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Engine Hesitation (All makes/models)
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What you said: "Turned out the cable from the gas pedal to the throttle had excessive backlash which I adjusted out" has some relevance.
Apparently there are some points of adjustment which can be made at the gas pedal DBW assembly and/or the throttle body assembly to mitigate some of the delay phenomenon.
That's one of the suggestions my Tranny Tech friend talked about, way back when the first time I introduced his ideas to this crowd.
But nobody here seemed interested at the time.
Another more recent comment he made (before he got PO'd with all the rhetoric here) also agrees with your thinking that Fuel Economy has more to do with adopting DBW systems than anything else--a cost effective strategy for the automaker to enhance fuel economy.
It's cheaper and more reliable than conventional throttle control systems.
I'd love to hear about how to do this, and would be very grateful if you could supply me with the info.
to the contrary, i think if you return to your posts where you mention your friend, you will find at least i was asking you to post the expert's insights.
so you have at least two votes in the positive.
"Simpler" is what I'm after.
My 2000 GS300 had a steel cable between the gas pedal and the bellcrank that moved the throttle butterfly shaft. There was about 1/2" of slop in the cable at the bellcrank mounting point which I adjusted out.
Nothing, absolutely nothing, about DBW involved.
I have a DBW gas pedal assembly and the servomotor assembly for the throttle valve for an 05 RX330. Trust me, there is NO adjustment needed or possible on either of these assemblies.
DBW helping fuel economy...??
Get real.
Other than using DBW to give the tranny the time to downshift back into a more appropreate gear by delaying the onset of engine torque how could DBW, of itself, increase fuel economy?
These vehicles have an absolute pressure sensor to measure atmospheric pressure to compensate for altitude, an IAT sensor to measure and compensate for intake air temperature variations, an MAF to measure actual intake airflow volume, and finally an oxygen sensor to make sure of the proper A/F mixture with the engine in a stable state.
Provided the throttle valve position follows the gas pedal position reasonably well, or even if it doesn't, I don't see how DBW design or implementation alone could help fuel economy.
conceptually, the ECU is capable of measuring the demand from the pedal, and based on the classification of the driver, command an economically profiled increase or decrease of the throttle.
the throttle wouldn't be forced to follow the pedal...the ECU could programmatically modify the input to provide a more efficient application of fuel delivery, while also coordinating the short-term changes in demand with the transmission as required.
i'm thinking we are seeing this "disconnect" (sorry, i can't help myself here: artifact of smart technology) with the hesitation. i mean when the operator hits the pedal, do the RPMs immediately jump up (as one would expect) while the transmission is being commanded to change it's configuration?
is the response of the throttle to the change in demand a function of the classification of the driver? why would one think just the transmission would be influenced by the new design? the throttle is the main variable controlled by the ECU, right?
Understanding is a two way street.
It could be said you misunderstood what I was trying to say in my post, however I humbly accept some responsibility for my share of any confusion.
You might be wise to do the same next time.
What happened was this:
I read your comment about cable "slop", and it triggered a reminder about what my friend had said might be done to modify throttle reaction characteristics in a DBW system (which we all know doesn't use a cable!!!).
I then recalled my friend saying that Toyota uses Denso DBW technology.
What I then tried to say (and caused you some grief) was there are ways to modify throttle response by mechanical means with DBW systems.
Here's a quote from a Denso technical publication re accellerator pedal modules in DBW systems:
"The electric output characteristics of the sensor can be set in accordance with customer’s specifications.
DENSO provides two types of accelerator pedal modules – resin rod type and iron rod type – to meet customer’s needs."
Furthermore, I believe you are incorrect in saying better fuel economy isn't part of the DBW equation.
The issue of better fuel economy coupled with lower emissions is "real."
It is consistently documented in technical papers as a prime consideration for adopting DBW systems.
For those who question reliablity of DBW systems, because they use less mechanical components, they are considered less susceptible to wear, and generally require less maintenance than conventional systems.
They are more reliable--but they don't behave like conventional systems.
Perhaps those who question reliability are confusing reliability with expectations in performance.
Make no mistake, currently about 60 percent of today's vehicles are equipped with DBW systems.
Within two to three years this technology will be adopted across the board.
What we're seeing today are mainly second generation designs.
