[xj-s] Adaptive idle fueling trim ...?

In reply to a message from sbobev sent Mon 23 Sep 2013:

You’d think so but no :slight_smile:

The purge valve is a solenoid operated valve that is normally
open, so ‘closing’ the valve will allow vapor to flow. The
amount of flow is controlled by a pulsed signal from the ECM

Cheers,

Allan–
The original message included these comments:

I do have a question for you. Below you state that the ECU
closes purge valves to allow canister regeneration in closed
loop?
The way you worded it (closes purge valves) implies the
opposite – purging is happening in OPEN loop. CLOSED loop
enabled would mean no purge. Do I have it right?


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In reply to a message from sbobev sent Mon 23 Sep 2013:

Steve,

I don’t know how to do a multi part response so I have had to
make separate posts to your questions, sorry about that.

Yes as I mentioned earlier the 45 sec timer was replaced by
ECM control for the 6.0. I’m not sure about the 1 min cutoff,
my understanding from the Jaguar documentation is that the ECM
switches off air injection using a strategy that looks at
injector pulses versus coolant temperature.

In terms of battery voltage correction, the fact that your
battery is always 100% will have no effect. The ECM just uses
a fudge factor to compensate for the actual battery voltage to
determine the pulse duration. For instance if the strategy
says that at 14V no correction is needed, then the calculated
pulse duration will go unchanged. If however, the battery
voltage dropped to say 13.5V then the ECM would apply a
correction based on the voltage correction strategy to
increase the pulse duration in order to maintain the required
fuel flow.

The reason this is necessary is that the rate at which the
injector pintle opens is directly related to voltage. If the
voltage decreases the pintle will open more slowly and less
fuel would flow for a given pulse duration. The ECM
compensates for this by increasing the pulse duration.

Sorry for being wordy but it’s sometimes hard to find an easy
way to explain things :slight_smile:

Cheers,

Allan–
The original message included these comments:

I have got an off-list email from Mr. Bywater, who explained
to me that the stand-alone 45-timer unit was phased out with
the introduction of the 6.0L (VIN188004) and the 36CU
switches to CLOSED loop (irrespective of engine temperature
or O2-sensor input) exactly 1 minute after start-up.


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In reply to a message from sbobev sent Mon 23 Sep 2013:

Possibly. During open loop operation the valves should not
allow vapor to flow to the manifold. If it did, that could
weaken the mixture and cause a stumble because the ECM would
have no way of correcting for it.

The valve is controlled by a series of pulses from the ECM.
The pulses vary in duration increasing as engine load and
speed increase. They should be about 10msSec duration at idle
with a periodicity of about 145mSec.

Cheers,

Allan–
The original message included these comments:

perhaps more, I wonder if EVAP function or the above-
mentioned voltage correction is what I need to check.


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In reply to a message from AllanG sent Mon 23 Sep 2013:

Allan:
Are we talking about the ‘Rochester’ valve here or the two
valves that are plumbed to both banks?
Closing the Rochester valve in order to purge the canister
is in order, otherwise the manifold vacuum will be sucking
the gas tank and collapsing it (well-documented issue)
I’ve had my gas tank lid open/closed during various test and
have not seen the ‘‘whoosh’’, so, I believe my EVAP system is
OK.
Is there are way to check the solenoids with a simple VOM?
Steve

PS. If you are curious, you can read my other posts under
the topic ‘‘6.0L idle woes…’’ Therein, I described a test,
whereby the ECU is put in forced open-loop operation by
removing the O2-sensors feedback. The idle speed increases
by 50-100 rpm, which I attributed to the slightly richer
mixture and more air into the manifolds through the carbon
canister vent… did I get this wrong too?–
The original message included these comments:

You’d think so but no :slight_smile:
The purge valve is a solenoid operated valve that is normally
open, so ‘closing’ the valve will allow vapor to flow. The
amount of flow is controlled by a pulsed signal from the ECM
Cheers,
Allan


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In reply to a message from AllanG sent Mon 23 Sep 2013:

Allan:
Related to what I said above. There is no stumble in open
loop. I think the ECU is tricked into doing something
excessive just as it transitions from open to closed loop.
Steve

PS From your signature I gather you are a 6-cylinder owner.
How do you know so much about the 36CU operation?–
The original message included these comments:

Possibly. During open loop operation the valves should not
allow vapor to flow to the manifold. If it did, that could
weaken the mixture and cause a stumble because the ECM would
have no way of correcting for it.
The valve is controlled by a series of pulses from the ECM.
The pulses vary in duration increasing as engine load and
speed increase. They should be about 10msSec duration at idle
with a periodicity of about 145mSec.


