Question for mine. Thinking about it maybe I’ll have to work back from the input to the odometer if it’s supposed to be pulsed from the transducer so I can find what’s possibly touching it
Does anyone have a diagram if the pin out on the back off the instrument cluster as the bernard Webb one seems to have disappeared off his site.
Possibly not related to to your other issues. I’ve seen this happen on a variety of cars, including my old Jags, when supply voltage is low and/or voltage connections weak and/or grounds are weak.
As a matter of fact, even as we speak I have some work to do on my own car in that regard. Here recently when I crank the engine in the morning the speedometer is starting to go crazy…although the engine has never run better.
Cheers
DD
Yea I think I’m going to have to check grounds and put another ground on the engine to chassy just to eliminate.
It’s the odometer moving round though that is so strange obviously it’s not like other cars which are linked directly through a coiled tacho wire. It’s electronic pulse instead but just bloody wierd watching the mileage change as the cars stationary!!
Its so annoying I’ve had the injectors out before without any issue. Typically I just thought as the car has hardly been driven whilst it was restored I would get them cleaned as although the car was running fine it was missing slghly on one bank. So as plugs OK thought I would get them cleaned. Wish I had never bothered now
You lost me there … 
I thought the odometer/speedometer on our XJSes involved purely a mechanical process, using a drive wire going through the cable assembly between the back of the instrument cluster box to the drive “gear” located on the rear differential box. ? I have wondered why lately I have a “quivering”/“shaking” speedo needle sometimes at speeds under 50 mph, and figured that had something to do with either the drive wire or the gear developing an issue of some kind (although I couldn’t figure out why it would be intermittent, if so). 
So it’s possible I have a blinky “transducer” instead? Where is it located and how can I test it?
I haven’t read the other answers, or questions in this thread, because it seems a number of folks have joined in with their own problems, and it’s all gotten a bit confusing.
But what I’m hearing from what you’ve said is that some of the critical wiring has checked OK.
Fuel at the rail is ok.
Injectors click with a 9v battery.
Here’s where I’m hoping I misunderstand:
WIth key on, you hear all injectors and they don’t stop making noise.
IF that’s true, I can think of NO mechanism that would cause the ECU to command the injectors with just key on. (There could be a short to ground in the control side of the loom).
Also, you should have a plentium that’s full of gas and you should be able to smell it… strongly at the throttle body. IF that’s the case then I begin to question the ECU itself. Sure the ECU could over-fuel due to a bad signal from the Temp Sensor, but it should NEVER just start fueling with key-on and no RPM signal.
Next… I’d try my possibly defective ECU in a known running Jag of the same year range. That’s probably the best check on your ECU at this point. If it were not for the ECU injecting with just key-on I’d be having you double check that the RPM signal was getting to the ECU by putting a test light between pin18 of the ECU connector and ground w/o the ECU attached and crank briefly to check for the light to blink w/ spark events (charge/open circuit / charge /open circuit etc).
Re the timing, that sounds right off the top of my head. All ignition takes place BTD. Statically at 0 deg the ignition event should have taken place at LEAST 10 deg prior at low pre-mech advance RPM. So yes initial spark event on 1A should should roughly be at 10 BTDC, and you should see that on the alignment of the distributer VR pickup and star-wheel trigger. At 0Deg crank, the star wheel should be 5 distributer degrees (1/2 crank degrees) beyond the VR pickup trigger.
The spark event occurs BTDC, and the whole air/fuel charge is compressed @ TDC early in that event, and then full expansion should take place around 30deg ATDC for maximum leverage on the crank. The rotor itself should point at roughly at 2B physical cylinder on the block where 1A is on the cap at 1A TDC. The rotor tip is about 13 distributer degrees wide so about 26 crank degrees of contact range usable by the vac and mech advances.
There are a few documents available on setting up the timing along with what’s in Kirby’s book (around page 136+) and the manual that may help. But I’d encourage you to look through Kirby’s book on this.
~Paul K.
No, that was only true for the early 70’s models. Jaguar went to an electronic speedo somewhere around 1980 I think, perhaps with the intro of the H.E. model. Then of course they replaced the pulse generator on the transmission with one on the differential much later, around 1990 or so.
Ut oh … so I might still end up having to pull that gear assembly from the rear differential to fix the issue? IIRC now, I think there is also something in the boot along the left hand side relay/module bank that pertains to the speedo, the same bank that contains the “anti-slosh” module. If so, could that be the culprit? 
