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Engine Hesitation (All makes/models)
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My guess is that it is this serial bit stream that is available at the OBDII connector so all functions can be monitored or faults read out. I know that there are also two other, alternative methods, for reading faults, blinking instrument light sequence, and an analog meter needle deflection sequence.
But if one wishes to gather operational data "real time" the information will be "coming" fast and furious. So some device with a loop "memory" for recording the data stream is necessary.
There are, were, multi-channel Oscilloscopes with "screen" memory and I suppose there were a few with actual memory.
But the ones with real utility in this venue are called logic analyzers. Logic analyzers have an Oscilloscope type displays that often can be used "real time" but hardly ever are.
But since any modern reasonably fast laptop computer can be used as a single channel logic analyzer I'm quite sure that would be the optimum solution provided the OBDII readout tool can be used to tell the system to continuously "stream" all data events down the "pipe".
Wish I could be of help here but I don't have a hesitation vehicle and don't know anyone here in the area that does. I have to be at Daytona Beach in late Jan. and I could fly NW through Minneapolis but Alaska has a direct flight to Orlando. Seemingly every time NW takes me through Minneapolis in the wintertime I end up staying in a nearby hotel overnight due to flight cancellations.
And by the way the MAF/IAT module us a fully integrated assembly containing the MAF and its signal amplifier and the IAT thermistor.
Logic Analyzers tend to handle TTL or CMOS or similar level signals. Throw a 12v signal on a Logic Analyzer and you probably fry the input.
Didn't know the MAF/IAT is a combined unit. Good to know. Looked online for Toyota Parts (tough going) and found some stuff on eBay. Don't know how much they go for.
I'd do the experimentation like this if I had a sympathetic dealer:
1). Swap out the MAF/IAT module and test drive.
2). Swap out the Throttle Body Assembly (Butterfly valve and sensor...maybe the actuator is part of it too...I'd want the full monte swapped ideally). The reason: could be sticktion in the butterfly valve, could be non-linearity of the position sensor, could be an inttermittent actuator (stepper motor?) problem nearer the closed/idle position).
3). Swap out the Accelerator Pedal/Sensor assembly and test drive.
from:
http://www.obd-2.com/
The maximum legal SAE acquisition speed is 10 Hz. per request. Speed is adjustable in menu-options-gateway-protocol in units of milliseconds delay for a response between requests. Some networks will respond within 25 ms allowing acquisition rates to 40 Hz depending on speed of the browser computer. Note: acquisition time is also dependent on other vehicle computers using the network, if your vehicle has a large number of computers on line, acquisition times will be reduced(under 10 Hz) and sporadic. Note: ISO protocol is slower(under 10 Hz).
((Toyota uses the ISO protocol))
check this out:
http://www.obdii.com/articles/Intro_to_Engine_Management.
The throttle position sensor (TPS) keeps the PCM informed about throttle position. The PCM uses this input to change spark timing and the fuel mixture as engine load changes. A problem here can cause a flat spot during acceleration (like a bad accelerator pump in a carburetor) as well as other drivability complaints
apologies again to everyone:
look, a MAF/IAT or O2 sensor reading, they aren't going to vary rapidly in time. other sensors and measurements will also be overwhelmingly of a steady-state nature when compared to a 4 or 8Hz sampling rate.
all i'm saying is at that ISO rate, capturing the toyota specific parameters of interest to us (did you go to the odb-2 link and look at the toyota specific list?) the laptop may miss the datum very close to the event where something of interest to us which doesn't have a steady-state nature compared to the rep rate (for example the exact speed when the ECU commanded the TCM to downshift, or a point where the TPS did not exactly track the Accelerator Pedal position sensor), we might miss the "who moved (or drew their guns) first". What we'd most likely capture is how the parameters of interest were trending before and after the initial onset of the hesitation. That would be very helpful, but control system engineers like myself prefer the highest sampling rate possible to limit ambiguity when trying to determine what preceeded what.
