[x300] Increased performance for AJ16 Engines - DIY modification

I have designed a new crank sensor bracket for AJ16 engines which
effectively increases the ignition timing by 5degrees under all
conditions. I have fitted this bracket to both my manual XJR6 cars.
Last weekend I measured some in-gear vehicle acceleration timings
using a laptop PC to log the vehicle speed signal from the
diagnostic plug using scan tool software. Below are the results of
my measurements. In each case the first figure is the time in
seconds to do the 20mph increment running std ignition timing and
95RON fuel. The second time is running with the extra 5degrees
ignition advance and 99RON fuel. If anyone wants any more
inofrmation about my bracket, please feel free to email me
directly. I think the results speak for themselves in terms of
demonstrating the performance benefit of this modification. It also
improves fuel economy by nearly 2mpg (imperial) so saves money too.
The bracket only took a few minutes to fit to my engine and could
be used on naturally aspirated versions of AJ16 engines too, in
X300 or XJS.

Gear 5th 4th 3rd 2nd
Gearing 30.1 23 16.4 11.3 mph/1000rpm

10-30
20-40 9.7 / 9.7 5.8 / 5.5 3.5 / 3.4 2.2 / 2.0
30-50 8.9 / 8.5 5.5 / 5.2 3.5 / 3.4 2.3 / 2.0
40-60 8.9 / 8.5 5.5 / 5.0 3.5 / 3.1 2.4 / 2.3
50-70 9.0 / 8.2 5.4 / 4.6 3.2 / 3.1–
Andy Stodart - 1995 & 1996 man XJRs and ex-Jaguar engineer
Northampton, United Kingdom, United Kingdom
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How would this bracket perform with 91 AKI/ 95 RON fuel, as that is the
best I can get here? I live at about 3500’ elevation, so I presume this
would also affect the octane requirements of the engine.

Craig

XJRengineer wrote:>. The second time is running with the extra 5degrees

ignition advance and 99RON fuel.

In reply to a message from XJRengineer sent Mon 16 Mar 2009:

This is very interesting. Was there any extra harshness to the
engine? Any pinking or anything else unusual? Would fitting a K&N
style induction kit be worth carrying out along with this?
Finally, If the air filter and bracket mod were both carried out,
would there be any modifications needed to the fuel system or would
the injection system compensate for the extra ‘‘whoomph’’ so to
speak!?
Sorry, its a lot of questions, but I would be interested in doing
this mod, and just curious if it might affect the engine long term,
or make the car noisier.–
octanejunkie
Somerset, United Kingdom
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In reply to a message from XJRengineer sent Mon 16 Mar 2009:

Andy,

Very interesting, my knowledge of the GM ODBII and its ECM would
have me believe the following. It depends on how the engine is
tuned. Clearly if tuned to run open loop in speed density mode you
would have total control of ignition timing. This is usually done
by making changes to the timing maps in the ECM.

In closed loop, the GM ECM looks at the knock sensor after each
plug is fired. If no knock is detected the timing is advanced (1/2
degree) for that cylinder the next time that plug is fired. If the
ECM hears a knock then the timing for that cylinder is retarded (1
degree) the next time that plug is fired. This process is
continuous and done individually for each cylinder. If a knock is
detected for the same cylinder 5 times in succession then that
event is recorded as a timing fault. AND � if you have the
capability to write into the ECU�s NVRAM you can change the size of
the steps that are used to advance and retard the timing.

So, in the case of the GM ECU. In closed loop, there would not be
a change in the timing if the crank position sensor were moved. On
the other hand there would clearly be a change in timing if a
higher octane fuel is used.

From your description and intrinsic knowledge of the AJ16’s ECU,
that is apparently not the case. So, to help me understand what is
really going on, what is the logic associated with the knock
sensors and their effect on timing?

One other note.
Several years ago around 1995 I built a device that could measure
the exact position of the crank as well as when (in relation to the
number of degrees after top dead center) peak combustion chamber
pressure occurred.

The goal was to dynamically adjust the timing to insure that the
plugs fired at the right time (regardless of RPM, fuel octane, or
speed of the flame front, etc.) to achieve Peak Combustion Chamber
Pressure at the best position of the crankshaft. I had a formula
to calculate the best position of the crank. It included the
stroke, length of connecting rod, and other stuff I’ve forgotten.
I do remember it was 42.5 degrees after top dead center for each
cylinder for the engine I was using as a test mule .