Response parameters still need work in just about all systems available today--and for all makes using 2nd generation technology.
Toyota isn't the only carmaker with this issue.
No question, there is still much room for improvement in these systems re throttle response under changing conditions.
We can expect a third generation improvement in response characteristics to be included many 2006 models, and by 2007,there should be improved systems available throughout the industry.
Hope this clears up any "misunderstanding"
I'm still the same old fart, but many years of experience have taught me a few things.
Among the things I've learned is not to show all your cards until you have a pretty good idea about everything the other players have.
I think I can honestly say you all may have underestimated what I know and don't know.
And yes, my remarks are still valid. You were speculating.
(Well, sort of--Actually I believe the one who raised the issue was just venting. And that's OK---just don't represent it as fact!)
In a face to face conversation one can easily convey thoughts wherein the other party sees facial expressions and voice intonations and recognizes that no testiness is intended. It's hard enough to do that over the phone let alone in type.
And if you can give us a tutorial on how the DBW system, of itself, alone, can provide increased fuel economy I for one am all ears (eyes).
But now a question for our "audience".
When I want to accelerate, gain speed, in any of my cars I simply do not hesitate to go into fully WOT mode, pedal to the foot, MAX. I always think of it as helping to blow out the carbon buildup.
It occurs to me that there is a possibility that other drivers are maybe more hesitant to put the engine and transaxle to this level of performance, at least not very often.
I have read several posts indicating that the hesitation can be alleviated, mostly, by being aggressive on the throttle, gas pedal. How many of you have tried that? When you need to accelerate even slightly, Stab, literally, the accelerator to the floor and then release it back into a more moderate position once the engine responds.
If I were controlling the specifications for writing the firmware that coordinates the transaxle shifting with engine torque and were given the mandate to provide the absolute best fuel economy possible I would probably do exactly what seemingly has been done here.
It is my understanding that the best fuel economy can be had using the lowest possible engine RPM that produces just enough HP to maintain a given road speed. So programming the transaxle for upshifting quickly into the highest possible gear would be part of the specifications.
So, the driver releases the throttle, IMMEDIATELY UPSHIFT.
But, this is a five speed transaxle, and the driver suddenly moves the gas pedal slightly away from "closed". Now what is the most appropriate gear to select for the best fuel economy? Basically the ECU is now trying to guess what the driver's intention is, just how much, how hard does he/she want to accelerate.
So the ECU delays the engine torque for a brief period while the transaxle downshifts into 4th(?), the gear ratio that the ECU decides will provide the driver with the most optimal acceleration while keeping the engine RPM as low as possible considering fuel economy.
But just now the driver senses the slight delay and depresses the gas pedal just a tad more. Oops, ECU says 3rd is needed.
Repeat the above until necessary to reach 1 to 2 seconds of engine torque delay.
If an old codger like me can cruise the internet and find multi references and many research papers on how DBW improves fuel economy and emissions, I'm sure someone as astute as you should have no trouble doing the same.
BTW, are you suggesting I open my mouth and insert my foot by arguing that DBW systems, in and of themselves alone, can provide increased fuel economy??
Not going to bite on that bait, my friend.
You, of all people, know perfectly well that DBW isn't a discrete system, but integrates with other on board electronic systems and controls--all working and communicating together to optimize many parameters--one of the many being fuel economy.
It wasn't so much as bait, but an honest request for clarification. You seem to be saying that DBW can be used to improve fuel economy and reduce emissions without qualifying the statement either way, of itself or in conjunction with other engine/drivetrain control aspects.
IMMHO it cannot, of and by itself, result in improved gas mileage and/or lowering emissions.
Implementing DBW in the most basic manner, as a purely functional replacement for a mechanical connection, cannot, in my opinion, provide any means for increasing fuel economy nor improved emissions. My 2001 Porsche C4 is likely a perfect example, the DBW gas pedal on it has the very same "feel" and resulting effect as did the mechanical one was on my 99 Porsche 996.
And I would be willing to bet that the DBW as implemented in my C4 is a totally "discrete" system. Not by any means saying that most DBW systems, especially those "coupled" to automatics, aren't integrated to interact, facilitate other control functions.
Let's say for example, someone (not me for sure!) decided to convert their conventional cable style throttle control to an electronic system (call it DBW if you will).
