[v12-engine] Engine HP, torque and wide-band O2 sensors data -- help read

V12-Engine
1

I hope someone can help me put two and two together.
Having asked this forum many times about persistent idle
woes for the 6.0L V12, documented here:

and here:

http://forums.jag-lovers.org/av.php?1621701o10

I’d done a lot of work. Just as I thought all is well and I
made peace with the idea that +/-50 rpm at idle is OK,
suddenly, I failed idle emissions (high speed test was OK).
This ordeal led to the nice discussion here:

http://forums.jag-lovers.org/av.php?1765068p42

As you can see, a member suggested I do wide-band O2 sensors
test. Well, I found a shop within 20 miles that had a dyno
and could do dual wide-band O2 sensors. The test they did
(I was present) confirmed the following:

  1. At idle, A/F mixture bounces of 14.7 with a regularity
    that matches the tach needle moving up and down. Idle speed
    should be 750 rpm. Mine was between 727 and 772. Kirby is
    absolutely right that the ‘‘EFI system is constantly trying
    to run it too lean. It’s constantly bouncing on and off
    stochiometric, and the cycling up and down of the mixture to
    hold it in that range results in an idle that’s not what a
    V12 should be.’’

  2. Removing the Marelli jumper changes nothing in idle.
    Same result over 2 minute of monitoring.

  3. Putting load on the engine. Power and torque increase as
    they should. Max power at the wheel was achieved at 5000
    rpm and was 313 HP (Jaguar spec for my US car is 278 HP/DIN
    @ 5400 rpm). Max torque at the wheel was at 4000 rpm and was
    347 HP (Jaguar spec for my US car is 334 ft lbs @ 2800 rpm).

Please read this carefully – at WOT, above ca. 3000 rpm
engine speed, the A/F ratio seems to fall off of a cliff –
both banks are at near 11, which suggests SUPER rich
condition. This was confirmed by the smoke coming off the
tailpipes.

Is this normal? I recall reading about someone driving his
XJS on the Gerrman autobahn and logging mileage around 8 MPG
for sustained speed of 120-130 MPH, which probably
translates to A/F in the neighborhood of 10 or 11.

Also, if I understand correctly, at WOT, i.e., after the
second fuel pump comes online (above 2850 rpm), the O2
sensors feedback is inhibited. The 36CU does the fueling
based on MAP and CTS alone.

If A/F = 11 is indeed super rich running, what does this
mean in the context of my recent emissions data. When I
passed he results were:
HC idle – 171 ppm
HC fast – 101 ppm (this will be engine speed ca. 2400-2500
rpm)
CO idle – 0.25%
CO fast – 0.46%

  1. Removing the Marelli jumper and repeating the dyno-test
    shows the same results – A/F drops after 3000 rpm. Power
    and torque were down 10%.

Please help me understand what is going on. I don’t race
the car, and rarely see the tach going over 3-4,000 rpm.
This is not a quest for more power. Adjustments at those
conditions are not what I am after, but I feel that these
results tell a story.

I am hoping someone knowledgeable can interpret the data.

Best regards,
Steve–
'95 XJS convertible - V12 6.0L
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2

In reply to a message from sbobev sent Sat 13 Aug 2016:

Dear Steve,

I’m not sure there is much to conclude here, other than confirming
that at WOT, it dumps loads of fuel into the engine, which we all
knew anyway, from reading the Roger Bywater website…

1&2. It suggests it runs closed loop with narrowband sensors and
cycles around 14.7:1, whether the link is in or not.

  1. That’s probably not unusual and has no implications that I can
    see for an idle or running emissions test. Who the hell does an
    emissions test at WOT?

  2. The link probably retards the timing a tad, hence the loss of
    power/torque. This is expected as I thought it was there for when
    you had a tank of bad gas which needs less advance.

You could always buy yourself a wideband like an Innovate LC-2 plus
a gauge and have fun watching it as you drive around.

kind regards
Marek–
v12 E-type running MS3/3X sequential lpg and petrol
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1 Like
3

In reply to a message from MarekH sent Sat 13 Aug 2016:

Thanks Marek.
Yes, loads of fuel. Apparently from the base 36CU map (or
enriched by some unknown to me mechanism). Which, from my
limited knowledge on EFIs could mean that there will be a
need for lots of fuel to trim in closed loop, which could,
in turn, explain the rolling idle and the harder time
passing idle speed test.

