ECU repairs

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Post by CitroJim »

I'll need to look at the release date for V6... Forgot to ddo that last evening :oops: Blame the heat :roll:
Sid_the_Squid wrote: Jim is that ‘immediate’ as in auto adaption reset done, engine start, doors closed, off we go?
Yes, that was it :D Lexia packed away, engine started and away ASAP...
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Post by xantia_v6 »

Re the warm-up period, if you put the transmission into snow mode it immediately changes into second, and if you then switch out of snow mode, it seems to go to normal mode, not warm-up mode.

I think the harsh change into first may be one symptom of the auto-adaptive function struggling due to a restricted transmission oil filter (which would result in reduced line pressure).

On my Mk2 V6, the upchanges are all very soft, which leads the auto adaptive to tighten up the changes, leading to harsh downshifts. Resetting the auto-adaptive evened things out for a few days.

My Mk1 V6 hardly ever has a harsh downshift, but does have the once a year select-2-gears-at-once experience.
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Post by Sid_the_Squid »

I think the harsh change into first may be one symptom of the auto-adaptive function struggling due to a restricted transmission oil filter (which would result in reduced line pressure).
Sounds feasible, but I don’t think that’s the case, if you take into consideration Jims auto box, its got a brand new filter and I should imagine very clean internals, yet behaviour similar to, if not the same, as mine and Stempys.
Resetting the auto-adaptive evened things out for a few days.
I think this is where one can get tied up in terminology, the auto adaptive reset, Jim and myself speak of is the ECU valve block values reset, where the ECU must re-learn the valve block operating parameters against its default reference values. Which according to the training manual will only happen during the road test, when “The ECU permanently adapts itself to the transmission”. This would suggest that once the initial road test is done, unless the ECU auto adaptive is reset again, it cannot ever change these values. Therefore once the initial road test is over, no amount of time should not alter the shifting quality, except with the usual wearing out of components.

I don’t mean to sound like I’m picking holes in what you’ve just posted xantia_v6, I’m trying to figure out how it all fits together. In particular the Auto ECU reset is something I’m most interesting in figuring out, the manual is fairly vague on what constitutes a ‘test run’ and when the ‘permanent adaptation’ values are actually stored, is it when the box is put into park? Or when the engine is switched off? When does the ‘test run’ begin, when you next run the engine? Only if you immediately turn start the car after the reset? Or is it when the box is put into D?
Is it really a one off test run completed these are the values stored forever, or as your post would suggest actively adapt over a period of days?
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Post by Stempy »

My impression was that the auto adaptation was a continual process as the ecu responds to your driving style. If like me you continually drive like a grandad then it will pretty much stay locked into one change algorythm. If however you lent you car to your teenage son for a while you might find that the next time you drove it it would rev higher before up changes until it got used to you again.
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Post by CitroJim »

Stempy wrote:My impression was that the auto adaptation was a continual process as the ecu responds to your driving style.
As I understand it Stempy, that's not strictly true. There are six main maps in the ECU, SK1 to SK6, which are used in normal operation. The auto-adaptive part monitors how you are driving and selects a map from the six that best-fits what the ECU believes your current driving situation to be. The ECU monitors a number of things and uses rates of change on these (e.g. engine speed, throttle position) in complex algorithms that result in a value to select the most appropriate map. This is a continuous process. Map SK1 is the most economical one and SK6 the most sporty.

The ECU tries to be clever and works out if you are cruising, going uphill, downhill, in a hurry, in grandad mode or coming to a stop. Invariably it gets confused at times and makes a wrong decision. Take the situation where 1st gear snatch will be most apparant. You are approaching a roundabout at speed. You're on an ecomonical map. You brake to slow down for the rounabout. ECU says ahh, ha you're decelerating to a stop going on the rate of change it is seeing. It keeps the TC in lock-up for engine braking and runs down the gears according to the law in the current map. There is traffic and you roll nearly to a halt. The 'box is in 2nd and the TC remains locked-up you slow a bit more and spot a gap. Your speed is now such that the map law says change to first but your road speed is still above the threshold for the TC to unlock (it unlocks only as an anti-stall and it happens at very low speed). You boot the car at the point that the TC is still locked up and the 'box is in the process of releasing the 2nd gear clutches and engaging the 1st gear ones. It engages 1st gear always with high line pressure ( I guess to ensure a very rapid engagement to prevent any slip and consequent clutch damage from the high torque of the engine under 1st gear running). Also as you were formerly decelerating and braking, the engine will be retarded to reduce power. Under this circumstance, a snatch as you go back on the power is inevitable and the ECU is powerless to predict this sort of thing. The ECU is not all-seeing and fails when you appear to be slowing to a halt and then rapidly reapply the power; it was not in its power to predict it and correctly react to it.