There’s a common issue of cross talk between the speedo and tacho. I’ve seen it a dozen times on the Facebook Groups and the same here and at the JaguarForums. The usual suggestion and prescription is that there’s an issue with grounds and contacts, and to remove the panel, clean the contacts, and even add a ground to a metal cross member inside. It seems to work for some people, but no root cause has been 100% established so that I’ve seen. I’m sure it has something to do with the fact that the little PCB pulse translator boards on the back of the units are nearly identical. (For years forward of the mechanical speedo and probably pre-facelift gauges).
~Paul K.
What you say there seem to be incorrect as far as I have experienced and read. When you key on the pump primes you get a single pulse to the injectors. If you turn the throttle quickly you get the injectors to click again.
Hmm… this is not my understanding of its operation, but I think we’d both agree there would be no sustained injection simply with key on.
It is my understanding that the WOT switch can trigger a SINGLE burst for every key-on. I’m not sure it can trigger more. The pump definitely primes, and as I understand the wiring/signals, will not come back on unless there’s a +12V event on the starter relay, the key is cycled, or the ECU gets an RPM signal. Re the ECU bursting the injectors simply with a key on event… It’s possible that I’ve missed that part of the ECUs operation. Roger, or documentation could clarify. I wish my car was close to test myself.
If it DID happen, could not the engine flood if say one was sitting in the parking lot… waiting for someone, and turning the key on and of and on and of and on and off periodically to listen to music?
~Paul K.
So from my understanding you key on and pump primes, at the same time the vehicle injectors trigger once and this is possibly from starter relay which primes the injectors before the ecu takes over once pulse signal is generated.
You can open the throttle quickly and the injectors should click each time. I believe from reading you can flood engine turning on and off.
In regards to injectors continually firing for the author of post, at switch on is this quickly or not? and does the pump prime each time they fire? Reading back through the post it sounded like you had power issues. I’m just wondering if your losing power again and then starting up again like you have turned the key switch on and off. Priming the pump and injectors each time.
Yes, there’s a “black box” between the pickup in the diff and all the things that get the signal. And yes, it reportedly fails more often than the pickup itself. I think the key symptom is that none of those things work right: Speedo, cruise control, trip computer.
It would make more sense if that starting squirt was triggered by turning the key to start.
There is no “priming” of this pump. You turn the ignition on and the fuel pump starts running. If you dawdle and don’t start the engine, the fuel pump circuit will turn it back off in 2 seconds as a safety feature.
It would. In this circumstance though, is there any use in actually firing the injectors without the ECU knowing that there was ignition? Ignition should happen simultaneously. It’s my current understanding that the +12V single from the starter relay re-triggers the ECU to re-start the pump, and the ignition signal sustains that activity. Whether the ECU injects at key-on (only), at starter relay signal, or with ignition signal is what seems to be in question. Again, it’s my current understanding that the RPM signal is the injection trigger (enabling calculation).
Is there some sort of cold-start burst with the starter relay signal? It would be nice to add that certainty to my understanding.
~Paul K.
Makes sense, bad choice of words I think from me.
I assume you have morelli ignition? my transducer is on the gear box for lucas. Morelli so I understand is diff.
Yes. There needs to be a starting squirt over and above the individual ignition-triggered squirts. I think the size of this starting squirt varies with engine temp and possibly air temp. I seem to recall Bywater telling us it was really impressive when it’s really cold.
I suppose there’s another reason it makes more sense for this starting squirt to be triggered by hitting the starter, and that is that the ECU must be awake and checking temps and the like. The fact that it is powered up as soon as the key gets to on means it has that quarter-second between then and the starter being engaged to get going.
This seems reasonable, but still should occur not just with key-on, but with the +12V starter signal… at least that’s the most sensible design to me. I may have to dig into the archives for that one. Looks like Roger hasn’t visited us since 2016.
~Paul K.
Re the little black translator box for the diff mounted VR sensor, it’s a low-tech breadboard job. Probably really easy to reverse engineer and have made in mass with SMT components by JCPBL. Don’t have my hands on one, but I have pics of the side with the working bits:
One LM2903N comparator and a TC4520B Dual BInary Up Counter, some resistors, transistors, a diode, caps…nothing that’s programmable that I can tell.
~Paul K.
In English, please? WTH does this thing do? I’ve been presuming that the number of pulses/mile is different for the diff pickup than the speedo, cruise, and trip computer were designed to see, so this circuitry should correct that mismatch somehow. Can these parts do that? Like maybe count X pulses from the diff pickup before sending one pulse to the speedo?
Or perhaps the number of pulses/mile is correct but they are the wrong shape pulse. So, would these components be capable of “squaring” the wave or some such?
Or perhaps the number of pulses/mile and waveform are fine, but the signal isn’t strong enough, and this whole thing is just a signal booster. Could that be it?