I was also surprised to see over 300 HP at the wheels.
Given the age of the engine, I expected a few dead ponies.

Out of curiosity, since your MS3 system logs everything,
what is your A/F at 3500 rpm?

Steve–
The original message included these comments:

I’m not sure there is much to conclude here, other than confirming
that at WOT, it dumps loads of fuel into the engine, which we all
knew anyway, from reading the Roger Bywater website…

–
'95 XJS convertible - V12 6.0L
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4

In reply to a message from sbobev sent Sat 13 Aug 2016:

It’s whatever I want it to be. To be honest, I rarely go there, so
I can’t really translate a meaningful answer for you.

Of more interest would be ‘‘What is the timing map on the 36CU
like?’’, but there is no obvious way to download that.

kind regards
aRmke–
v12 E-type running MS3/3X sequential lpg and petrol
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5

In reply to a message from MarekH sent Sat 13 Aug 2016:

Marek:
Nobody, even R. Bywater can tell you the timing map. The
36CU does NOT do the timing, the Morelli-sourced ECU takes
care of it and the only adjustment that I know of is the
jumper:

http://www.jag-lovers.org/xj-s/book/MarelliJumper.html

There is at least one or two sources of information on the
fueling map, but the ignition…

Anyhow, I needed some closure. So many listers contributed
to my posts, I learned a lot along the way, and I am hoping
my experience will be helpful to others.

One day I will sit down with the MS3 manual and read it very
carefully. Cursory glance at it was very intimidating, but
so was the thought to buy a V12 powered car and maintain it
myself…

Many thanks again,
Steve–
The original message included these comments:

Of more interest would be ‘‘What is the timing map on the 36CU
like?’’, but there is no obvious way to download that.

–
'95 XJS convertible - V12 6.0L
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6

In reply to a message from sbobev sent Sat 13 Aug 2016:

FYI, mine is probably about 15+:1 at very low load and about 12.5:1
at full load at those revs on petrol, but I mostly run lpg, because
it’s ~half price.

kind regards
Marek–
v12 E-type running MS3/3X sequential lpg and petrol
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7

Steve,

My recollection (and I’m rusty on this) is that there is a micro switch on
the throttle cable for fuel enrichment at WOT.
I thought this was for acceleration (kick down) enrichment. However, it
would also activate at WOT and might trigger the excess enrichment you are
seeing. I assumed it was for transient enrichment only.

Given how rich it is running, I wonder what happens if you pull the wires
off the switch? Won’t change your idle issue.

Other thought is that perhaps your fuel pressure is increasing with the
second pump coming online. I won’t have thought it should. You could
disconnect the second pump and re-run the test. Bearing in mind it should
theoretically run dangerously lean once it “runs out of fuel” at higher rpm.
But if the sudden onset of rich running moves (or disappears) that would
tell you something.

Also, given your idle result seems to be “designed in” as a result of the
slow response of the control loop, it is worth asking the question of the
list whether anyone with standard ECU actually has a smooth idle? Slow
response of O2 sensors is usually a sign of contamination, but I seem to
recall you had new ones fitted.

Rgds
Mark

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8

In reply to a message from Mark Eaton sent Sun 14 Aug 2016:

Hi Mark:
No, the 6.0L throttle capstan is different – you’ll find
only the idle switch (different design) there; TPS is
different too.
I have a pressure gauge mounted permanently on the fuel
rail, have revved the engine to 3000 rpm in my garage and
have not seen anything unusual. Would not expect this to be
an FPR issue.

Steve–
The original message included these comments:

My recollection (and I’m rusty on this) is that there is a micro switch on
the throttle cable for fuel enrichment at WOT.

–
'95 XJS convertible - V12 6.0L
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9

In reply to a message from sbobev sent Sun 14 Aug 2016:

Steve,
It’d be easier to just map all of this electronically now, rather
than have the cocktail of solenoids and microswitches as Bywater
described them, i.e. it’s probably still there, just via another
method.