Essentially we have a polled data collection mechanism, or rather periodic broadcast (i'm not exactly sure of the OBD-II interfaces role and the details of the protocol...if your node is signed up as a consumer of particular items of interest from a source, or if the node asks for individual elements and gets them as a response to a message sent... that brings up another point, with slower sampling, if the data isn't time-coherent and comes from the producer in the same packet (collected at virtually the same execution pass of the ECU assuming it is the producer), you can draw some really bad conclusions, because the data elements are not "in-phase" (or from the same frame), and a lot could happen between subsequent capture frames.
For very slowly changing data coherency is less of an issue than rapidly changing data where you want to infer sequence of events (what preceeds or follows or happens at the same time).
NipponDenso, Denso US' engine management systems, which most asian manufacturers use including Toyota/Lexus, apparently has adopted a lean burn, lean combustion technique to further enhance fuel economy and lower emissions.
I have begun to suspect that vehicles slightly more subject to engine knocking/pinging, even in just one cylinder, in the lean burn mode are the ones most readily exhibiting the engine/throttle hesitation symptom.
If that is truly the case then almost any engine can begin to exhibit the symptom somewhere in its life cycle.
That would also fully explain why Toyota/Lexus' recommended solution is to switch to premium fuels and that some owners are now on record saying that solution does seem to help.
It also explains why switching the MAF/IAT sensor out might, purely by happenstance, solve the problem. It would be easy to see that again, randomly, a given MAF/IAT sensor might result in running a slightly richer mixture than the one setting next to it on the parts shelf.
Additionally it becomes a valid explanation for why Toyota/Lexus has not, cannot, supply a fix absent some level of approval or waiver from the EPA, CARB, and now maybe New York State's regulatory agency.
I have a modified, self-contained, MAF/IAT sensor module that I am willing to send to anyone willing to install and test. The three position switch, Lean, Normal, and Rich, is mounted on the top of the module so all one need do is remove two phillips head screws, remove the OEM module, unplug the single electrical connector, insert the modified one, re-install the two screws, and reconnect the cable.
I would recommend disconnecting the battery for ten or fifteen minutes to erase any memory of the OEM MAF/IAT parameters. I would also suggest initally running the modification in the Rich position since right now that seems to be the one most likely to solve the problem.
Anyone?
My email is in my profile.
2. Engineering challenge.
3. Empathy
4. Experience
5. Vested interest.
6. Willing to take posters at their word.
As for me, I fully expect that I will move on from my AWD RX300 at some point in the future. I wouldn't want to blindly make that decision.
Do I own one of these vehicles or have I had the expereince while driving one?
NO!
But that certainly doesn't mean that my life's expereince has been so limited that I can't relate, understand and comprehend what the posters who have are saying.
Not all owners report improvement with premium fuel. As a matter of fact, someone on one of the Lexus forums reported the problem being worse with premium fuel. I don't know how it could help some, not help others, and even make some run worse if this the problem.
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Technical Questions
MrShiftright
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Earlier you said: "I can reproduce it now at this one spot on my drive consistently."
Is this still the case post-TSB?
Keep us posted.
scoti1
Like I said though: give me some time, I've only taken a few short trips. No parking lots yet - the worst offender.
I made an appt. at my dealer to have the TSB done (they say they have to verify the problem..which I don't think should be too hard).
My question is: Is there any downside to having the TSB done?
While my wife is complaining of sluggishness..and I see this as the car not wanting to downshift very willingly, I don't want to end up making it worse...!!
Please give me your insights..
Thx, Buick72
for example, in my '02 Honda Accord manual on the section dealing with the Automatic Transmission, it states: "You may notice the transmission shifting up at higher speeds when the engine is cold. This helps the engine warm up faster."
jmcdon: do you still notice some hesitation?
I still have some, but nowhere near what it was before.
Not a tech either, but so far that's how I would describe it too, except sub my wife's '99 Camry for your Tacoma.
It's really been a lot more pleasurable to drive.
I was just asking in a recent post about the TSB..and whether there is any risk in having it done..
