Hi guys - I've been reading some posts from this forum and seems like there is a great wealth of knowledge out there and some very helpful minds alike.

About 1 month ago I replaced the oil pressure sender on my 1989 XJ12 (Daimler Double Six here in the UK) as the original was leaking. I had to unbolt the throttle pedestal of course, to gain access to change the oil sender unit.

The job took a few hours of careful work and patience, like all "small" jobs on these cars :->)

After the job was done, I directly took the car out for a test-drive and all was fine for about 10 mins. Then, without any warning or misfiring, the engine cut out and I coasted to the side of the highway. The engine refused point blank to restart and I had to call the recovery service to come and move the car just 2 miles back home.

I called a local fuel injection specialist and although he is not a Jaguar V12 expert, he was able to diagnose the following:

1. Spark is good and strong.
2. The injectors are pulsing and click when depressing the throttle, with ignition switched on. For good measure, he also substituted the Power resistor / ballast pack for the injectors, with a known working unit, but the motor still refused to start.
3. The fuel pump runs for 1 - 2 secs when you turn the key to ignition stage.

Yesterday, I was reading through the Jaguar Technical checklist and I noticed the following:
"If fuel pump runs for 1-2 secs with ignition on, next check fuel circuit is active when cranking the engine. If not active, check trigger unit multi connector behind throttle pedestal"

Further reading on the trigger board unit explains this controls operation of the fuel circuit whilst the engine is running. This sure was news to me - but every time I read up on these cars, I learn something new, so I was not surprised to learn about the complexity of the fuel circuit. :->)

I then found the following nugget of advice in an old thread, posted by Grant Francis:

"In all my years with these beasts the trigger board is the main injection failure issue."

So, I'm now wondering if my 1989 XJ12 with the Lucas single coil system has this Trigger board unit? If so, it seems I may have broken / disturbed the wiring to the trigger board when I removed the throttle pedestal during the replacement of the oil pressure sender.

All the wires that I previously disconnected to lift the throttle pedestal appear ok, but as its clear the wiring harnesses suffer from V12 heat and age deterioration over the years, it may be the break in the wiring to the trigger board is simply not visible?

Do the symptoms that I have best tried to describe now point to an issue with the trigger board unit?

Obviously, I need the Fuel Injection guy to come back and test the fuel pressure, when cranking the engine, in order to confirm the situation, but in the meanwhile I'd be grateful to know what you guys perceive to be the root cause?

BTW, prior to changing the oil sender unit, the car / motor never had any issues, when starting or driving.

Very best regards,
Richard Morgan
Cheshire, UK

 

Welcome to the forum Richard, when time allows please post an intro in the new member area.

https://www.jaguarforums.com/forum/n...-intro-must-5/


I'm sure people who can help will be along soon, I'm an XJ6 owner so V12 stuff is out of my league.

 

Welcome.

That trigger board is for the PreHE engines, and that ts NOT yours.

The HE has its own issues.

DO NOT get confused with Marelli, as the Sedans DID NOT get Marelli until the 6ltr in 93ish?.

At the top of the XJS section, next one down, is a sticky I wrote for the NO start of a V12.

Have a read whilst I make an after midnight coffee, and ponder your issue a bit.

You have upset something for sure, just finding it is what we need.

 

OK.

At the rear of the engine is a wiring loom, it would have been shoved and pushed to change either oil switch, FACT.
Inside that loom covering is the dreaded shielded wire for the Ignition Pulse TO the ECU to activate the Injectors during cranking AND running. This wire fractures with the greatest of ease, and moving that loom to do that switch MAY have fractured it.

BUT

The CTS (Coolant Temp Sensor) located in the rear section of the LH thermostat housing, and has a 2 wire plug on it, the same style as the Injector plug. This CTS will stop a V12 in less than a heart beat. Example, running V12, unplug the CTS, dead V12, no coughing etc, just dead.

The wires FROM that CTS TO the ECU are also in that loom, and are spliced into the TPS (Throttle Position Sensor) wires. Splices fail from movement as you have just done.

I have an ECU pin out chart if you need it, so you can check continuity from engine bay items TO the ECU.

If you are handy with a DVM and can poke pointy things into wires, you can do this, but let us know where you sit with DIY stuff, as that is helpful with answers, as I always assume people work on their own cars like I do, OOPS.

Back later, its 1am now and I need my beauty sleep.

 

ANOTHER quicky.

You got spark, you got Injector click, you got fuel pump running, BUT, have you actually got fuel.