The real trick was measuring the peak pressure. The way I did this
was to apply a relatively low DC voltage across the sparkplug after
the plug was fired. As I recall it was 400volts or thereabouts.
While this potential was applied (starting shortly after TDC and
ending at 60 degrees ATDC I would measure the amount of current
that was conducted by the plasma (fire) in the cylinder. When the
plasma was at it’s most dense it would conduct the most current.
Taking note of the crank position relative to TDC for that cylinder
when the conductance was at it’s highest, I would adjust the
ignition timing in one degree increments until I got the Peak
Combustion Chamber Pressure at 42.5 degrees.

Continued in following post
Pete–
SpeedyPAL 1995 XJR
Milford / OH, United States
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In reply to a message from XJRengineer sent Mon 16 Mar 2009:

Andy,
Continued from previous post, I’m sorry I missed the exact place
that I ran out of room. So I may repeat some of it.

The real trick was measuring the peak pressure. The way I did this
was to apply a relatively low DC voltage across the sparkplug after
the plug was fired. As I recall it was 400volts or thereabouts.
While this potential was applied (starting shortly after TDC and
ending at 60 degrees ATDC I would measure the amount of current
that was conducted by the plasma (fire) in the cylinder. When the
plasma was at it’s most dense it would conduct the most current.
Taking note of the crank position relative to TDC for that cylinder
when the conductance was at it’s highest, I would adjust the
ignition timing in one degree increments until I got the Peak
Combustion Chamber Pressure at 42.5 degrees.

It was a really impressive system that caught the eye of the folks
at Delphi. At the time they built most of the ignition and
electronic stuff for GM as well as other auto companies. I was
invited to their plant in Michigan to look at what they were doing
in terms of arriving at the same goal in very much the same way.
With the exception that they were also measuring knock or pre
ignition with the same device i.e., I called them spark plugs.
They had a fancy new name for them.

As a result, I stopped work on the project and decided to wait for
them to solve the problems associated with turning the idea into a
robust product. Some tine later they fell on hard times and
declared chapter 11 � (time to reorganize) rather than bankrupt.

I�ve heard that the system is called something like Ion Sense
Subsystem and was intended to go into production automobiles by
1999 but I have not heard anything about it for several years. I
did hear that they were going to sell part of their business to GM
but I find it hard to believe that GM can buy anything, I bought
1000 shares of their stock a few days ago for $1.50 a share.
What�s up with that � once the largest Auto Manufacture in the
world??

Back to the subject.
Please let me know how the logic of our AJ16 ECU�s do their timing
adjustment in closed loop?

Thanks
Sorry for the long read
Pete–
SpeedyPAL 1995 XJR
Milford / OH, United States
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In reply to a message from XJRengineer sent Mon 16 Mar 2009:

Sent you an email…
Very, Very, Very Interested…

Would love to see some sort of how to…–
Dennis_B
Melbourne, Victoria, Australia
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In reply to a message from Dennis_B sent Tue 17 Mar 2009:

The ECU on X300 cars is GM sourced?–
AJ16er
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In reply to a message from AJ16er sent Tue 17 Mar 2009:

AJ16er,

Sorry, I didn’t mean to imply anything like that.

I was using what I knew about the GM ECU’s to try and understand
what is going on inside the Jag ECU.

Sorry for the confusion
Pete–
The original message included these comments:

The ECU on X300 cars is GM sourced?


SpeedyPAL 1995 XJR
Milford / OH, United States
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In reply to a message from SpeedyPAL sent Mon 16 Mar 2009:

Dear Andy,

Very interesting… But I think it may be better if this
test is performed once more with the old sensor bracket and
99RON fuel. You have changed 2 things simultaneously
(sensor bracket and fuel octane value), so it was not very
clear which caused the observed effects.

Dear Pete,

I am not a specialist, but I thought there was a limit in
how much timing advance the ECU can do. I thought once the
timing was advanced to the limit in the map, even if no
knocking was detected, further timing advance was not going
to occur… I was apparently wrong…–
The original message included these comments:

In closed loop, the GM ECM looks at the knock sensor after each
plug is fired. If no knock is detected the timing is advanced (1/2
degree) for that cylinder the next time that plug is fired. If the
ECM hears a knock then the timing for that cylinder is retarded (1
degree) the next time that plug is fired. This process is
continuous and done individually for each cylinder. If a knock is
detected for the same cylinder 5 times in succession then that
event is recorded as a timing fault. AND � if you have the
capability to write into the ECU�s NVRAM you can change the size of
the steps that are used to advance and retard the timing.
So, in the case of the GM ECU. In closed loop, there would not be


Momo (or 100 when written in Japanese Kanji), '98 4.0 XJ8 L
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In reply to a message from 100 sent Tue 17 Mar 2009:

Dear Ymomozaki-san

I believe you are correct, thank you for pointing that out.