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In reply to a message from sbobev sent Mon 23 Sep 2013:

Steve,

I’m not sure I’m quite tracking with you.

The Rochester valve controls vapor flow to the charcoal
canister. It has three functions, it provides fuel tank
pressure relief, fuel tank vacuum relief and vapor flow
control. It is controlled by vacuum from the intake manifold
when the engine is running and by fuel tank pressure when the
engine is off.

The two purge valves control the flow of vapor from the
canister to the intake manifold which purges the canister.
These valves are solenoid operated via a series of pulses from
the ECM. The solenoid is normally open and the ECM determines
when to ‘close’ the solenoid based on a load vs engine speed
strategy and only operates when fueling is in closed loop
mode. As the solenoid closes the valve allows vapor to flow.

So just because you don’t have a whoosh when you open the tank
does not necessarily mean the purge valves are working
properly.

I’m not sure about mechanically testing the valves. You can
hear them energise when the ignition is turned on and if you
hold them during closed loop operation you should be able to
verify they are working by feel but it doesn’t mean that they
are not leaking a little vapor in open loop mode. I would
think that you could put a handheld vacuum pump on the valve
with the engine running in open loop and see if vacuum holds?

Does this answer your question?

Also yes I own a 6 but have owned a number of Jags over the
years including an XJ12 which had the 6.0. Many of the
systems, such as evap control are identical between the 6 and
the 12 and many processes such as fueling use similar logic.
However, I am certainly no expert on the V12 :slight_smile:

Cheers,

Allan–
The original message included these comments:

Are we talking about the ‘Rochester’ valve here or the two
valves that are plumbed to both banks?
Closing the Rochester valve in order to purge the canister
is in order, otherwise the manifold vacuum will be sucking
the gas tank and collapsing it (well-documented issue)
I’ve had my gas tank lid open/closed during various test and
have not seen the ‘‘whoosh’’, so, I believe my EVAP system is
OK.


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In reply to a message from sbobev sent Mon 23 Sep 2013:

I just quickly browsed those threads and am not quite sure I
understand? You state that the engine stumbles on cold
starts. Cold starts are always in open loop mode, does your
stumble continue after the engine has warmed up?

If you force the fueling into open loop by disconnecting the
O2 sensors, the purge valves should not allow any vapor to
flow to the intake manifold.

There could be a number of reasons why your rpms increased
when you did this, perhaps the engine was running leaner than
the programmed values in the matrix, in which case the ECM
would now use a richer mix.

Also, if the purge valve did allow some additional air in when
in open loop, that could also rise rpms.

Cheers,

Allan–
The original message included these comments:

PS. If you are curious, you can read my other posts under
the topic ‘‘6.0L idle woes…’’ Therein, I described a test,
whereby the ECU is put in forced open-loop operation by
removing the O2-sensors feedback. The idle speed increases
by 50-100 rpm, which I attributed to the slightly richer
mixture and more air into the manifolds through the carbon
canister vent… did I get this wrong too?


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In reply to a message from AllanG sent Mon 23 Sep 2013:

Thanks Allan:
It seems I’ve got it all wrong with regard to the purge
valves.

Yes, car starts fine, idles normal for a minute, then
stumbles and idles bad for a short while, and then again
runs normal. I cannot find any faults with the inputs to
the ECU.

The only thing that I noticed makes a big difference is the
forced open loop operation. Runs very well w/o feedback.
One would immediately reason that my O2 sensors are not
good, but they are new, OEM style BOSCH 13313 and I had
similar cold engine woes with the ones that were there when
I bought the car.

I’ve never had DTCs FF44 or FF45 due to O2-feedback.

I think what I will do is plug the vacuum tubes to the purge
valves and try it out. This simpler test should tell me
whether if I need to dig deeper into the left front fender
well.

Thanks much for your insights.
Steve

PS Do not know if you noticed, but I have swapped ECUs as
well. Have another one with the EPROM reprogrammed by
AJ6engineering to their S.E. map. Both work similarly.–
The original message included these comments:

I just quickly browsed those threads and am not quite sure I
understand? You state that the engine stumbles on cold
starts. Cold starts are always in open loop mode, does your
stumble continue after the engine has warmed up?
If you force the fueling into open loop by disconnecting the
O2 sensors, the purge valves should not allow any vapor to
flow to the intake manifold.
There could be a number of reasons why your rpms increased
when you did this, perhaps the engine was running leaner than
the programmed values in the matrix, in which case the ECM
would now use a richer mix.


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In reply to a message from sbobev sent Mon 23 Sep 2013:

One easy way to see if they have an effect is as you say,
disconnect the tube that runs from each purge valve to the
intake manifold. Make sure you plug the tubes well so no air
can enter the manifold. Then start the engine when cold. You
will be in open loop mode and if the valves are letting any
air through this will now just vent to the atmosphere. If
your engine runs well, you may have found the problem.

