Depends on the definition of a " Hard Reset "

It baffled me for a while until I put my head around it with a whats going on pysically ( relays )

There are a couple ways to do it from reading others by taking the positive battery cable feeding the car items to car frame ground

To reseat the item ( ECU in this case ) the ECU would have to be wired to the battery to be hot at all times

But the ECU has to have the right engine bay fuse box " king " relay closed ( ignition positive relay ) to be powered but is not the instant you remove the positive battery cable to put that on car frame ground ( as an electron well )

This is not the case with the SLCM and Body Processor Module as they are hot at all times directly wired to battery albeit a fuse , so the electron drain can go reverse current down positive cable to electron well

If a " Hard Reset " is a software command / path to return the item to zero state that would be a different thing but accomplish the same end result

I have thusly reached the limits of my credibility

 

What is it that this hard reset accomplishes?

The much desired reset of idle adaptations is held in nonvolatile memory (EEPROM) and will be retained even if the battery is disconnected.

You cannot erase codes either as codes are also held in nonvolatile memory (EEPROM) so that disconnecting the battery does not erase stored codes.

So what is this alleged hard reset, what does it reset?

 

I don't doubt your qualifications, just not in this case.

The AJ16 engine controller does not use the LTFT for fuel adaptations at all. It is simply an long(er) term average of what the STFT is showing. The may not be the case for other engines, and other car manufacturers, but it is how the Jaguar AJ16 operates.

The computer does check for discrepancies between STFT and LTFT reports, and if they deviate too far apart, it will set a code. I think STFT has to be reporting within 5%, and LTFT has to be reporting above 25%.

I own a PDU. I can reset the LTFT at any time. It doesn't change the driving, fueling, mileage, etc one iota. I have reset it from 10.2% without any effects.

 

A reversing or draining of electrons from the unwanted charged capacitors or electronic latching devices ( relaxing ) in the item's logic steps say in the SLCM to get it to 0 logic steps state is different than commanding or relaxing ( if can be done as a termed " Hard Reset " ) the ECU's LTFT to 0

So hard reset as it is coined and not really reality ( not a command ) only to SLCM and BPM and not for Engine ECU ( ? )

I have a weak recall maybe from XJREngineer ( Andy ) that something can not be modified ( maybe in the area of engine performance enhancement and not so much as normal engine regulation )

That recall my come back later in the day

Some other car manufacture's do have a direct effect in removing ( not draining ) the B + power source ( battery change out also ) and takes some running time for the Engine ECU to " relearn " optimum engine regulation before it settles down ( at least in the initial idle range )

 

one thing i can say for certain (as certain as i can be from my very recent experiences) is that there is some learning that the ECU must do. which is reset by a simple removing battery.

the reason i say this with clear confidence (as much as one can have), is simple.

recently after all this my car has been running well.
ltft reading at 10.2
stft fluctuating a little too much but reading mostly -7 to + 7. (generally within 5)
fuel economy being ok and car running well.
idle in D is 580-600.

however when i fixed alternator wiring the other day i disconnected batter for bout 1 hr.

after i got the car running again, idle was high, about 700rpm, STFT was going to -25 and the car was hesitating on acceleration due to overfueling.
it took running the car for a while, really giving it a flogging and running it through 4-5 restarts for it to begin to run good again.

so clearly it does not like to run on whatever the base fuel map etc is.
it needs a few restarts to learn the sensors and make some calculations and adjustments.

so now i am thinking whenever i disconnect my battery the car will run like *** for a few trips.

back to running with stft in the -7 to + 7. (generally within 5).
back to idle just under 600rpm

 

re "The AJ16 engine controller does not use the LTFT for fuel adaptations at all. It is simply an long(er) term average of what the STFT is showing. The may not be the case for other engines, and other car manufacturers, but it is how the Jaguar AJ16 operates.

The computer does check for discrepancies between STFT and LTFT reports, and if they deviate too far apart, it will set a code. I think STFT has to be reporting within 5%, and LTFT has to be reporting above 25%.