There are such aftermarket systems available BTW.
In all likelihood, I agree fuel economy wouldn't change much in that scenario.
I think that's basically what you've got in the essentially "discrete" system in your C4 (BTW, wanna trade for one of my classics!!)
I'm talking about the holistic DBW approach--like Denso's system design philosophy.
Indeed, fuel economy/reduced emissions has been a significant factor in their evolution.
Are you OK with this, and are we at peace now?
For Scoti1:
I know you don't like me much, especially when I respond to you, but in your query to Wwest, you're only partly correct.
Improved fuel economy is only one piece of the equation.
For Shifty:
Yes, fly by Wire systems have been available in aviation for about 20 years now. I have such a system in the Aerostar. It's a Flight Director/Autopilot which is coupled to all flight control surfaces, and driven by a Garmin GPS Nav System.
I can do "hands off" approaches and en route navigation with it. Just program what you want the a/c to do, and the system does it all by itself.
I think that previous to say, 2001, there was a definite delay period before the engine/transaxle ECU would command an upshift when the driver fully, or even partially, released the gas pedal.
First, think about how most drivers would manage a stick shift in situations simulier to those in the TSB.
Coming slowly to a stop you would most likely disengage the clutch and then delay shifting down into first only after the vehicle comes to a full and complete stop. So if the traffic light changes to green before you come to a complete stop you're already prepared to pop the tranny into gear, release the clutch pedal and GO!
Now, the engine/transaxle ECU has neither your eyes nor can it see your thoughts. But it does know the throttle is fully released and that ALWAYS indicates a coastdown circumstance. Finding some way to extend the coastdown distance will in many cases result in slightly improved fuel economy. Not only that, in this case it just might prevent loss of control if engine braking should be enough to overcome roadbed traction.
And how about the throttle on and off, dithering, in trying to coordinate your entry into that upcoming space in the faster moving freeway lane?
You know, with absolute certainty that you will soon need to accelerate, possibly quickly and rapidly. But the ECU only knows that the vehicle is in a coastdown situation and from that narrow viewpoint it will want to extend the coastdown distance and will likely upshift the transaxle when the throttle is fully or retarded from a position that indicates acceleration torque is needed.
Our 88 Porsche 911 has a light in the instrument panel which illuminates to advise the driver when an upshift is necessary to achieve more optimum fuel economy.
So, what's the harm in all of this upshifting anyway.
The "harm" is a lot more wear and tear on the transaxle clutches, especially downshifting as the engine RPM is already rising in non-DBW vehicles such as my 2001 AWD RX300.
So, the engine/transaxle shift control firmware can be readily modified, even absent DBW, to improve fuel economy and reduce emissions. Exactly what would happen if the driver of my 88 911 religiously and blindly followed the shifting "directions" provided by the "best" fuel economy indicator on the instrument panel.
But now look what happens, and will happen much more often than otherwise, when I suddenly decide that I wish to accelerate. If the engine is allowed to rise in torque development at the same time the transaxle is downshifting I might wear out my transaxle clutches, and/or overheat my ATF, and/or contaminate my ATF unduly with clutch frictional wear debris, long before their predicted lifetime.
But, install DBW and I can delay the onset of engine torque during any down shift sequence, wait for the newly selected gear ratio's clutches to be fully and firmly seated, and only then start opening the throttle in response to the new gas pedal position.
So, initially, as in my 2001 RX300 the engine/transaxle ECU firmware is modified to improve fuel economy and reduce emissions, and maybe to prevent a few loss of control incidents here and there.
But then Lexus soon discovers that the ATF in these transaxles, the stuff they clearly predicted would be good for the life of the vehicle, is being over-heated and contaminated at only ~40,000 miles of non-rough use. Not only that, not just a few are actually failing at 70-80,000 miles, possibly due to the overheating and contamination which dealer technicians and owners are "overlooking" due to the maintenance guidelines in the owners manual.
So as of 2004 (RX330) they go to DBW and a 5-speed transaxle simultaneously. Can you imagine having to write the algorithm that decides what gear you should be in when the driver fully releases the gas pedal and then re-applies pressure?
It cannot read my mind.
I have enough trouble deciding just what gear to be in for these same circumstances with my 6 speed stick in the C4, and I KNOW whats ahead and have a good idea of how fast I want to accelerate and generally at those times care not a wit about fuel economy.
