6L V12: running on six
 

Folks,

I've started investigating a loss of power and acceleration on an X305, MY 1995 which I just bought. Checks carried out revealed that no ignition and no injection signals to B-bank. This is an X305 with a 6L V12 engine, running full distributorless on a Denso system (v1.1 I believe, so the latest for these series cars).

Trying to brain dump to get second opinions please.

Carried out the following checks:

1. Loom continuity:
   • All Injectors to ECM: OK
   • Ignition modules to ECM: OK
   • Coil packs to Ignition modules: OK
2. Coil Packs: two new coil packs installed
3. CMP ohmic resistance checks: slightly out of the 322K bound, so replaced that
4. CKP ohmic resistance: OK (2.2K, well within tolerance)
5. Engine Speed Sensor: OK (1.2K, well within tolerance)
6. CMP signal: this one is weird. Not seeing the expected semi-sinusoidal signal, but rather some fraction of the signal
7. Ignition signals at the ignition amp modules: oscilloscope checks revealed no driver signal to B-bank module
8. Injector signals at the B-bank injectors: oscilloscope checks revealed no driver signal at any of the 6 injectors for B-bank
9. ECM: replaced with a working ECU from another known working car, same model, same serial numbers. Made no difference
10. New coolant temp sensor installed for prudence - I do that with any new cat I buy

As far as 6 above is concerned, I am puzzled. There is no reluctor I'm aware of attached to the A-bank camshaft to conclude a reluctor fault. Or is there?

7 & 8 seem to indicate some form of limp home, so I would expect the ECM to have disabled the B-bank ignition signal and similarly the B-bank injector signals. From what I read in the tech manuals, these babes go limp home on engine over-run, engine speed and I would suspect on loss of essential engine position signals. Is there anything else which would take it limp home?

Fault codes are not very helpful - ignition missing is logged, but I expected that given the above investigation.

Any wisdom gratefully received.

Many thanks ..

UDATE

I managed to narrow down this problem to a misfiring on B-bank - or at least I think this to be the case. My rationale is supported by what the Jaguar docs are stating - when misfire is detected for a few consecutive cycles, the ignition amp module raises a fault and the ECM will then disable that bank's injection and ignition - exactly case and point here.

Further, some genius garage changed the rocker cover gaskets for the previous owner, after which this problem started to manifest itself, so I cannot be sure if the sparks were rewired in the correct order to the coil pack.

Does any kind soul have the correct wiring sequence of sparks to coil pack? I could not find it in any of the Jaguar service manuals.

Thanks.

That's some nice troubleshooting! I know it is tough if not impossible, to find a diagram of the coil-to-plug wires in service documentation. One mixup could be the cause of your problem. Considering it just had work done in the area which required removal of the wires, and it is quite the spaghetti bowl down there... You'll be glad you came to the forum, because... IT'S HERE!!

X305 XJ12 Coil Pack Diagram

Thanks again to NICK (NTL1991) for documenting that. Someone had to do it eventually, before all knowledge of the subject was lost.

If you find a discrepancy with that, it is very nice to know that the ECU will shut down the bank's fuel and spark to avoid damage. True for any persistent misfire.

As far as the CMP, Camshaft Position Sensor on the A bank, I always assumed it read the 1A exhaust cam lobe directly. I've never had it out to look inside, but that would be a way to verify. On the other hand, the parts diagram shows a small ring just behind the cam sprocket. Too hard to tell if that is a reluctor ring.

I really hope you just have two wires crossed. Then it could (almost) be considered a zero-cost fix! Just like Nick had when he bought his XJ12 with a running problem. He discovered one bank's throttle linkage was loose, so that side was not opening at all under any throttle input. I just love zero-cost fixes. Especially for a "super complicated" Jaguar V12.

Thanks to SleekJag12
 

@SleekJag12, you are a gentleman and a scholler sir!

Not just glad, but grateful for your help and the collective wisdom. I'll check and update the thread for the reference value.

Best,

Ahmed.

Error

Swap coil pack position and see if the problem follows

The coils have a ground wire ( usually ) that can be off

See page 75

http://www.jagrepair.com/images/Auto.../jagxj1996.pdf

Thanks for this.

The coil packs are verified working, both by swapping and replacement with known working units.

I'm now going over loom integrity again and speed/cam/crank signals.

Thanks,

Ahmed.

Update
 

UPDATE

I thanks to the coil packs-to-sparks diagram from @SleekJag12 , I have gone over the cabling sequence of both banks, starting with B-bank, and all's well. Still same issue.

My next port of call:

1. Loom integrity checks again
2. CPK, CMP and engine speed sensor output. In particular, I do not like the shape of the signal coming out of the CMP (Cam Position Sensor) not one bit - it is not the usual twin-peaks per revolution, but rather some sort of sine portion. Anyone knows if there's a reluctor of sorts underneath the rocker cover? I cannot speak with authority for the V12 X305, but know that the X308 does have a reluctor at the end of one or both exhaust cams of either bank, depending on model. Is there such a reluctor on the X305 6L V12? if there is, then it could well be that it has been displaced and the CMP is not returning correct signal.
3. Following on from (2) above, assuming this to be the case, anyone knows if this will trigger a limp-home mode at the ECM, thus being the cause of no ignition driver and no injection signals?