And my wife and I were in the car (05 Camry V6 XLE)yesterday and we simultaneously remarked to each that the car now (at 9000 miles) seems to be much better, less hesitation and more willingness to downshift.
Nothing has changed, though. The gas is the same(usually Mobil, mid-grade, the drivers (her, mostly) are the same. The Winter weather has arrived..but I haven't heard of a cold weather effect..
I am considering now postponing any visits to the dealer to see if the car stays the same.
But am I confused..or what!
Any help out here???
Thx, Buick72
Cold and dense air of itself would tend to reduce any knock/ping that the engine might otherwise be subject to.
I thought it was all in my head though.
Does this mean the MAF would further reduce the hesitation?
I drove my car up & down the parking lot today, there's been remarkable improvement.
rennybosch, "Lexus LS" #7718, 10 Dec 2005 5:25 pm
Apparently the IAT signal is only used dynamically, say when switching from cruising to acceleration. I use cruise control most of the time so the result is not surprising.
At this point I don't see how anyone can question whether or not the Toyota and Lexus 5-speed transaxle has a firmware flaw within the engine/transaxle ECU. Such flaw only exhibiting itself under certain unique circumstances.
Some of those circumstances are clearly driver action (inadvertent) related but the base flaw lies at Toyota's feet.
It is begining to look as if the problem relates to an attempt to squeeze the highest possible mileage out of the fuel.
All of the vehicles involved seem to have been upgraded to a newly developed wide bandwidth more sensitive non-resonant knock/ping sensor. My guess is that this allows the engine, during cruise, to be operated beyond the
standard A/F mixture ratio, 14.7:1, well into the area of leaner mixtures.
Prior to this development the downstream oxygen sensor was the sole feedback source for controlling the mixture ratio, and it would not work either above 14.7:1, or below. Under acceleration or high engine torque the ECU uses the MAF/IAT sensors in order to run the mixture RICH.
With the advent of the new more sensitive knock/ping sensor the mixture can be deterministically "tuned", leaned, in realtime, using the knock/ping sensor to be sure the engine isn't damaged via even the slightest
knocking/pinging.
So now the engine/transaxle ECU has a "map", detailing the A/F "leaning" level each individual cyclinder can withstand before knocking. Due to the inadvertent uniqueness of each individual engine this map is "learned" after the vehicle leaves the factory, and is likley, of obvious necessaty, continually relearned as you drive.
I now have ~20,000 miles on my manual 6-speed 2001 Porsche C4. Over time "my" ECU has learned just what gear I need to shift down into when I wish to accelerate, slowly or quickly, rapidly, from my current speed to a higher
one.
Your Toyota/Lexus engine/transaxle ECU, by factory design, "wants" to be in the highest gear appropreate to best fuel economy at any given time based on roadspeed and throttle position.
Remember it's a five speed gearbox, and when you go from closed throttle where it may very likely be in, have shifted into O/D, to open throttle, the ECU must quickly decide "your" intent, all without knowing what's in your
mind or seeing the road and roadway traffic conditions ahead.
Slowly open the throttle, or open the throttle quickly but to a mid-position and it will always default to the highest gear that would yeild the best MPG.
But now you sense a lack of response to your throttle input and push the gas pedal farther down. Oops, the ECU now wants to put you into third instead of the previously commanded downshift into forth. But now it must want for the downshift into 4th to be complete before commading another downshift.
At this point things within the transaxle may be getting a bit dicey. During the previous coastdown period the engine RPM was dropped to idle so the transaxle's hydraulic fluid pressure pump isn't moving very much fluid. Besides which during coastdown the transaxle's line pressure is dropped to an absolute minimum by the ECU inputs to the control solenoid.
So, the initial downshift into 4th may have exhausted the pressure reserve in the transaxle's accumulator and now the next downshift must be delayed until the pressure is again built up, with the engine still at idle.
But now guess what?
Just as the downshift into third begins you push the gas pedal to the floor. Oops, again, says the ECU, now I need to be in second....
One second,...two seconds......maybe even three seconds..