But I'm guessing that since fuel economy and lower emissions is a prime directive for the Toyota engine/transaxle ECU firmware programmer the "shift" algorithm ends up being very complex indeed.
And here we are again down to the EPA and CARB issue.
this is a very sobering recounting of a complex computer-controlled system with faulty user interface, and numerous failure modes / poor design, with rather drastic consequences:
http://sunnyday.mit.edu/papers/therac.pdf
it's a bit off topic, but you can see how trained professionals and patients placed inappropriate confidence in the technology, and operators had an incomplete mental model of the system's implementation and the significance / consequence of certain input actions, and indications.
follow the various links for engine management and you will find the ECU monitors the pedal, controls the electronic throttle, fuel pump, and it looks like duty cycle of the injectors, so a defined Fuel/Air ratio can be followed under various driving conditions.
wwest, you know the ECU can run the unit on the lean-edge of the combustion envelope to minimize fuel consumption and emissions.
The engine would be much more prone to knock/ping, which helps to explain why they went to the more expensive high resolution wide band (non-resonant) knock sensor.
The part I don't get, don't completely understand, is the bit about modifying the throttle servomotor's response to pedal position for improved driveability when running with a lean A/F ratio or retarded ignition (reduced engine output for a given gas pedal position).
I can't imagine that there would be enough engine power reduction to notice the resulting slight changes in the pedal position needed to produce a given level of engine output.
In the past the idle air bypass solenoid has been used to compensate for A/C compressor and/or power stearing loading and unloading. I would assume that with the advent of DBW supplanting the need for the idle air bypass the DBW now provides that functionality plus the new ones.
Running the engine continually on the lean side of the stoichiometric ratio would certainly require more diligence about just what gear ratio to downshift into in the key TSB circumstances.
Until just now I had given up, basically, on the MAF/IAT module IAT signal modification having any affect on the hesitation symptom. But now upon reading about this, Toyota/Lexus running with a LEAN A/F mixture as the norm, I am more convinced than ever that the modification will work.
My 2001 AWD RX300 has now been through 4 tanks of gas, ~15 gallon refills, all "city". For each tank I have alternated between the switch being in the lean position and the rich position. In lean the RX averages ~15.8 and in rich about ~14.6.
am i close?
It seems we started out (as in my 88 Porsche 911) with simply an oxygen sensor for controlling A/F mixture to keep exhaust gasses in the correct range for "scrubbing" via the catalytic converter and therefore lower emissions when the engine is at a constant level of output for a period of time.
But that didn't address the need to run a much richer mixture during engine high performance needs.
So next we had MAFS and TPS to allow us to run much richer mixtures but still under a high level of control.
And my guess is that someone realized that even a lean mixture could have low emissions and even better fuel economy provided the lean-ness level could be controlled without doing damage to the engine itself via persistent knock/ping.
So along came the non-resonant knock sensor.
At this time I'm guessing that the ECU continually tries to increase the mixture ratio, with certain parametric limits, until slight knock/ping is detected and then backs off of that mixture ratio slightly and establishes that as the most lean level it can run until the next "test".
If the IAT, for instance, indicates that the incoming intake manifold airflow is already HOT, then the leeway the ECU has, is allowed to use, to lean out the mixture until slight knock/ping is incurred is reduced.
So an IAT that always indicates an incoming airflow temperature that is HOTTER than reality would result in an A/F mixture that is already inherently RICH, making it extremely difficult for the ECU to lean it out to the point of knock/ping.
An engine that does not knock/ping makes the decision about which gear to downshift into much easier.
This is a good technical guide to the citroen's implementation of Fuel Injection. Read at least as far as Drive by Wire (just before Deisel Engine):
http://xantiaclub.net/techguide/
This site has some very useful information for automotive specialists, but it's written in a way many can grasp. Here is a link right to Engine Control / Management. You might find going back to the table of contents useful for learning about other things (for example read about Drivability Troubleshooting):
http://www.aicautosite.com/garage/encyclop/tocdoc13.asp
Shifty, this reminds me, it would be nice if the editors at Edmunds were to put some "technical topics" information like for example: Fuel Injection, Drive By Wire, ABS, Traction Control, Stability Control, etc etc presented in layman's terms for non-technical types on the site here somewhere in a set place for it, so all could benefit by descriptions of these technologies. Our cars are getting so technologically rich, we need to understand more about them to be conversant with dealer reps.