You can see this if you play the same scenario in a manual car. Imagine changing right down to 1st as you come to the roundabout, spot the gap and accellerate away again without feathering the clutch. First is too low and the car will snatch. Such a scenario will have a manual car in second or even third at the point of slowing right down, possibly with the clutch partially disenagaged and the lowest egar you'd use to accellerate away is second under clutch control.

High line pressure is used (under ECU control) only to enagage first and reverse. All other gear changes are made with low line pressure to ensure a smooth change.

That's my thoughts from reading and re-reading the section on auto-adaptivity and gear changing laws. You're right Stempy, it is headache inducing stuff!!!
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Post by xantia_v6 »

I think we are talking about 2 different mechanisms. Stempy and Jim are talking about the mode or map selection which is driven by driving style, the behaviour of the individual map themselves are hard coded into the sofware, and do not adapt. The map selection process appears to be quite short term, with a memory of only seconds or minutes.

Sid and I are talking of the lower-level adaption of the gear changing parameters (how quickly and how hard the clutches must be engaged) to take account of component tolerance and wear in the transmission. This process seems to be mainly driven by measurements of clutch slip during gearchanges, and recalibrates the valve opening charactoristics to give the gearbox the right "feel" with smooth changes that don't wear the clutches too much.

This adaption problably has a fast mode, where it learns the approximate settings in a few dozen occurrences of each gearchangethe fast mode is initialised by the Lexia reset. I am sure it also has a slow mode that fine tunes the changes over the rest of the life of the transmission, and my observation of my Mk2 is that that the change quality can vary noticeably over after a few hours driving.
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Post by Stempy »

Well I guess it's kind of good to know that the problem is a software issue rather than a mechanical fault. Hopefully the snatching won't be doing any damage. Which reminds me that I must try and find some suitable engine tie rod bushings.

Perhaps I'll change the oil again and get the ECU reset. I was quite please to see that the colour of the oil was still pretty golden and clear when I repaired my leak a while back. I've changed it twice since I've had it so another change wouldn't do any harm (except to the wallet).
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Post by CitroJim »

xantia_v6 wrote: This adaption problably has a fast mode, where it learns the approximate settings in a few dozen occurrences of each gearchangethe fast mode is initialised by the Lexia reset. I am sure it also has a slow mode that fine tunes the changes over the rest of the life of the transmission, and my observation of my Mk2 is that that the change quality can vary noticeably over after a few hours driving.
I'd agree completely. The initial happens quickly it seems and yes, a slow mode sems to be there based on the fact that the ECU can detect excessive slip and log it as a fault in the ECU if it detects too much. I believe the ECU has a default set of values for gearchange paramaters which it fine-tunes and then stores. I guess it has a preset ideal time in which a complete gearchange sequence takes place for each change and this is fine tuned based on the actual line pressure in force as this will vary between gearboxes. Similarly, the ECU needs to learn the characteristics of the indivual electrovalves and how the signals applied to them affect the operation of the gearbox. This bit must be quite clever because as I know from experience, the ECU can detect if the valve block is changed and effectively shuts down until re-initialised.

My initial initialisation was done before the car was on the road so it did not have a chance to learn the 'box properly until much later. My second re-initialisation seems to have improved things considerably.

Time will tell but I'm thinking that a regular re-initialisation is not a bad thing to do.

The "snatch" will not be harmful Stempy but in the interests of mechanicay sympathy it's good to avoid it. To understand how andy why it comes about helps to avoid it where possible. Just shows that however clever they try to make electronics, they will never beat a human brain!
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Post by Sid_the_Squid »

xantia_v6, interesting concept of the 'fast ' and 'slow' learning modes. So like tuning a radio whilst in the car, you set the station, but there is always a little bit of fine tuning being done. Could very well be, it would make sense for the gearbox to have some kind of adjustment mechanism to handle the inevitable wearing of clutches and valve block springs.

