What parameters are needed to initiate a WOT downshift?
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From: Schiller Park, ILL Member: #317
What parameters are needed to initiate a WOT downshift? Ok, I'm going to try to make this a simple as possibile as it's a rather long story.
I've been having lots of tranny issues up until I recently bought my last trans (FLP) which finally cleared up all of the issues but one; here it is:
On occasion, my PCM will not command the proper gear for a downshift when going WOT. To explain further, I have programmed in Edit for the trans to downshift back to 1st at up to 37mph in every table that I could find. Issue is, sometimes when at speeds in the 30 to 37mph range the PCM will only command 2nd when going WOT. Why? What are the other parameters that the PCM looks at when deciding what gear to downshift to? I have verified that the VSS is showing correct speed, that the TPS is showing 99-100%, and that TPS voltage is above 4.3v. And I know that this is not a mechanical issue, because it only happens once in a while, because it's been happening with 3 different transmissions, and because when this occurs Atap is showing that the PCM is only commanding 2nd, so the trans is just doing what it's told to. The question is, why is the PCM only commanding 2nd if the TPS and VSS are within the range of a programmed downshift to 1st? Am I missing something?
Sorry this is so long, but hopefully my explaination is clear. If anyone has any insight, please post up. Thanks,
I've been having lots of tranny issues up until I recently bought my last trans (FLP) which finally cleared up all of the issues but one; here it is:
On occasion, my PCM will not command the proper gear for a downshift when going WOT. To explain further, I have programmed in Edit for the trans to downshift back to 1st at up to 37mph in every table that I could find. Issue is, sometimes when at speeds in the 30 to 37mph range the PCM will only command 2nd when going WOT. Why? What are the other parameters that the PCM looks at when deciding what gear to downshift to? I have verified that the VSS is showing correct speed, that the TPS is showing 99-100%, and that TPS voltage is above 4.3v. And I know that this is not a mechanical issue, because it only happens once in a while, because it's been happening with 3 different transmissions, and because when this occurs Atap is showing that the PCM is only commanding 2nd, so the trans is just doing what it's told to. The question is, why is the PCM only commanding 2nd if the TPS and VSS are within the range of a programmed downshift to 1st? Am I missing something?
Sorry this is so long, but hopefully my explaination is clear. If anyone has any insight, please post up. Thanks,
Re: What parameters are needed to initiate a WOT downshift? The only table you should have to adjust is the "Normal Mode Shift Speed" table. I haven't seen the the other tables have any effect unless your working on a C5(performance mode) or truck (tow/haul mode). What are the "Speed vs TPS" cells adjusted at for first, second and third gear?
Richard
Richard
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From: Schiller Park, ILL Member: #317
Re: What parameters are needed to initiate a WOT downshift? WOT Shift MPH tabs and MPH vs TPS in the 100% range are all set to the same values. However, I'll have to double check my MPH vs TPS tables for the 93% range, not sure what I set those to. But either way, the intermittent nature of my issue makes it hard to point the finger at any absolute parameters, which is why I was leaning towards some other sensor input values that the PCM might use as input when making downshift gear selections at WOT. For some reason, on occasion, the PCM is commanding 2nd when it should be commanding 1st. What all could possibily cause that to happen (on an intermittent basis)?
Re: What parameters are needed to initiate a WOT downshift? Try raising the "Normal Mode Shift Speed" table for "2 to 1" shifts from 0%TPS to 100%TPS. Follow the "1 to 2" shift speeds -1 mph @ 0-18%TPS then gradually let the upshift and down shift tables diverge until a 5-6 mph difference @100%TPS. (I find the graph function very useful for this). If you don't want the trans to downshift at part throttle (0-50%) then don't change those cells. Maybe start at 50% and work towards the east end of the table. Try creeping up to within 1 mph of the "1 to 2" shift @100TPS. This should command the trans to downshift sooner than waiting for WOT.
Perhaps your RPM threshold was right on the border of commanding the downshift @WOT?
Do let us know what you find out.
Good luck,
Richard
Perhaps your RPM threshold was right on the border of commanding the downshift @WOT?
Do let us know what you find out.
Good luck,
Richard
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From: Schiller Park, ILL Member: #317
Re: What parameters are needed to initiate a WOT downshift? I don't quite understand what you are recommending? Maybe I just need to look at the table while re-reading your post and I might understand.