The catalytic convertor operates as high as 800C...?
Wow.
Now I know why the RX400h and Hybrid HL must run the engine so often just to keep the catalyst heated.
The Hpi part reads as if its a direct injection like the new GS3xx, or did I get that wrong?
I really believe the problem may reside here for people with a significant problem. For that matter, it could be the IAT sensor (I think that was it), that wwest was proposing to test with a modified device.
It would fit all the anecdotes from those with a minor, major or no issue.
It could be a non-linearity (ie the position read by the ECU doesn't uniformly change as the device is moved), or it is not calibrated properly (zero is not where the mechanical stop is located), or there is some slop in the linkage of the pedal or valve, or there is some sticktion in the throttle / butterfly valve assembly.
No one wants to instrument their vehicle with the OBD-II reader with data capture capability I suggested.
OK, what if one of you with a significant issue were to ask a Shop Foreman / Service Manager if they'd be willing to perform an experiment with your vehicle, that being swapping out the Throttle Body (I presume the sensor comes with it, or perhaps just the sensor if they are separate), or the Accelerator Pedal, or this IAT (or MAF - can't remember now) and see if the problem characteristics change? Dealers have access to other cars. Surely there is a "hanger queen" (I believe an aviation term for a plane that is robbed of parts to get others in the air) or total wreck, from which to borrow some parts for the experiment.
What if the problem were not with the Transmission, nor the ECU programming?
I still cannot believe the Engineering group would release a vehicle from design, nor the people responsible for QA road testing the vehicle pre-production would indicate all was well if the vehicle exhibited significant hesitation. Some (I presume the majority of) owners just don't have a problem.
If a dealer rep wouldn't try the experiment, then maybe you could convince an independant shop very familiar with servicing Toyota/Lexus to try the experiment.
What's the saying: no guts, no glory?
Someone should be able to tell you the cost of these parts, and how much they would charge you to swap them out for experimentation purposes. Maybe a REALLY sympathetic dealer or independant shop would do it to try to determine root cause or narrow it down, and charge you nothing.
If someone did need to charge you, you could compare that to the cost of the OBD-II reader.
But seriously, it's clear we aren't going to get anywhere unless we narrow the problem / solution space and we need some experimental data to do so. Is it a sensor? Is it ECU programming? Is it the Transmission?
Someone somewhere needs to gather the information that others would be able to take to their dealer, and get thier cars working as expected, (or hopefully not - determine that nothing tried helped, and the root cause lies elsewhere).
Anyway, it may be clearer now, if a third party like Denso or other is producing these parts and perhaps the ECU (with high-level of integration with other systems), supplying it to the vehicle manufacturer, the manufacturer may be at the mercy of Denso to develop and test a ECU modification which would not negatively impact the other subsystems (TRAC, VSC).
Frankly, dealing with sensor non-linearities, or sensor zeroing/calibration issues, or actuator sticktion (actually another non-linearity) may be a slippery slope for the ECU manufacturer... I would not want to mod the ECU to accomodate sensor problems to that extent.
I don't know if they release the proprietary code under non-disclosure to the vehicle manufacturer, but I highly doubt it (at least for purposes of modification). Inspection / QA perhaps, but not to modify it.
Does this position and potential way forward seem reasonable to anyone else? Does anyone else have ideas on a relatively low-cost means to test this theory?
One more thing re a test case scenario.
My friend said quite a while ago that the OBDII approach might not be doable.
Seems to me he said an oscilloscope would be the tool one would use.
Comments?
Park your SUV in a hay field and pretty soon there'll be a grass fire under it!!
According to Sherlock Holmes... 'When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth.'
There is widespread testimony that many drivers note little if any problem with this hesitation topic that transfixes us. However, there are a considerable number of drivers who
report significant problems.
I must speculate that the apparent principal variable, given the similarity of the complaint - or lack thereof - across various makes and models, is the operator.
We witness much variation in operator practice on the roads - some are fast or aggressive, or both; some are slow away from the light, checking sideways and defensively awaiting latecoming redrunners; others leaving rubber to mark their departures; some road-users regard the vehicle as a necessary implement - to move from here to there; others delight in driving with spirit, taking pride in what they consider akin to a sport - an adventure between destinations.