Stempy, its easy to get cross-talk, when it comes to the box ecu, the manual refers to the 'auto adaption' to mean
1. The constant driving styles changes as Jim described above (far above),
2. The ECU to valve block 'learning' as xantia_v6 and myself (and now Jim) are discussing, that’s the bit which gets reset by the Lexia which then must have a 'road test' for 'permanent ecu adaption'
If you look at pages 189, and 197 of the 4hp20 training manual it contains a fairly vague description of the procedure xantia_v6 and I (and Jim) are discussing, and that Jim has just performed on his v6.

I’m so interested to figure out the exact steps of the auto reset procedure because I had Jim do a reset at the DSM rally, but I did not go for an immediate ‘road test’ I actually turned the engine off and on a few times afterwards (who wants to hear a V6 roar ;) ), so when I finally came to drive, there was a noticeable difference in the box, better in some aspects, but worse in others. So I’m going to see Jim for another box re-set this time driving immediately afterwards, not even going to turn the ignition off, obviously wait for the lexia to be disconnected, but then engine on doors closed off we go. I am most keen to see the results.

As for avoiding the ‘snatch’ I find if I’m cautious with the throttle when slowing down then speeding up, it avoids any harsh snatch, where as if I’m throttle off, throttle on hard, its far more likely to be jolty.

*edit, wrote the post before I saw Jims latest post, added corrections in ()
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Post by Stempy »

CitroJim wrote:
The "snatch" will not be harmful Stempy but in the interests of mechanicay sympathy it's good to avoid it. To understand how andy why it comes about helps to avoid it where possible. Just shows that however clever they try to make electronics, they will never beat a human brain!
Funny that I can indeed almost predict where it will happen, and there's one particular junction where it always happens if I'm not very careful how I negotiate it, so there must be a preset set of circumstances where the ECU does get its wires crossed, which makes me think that a software modification would be the answer. Whether that is included in the update is another matter.

My Kangoo is also an auto and has a similar ECU control set up but it is generally faultless so I suppose it must have a higher IQ than the Xantia.
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Post by addo »

Stempy wrote:Funny that I can indeed almost predict where it will happen, and there's one particular junction where it always happens if I'm not very careful how I negotiate it...
That sounds remarkably similar to my AL4 issue, for which I've come to suspect the TPS assembly. You're approaching with very light pedal pressure and the car is slowing moderately on the grade; all of a sudden it lurches and downshifts?
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Post by Sid_the_Squid »

I've had that behavior with my 4HP20 addo, but never seen with my AL4, neither box report any faults to the lexia so I assume its to do with software control, maybe a certain revision is more effected than another.

Continuing with the discussion about the 4HP20 learning modes, on Saturday I was at Jims, among other things the 4HP20 got its 3rd oil change in 2 months, (lovely and golden now, so no more changes for another year methinks) and a ECU 'auto adaption reset', Immediately after the reset, Lexia disconnected, engine started, and away for a 33 mile 'road test', with lots of varying conditions. So that should be the 'correct' reset procedure to satisfy the 'fast' ecu to valve block learning mode. Tomorrow I'll be able to compare how the box performs. will report findings back here.

My 4HP20 software revision; if I remember correctly was it program 3, revision 8, that sound right Jim?
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Post by CitroJim »

Sid_the_Squid wrote: My 4HP20 software revision; if I remember correctly was it program 3, revision 8, that sound right Jim?
Thats it! Mine is older, on program 2, revision 5...

Looking forward to hearing how the re-initialisation has changed anything on the test run...
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Post by Stempy »

So is that the latest revision you have in yours Sid?

Going back to the HA ECU, in the interest of science I pulled mine apart today and found there to be three electrolytic caps in there, one with legs and two SMD types. I have a replacement for the leggy one but will have to acquire a couple of SMD's. The leggy one is 100uF at 35v and the other two are 47uF, one at 16v and one at 35v. While it's apart I will replace all three. One of them certainly looks a little distressed so we will see what happens.

I also noticed that the solid state relay device that drives the rear electrovalve looks to have been getting hotter than the front one, and its the rear that's been chattering.
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Post by Sid_the_Squid »

So is that the latest revision you have in yours Sid
Don't know Stempy, at this stage its just data gathering.

I'll be interested to know if replacing those electrical do-hickies make your gearbox behave better.
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