I own a PDU. I can reset the LTFT at any time. It doesn't change the driving, fueling, mileage, etc one iota. I have reset it from 10.2% without any effects."


I find it very hard to believe that the entire auto industry, absent Jaguar, would use the STFT and LTFT as I described. Why would Jaguar even maintain a LTFT parameter if it were not used? And why would it set a code if LTFT exceeds a threshold if it were not used?

The post by Spud Maat describes what I am talking about. Apparently both fuel trims were reset to zero when the battery was disconnected. When the engine was restarted STFT maxed out at -25, at which time the LTFT was decremented and STFT was increased (or cleared). After a sufficient period of time, both LTFT and STFT reach a steady value, or more likely a small band. Both are used to calculate fuel trim.

 

Something going on with my computer to be able to say thanks with the corner icon as inputs bring this along in discussions to get a better understanding of then designed engine regulation

The ECU as a very early best try from the ECU manufacturer to deliver to the Jaguar engine design team and integrate with their limited resources

The end result is milage number on the dash ( but then that's iffy compared to fuel station amounts mileage calculations )

Hi Andy

What's in the box ?

Happy Holidays, Joseph Barry AKA Lady Penelope's owner

Took me putting together 4 cars to get to dialysis this morning , but got there and pure now

Batteries , alternators , and battery chargers are garbage these days , been through a bunch of them I can't count , at least a meter can tell the truth to troubleshoot / resolve , one battery could only charge to 50 % ( 1 year old ) and another 60 % ( age tag not seen ) and the 3rd truck hood would not open ( found help resources on truck hood ) , the 4th car battery was completely dead

Too cold for 3rd moped as found another for $ 150 and got it running somewhat

Working with what I got

Blood pressure ( 200 / 120 ) coming down with 5th recent change in meds

 

I'm sure Land Rover and Aston Martin probably also used a similar approach to LTFT. It maintains the parameter so that (a) it would aid in the diagnosis of fueling issues, afterall you STFT only give you immediate snapshots of what the engine is doing. Not easily used to help determine long term issues. (b) it aids in sending a CEL. Having a long term number to compare against a short term number would help the OBD2 computer figure out if something is very wrong.

Why would Jaguar only provide a means to reset the LTFT in the PDU, and not the WDS, VCM, or any other device? (actually, I'm not sure it's ever been confirmed that the VCM cannot reset the LTFT)

While we're asking questions, why would Jaguar hide their use of LTFT in fueling adaptations? Training manuals would clearly indicate if it did, therefore clarifying the value of resetting it with the PDU.

 

With the notion of the LTFT and how it is used and if it changes naturally in running engine over time

It has been proven that it can be reset back to 0 " reference " point ( different than absolute pulse width time value ) with devices , I don't have these devices except ELM - 327 that can read only ( not working now as a free trail can only be used X amount of times )

The battery reinstall does show how it can commonly be reset to 0 LTFT reference ( to what time value ?)

In the beginning as a cold just started engine is it a ballpark reference for fuel injectors pulse width before closed loop when pulse width changed to satisfy the O2 sensors final gas output as a closed loop

So after closed loop is the LTFT stored for the next time it is needed for a cold engine start ?

Chasing a perceived bad LTFT may be chasing your tail and not necessary as long as STFT comes in range as a warm engine in closed loop ( + or - 3 % best expected ) and the next cold start idle speed is in reasonable range just above stalling and smooth idle

We still have the open variable on his example of confirmed cracked manifolds and other maybe not confirmed vacuum leaks and sensor reading devices and IAC response and not a good " base " to work from

Then we get into correct EGR response and accuracy of the opening gap , Smog pump and it's check valves , Evap vacuum system correct so that opens a lot of worms thinking too hard

 

1. The PDU is the only known device to be capable of resetting the LTFT on an AJ16 engine back to 0. You can disconnect the battery for 200 years. When you fire it back up, the LTFT will be the same as before. I am unaware of any other proof that exists out there. I know for a fact that neither the WDS nor the Mongoose/J2534 devices have that ability. Can the VCM, possibly, but doubtful. No ELM device can reset it.