Cheers,

Allan–
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During open loop operation the valves should not
allow vapor to flow to the manifold. If it did, that could
weaken the mixture and cause a stumble because the ECM would
have no way of correcting for it.

That’s backwards, isn’t it? The concern is that the vapor will
RICHEN the mixture, since it has all those fuel vapors in it.

But the adaptive idle strategy would need to do the opposite and make
sure the vapor flow is shut off. Otherwise, the richening due to the
vapors would cause an incorrect correction.

The valve is controlled by a series of pulses from the ECM.
The pulses vary in duration increasing as engine load and
speed increase. They should be about 10msSec duration at idle
with a periodicity of about 145mSec.

Fascinating. The earlier cars had two purge valves, and they’d open
one at idle and the other with more throttle, with a delay valve in
the line so it wouldn’t open too soon. It sounds like they got much
fancier here, carefully controlling the level of purge so as to avoid
swamping the engine with vapors.

– Kirbert

// please trim quoted text to context onlyOn 23 Sep 2013 at 7:41, AllanG wrote:

Thinking more about this, it sounds like it may be more intended for
correcting for issues in the injectors themselves than in wear in the
engine. I dunno what happens with injectors in time; I guess maybe
they get gunked up a little and flow slightly less than they
originally did. So, after a few thousand miles, the system runs
through the adaptive idle trim process and finds that things are
running a bit lean. It corrects this by adding, say, a coupla
microseconds to the duration of the injector pulse – across the
board. Hence, this would hopefully put the injectors back to close
to the correct fuelling at all power levels, not just idle.

The only problem I have with that theory is the concept that ALL of
the injectors would get gunked up at relatively similar rates. Maybe
they do, I dunno, but the reports we’ve had from people who had their
injectors serviced was apparently that they were all over the place.
If that’s more typical, then the adaptive idle scheme would forever
be richening up the fuelling across the board to deal with the
leanest injector on that bank. Maybe that’s a good thing, I dunno.

– Kirbert

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In reply to a message from Kirbert sent Mon 23 Sep 2013:

It actually could be either way. The canister has an air
inlet that allows fresh air to enter the canister and is drawn
through the charcoal which has trapped the fuel vapor, as the
purge valves purge. There may or may not be much fuel vapor
in the canister. The ECM does not know the mix, it could be
higher or lower than Lambda = 1, that’s why it can only
operate in closed loop with the O2 being the final arbiter.

Cheers,

Allan–
The original message included these comments:

That’s backwards, isn’t it? The concern is that the vapor will
RICHEN the mixture, since it has all those fuel vapors in it.
But the adaptive idle strategy would need to do the opposite and make
sure the vapor flow is shut off. Otherwise, the richening due to the
vapors would cause an incorrect correction.


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It actually could be either way. The canister has an air
inlet that allows fresh air to enter the canister and is drawn
through the charcoal which has trapped the fuel vapor, as the
purge valves purge.

Yes, but additional air won’t lean the mixture. All it will do is
raise the idle. The MAP sensor will pick up on the change in
manifold pressure that results from the additional airflow and
provide additional fuelling in accordance. Hence, if the purge flow
contained nothing but air, the mixture would not be affected – but
if it contains ANY fuel vapors at all, the result would be rich.

– Kirbert

// please trim quoted text to context onlyOn 23 Sep 2013 at 13:48, AllanG wrote:

In reply to a message from Kirbert sent Mon 23 Sep 2013:

Steve, after reading your description above, are you sure
the aux air valve isn’t closing down too fast?–
John. '95 XJS 6.0L convertible. Southlake, TX
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In reply to a message from Kirbert sent Mon 23 Sep 2013:

Kirby,

You are quite right, I was being a dozy kipper!! :slight_smile:

Cheers,

Allan–
The original message included these comments:

Yes, but additional air won’t lean the mixture. All it will do is
raise the idle. The MAP sensor will pick up on the change in
manifold pressure that results from the additional airflow and
provide additional fuelling in accordance. Hence, if the purge flow
contained nothing but air, the mixture would not be affected – but
if it contains ANY fuel vapors at all, the result would be rich.


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In reply to a message from Kirbert sent Mon 23 Sep 2013:

I think it is anything that may effect the strategy map.

We know that the adaptive trim routine runs every 8 mins but
what signals it to actually make a change in the map? I know
in the AJ6, the ECM runs the routine every 8 mins but only
makes a change if the O2 sensor feedback is outside normal (2

  • 3V)

It actually makes a lot of sense and I would think that the
6.0 uses a similar routine. This would correct for any long
term drift and keep the O2 sensors operating in their normal
range.