Clues:
The dealers have told some owners who are experiencing the engine hesiation problem to switch to premium fuel and at least a few of those owners have indicated that helps.
Now that winter, cold weather, is upon most of us some owners are saying the problem is somewhat lessened. Cold weather, denser air, more fuel (absolute), less likely to knock.
One owner had the MAF/IAT module changed out and that seemingly cured the problem.
It appears that rapid and quick gas pedal application also alleviates the symptoms.
And I thought we had established that the vast majority of owners are not reporting any problem at all and are perfectly happy, as am I and others I know. So I dispute that All similar drivetrains have a firmware problem, and I am mystified why someone who has never even driven one of the affected cars would insist otherwise. Just what would be the motivation?
And I didn't say that all cars "have" the problem, I said all cars have the flawed firmware design/programing that will result in a few cars randomly exhibiting the problem but only under certain unique circumstances.
There is likely a fixed "target" for maximum leaning of the mixture during cruise "mode", say 16:1 as purely a guess. If a given vehicle's A/F mixture can be leaned to this level without incurring knocking or pinging then the owner isn't likely to ever encounter the hesitation symptom.
For instance:
An IAT with tolerances that happen to result in a richer mixture than 16:1 even with the ECU commanding a mixture at that level.
Premium fuels.
Predominantly cold and dense intake airflow.
Compression ratios of all cylinders slightly below the design target.
On the other hand if the engine does happen to ping at these mixture levels then the downshifting algorithm, downshift decision "tree", becomes a lot more complex. Then add in a little inadvertent hesitation or dithering of the gas pedal by the driver and that poor ECU gets very confused, indecisive.
And finally...
Why am I posting since I don't have a vehicle of this type?
Well, the above post was a duplicate of one I responded with over on the Avalon thread.
And two, some people work crosswork puzzles...I get a lot more fun and enjoyment out of solving multi-faceted problems such as this one appears to be.
Nevertheless, Wwest has suggested some rather serious conclusions, not the least of which in stating there is a "flaw" in the design of the DBW systems used by Toyota in these vehicles. I don't believe this is true, for a variety of reasons. All automakers today are faced with a multiplicity of challenges. First and foremost of these concerns simultanious management of three major variables, fuel economy, emission control, and driveline management of their internal combustion engines. A daunting task, considering stringent State and Federal legislation governing those parameters.
This forum has clearly shown the "hesitation" phenomenon being reported affects some but not others. It apparently only occurs under specific driving conditions. It varies in intensity from one owner to another--from barely noticeable to prolonged intervals in a few instances.
Furthermore, it exists in other makes as well.
All of these factors would tend to support that it may be design related but not a "flawed" design.
Either way, it must be recognised that Wwest has put forth an opinion--his diagnosis and his alone. That doesn't mean his "flaw" concept is correct. There are many different ideas and theories on why this condition gets attention. We have to accept all of them for what they are--opinions and theories. Some day the answer to this question will be known. It should be interesting to see which of the opinions and theories set out in this forum comes closest to the truth.
Meanwhile, Toyota and Lexus are pretty good automobiles. On that, we would all have to agree.
IMMHO when the driver activates the defrost/defog/demist function the design engineers should ALWAYS assume that the situation is worse case, the windshield has suddenly, for some reason (just a few moments ago picked up two sweaty snow skiiers with clothes completely soaked), completely fogged over and I'm driving down an ice covered roadbed with it snowing furiously. What, exactly, is the harm?
But no, owners of Toyota/Lexus vehicles with automatic climate controls are stuck quickly manually manipulating the system to clear a windshield that very likely wouldn't have fogged over to begin with were the climate control system properly designed for cold weather operations.
European automatic climate control designs will always, even on the hottest day of the year, quickly route high volumes of HEATED airflow to the interior surface of the windshield when the defrost/defog/demist function is activated. If the OAT is above freezing the A/C will also be activated in case the local climate is such that it can aid in defogging the windshield by dehumidifying the incoming FRESH airflow.