I don’t think disconnecting the second pump is a good idea,
although if you rev it up slowly, I doubt you’d notice any step
change as it cuts in. In theory, you’d just get more volume coming
back in the return as it cuts in such that the excess is diminished
but still an excess at very high revs.

kind regards
Marek–
v12 E-type running MS3/3X sequential lpg and petrol
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10

In reply to a message from sbobev sent Sat 13 Aug 2016:

I received several off-line comments.

This is just to confirm it for everyone interested/reading
this thread.
My car is not heavily moded – just a chip for the 36CU
supplied by Roger Bywater, and slightly bored throttle
bodies. Please refer to these two images:

http://www.jag-lovers.org/v.htm?id=1419987798

I’ve got catalytic converters, albeit, not original – they
are aftermarket 3-way Magnaflaws.

For some reason, everyone that contacted me was either
skeptical of the test or asked what kind of mods I’ve done
to get this many horses at the wheels (the HP and torque
numbers quoted below are apparently not typical of a Jaguar
V12)

Am I missing something here?

Steve

PS The only other example of XJS HP/torque testing
documented here (and I know of) is this one:

http://www.jag-lovers.org/v.htm?id=1147136418--
The original message included these comments:

  1. At idle, A/F mixture bounces of 14.7 with a regularity
    that matches the tach needle moving up and down. Idle speed
    should be 750 rpm. Mine was between 727 and 772. Kirby is
    absolutely right that the ‘‘EFI system is constantly trying
    to run it too lean. It’s constantly bouncing on and off
    stochiometric, and the cycling up and down of the mixture to
    hold it in that range results in an idle that’s not what a
    V12 should be.’’
  2. Removing the Marelli jumper changes nothing in idle.
    Same result over 2 minute of monitoring.
  3. Putting load on the engine. Power and torque increase as

–
'95 XJS convertible - V12 6.0L
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11

In reply to a message from sbobev sent Sat 13 Aug 2016:

‘‘Also, if I understand correctly, at WOT, i.e., after the
second fuel pump comes online (above 2850 rpm), the O2
sensors feedback is inhibited. The 36CU does the fueling
based on MAP and CTS alone.’’
this is not the case as some states at the time required a
wot pass with the sensors in the tail pipes and federal
emissions had standards that the car had to adhere to
throughout it’s range of operation so the engineers wouldn’t
have written code that allowed an 11 to 1 ratio to happen
unless a default condition existed to activate an
alternative operational condition to keep holes in the
pistons from forming.
there is apparently such a condition happening at the
present time. as I have written recently there are some
sensors that although apparently have no interconnective
relationship with others if they fail or send inconsistent
data back to the ecu will cause problems elsewhere in the
system.there is probably a serial data loss(inconsistent or
missing) somewhere that the main chip is unable to process.
as a primary step…and mind you,we are still sorting out
the quirks of the system even though new adapted code has
been written, check the wiring between the sensors and
header connections(pin to pin). yes…there a lot of them
but patience,time and an ohm meter with clips are the only
tools that are required for that first thorough diagnostic
step.the wiring used on these cars is of small gauge and
termination although better than it was in previous
incarnations still leaves a bit to be desired.
once this is completed and all is well(hopefully) only then
should one look into faults with the control heads.
again…things like faulty components(as was the case with
nigels ecu)or weakened solder joints or even tin
whiskers(temp and moisture cycling problems being the cause
of these) can and do happen given the age of these units.
what people all too often forget is that electronic
components weren’t designed to last forever nor were they
expected to.failures will happen and often do in quite
unexpected ways.
take an older automatic trans vs a computer controlled
trans for an example.
older auto trannys used a kickdown linkage of various and
sundry sorts and a vacuum modulator to sense what the engine
and driver wanted from it and responded in kind.
look at what is required to operate a computer controlled
trans.a control head that talks to other sensors and control
heads located throughout a car/ wiring/relays/connectors.
the order of complexity has magnified and the benefits of
this are negligible at best unless you are after keeping an
engine within a narrow range of operation
because of some mandate by a governing body that required an
easy out for the manufacturer but that’s all about politics
and the epa here in the states.
much more complicated…much more to go wrong.
wire by wire through the connector ends first and then it
will be time to look elsewhere.long leads on the ohm meter
await to start to solve the problem :slight_smile:
=dok=–
thewytchdoktor=v12 fun!/94 xjs 6 litre/ s=k.log w
Winchester Virginia, United States
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