Cheers,

Allan–
The original message included these comments:

Thinking more about this, it sounds like it may be more intended for
correcting for issues in the injectors themselves than in wear in the
engine. I dunno what happens with injectors in time; I guess maybe
they get gunked up a little and flow slightly less than they
originally did. So, after a few thousand miles, the system runs
through the adaptive idle trim process and finds that things are
running a bit lean. It corrects this by adding, say, a coupla


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We know that the adaptive trim routine runs every 8 mins but
what signals it to actually make a change in the map?

Hmmm. Didn’t the description indicate that it changes the injector
pulse length? If so, wouldn’t that indicate that it’d be looking at
O2 sensors only? Everything else mentioned is “permissions” to go
INTO the adaptive trim routine, not what it looks at once it’s in it!

So, presumably it shuts off the purge flow to avoid confusion caused
by any fuel vapors, and then it adjusts the injector pulse length in
the same manner that the closed loop system does – except, in this
case, it changes it once and then leaves it alone for 8 minutes.

Does anyone know what should ideally happen to fuelling as an engine
goes through “normal wear”? Should it get leaner? Richer? I woulda
thought that stochiometric was stochiometric regardless of engine
wear. Perhaps as it wears it leaks more oil into the combustion
chamber and the fuelling system must lean back to compensate?

I know
in the AJ6, the ECM runs the routine every 8 mins but only
makes a change if the O2 sensor feedback is outside normal (2

  • 3V)

You’re saying the engine is operating in closed loop already, so the
only way the adaptive idle strategy goes into effect is if the closed
loop system is currently unable to hold the fuelling within
acceptable range? IOW, the closed loop system can correct within +/-
20%, and the adaptive idle strategy adds another +/- 20% on top of
that?

It’d be fun to monitor what that adaptive idle strategy does after an
Italian Tune-Up!

– Kirbert

// please trim quoted text to context onlyOn 23 Sep 2013 at 17:09, AllanG wrote:

Does anyone know what should ideally happen to fuelling as an engine goes
through “normal wear”? Should it get leaner? Richer? I woulda thought
that stochiometric was stochiometric regardless of engine wear. Perhaps
as it wears it leaks more oil into the combustion chamber and the fuelling
system must lean back to compensate?

While chasing D-Jetronic daemons in my engine I learned that the Porsche 914
(also D-Jetronic) crowd routinely does various things to bump up fueling on
the grounds that more is necessary on aging engines.

Ed Sowell
'76 XJ-S

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In reply to a message from Kirbert sent Mon 23 Sep 2013:

I was teathed using Holley jets. I never re-jetted a carb
because I rebuilt an engine. I think you are probably
right thinking its for the injector wear, rather than
engine wear.–
The original message included these comments:

Does anyone know what should ideally happen to fuelling as an engine
goes through ‘‘normal wear’’? Should it get leaner? Richer? I woulda


John. '95 XJS 6.0L convertible. Southlake, TX
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I am resurrecting this old thread. Really good discussion here, but at the end of the day, there is still no closure and my fueling problems continue.

I doubt anyone will read through all, but here is a snapshot of what has happened in the last couple of years

Most recently, I’ve been having the entire B-bank misbehave and a FF36 code.

Tried many things – cleaned connectors, wiggled wires, check spark – the intermittent fault persists.

Put in new O2 sensor, all was good for a week (100 miles or less) and the B-bank problem returned.

THEN, I unplugged the battery (different reason) and when I reconnected and restarted – the engine ran beautiful.

My question to everyone reading:

Will unplugging the battery ERASE the adapted fuel trim? I think it does (just like it does the error codes) but would like a confirmation. On other cars I’ve owned (2000 Audi A8) the adaptations are not erased, and after an O2 swap, a trip to the dealer is needed to get everything back to normal.

If the 36CU is indeed reset by disconnecting the battery, I would be willing to declare that the adaptive fueling trim on the 6.0L is the ENEMY to fight.

Based on everything I’ve seen so far, the engine always runs great after the battery is reconnected, and then the condition worsens, presumably because on an old engine, nothing is within the built-in specs and whatever the ECU does in closed loop eventually leads to an overcorrection.

It is a naive way of thinking about it, but perhaps the engineers had it done this way on purpose – to send you back to the showroom and get a new Jag (which btw will be a very easy thing to do when one is so tired from bringing their old car to the shop every 2-3 weeks for a reset).

Second question:
If the adaptations are NOT erased by unplugging the battery, what do the above observations mean? I regret to admit it, but I have no explanation for this scenario.

Please chime in, someone among us should know this “stuff”

Best regards,
Steve