Now, I have come to believe that these variations simply are not as readily accommodated by new control features as by the older designs. Designs that gave more responsiveness or 'feel' at the cost of fuel economy and the environment.
Some of us may revel in the new designs and overlook or adjust to any negative aspects; others among us cannot accept that we have lost some part of what we valued in immediate response to our skill and verve.
Perhaps Sherlock would have termed this a conclusion... 'elementary.' I offer it as the only position I find likely at this point - it ain't so much due to the machine, as it is 'different strokes for different folks.'
You have not reconciled reports by people, (even the article you posted a link for) which indicate some cars have it and some don't:
What makes the issue perplexing is that no two models of a given car brand may have the same problem. Some owners of the makes involved say they've noticed nothing, while others will say the problem is chronic.
One Lexus dealer, for instance, has said he was able to duplicate the problem only on a few of the cars on his lot, while many others didn't have the problem at all
Second paragraph:
Recently, lean combustion is induced (was introduced??) to reduce fuel consumption and, during engine warming, the ignition timing is retarded to reduce emissions. The electronic throttle control prevents a decrease in engine output resulting from lean combustion and retarded ignition timing, providing excellent drivability.
Recently.....
Prior to DBW the idle air bypass control was used to "boost" engine output when the A/C compressor clutch engaged and/or the power stearing was used when parked.
With the advent of DBW the idle air bypass control and system is obsolete.
The way I read the above Denso document is that for a given gas pedal position the corresponding throttle valve position can vary in order to keep engine output (to the drive wheels??) constant under varying accessory loading and engine combustion parameters.
But the thing that really jumps out at me is the "recent introduction of lean combustion".
Obviously running the engine under load with lean combustion would result in the need to detect even the slightest onset of knocking. Lean combustion would also make selecting the proper gear to downshift into upon the driver's sudden wish to accelerate a lot more critical.
Before I go much farther with this thought train I should state that it appears that if one could prevent the ECU from using the lean combustion mode, say by modifying the IAT signal, then maybe the downshift hesitation delay wouldn't be so prevalent. If the engine were already running lean due to the false IAT signal then when the ECU tries to lean out the mixture knocking would quickly result and maybe the ECU would "decide" that for some reason or another this particular engine cannot run in the lean combustion mode.
But a little side note is in order.
With cruise control in use, active, in my 2001 RX300 (not DBW) if I wish to accelerate I must depress the gas pedal through the "slack" area until it reaches beyond the point where the cruise control already has opened the throttle.
On my C4 with DBW even the slightest depression of the gas pedal results in acceleration.
And a final note.
There are two basic ways to overcome the hesitation symptom. 1, prevent the transaxle from upshifting during coastdown, and 2, somehow cause the downshift to be "decisive".
It occurs to me that part of the randomness o f these events might relate to differing driver operations, use o f the gas pedal. Do you completely release the gas pedal in these instances, or do you "feather" the gas pedal, almost release it entirely.
If the latter case I can see that this might confuse the ECU into "thinking", taking the path to, "oh, now he is done accelerating and just wants to cruise".
It also seems to me that a sudden and quick movement, all the way to WOT, might alleviate some of the delay/hesitation.
This undoubtedly comes as no surprise to my critics, but I honestly believe some assessments of this issue are not, as you say, a function of what the machine does, or doesn't do.
I fully agree there are reports of hesitation, lurching, ragged shift patterns, etc.; some even reporting prolonged hesitation.
I have to believe there's enough of an issue out there to warrant concern that some reported situations may in fact be an electronic or mechanical anomaly.
At the same time, reality tells us that broad variances in driving technique and conditions, at least to the point where these factors may bear on results, cannot be ignored when looking for causes.