2. Fuel metering strategies are held in memory (EPROM) in the ECM and form an engine load versus engine speed matrix. The load and speed range of the engine is divided into 16 loads and 16 speeds (256 memory sites). Digital numbers representing injector pulse duration in milliseconds fill each site and cover the entire engine load and speed range. Fuel metering correction is applied for all six cylinders simultaneously, not for individual cylinders. Fuel metering is controlled primarily as a function of engine load and speed. Engine load is sensed by a mass air flow sensor (MAFS) located in the engine air intake before the throttle housing. Engine speed is sensed by a crankshaft position sensor (CKPS) located behind the front pulley. The ECM processes the input from the MAFS and the CKPS to access pulse duration from the fuel metering strategy.

Secondary fuel metering control adjusts for engine coolant temperature, cranking signal, throttle movement and position, exhaust oxygen content and battery voltage.

 

my elm is set on my device to display both STFT and LTFT.
after my batter disconnect when the car was running like a bag of s**t the LTFT read 10.2
which is exactly what it read before the battery disconnect and still after a few resets when the car was behaving it was reading 10.2.

so not sure exactly what it was reading that it was using to influence its fuel map but it does not seem that the LTFT was a factor in this instance.
probably things like IACV.
the car probably has a base point of where the IACV should sit. however due to air leaks mine needs to sit somewhere different and it takes the car a few resets to learn and adjust where this should be?

 

According to the wiring guide the 4 wires to the IAC will read 8 volts DC inactive not moving ( idle ? ) as the command signal

But that's on paper between the technical writer's and what the real delivered product ( to make it work / is it tuned ? ) is

May be more info in the very large 521 page X300 manual ...........................NOPE ,checked section 5.1 and nothing

No real specifics in the 801s engine doc


" however when i fixed alternator wiring the other day i disconnected batter for bout 1 hr.

after i got the car running again, idle was high, about 700rpm, STFT was going to -25 and the car was hesitating on acceleration due to overfueling.
it took running the car for a while, really giving it a flogging and running it through 4-5 restarts for it to begin to run good again. "

Sorry Vee , as I did totally get this statement from Spud Maat backwards and took it as a LTFT back to 0 reset

 

yes the IACV moves a certain amount based on voltage.
however each IACV can be manually wound in or out to a different amount.
so that at any given voltage it will be sitting at a slightly different point.

so if my IACV is manually wound in a little further. (which is possible from back when i was trying out to fix high idle)
it will get the command to sit at its given point
which will lead to higher airflow and higher rpm.
or too closed will result in reduced airflow and potentially excess fuel.

after a few resets however it learns the position that it needs to sit to maintain the proper idle.

as we know the ecu commands the IACV to open a particular amount to maintain a particular rpm range.
so base map might tell it to open to 5v and hope that provides it 600rpm.
but after running a few times it learns that it infact needs to signal it to open to only 3.5v to get the correct rpm.

i do believe this is how it operates as when i was playing with my iacv back long time ago i did wind it in and out. and it did affect the idle speed on the next restart. making it lower or higher but after a few restarts it just went back to where it was.


TL;DR if the IACV is wound outside of factory spec it will initially open too far or not enough resulting in fuel and or rpm issues however after a few restarts the ECU will learn the right voltage to send it to get the RPM at the correct range.