Thanks,

Ahmed.

My two cents as remember all these v12's were under FORD , including the db9 and Vanquish.
Same problem with a Vanquish, the ecm was bad. In that car there is a left and right side, Switch the boxes.
If issue goes to other side its the box.
Not uncommon.
Did you do a hard reboot, kill the car and pull the battery for 30 minutes?
Lastly I had a mouse that ate through 6 wires in the harness which lead to the ecm feed.
Good luck.
gtjoey1314

Hi @gtjoey

Thanks for this.

ECM was swapped out for a known working unit from one of my other X305s, as were the coil packs and ignition amps.

Re: your Jerry mouse, I am indeed looking at loom integrity again, with a fine toothed comb, so let's see what that brings.

Lastly, I want to know what conditions instage a limp-home apart from erratic ignition and engine over-run. Not seen a CMP or a CPS throw a limp-home, but stranger things have happened!

I'll keep this thread updated with progress.

Thanks again,

Ahmed.

Your welcome, do your coil packs have 2 or 3 wires...…
On the Vanquish I found out about the mouse by hooking up a test light to the trigger wire on the coil.
I had current to the feed wire on the coil , the check light came on for the second wire but the TRIGGER wire or third wire was dead, which went back to the fire wall where I found 6 eaten wires.
On another note, the trans on your car is the BULLET PROOF OLD GM 400 updated.
BUT, The wires and relay would crap out from water and road junk.
The ground wire would short or break as well. Theres a harness plug , pull it and clean the contacts.
But I cant see that cutting out the right bank?
Mine were new at the time.
Good luck.
p.s. YOU HAVE FUEL ON THAT BANK? Check the schader valve, you might have a dead pump?

Four wires: three triggers + positive

Well; triggers are all dead. There's 12V, but that's it. Stands to reason: the ECM is not triggering. Big question, and subject of this investigation is why.
I have checked physical integrity, and nothing's cut, so at least that bit is sound. My initial continuity checks were good, so now revisiting to check other connections.
I'm also still in need of model experts' wisdom on what conditions would kick the ECM into limp home - pleeeeez someone. Also the question of the cam pos. sensor reluctor.

And boy do I love the 4L80E and GM boxes versus the ZF pile of junk. Trouble is that GM, by some fluke deal, seem to have sold the rights to their boxes to ZF, which is a major, major bummer IMHO

I'm tracing all the harness connectors now, so will probably find it, unless you know it's location or a harness reference?. And you'r right: why would this force the ECM into limp?
Oh, I'll need plenty of that :)
I shall check and update the thread. Good point.

Ok we are getting somewhere...…not in particular order, lets keep this simple
1. With a simple test light can you trace each wire in and out from the ecm?
2. key on key off should explain which wire does what to a coil, pick one coil.
3 Then we know which is the hot feed to the trigger.
4. Im telling you the ecm s go bad.
5. this sounds crazy but go to all the fuse boxes and see if any fuse is pushed out, the mouse shorted the wires so when I turn the key .
The short was so hard it pushed back 3 fuses! wild stuff
6 I cant see screwing up the wires to each coil from another mechanic, they go ONE WAY.
7.Please check gas at valve first, if dead pump the fault shuts the side down as a limp mode, but Im banking on the wires or box.
Just touch the valve with a pen cap, no fuel, we are talking pumps!
Goodluck, that should take a minute. :)
update number 3 im saying that so you trace that color wire throughout the car.
Check the schraded first.

I don't know of any particular engine Limp-Home mode except as caused by a transmission MIL (upper left warning light). In that case you will get only one forward gear (plus reverse), and extremely harsh engagements into gear. It is very noticeable since there is an odd feel and lack of power. It has happened to me on rare occasion but did reset with an ignition cycle. I don't know of the method by which the engine itself operates while in "transmission limp-home" mode, or whether there is any difference in the engine operation during that mode at all. Anyway, check that connector at the rear of the transmission if you can. Its way under there near the driveshaft.

I suspect that the ECU is not programmed to shut down a whole bank, or even one cylinder, based on misfires.

Any MAP sensor OBD codes? The two MAP inputs are one of the main indicators to the ECU of engine load. Air leaks or mis-adjusted throttle linkage could cause problems for the ECU.

What does it look like inside the cam cover if you remove the CMPS and look inside? Is the exhaust valve right there? Seems like the sensor would line up with it.

Gtjoey: No Schraeder valves on this fuel system. One line supplies all 12 cylinders via two pumps (in "parallel"). Ahmed will report about fuel pressure and presence.