However, the fact still remains that I could go WOT 30 times in the 30-35mph range and only observe this condition maybe once or twice. I would think that it would happen more often if it was an absolute parameter that was out of wack. This is why I began to think of this as a condition occuring due to a unknown variable (i.e. MAP or MAF related perhaps?). To expand further, it actually doesn't ever happen at 34-35mph or under 30mph, but rather in the 31-33mph range. Weird? If it was a max rpm or mph issue, I would think that it'd be occuring more as speeds went up rather than going away?
However, the fact still remains that I could go WOT 30 times in the 30-35mph range and only observe this condition maybe once or twice. I would think that it would happen more often if it was an absolute parameter that was out of wack. This is why I began to think of this as a condition occuring due to a unknown variable (i.e. MAP or MAF related perhaps?). To expand further, it actually doesn't ever happen at 34-35mph or under 30mph, but rather in the 31-33mph range. Weird? If it was a max rpm or mph issue, I would think that it'd be occuring more as speeds went up rather than going away?
Re: What parameters are needed to initiate a WOT downshift? I agree, it does sound wierd. 
Under the "Trans Cal" tab, there is a button to access the "Normal Mode Shift Speed" table. This table commands the appropriate gear when MPH and TPS are met. You can program the trans to upshift or downshift across the TPS range at a variety of speeds. Rather than wait for the TPS to go to 100% before commanding a downshift, you can program the trans to downshift at an earlier TPS (75%). I had the wife's truck upshifting and downshifting like a manual trans........it was pretty fun but can cause premature trans wear (lots of shifting). It always kept the engine in a higher rpm range for much improved pedal response. If you need, you can call me and I can explain to you on the phone. My number is listed on the website.
Good luck,
Richard
Under the "Trans Cal" tab, there is a button to access the "Normal Mode Shift Speed" table. This table commands the appropriate gear when MPH and TPS are met. You can program the trans to upshift or downshift across the TPS range at a variety of speeds. Rather than wait for the TPS to go to 100% before commanding a downshift, you can program the trans to downshift at an earlier TPS (75%). I had the wife's truck upshifting and downshifting like a manual trans........it was pretty fun but can cause premature trans wear (lots of shifting). It always kept the engine in a higher rpm range for much improved pedal response. If you need, you can call me and I can explain to you on the phone. My number is listed on the website.
Good luck,
Richard
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From: Raleigh, NC
Re: What parameters are needed to initiate a WOT downshift? Forget the tables for WOT shift points.
A WOT shift is commanded when two conditions are met:
1 - Normal Shift MPH Threshold is met
2 - Normal Shift RPM Threshold is met
The tables are for Normal, Performance, Hot and Cruise Control Part-Throttle shift speeds.
The "trick" for you then is going to be finding the threshold shift-points that makes the shift happen where you want it to. I make it simpler by making the MPH Thresholds valid earlier than I want. This makes the MPH threshold condition set, and all I have to do is adjust the RPM Threshold to find the spot I want. The faster your car revs up, the farther it is likely to overshoot the RPM or MPH you set.
The same thing applies for downshifts at WOT or coming off WOT... the Threshold conditions must be met.
Hope that helps.
A WOT shift is commanded when two conditions are met:
1 - Normal Shift MPH Threshold is met
2 - Normal Shift RPM Threshold is met
The tables are for Normal, Performance, Hot and Cruise Control Part-Throttle shift speeds.
The "trick" for you then is going to be finding the threshold shift-points that makes the shift happen where you want it to. I make it simpler by making the MPH Thresholds valid earlier than I want. This makes the MPH threshold condition set, and all I have to do is adjust the RPM Threshold to find the spot I want. The faster your car revs up, the farther it is likely to overshoot the RPM or MPH you set.
The same thing applies for downshifts at WOT or coming off WOT... the Threshold conditions must be met.
Hope that helps.
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From: Schiller Park, ILL Member: #317
Re: What parameters are needed to initiate a WOT downshift? I understand what you guys are saying about the tables now, and I can see how that would help...if this was a more regular issue. What I still don't understand, is why it works perfect most of the time but once in a while sends the wrong signal? And why only in a very small mph range?
Also, Black LS1 T/A, unless the newer Edit versions are different, I don't see how you can set RPM vs TPS in Edit for up or down shift points? The only place I have to set rpm in my version is in the main shift speed tab where you input absolute values for WOT only. My shift speed tables only show MPH vs TPS, and lowering the speeds there would only serve to lower the max speeds at which I could get a WOT downshift which is the oppsite of what I want to do. Or perhaps I misunderstood your post?
