monitoring then has to be an inference on the current flow in the two wires. This is different than the later 4 wire coils.

That leads to two possibilities, both related to current draw.

The ECU may cheat a little bit and have the circuits for the injection and ignition closely tied without adequate insolation. This is due to the fact that the injection and ignition for each cylinder happen close together. If the ignition module sags the voltage, it may affect the injection circuit or at least the perception of the injection circuit from the viewpoint of the ECU. As the codes match the cylinders tied to one particular ignition control module, a good place to be looking would be the harness between the ECU and that module, the power to that module, and earthing for that module.

 

Plums,
Accordin to my JTIS for the 2000 XK the ECM drives the injectors directly

 

I think that plums was perhaps referring to the ignition coils and not the injectors and that the wiring to these could affect the injector circuits in some way?

Do I definitely have two seperate ignition modules on my 2000 XK8 and if so where are they fitted?

 

I was relying on the description as given in post 101 and bits from other posts which refer to "modules".

The likelihood remains that the problem is to be found where the identified cylinders converge. The injector problem is flagged by the ecm, but the ignition circuits are also terminated at the ecm. The ecm likes clean signals. If bad signals are suspected, and they show a pattern, then you have to go where the pattern is reproduced.

BTW, injector circuit integrity is often determined by reading flyback voltage at the moment the power is cut by the ecm. An out of range signal equates to an inference of an open circuit from the point of view of the ecm.

So, the commonality is the key. The problem is in determining the mechanism by which that commonality is influencing the ecm's view of reality.

 

No, each coil on plug is triggered directly from the ECM.
Each coil is supplied with 12V from the ignition coil relay, ground, and two trigger inputs from the ECM.
I'm afraid you'll just have to check resistance, clean grounds and connectors and hope for the best.
I can see nothing in the circuitry that links those injectors into a group.

 

Was it earlier vehicles that had the ignition modules? I definitely remember reading somewhere that one module supplied cyls 2 3 5 8 and the other supplied 1 4 6 7. It's only that the 2 3 5 8 corresponded to my injector faults and I thought there might be a link but obviously not.

Never mind perhaps by the time I sort out this problem my car will be a classic and I will be able to sell it for a huge profit. At the moment I would be happy with 4 grand, any takers ? !!!