One other question, is there any differance in the timing logic
when the ECU is in open loop vs closed loop??

Regards
Pete–
The original message included these comments:

Very interesting… But I think it may be better if this
test is performed once more with the old sensor bracket and
99RON fuel. You have changed 2 things simultaneously


SpeedyPAL 1995 XJR
Milford / OH, United States
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In reply to a message from SpeedyPAL sent Tue 17 Mar 2009:

Wow, My post has generated quite a bit of interest and plenty of
good questions. My responses in the order the questions were asked
is as follows…
Craig - there will be less benefit, but still some if you only run
on 95RON fuel (90 pump octane). Altitude reduces performance, but
does not really increase octane requirement.
Octanejunkie - The engine doesn’t sound much more harsh other than
due to the increased rate if prssure rise commensurate with the
increased ignition timing. The EMS includes individual cylinder
knock control which I personally calibrated when I worked for
Jaguar. This system will stop the engine knocking/ detonating/
pinking if the engine is run on 95RON fuel at high load with the
bracket fitted. The modification is compatible with other
performance mods such as K & N filters, larger crank pullies and
especially low back pressure exhausts systems. Modifications which
increase air flow will saturate the air meter resulting in no extra
fuel. However the fuelling was mapped rich to keep the exhaust cool
so can cope with being up to about 10% less rich.

Speedypal (Pete) - If the engine was originally mapped at
borderline knock on 95RON, then you would be right that my bracket
would advance the ignition, but then the knock sensing would retard
it back to where it had been. However, the ignition timing was set
3 degrees retarded from borderline on a mid-limit compression
ratio. I am also advocating using the bracket in conjunction with
97-99RON fuel which is widely available in Europe. This further
increases the margin of the std ignition timing from borderline
detonation. Thus the full effect of increasing the timing by
5degrees with my bracket is fully realised.

Ymomozaki-san - running an engine on higher octane fuel than that
for which it was originally mapped without increasing the ignition
timing will not significantly affect performance. However, you are
right I have changed 2 variables, which is not ideal in an
experiment. In my professional judgement (20 years as an automotive
engineer) the effect of the ignition timing change will dominate
the result compared with just changing the fuel octane.

If anyone has any other questions, please feel free to ask.–
Andy Stodart - 1995 & 1996 man XJRs and ex-Jaguar engineer
Northampton, United Kingdom, United Kingdom
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In reply to a message from XJRengineer sent Tue 17 Mar 2009:

Dear Pete and Andy,

Thank you for your replies.

If the ECU has a limit in timing advancement and if in the
timing values in the map, there is indeed a little embedded
margin until the engine actually starts detonating with
high-octane fuel, I think what Andy did is an excellent way
to improve the performance. That was something that I was
not too clear about it.

Sounds like the Jaguar timing map is somewhat conservative
and knock control is done only occationally (so that most of
the time, the ignition timing is set by the map, not
actively controlled by the feedback from the knock sensor).

By the way, maybe it can be done electronically and could be
also applicable to V8 cars…–
Momo (or 100 when written in Japanese Kanji), '98 4.0 XJ8 L
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In reply to a message from 100 sent Tue 17 Mar 2009:

I’ve finally managed to fit this part the Jag in the last week or
so.
The Differences in terms of throttle response and acceleration is
epic, however I’ve developed some issues since.
My Idle is really bad, to extent of where the Vehicle has actually
been stalling on my father when he’s driving it.
(At the Lights ete)
(He’s got it at the moment as his car is out of action)

Did you anything different with your car after fitting the
modification.
i.e. Reset Battery for the ECU to Learn the Car… or get a
Recalibration done at the dealer for something?–
Dennis_B
Melbourne, Victoria, Australia
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In reply to a message from Dennis_B sent Thu 21 May 2009:

Dennis, can’t help you as I haven’t tried the mod but I saw
the original thread a few weeks back and it did sound
interesting…would love to know what and where the sort of
gains are.