But not NipponDenso. Apparently out of fear that the driver will be somewhat discomforted by HOT airflow reflected from the windshield to their face. Or maybe they just want to keep the blower noise level as low as possible.
Now to engine/transaxle ECU firmware flaws.
What would be the harm when leaving a coastdown situation wherein the transaxle has already been upshifted and now the driver re-applys gas pedal pressure the decision algorithm simply shifts, immediately, into the LOWEST gear ratio possible given the roadspeed?
In other words in these circumstances the firmware designers should always assume the driver wants to seriously accelerate.
Like the fogged windshield example I am perfectly capable and willing to interact with the system AFTER the windshield is cleared.
Just how many times do these circumstances, as very well described in the TSB, occur that warrants trying to conserve fuel by selecting the best case downshift insofar as fuel economy is concerned rather than considering that the driver intends to accelerate, needs a fairly high level of engine torque conveyed to the roadbed.
Luckily I have a clutch in my Porsche for "upshifting" during coasting or brief coastdown situations. Notice that word there, BRIEF. If the transaxle firmware delayed the upshifting sequence.....BRIEFLY....??
Since I tend to believe this problem has to do with the engine's propensity to knock/ping, or lack thereof, is the I4's compression ratio as high as the V6?
As you well know, while I am a champion of Lexus, I don't hesitate to complain, anywhere and everywhere, about the few nits and warts the vehicles seems to have.
I quite firmly believe that it is these various complaint channels that lead directly to increased "perfection" of future vehicles.
So, yes, I could trade my 2001 AWD RX300 in for a new BMW X3, but then someone on those threads would be complaining about my own, and other posters, complaints about the X3's nits and warts.
"...Obviously you have a car that is way outside the norm, because what you are experiencing doesn't deem to be all that common....."
Back in about 2003 when I first started hearing/reading about this particular problem I would have wholeheartedly agreed. But not today. When I first began asking salespersons and service managers and technicians about this absolutely no one would acknowledge that the problem even existed.
Nowadays the salespersons just roll their eyes and walk away while most of the service personel readily acknowledge the problem and many will even discuss it in great depth and often express their own frustration with Toyota for having not yet come up with a fix.
My salesperson has a standing order from me for a new RX3x0 provided he can assure me that the engine/throttle hesitation has been satisfactorily addressed.
And keep in mind that this type of TSB can be considerd as nothing other than adverse publicity. Something no manufacturer is likely to do readily absent a real need for widespread corrective action.
Bkinblk, as I recall you refused to allow the second arbitrator to actually ride in or drive the car, and choose instead to simply state that the current design is flawed. Yet you report it as a serious, very noticeable flaw, and I would think the arbitrator would have supported the claim, if it is really that bad.
The problem with simply stating that the design is unacceptably flawed is that the vast majority of owners don't report anything like what you seem to be experiencing. My car and others I know drive just fine.
I hope the accident you predict never happens. I can tell you that if I felt that strongly that an accident was inevitable you can be sure I would not be driving that car anymore.
wwest, the one thing you seem to never mention is the fact that the current TSB resolves the problem for many people, as I have read here and on other boards. Obviously bkinblk has a problem that is beyond what the TSB takes care of. But, I have read of many people who consider their car's performance as satisfactory after the current TSB is applied.
"The upgrades produce "incremental improvement in shift quality," spokesman Wade Hoyt said. The problem may still exist for some owners, and the company continues to work on other fixes, he added."
I've been there, thanks, and long ago learned a common sense lesson that if you allow something to bring as much stress as this issue apparently does, it way past time to get rid of it! Most would have done that already.
People in that situation appear to possess one of three hangups....
Either they "Lives to Hate Toyota"; or they "Hates to Live with Toyota"; or the whole thing is a charade. Pick one for yourself! I've already done that.
What was said last year isn't necessarily gospel today.
That is true, and most seem to be satisfied with their car's performance after the TSB. It may not work for all, but it seems like a logical first step for anyone who has hesitation. Instead however, some here prefer to continue to state that there is a serious design flaw for which there is no fix, which is untrue and misleading.