Kinda debunks the "it's the driver's fault" theory.
when the same person using the same driving style drives a number of cars, and some have an issue, and some don't i conclude the variance is in the parts comprising the system, or the system implementation, not the driver.
logical right?
and further, i recall posts by people reporting significant delay, where they have alluded to a normal style of driving. you just have to believe them. surely - think about it, anyone who's got a problem would probably do their very best to adapt to the technology. it's just not working properly.
this really begs of faulty sensors, causing the system to run to some extrema, or sensors conflicting with one another and the ECU having to take a fall-back / default / sub-optimal profile or response that isn't characterized by smooth shifting and acceleration.
logical?
it's just too easy to blame it on the human. it's also blatently wrong in my opinion.
here's another experiment. if you're an owner of a vehicle with significant hesistation, go to your dealer and demand (in writing) a description of the technique you should be using when driving the vehicle so that it doesn't have the behavior. post the written description here please because there are fellow owners who haven't figured out "the obvious" and they are at a loss to make their car operate like the others who report no hesitation.
ok, assuming there's a low-probability of the manufacturer or dealer representative documenting the technique of driving which will fix the problem so there is no hesitation, rhetorically we may ask, why design a system which the manufacturer or dealer reps can't describe it's use to an end user so it has satisfactory / typical drivability characteristics they paid for, were expecting and that other people are experiencing?
there's a problem with a population of cars, not their drivers...
I did consider this anecdotal item and offer the following thoughts...
My high school French teacher used to emphasize, 'It is the exception that proves the rule!'
The mention of the Lexus dealer is what a court would term, hearsay - needing more direct corroboration before warranting consideration.
If true, it suggests that one Lexus dealer said something about something he may have done.
A more disciplined evaluation by an objective and qualified, accepted test body would be worthwhile, as I suggested in an earlier post.
Charging 'fault' doesn't seem likely to be helpful in setting out as well as possible an objective evaluation of what clearly is a perplexing matter. It does appear definite that some drivers are not getting satisfying results from activities that formerly were effective for them, and at least some of said drivers do not believe that it should be necessary either to accept the new responses or to consider whether modifying their approach might improve things.
thanks,
Shifty the Host
unfortunately, we have only anecdotal evidence: we have reports by drivers with the problem, second-hand reporters serving up comments based on reports from same in a safety database, plus we have comments from 1 lexus dealer / salesman, and some vehicle testers from consumer reports and from edmunds, etc.
it's also unfortunate that we are forced to try to reverse engineer the design of a very complex system from piece-meal information we find on the web, describing the technology in mile-high terms, just so we can talk about it in a more informed and correct manner.
some objective data from an OBD-II device capable of real-time capture may be helpful to describe and communicate what is occuring in time (although there is a limitation to the rep-rate of the sampling).
now if something blatently obvious in that data, opportunistically captured showed probable / possible cause, great...but i suspect it wouldn't all by itself.
ideally we'd have to have the same data from another car without the hesitation to be able to compare it to.
there's all sorts of problems with that experiment design anyway - but it would be a useful exercise none-the-less.
however, if we had a driver/vehicle with the problem that managed to fix or significantly mitigate the problem (or perhaps even made it worse) via a parts swap (we only have 1 report from an independant mech who did changeout an IAF (or MAF, I forget) on a Lexus with a Toyota part who indicated good results)... that would be a very useful result.
a side note, i find it interesting, we have heard no reports by anyone else that i can recall who's had anything more than a re-flash: no transmission or solenoid changeouts, no accelerator pedal, throttle body and / or position sensor, IAF/MAF, ECU or what have you swapped out. why is that? what i proposed in a recent post (thanks pilot130 for the kudos on that post - i tossed the term "hanger queen" in there because of your aviation experience) is I believe, practical, not overly ambitious, and the thing we need to move us forward.
BTW, any further thoughts on the oscilloscope technique I mentioned??
yes, i've thought about the technique you mentioned.
apologies to everyone. skip this message if you'd like or the content of this message between the ----.
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an o'scope is really quite good for looking at time-varying waveforms (AC) that are periodic in time; you can synch the scope to trigger on zero-crossings or a given voltage / trigger level and see the periodic waveform.
for non-time-varying waveforms (DC), they can and are used for determining the voltage level by the displacement of the trace from a calibrated "zero" reference, but interpretation of the voltage levels does mean looking at a scale on a CRT and estimating / eyeballing the resultant value.
a digital o'scope is a bit better in that they can actually sample and hold a waveform and trigger on some attribute of a signal. some of them even have FFT (Fast Fourier Transform) capability to take the time varying wave-form, and convert them into the Frequency Domain - apologies for the explaination: where you can look at the frequency components making up the waveform (it can be shown that any sinusoidal waveform, and many others too are comprised of (or can be approximated by) a sum of sinusoids of individual discrete amplitudes and frequencies). An FFT pulls out the frequency and relative power of the constituent sinusoids comprising the signal.
they also have the ability to convert the input signal if DC into a numerical value displayed on the CRT, which is convenient.
one would think, both are probably overkill, unless we are talking about some pulse-train or sinusoidal output from the device being looked at.