I had 2 of those wonderful xj12's but didn't remember if it had the valves they were new at the time....
I agree with the limp mode, two different issues, but I have had issues with the box in this form and not cycling evap loops.
He will get it, I doubt the actual valve train in shot, its a hefty motor.
gtjoey1314

UPDATE

Folks, thanks for all your input. Here's where I am so far:

1. Sensors output: all sensors are now verified working and returning correct waveforms with a scope. Checks performed both at each sensor- and ECM- end
2. Continuity checks: Coil packs -> ign amp modules checkout. Each ign amp module -> ECM checks out. Each sensor -> ECM checksout - and I mean all sensors (CMP, CPK, engine speed, lambda, MAP - the lot). Ign amp modules -> ECM checksout.
3. Voltage checks:
   • 12V present at ign amp modules
   • 12V present at coil packs
   • 1.7V present at A-bank ign amp module, pin 7 (this is the ignition error pin; when 1.7ish is there, it means the ign amp module, bank and injectors for that bank are enabled; 12V indicates an error code)
   • 5V present at B-bank ign amp module, pin 7. Now this is where I'm poking: according to literature. limp home is instigated by engine over-run or misfire, in which case the ECM will disable the culprit bank by signalling the appropriate ign amp module with +12V and disabling injectors on that bank. This is exactly what I have, with one crucial exception: there is no 12V present, but 5V
   • Lambda sensors: some genius went there and cut the wires to the sensor, then reattached them, insulating them with some crummy insulation tape. Net result is that continuity is there, and the sensor checks out with basic DVM tests. Question: could it be going astray when heating up? and if so, is this signalling the ECM to go limp home - an extra condition which is not documented?

Will keep the thread updated.

@SleekJag12 thanks for this.

Docs states three conditions where the ECM will instigate limp home, one of which is engine overrun; the other is no engine speed signal.

I'm now almost convinced that a short circuit somewhere is the cause of the 5V on pin 7 of the IGN amp module (misfire indication). What's leading me to this conclusion is that when I disconnect the IGN amp socket to B-bank and measure voltage on said pin 7, I'm reading a clear 5V, when I should not be reading anything at all - this is a feedback pin which according to docs should return ~1.7V on correct firing and a straight 12V on misfire, back to the ECM. So, simple logic dictates that if a disconnected wire is carrying current and giving a clear value voltage reading, then there must be a short to that wire.

Looking at the electrical diagrams, there is a 5V common sensor reference powering both MAP sensors and the throttle position-cum-idle switch unit. A splice (PIS2) is indicated in the diagram, but no location - so could be somewhere inline inside the wiring loom.

Next port of call: I've ordered PI46 (the AMP 28-pin connector) on the ECM from RS, and going to completely rewire this socket back to the engine bay, repinning the sockets at the other end. PI46 from what I can see is the heart and soul of the engine loom, carrying most sensors and the two ignition misfire error signals.

Thanks,

Ahmed.

I have this identified, checked and verified, per my latest update.
Already swapped with a known working uint from my other X330 (Daimler double six, 6.0L, MY1996)
I have checked every single fuse, in every single fuse box. Earlier in the diags, I discovered that the genius who worked on this when changing the rocker cover had removed the lambda sensors' heater circuit fuses; was thus getting the appropriate error codes. When fuse was replaced, lambda sensor fault disappeared - unremarkable.

@SleekJag12 kindly supplied the relevant diagram - coil packs to sparks. This was verified and checked; also the 1-1 correspondence between coil pack drivers and ign amp modules. Checkout OK.

Now this, I have not doe. Will check and report.

Much obliged.

!!! EUREKA !!!

Problem finally solved.

Root causes:

1. Backtracking a little bit, I had lost the +ve supply at the coil packs and ignition modules, and no amount of tracing would identify the problem; parked this, and fed +ve through a 20A fuse, so that got the +ve supply back to the ignition amps and coil packs
2. Checks at the coil packs and ignition amps +ve pins showed 12V present from thereon, so parked that to focus on the downed B-bank
3. Although 12V was present at the ignition amplifiers and coil packs, B-bank coil pack +ve was dislocated underneath waterseal of the 4-pin connector of the B-bank coil pack. Terminated that onto a new pin and reseated, and voila!! B-bank alive and kicking again. Recall from (2) that I've fed +ve from elsewhere to get the ignition components working.
4. Now the disappearing +ve supply. Looking carefully at the wiring diagram, it pointed to a PI6 connector, which I could not find any location for from the docs, so I started my search form the ignition components and back to the ignition relay. +Ve present at the feed pin from Fuse #7 (25A), but no switched live on the relay coil. Traced this back and found PI6 - one of two sockets underneath the front, right headlights module; it is the black sockets. Undone that, and found the culprit: water had seeped inside the socket and corroded the pin beyond recognition. Ordered a new econoseal 13-pin to fix it, and meantime repaired the loom with silver solder bullet connectors and heat shrink sleeves.

Phew!! hope this helps folks ..

Atta boy!
Now put dialetric grease on all the connections and youll be set for years.
My advise as well, make them bullet connectors too.
Off to my DB4.
good luck!
gtjoey1314