 

The ideal way to regulate the IAC is to have a feedback that it is arriving on the desired RPM target and tweek the IAC command to meet that target

The IAC valve does not have a position sensor like on this car's EGR valve position sensor ( which I recall you don't have ) to say it is in wrong commanded position

parameter ID ( PID ) on ELM- 327 : EGR_ERROR

But the other way is to have the factory components and their specs and everything working correctly and commanding those components to a set point ( EGR , Smog pump running , EVAP system included ) and arriving on an RPM

What I found on mine was the connector lock bar was missing on the TPS connector so possible biased TPS signal , but I replaced the lock bar before good TPS % seen on ELM -327 decvice

Like in you example on the IAC maybe they tried 7 volts and didn't get a desired idle , but 8 works '' but then again the communication between the technical writers and what they have to do to get the car out the door

We had strict rules in aviation on following the written doc or a designated engineers written deviation to the written original doc and a procedure to correct the docs which I did many times

As you know Boeing is not perfect

With the idles that can be so far out from reading others I'm assuming without facts the later is what the design team did , but then again there can be some truth to both ways that if a component is so far out of whack the ECU can't " tune " in idle into range

 

yep.
it seems all my components are withing range and the ECU can tune the car to run right.
however straight outta the box under factory settings it does not.
and everything it learns it forgets on a battery pull.

exactly why sometimes when replacing a sensor or similar you should always run the car a couple times before deciding if part is good or bad....

 

Except what it stores in EEPROM.... those things it has learned, such as fueling adaptations is there forever, or until relearned, or reset by a specific device with specific software.

 

certainly is interesting trying to learn how these things work....

 

ok so back to this.
i have not been driving the car as it runs really bad and i now have another car to daily atleast.

started it up today and upon start blew a lot of white smoke.
OBD reader puts fuel trims at -25.
if i depress the accelerator the trims momentarily improve to around -3 however the then fall back to -25.
obviously the exhaust is stinking of petrol at this point.
the car idles fairly smooth.
was just under 800rpm in park in the driveway.
i had it running for a while, and my OBD indicated to me that the temp had reached 84c.
I unplugged the MAF and it stuttered and then began to idle normal again.
so i plugged it back in noting that as clearly giving a reading (have previously tested)

however when i disconnect the engine temp senso there is no change.
my assumption was that disconnecting the temp sensor should cause the idle to climb.
so if this is the case and it is not,
it indicates 2 things to me.
either the car is not switching between open and closed loop even though the sensor is giving a reading in the range where it should.
or my IACV is not opening and closing and it is stuck too far closed not allowing enough air in causing the car to flood itself.

all i can say is all this drama is really doing my head in.

**edit
so even tho idle speed seemed to be good, I just ran the IACV test procedure thinking that maybe if it is stuck too far closed whilst reporting it is open it might cause excess fuel, no i ran the test and as expected after i did not notice a change in my idle speed, however i did notice that the fuel trims were now looking really good.
so not sure exactly what is going on but it certainly seems like something around closed loop and open loop and the engine getting less air than it is reporting itself as getting.
for now not driving the car but have disconnected the IACV now with it last having good fuel trims.
so i now expect that next time i start it that it may have trouble due to cold start. however hopin that fuel trims are good.

will leave it unplugged for a while and see how it goes.

 

OBD Tools can show whether the car is in open or closed loop.

White smoke on startup could reveal leaking fuel injectors? I'll have to review this thread to remind myself what has been done already.
Reread it. I see that you have addressed fuel injectors. So nevermind that.

I wonder if there's simply something wrong with the TPS, which historically does create strange issues. It's a pricey part, so I'd hate to just throw a part at this problem.

It would be great to see if the car does enter closed loop or not. I also now have to do a thread search on oxygen sensors....

IACV is cheap and straightforward to replace.

I think you need to confirm whether car is indeed capable of entering closed loop.

 

tps appears to give correct values. have had reset, it reads 11% at idle and climbs with accel to 100% at WOT.
i have tried my bluetooth elm and some apps on android but have not seen where in any of them i can see clearly if open or closed loop has been achieved.|}

i mean yeah its possible there is leaky fuel injectors, you never know.
but unlikely as they have been recently serviced.

will be interested to see how the fuel trims look over the next few runs of the car with the IACV disconnected.