A DVM (digital voltage meter, or even analog VM) could be used to check the linearity of the pedal or throttle body position sensor, if the sensors are of the variable resistance (potentiometer) variety. to be honest, i don't know the exact sensing technology which is actually employed, but assume a variable voltage or current is the ultimate output of these devices as they change position and are excited by a fixed voltage or current source.
therefore as the device is slowly slewed through it's range of motion, theoretically you check the various voltage readings against position. the problem is, you don't catch what is happening in intermediate positions, and non-linearities can exhibit themselves at fixed positions and not at others, because your eye and brain aren't capable of seeing the event (and many meters perform filtering) because it is short in time. only large non-linearities, spanning a good deal of the range of motion of the sensor could practically be investigated using these devices.
therefore, back to the DVM (if it has storage capability or can be interfaced to a laptop) or the Digital O'scope - I think these are called DSS - Digital Storage Scopes, ideally, you'd set a long sampling "window" (full duration of the experiment) of perhaps 5 or 10 seconds, but a very fast sampling rate (interval between samples) of perhaps 0.1sec - .05sec (10Hz-20Hz or samples per sec).
then you'd slowly mechanically slew the device from one end to the other end of travel, and allow the DVM or DSS to capture the data. With the DVM, you'd review the data on a laptop, or if the DVM has the ability cursor through the samples looking for the non-linearities. The DSS would show you the resultant window record of samples acquired.
whew sorry about that everyone.
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its probably going to be easiest just swapping parts.
however, one would hopefully expect the mechs to have a procedure for using any kind of Multi-Meter, or O'Scope to check the readings from the assemblies when the device is at both extremes, and here I'm talking really about calibrating the "zero" on the pedal and throttle body sensors.
chances are though, the mechs are encouraged by the manufacturers to just swap the sensor if there is a suspected problem.
Even If it is proven that some driving styles don't work well with Toyota products that does not make it the drivers fault. My new Honda Pilot with DBW down shifts alot and clearly does not have the feel of my old power glide but I have never felt a hesitation like the Camry.
Shifty, I thought this last go round was on the healthy side and should not worrent host action. My Camrys long gone but I still stay tuned to see if I should ever consider looking at another Toyota product.
My advice to everyone which I have been trying very hard to follow myself.... don't respond to antagonistic posts.
Although I haven't been able to contribute much, I have found the recent discussion very interesting.
The classic car equivalent of a "hanger queen" is "trailer queen" referring to a car that is only driven onto a trailer to go to shows. I prefer to drive my cars. Its much more fun.
In the absence of anything better, I wonder whether there might be a couple of users in proximity - one with, one without the problem - who might get together to try some tests. Each would drive both vehicles in an effort to quantify if possible the extent to which operator/machine influences may determine results.
I don't see this as an ideal approach but, like chicken soup it couldn't hurt. I am in Sun City, AZ, at present if there's anyone nearby who is interested in a 'swap meet.'
Looks like you posted in the wrong place.
I would suggest this forum: Transmission Traumas.
Just cut and paste your question and then click on the link I provided and you're all set.
Shifty the Host
In one of the links I provided (can't remember which), there was a description of what happens if the IAT fails, and the system have to revert to the MAF and the resulting sub-optimal scheduling of air/fuel.
And as far as prepping to be most responsive to take-off, you'd think the ECU might move to the center or slightly rich regime when it determines the vehicle is slowing down below some threshold, until such time it determines if you are truely at zero speed / true idle, then it might lean you out again, until the accelerator is punched.
The overall strategy / programming of the ECU would be an interesting topic presented at just the right level. And like I mentioned in an earlier post - vehicle manufacturer's would have to work with the ECU manufacturer to modify functionality, and that could have a good cycle time due to all the regressive testing one would have to do, to make sure you didn't break some other functionality.