And strangly, most of them are people who have never actually driven one of the cars with the hesitation. They have no first hand knowledge of the intensity, duration or frequency of the hesitation, nor the effect of the TSB. Yet they post over and over about how bad it is, and usually ignore or downplay the improvement that may be possible with the current TSB. I have to wonder why.
Earlier on you stated you had the TSB done, and the improvement was dramatic--"No more of the annoying stuff" was what you said I believe. Before that you reported it as very serious--words like "severe", "dangerous", "safety hazard" were frequently used to describe it. It was pretty scary. My question is this: Would you say the improvement you now have is "Incremental", or perhaps something more?
Second point has to do with what the Toyota rep supposedly said re "not getting rid of the delay completely" So, does that mean delay will always be a characteristic; does it mean the problem cannot be fixed; does it mean the delay remaining is normal; does it mean the delay remaining is excessive;----what exactly would you have us believe that it does mean??? And does what one person say what another person supposedly said assume the first person isn't hearing only what he wanted to hear--or perhaps repeating only that part he wanted others to hear?
My question, I guess, is this: What is the message you're trying to get across in your post?
If my post seems a little offbeat, it's mainly because of a sense some in this discussion don't seem to want to look at both sides of the issue. Every time other possibilities are suggested, or someone speaks to a positive, we get reminded of something a news article or someone else said. It's almost like it's not allowed raise any doubts, look at other ideas, or bring up anything which goes against the "Lives to Hate Toyota" philosophy which seems to prevail here. I'm wondering why that is??
Example. I said that the severe symptoms which bother a poster seem to be an exceptional case. Someone else agreed with that.It really does seem that way if you go by what most posters say. Yet, immediately a bunch of folks jump in and strongly imply this is wrong. Well, maybe it is, but then again, perhaps it may possibly be true. Why must we be constantly told that it's not?
And yes, I agree that the latest TSB seemingly solves the problem, but for all models and and in all instances?
And early reports of the TSB having solved the problem can be unintentionally misleading. I don't know what procedure is used to clear the previously "compiled" parametric memory as concerning control components and sensors but I'm relatively sure that with a reflash that would need to be done.
So it may take more than a few miles of various city/hwy driving types, say just as an MIL reset requires, to re-establish a particular vehicle's overall "personality".
Actually, I said this:
3x: there's still some hesitation [less than a second???], but I think the really annoying stuff is gone.
Before that you reported it as very serious--words like "severe", "dangerous", "safety hazard" were frequently used to describe it.
I said it didn't feel safe in bumber to bumber high speed traffic, because you never knew if it would respond if you had to punch it. I think in an earlier post I actually said I didn't feel it was a safety issue.
Would you say the improvement you now have is "Incremental", or perhaps something more?
No, incremental. Like I said "I still have some, but nowhere near what it was before."
Second point has to do with what the Toyota rep supposedly said re "not getting rid of the delay completely" ... what exactly would you have us believe that it does mean???
I didn't speak with the rep, but I would say it lends credence to wwest's theory that there's a built in delay to protect the drivetrain. Maybe that's what the rep said too, can't remember. You'll have to ask bkinblk.
My question, I guess, is this: What is the message you're trying to get across in your post?
That the TSB has result in improvement for me, but it has not eliminated the problem. Right now, I think it fixes it "Good Enough", but I'll try it a few more weeks then give wwest's MAF a try if I don't think it's acceptable.
I think the rest of your message is just a fishing expedition that doesn't deserve a response, so I'll just ignore it. It's just wanting to bring up the whole "Is there really a problem?" debate, and that's tired.
I'm not a Toyota basher, I own stock in the company and my last 3 vehicles have been Toyotas.
Hopefully they have this issue fixed when it's time for my wife to trade in her '99 Camry. Otherwise I'll become a Honda owner.
If there had never been a hesitation issue, and when you first got your car, it performed like it does now; Would you consider it a problem?
I have read some say they would notice it but not consider it a problem, and others who say they consider their car to now operate normally.
Either way, I am happy you were able to experience some improvement.