My reasoning is simple, like me:

If the injectors have sprayed fuel with the Ign ON and throttle activation to confirm that clicking, and you got spark, it should FIRE.

It may not continue running, that would then be that shielded wire, but it should give a blast of something as that sprayed fuel is ignited.

See ya this time, I'm gone.

 

Hi Grant,

A massive thanks to you for the super quick response and the pearls of wisdom you've shared.

I'm working away currently but will be back one week and from what you say, it seems to confirm I've caused a problem in that rear wiring loom. It was indeed pushed around a few times whilst lifting and refitting the throttle pedestal, I'd have been a good deal more delicate if I'd known it was so fragile....another V12 lesson learnt the hard way, eh?

Sounds like the next steps are to make some continuity checks - if you could send me the ECU pin out chart I would be much obliged.

Question - if I'm able to locate which wire is broken and if it turns out to be the shielded wire for Ignition pulse to ECU, what's the best way to repair the damage?

All the very best !

Richard

 

OK,

Pin out attached.

XJ-S ECU Pinout table.doc

That shielded wire is NOT special, I use standard Television Antenna Coax, available anywhere, and replace the section from behind the brake booster (where it will still be soft and pliable), to the Ign amp itself. About an hours steady work.

Dont blame yourself here, that coax can fracture from engine vibrations as age sets in.

Doug has a fix that works sometimes, Its called the "fiddle factor". Reach down and move that loom slowly, then try again, then fiddle some more, you might get lucky????, and that fix may last years, or seconds. Always fun these V12's.

When you are ready let us know and we can fine tune the doings.

 

Fantastic stuff Grant - another big thank you!

Will make a printed copy of the ECU Pin out chart and work through the continuity checks - will be back in touch in about a weeks time.

One last question for now - as the Injectors have shown they are pulsing during cranking, it appears the shielded wire for the Ignition pulse is sending its signal to the ECU, if I understand correctly.
If this is the case, seems the more likely culprit could be a break in the CTS wiring? But, if this is the culprit, how is it that the Injectors are pulsing when cranking?

All the best!

 

Have you checked to see if there is fuel to the line? All you really have to do is crack the line at the rail to see if fuel comes out.

 

I agree all round, and the mud is a tad clearer with your last post.

If there is injector pulse whilst cranking, that shielded wire IS doing its task, leave it alone.

Go to the CTS, follow the wires back, and you will find a splice where teh ATS (Air Temp Sensor) attaches to one wire, and then near the rear of the engine, more splices for the TPS.

Most common issue with the CTS is broken wires INSIDE the 2 pin plug.

To have a sudden shutdown that yo stated in post #1, is CTS wiring failure, after the shielded wire. These 2 items share #1 at the top of any sudden shut down list.

The CTS do go flaky, and are cheap and are NOT Jaguar specific. Its a Bosch thing, Merc, BMW, SAAB, Volvo, Holden (Vauxhall) all use the same CTS. I have the Bosch number somewhere??????, and will come back with it when I find it, so glad you are not roadside waiting for me, HAHA.

 

Thanks again Grant.

BTW, Re. questions about fuel supply, the fuel injection guy cracked the supply pipe & confirmed fuel present. He also mentioned he could smell fuel at the exhaust tailpipes, after several attempts to start the engine. However, he did not have time to test the fuel pressure during cranking.

But, with fuel present, spark and the injectors pulsing during cranking, he was puzzled as to why the motor would not start. As stated before, he has no previous on V12 Jaguars.

As it seems like everything points towards the rear wiring loom, if it is the CTS circuit that has gone AWOL, would this explain the scenario as observed above?

 

With fuel in the cylinders, and spark in the cylinders, there should be an attempt to fire, CTS or no CTS. The CTS being dud would prevent it from continuing to run, coz the ECU has no temp signal reference to work out Injector pulse length.

It may be flooded from trying to start it.

It will dry out by the time you get back.

Check the CTS and the wiring, and then try the start again, but dont touch the throttle pedal.

I doubt your market or that year has the 2 cold start injectors in the manifold. If it does they be suspect, they leak and dribble fuel into the engine, thus flooding it. Easy fix if you need it.

Next, FPR's (Fuel Pressure Regulator/s), one on the front of each Inlet manifold. Small vac hose in the end of each. Turn ON the Ign, Turn OFF the Ign. Pull that vac hose, is it dry inside?????, it MUST BE dry. If its wet with fuel, the FPR has failed and you need a new one.

The RH FPR can be deleted, it is redundant.

