Thanks for allowing me to post here, I hope to draw on someones expertise and experience inorder to solve this problem which has been exercising the minds of members of the Jaguar-Lovers Forum since early April, the total number of posts must now total several hundred. Steve Sparrow has infact used a borrowed Picoscope early in his investigation, I'll outline the problem and copy & paste in his first post on it which can be followed on the J-L website ( http://www.jaguar-lovers.org
) in the X300 Forum:
The car is a UK X300 Sport, which first had this problem after the owner switched to Sport mode and used Kickdown whilst traveling up a steep gradient since then the car would start and run for about 40 seconds at which point it turned out that the coils on cylinders 1, 2 & 3 ceased to fire, loosing power and idling roughly. thus followed a long saga and when Steve eventually examined the exhaust the forward cat on Bank 1 had been destroyed and after much agonising by the owner he decided to try fitting a replacement which was done recently but Steve noticed that it became yellow as it heated due to the start of a meltdown when Bank 1 shut down and that is really where we are now.
I'm afraid that it will be quite a long read especially if you backtrack through all of it from the beginning, but I hoping that this may trigger something that we haven't thought of.
Steve's 1st. post:
Every 6 months or so I'm delighted to receive a car that many
have 'had a go at' but not quite managed to fix. Unsure whether
this makes me the ultimate trouble shooter or simply the last
resort, I just carry on regardless!
The latest problem is a really interesting and I haven't
yet. As you would guess, I've checked through many basic and
basic things which I won't list here, there are too many, but
please don't be offended if suggesting something I've
already done .
X300 4.0 150k miles
The engine will start immedialtely from 12 hr. cold and run on 6
cylinders for about 40 secs.
After that, it will stumble and drop onto 3 cyl.s only, the
wreaking of petrol. It will misfire, backfire and the eventual
stall will see it refuse to start again. After 12 hrs. or so it
will start once more and the cycle is repeated. The Crank Sensor
has been replaced as step 1.
After very (very!) much ado, and checking for a blocked B1 Cat.
I've confirmed that B1 cylinder ign. coils (1,2 and 3) are not
firing after the initial 40 seconds running, although they still
have 12V supply on the white wires. Naturally, the swapping
of coils and plugs etc. has been done. Coils 123 will run cyl.s
456 with no problems when moved, as will the plugs.
Trouble Codes = None. Pending or Latent Codes = None.
Compressions are 160-170 psi on all 6.
STFT's when running are on + 24.2%. Both B1 and B2 02's are
flatlining at 0V, the TPS is working fine, as is the Air Mass
meter. No air leaks are present, smoke machine confirmed. B1
injectors are working and all 3 cylinders are inducting air.
At close of play today I have pulled the ECU (no water
will try that on another properly runnning car on Monday to see
what it does. I can accept that the ECU may be failing to fire
(earth out) one coil, but why would it fail to fire 3 in one
This brings me to my question, I'm hoping someone will know the
answer as I suddenly realised I don't. Are X300 coils fired
sequentially, or are they fired as a group of 3 with a wasted
I have the wiring diagram. The fact that all 6 coils have
individual green negative wires with different trace colours
suggests they are fired sequentially, but it is possible that
within the ECU, those 3 wires for one bank all go to the same
place, and that could explain the dead 3 coils.
All of this makes me wonder if the ECU actually shuts down a
of 3 cylinders if it see something it does not like? I've always
beleived X300's not to have the 'cylinder shutdown' that Merc.s
have, but maybe they do, and it does so 3 cyl,s at a time
never been seen before??
A MORE RECENT post:
Neil and All,
I think I need to pare it back to basics, as much for me as
anything as I can't get at my earlier records on this thread.
The engine runs fine on petrol until it is quite warm, where
misfiring and backfiring will begin. Eventually, coils 123 do not
spark the plugs at all, although there is a good 12V feed to the
positive side on all 6. There is no signal., ripple, spike or
waveform of any kind on 123 coil negatives when coil failure
occurs. When this happens, the front manifold goes cold.
There is significant 'noise' in the 12V supply.
As a result of the coils not firing, the B1 front cat. glows yellow
with heat as it burns the unburned petrol/ air mix that is being
The problem is definately temperature triggered as the engine will
start just fine after 12 hrs or so of cooling. The colder it is
before a start, the longer it will run before the misfiring begins
and the coils eventually stop firing. I have yet to measure the
exact coolant temp. the failure occurs at.
The exhaust has just been fitted, it has no blockages but it does
have 3 good cats, the original front one was burned out by the
The car has been fitted with 2 other identical ECU's which made no
difference at all, and ran another car just fine, as does the
All 6 compressions are fine.
All 6 injectors have good seals at the manifold.
Cam timing is correct.
Valve timing is correct.
No air leaks are present
The Alternator has been removed to rule out earthing or other
All of the earth points front and back have been checked and
cleaned. The engine to body earth strap has been removed and
The battery is brand new and does not dip below 12V.
A temporary 12V supply was rigged to the coils which made no
All of coils 123 have a good path to the ECU as continuity has been
The coils pull 6.2 A when working, which falls to Zero Amps when
the failure occurs.
The spark plug gaps were narrowed to 0.020'' to reduce spark
voltages and load on the coils - no difference.
Other parts swapped (known good ones) and the originals proved OK
on another car;
All 6 coils and spark plugs
Cam sensor and body
B1 Knock Sensor
Air temp. sensor
Coolant temp. sensor
Throttle body incl. TPS
Air Mass meter
The only trouble code which has been logged is P1621 - 'Engine
Control Module' which may be caused by me swapping parts, I will re-
That's pretty much where I am.