I’d probably do a battery disconnect as a matter of course,
although it should adapt its settings over a few miles.–
The original message included these comments:

I’ve finally managed to fit this part the Jag in the last week or
so.
The Differences in terms of throttle response and acceleration is
epic, however I’ve developed some issues since.
My Idle is really bad, to extent of where the Vehicle has actually
been stalling on my father when he’s driving it.
(At the Lights ete)


Regards, Bruce. 1995 XJ Sport 4.0
Colchester, Essex, United Kingdom
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In reply to a message from XJRengineer sent Mon 16 Mar 2009:

I bought and installed one of Andy’s brackets…

It works as advertised. :slight_smile:

It has been only one day and 60 miles but I do notice an
improvement in power, throttle response and, according to the t/c,
fuel economy. IOW, everything you’d expect with more advance dialed
in.

I don’t have a dyno or any actual measuring equipment but from a
standstill it’ll break traction much more easily. That’s proof
enough for me :slight_smile:

More details after a few days of driving

Cheers
DD–
The original message included these comments:

I have designed a new crank sensor bracket for AJ16 engines which
effectively increases the ignition timing by 5degrees under all
conditions. I have fitted this bracket to both my manual XJR6 cars.


Doug Dwyer
Longview Washington, United States
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In reply to a message from Doug Dwyer sent Wed 15 Jul 2009:

Doug

Please can you share a little more info on this please?

What is it exactly an did you go about installing it.–
1995 XJR 4.0 Straight 6, Surrey, United Kingdom
Surrey, United Kingdom
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Its a bracket that repositions the crank sensor to advance the timing 5�.

Installation is straightforward: loosen supercharger belt, remove
supercharger belt tensioner and bracket, disconnect sensor, remove sensor
and bracket…then reassemble using new bracket.

That’s about it, really.

Cheers
Doug Dwyer
Longview Washington USA
1995 XJRFrom: “Paul Jay” paul.jay@gmail.com

Please can you share a little more info on this please?

What is it exactly an did you go about installing it.

In reply to a message from Doug Dwyer sent Thu 16 Jul 2009:

Thank you Doug. That’s the best ‘‘endorsement’’ yet I have heard
about. I will definitely consider it.–
JagNewbie XK8 '00 DHC, 97 XJR, 76XJ12L 58K Miles
Charlotte/NC, United States
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In reply to a message from 3 Jag- Owner sent Thu 16 Jul 2009:

What a great idea but…
In California ignition timing is strictly checked in the
biennial Smog Check. XJRs have a ‘‘High Emitter Profile’’ so
are checked every year. The 5 degree advance may cause you
to fail the Smog check or need to substitute the OEM
crankshaft sensor bracket every year?
1995 XJRs have no EGR and are marginal for passing Nox. The
advanced timing is the exact opposite of what you need if
your Nox levels are close to a failing measurement(I know
the Europeans do not measure this but it is a major issue
here). If somehow the bracket could be flipped to give
instead 5 degrees retard it might help solve the Nox problem
for some?–
95 XJR, 69 E-Type ots ,97 Miata ,‘X’-type SUV
Sierra Madre Ca 91024, United States
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In reply to a message from anthony davenport sent Thu 16 Jul 2009:

My NOX in Feb was…

15mph:
Max 681
Ave 150
Meas 322

25mph:
Max 687
Ave 136
Meas 319

Remainder of measurements.

15mph:
%O2 .62
HC Max 80
HC Ave 21
HC Meas 0
CO Max .46
Ave .06
Meas .02

25mph:
%02 .62
HC Max 45
HC Ave 13
HC Meas 0
CO Max .43
CO Ave .05
CO Meas .01

LTFT is 41% due to a rear header split and old O2 sensors.

I have timing readouts with throttle position, RPM, speed, and air
flow in grams.

I haven’t convinced myself that I should get the bracket due to
ignorance not knowing if that I’m already pulling max timing under
high load or cruise.

RPM 675
MPH 0
Load 12%
Deg 15

RPM 2276
MPH 0
Load 19%
Deg 32

Pedal from crawl to floor…
RPM 1602
MPH 20
Load 25%
Deg 19

RPM 3252
MPH 30
Load 90%
MAF 1.9g/sec
Deg 21.5

Pedal from crawl to floor…

Time 00:00 33.4sec
RPM 2407
MPH 22
Load 90%
MAF 1.45g/sec
Deg 18.5

Time 00:00 35.5sec
RPM 4964
MPH 47
Load 93%
MAF 2.32g/sec
Deg 18.5

Time 00:00 39.6sec
RPM 2190
MPH 53
Load 12%
MAF .07g/sec
Deg 27.5

Time 00:02 9.5sec
RPM 1418
MPH 40
Load 16%
MAF .14g/sec
Deg 31.5–
http://www.jag-lovers.org/snaps/snap_view.php3?id=1241471427
Agoura Hills, CA, United States
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