The LH FPR is the actual regulator, and MUST be retained.

The RH and LH are different, so no swapping and cheating please.

Having typed all that, NONE of that will caue a sudden shutdown as you said happened. They would cause a spluttering and so on until it died.

Recheck that spark AT the spark plug, a nice Fat, Blue, Cracker of a spark it required. Anything less, and that HE will not run.

That Bosch CTS # is 0-280-130-026. Any parts mob should be able to convert that # to their # etc.

 

Yes, I also expected it to attempt to fire under cranking, but it has shown absolutely no sign of life, since the moment it cut dead on the highway.

I've re-read your Sticky on HE V12 that won't start: "You are looking for a FAT Blue CRACK of a spark."

After the car was recovered back home, the recovery guy checked for a spark at the end of a plug lead, whilst I cranked the engine. We both saw a spark, but the spark I saw was not a Fat Blue Cracker, it was actually a bit on the dull side. But, at the time, it was a spark, which confirmed the ignition system was still alive.

Am I correct in thinking the wiring from the Ignition Amplifier passes around the throttle pedestal and into the same rear wiring loom, that I have disturbed?

If so, it now seems the wiring to/from the Ignition Amplifier could be the root cause, hence lack of strong enough spark and sudden / total loss of life ?

 

OK,

Coffee 4 just arrived.

Your HE engine is probably 11.5:1 comp, but may be the last of the 12.5:1 engines. That requires a Cracker spark to start it and keep it running. The higher the Comp ratio, the Fatter the spark required to jump the gap in the spark plug.

Next:

Remove the HT lead from the centre of the cap, leaving at attached to teh coil. Do teh same test, note the spark quality.

If you get a Cracker there, the issue is inside the distributor, and NOT related to your work that I can think of.

There is a carbon brush inside that cap, directly under the Coil HT post. This brush passes the current TO the rotor for distribution to the spark plugs. This Carbon brush wears away/breaks/falls out. Even with it missing, that engine will still start, albeit hard to start and run odd.

There are Ignition Amp wires inside that loom, and they are the Power supply wires TO the amp, the shielded wire, the Tacho wire, and I forget?????

What I suggest when you return to the beast, is 100% check that spark, then 100% check the Injector clicking as it cranks.

Those 2 will steer the search a lot clearer than rebuilding the engine loom. That will come later.

Coffee #5.

Your man claims that there was a fuel smell at the pipes, mmmmm, doubtful. These engines really STINK at the pipes if you are trying to start one without fuel in the cylinders. That I have had many times, and that stink has that fuel smell about it for some strange reason.

I will PM you later today, just got a better offer from the wife.

 

OK thanks again Grant - I'll start by checking the spark quality at the coil lead and work on from there.
BTW, the fuel injection guy noticed the injection pulse was a tad intermittent when he first tested.
After he swapped over the Power resistor pack, he said it was better than previous, but still not 100%, in his opinion.
Sounds like it all now points at the Ignition Amp wiring....just wish I'd been more careful.
I changed all the plugs earlier in the year, so this was the second time I had to lift the throttle pedestal.
Maybe the rear wiring loom decided this time enough was enough...:->)

 

OK,

That resistor pack is NOT a known problem in itself. The cleanliness, or lack of, of the multi pin plug at the bottom IS a problem. It needs a GOOD CLEAN, and then do it again. That has cured many an intermitent injection issue.

His removing it, and replacing it, among other things, has disturbed more wiring loom/s. That good old fiddle factor again.

It is hard to "hear" the injectors during cranking, as the starter etc is making too much noise, you will need to place something like a stethoscope etc to actual hear them clear enough to be sure.

The intermittent he mentioned could be that shielded wire making and breaking, but I seriously doubt it. Once taht fail, they be dead.

You will find it, for sure.

 

Happy New Year Guys!

Finally got 5 mins of free time to update this thread, with some good news.

The culprit was the coil.

Spent a couple of hours with the fuel injection guy, checking fuel pressure under cranking (70 psi), then tried Easystart but made not one iota of difference, so re-checked spark at coil lead & plugs. Spark was able to jump a 5 mm gap, but with the workshop lights out, we clearly observed the colour of the spark to be yellow. In other words we had a big, fat Yellow cracker, hence the dead HE engine.
Ordered a new coil, cap & rotor arm from SNG Barratt & 24 hrs later, after swapping only the coil, the engine purred back into life.

Hooray!!

A massive thanks to Grant for his invaluable advice!

Best regards,
Richard