I could try to change the MPH tables in the 75% range and higher I guess... to match the current 100% table and WOT tab settings. But somehow I doubt that will fix this issue. I'm guessing it's gotta be somehow related to the input of another sensor that causes the PCM to overlook what the shift speed tables we have access to in Edit are telling it to do. Maybe something like MAF or MAP vs VSS = gear selection for WOT downshift, a table that we don't have access to changing....
Also, Black LS1 T/A, unless the newer Edit versions are different, I don't see how you can set RPM vs TPS in Edit for up or down shift points? The only place I have to set rpm in my version is in the main shift speed tab where you input absolute values for WOT only. My shift speed tables only show MPH vs TPS, and lowering the speeds there would only serve to lower the max speeds at which I could get a WOT downshift which is the oppsite of what I want to do. Or perhaps I misunderstood your post?
I could try to change the MPH tables in the 75% range and higher I guess... to match the current 100% table and WOT tab settings. But somehow I doubt that will fix this issue. I'm guessing it's gotta be somehow related to the input of another sensor that causes the PCM to overlook what the shift speed tables we have access to in Edit are telling it to do. Maybe something like MAF or MAP vs VSS = gear selection for WOT downshift, a table that we don't have access to changing....
Thread Starter
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From: Schiller Park, ILL Member: #317
Re: What parameters are needed to initiate a WOT downshift? Ok, I have re-read my posts and the replies and I think maybe I am not making my issue clear. I'll try to explain it better.
First off, I have tuned the PCM to command a downshift to 1st at up to 37mph when at WOT and/or 100% TPS. Say I'm cruising at 31 to 33mph and floor it. TPS shows ~100%, TPS voltage is 4.3v or better, and VSS is reading correct. Now, watching a-tap, somtimes the PCM will command to go to 2nd (incorrect) and sometimes 1st (correct). Usually it commands 1st (correct). The trans does whatever the PCM tells it to (therefore not a mechcanical condition). Why would this happen?
Now, to further narrow it down, this condition never happens at 30mph or less (always commands the correct gear) and not that I can remember at 34-37mph (also commands the correct gear). So why in the world would it only do this in the 31-33mph range (not above or below) and why does it only happen every once in a while? Understand that there are no problems with part throttle opperation, this is all about WOT downshift gear selection by the PCM being incorrect per the tuning I have installed, but only sometimes.
I hope that made sense, and I do thank you guys for the help so far but I think I didn't properly explain my issue the first time around. Maybe this will make the problem easier to understand....
First off, I have tuned the PCM to command a downshift to 1st at up to 37mph when at WOT and/or 100% TPS. Say I'm cruising at 31 to 33mph and floor it. TPS shows ~100%, TPS voltage is 4.3v or better, and VSS is reading correct. Now, watching a-tap, somtimes the PCM will command to go to 2nd (incorrect) and sometimes 1st (correct). Usually it commands 1st (correct). The trans does whatever the PCM tells it to (therefore not a mechcanical condition). Why would this happen?
Now, to further narrow it down, this condition never happens at 30mph or less (always commands the correct gear) and not that I can remember at 34-37mph (also commands the correct gear). So why in the world would it only do this in the 31-33mph range (not above or below) and why does it only happen every once in a while? Understand that there are no problems with part throttle opperation, this is all about WOT downshift gear selection by the PCM being incorrect per the tuning I have installed, but only sometimes.
I hope that made sense, and I do thank you guys for the help so far but I think I didn't properly explain my issue the first time around. Maybe this will make the problem easier to understand....
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From: Raleigh, NC
Re: What parameters are needed to initiate a WOT downshift? I think engine load also has to do with whether it will downshift to the lower gear or not... and how quickly it gets to WOT. But, that's just a guess.
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Re: What parameters are needed to initiate a WOT downshift? I don't think the normal, performance, et shift mode tables do anything. At least based on my car. All the shift table were set at 255 mph from the factory (WS6) so that tells me there are other table we do not have access too.
Gary
Gary
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From: Schiller Park, ILL Member: #317
Re: What parameters are needed to initiate a WOT downshift?
I think engine load also has to do with whether it will downshift to the lower gear or not... and how quickly it gets to WOT. But, that's just a guess.
I will probably try changing the downshift tables for Normal Mode to initiate the downshift at an earlier TPS % and see if that helps any. Otherwise, I don't think there is anything else I can do
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From: Schiller Park, ILL Member: #317
Re: What parameters are needed to initiate a WOT downshift?
I don't think the normal, performance, et shift mode tables do anything. At least based on my car. All the shift table were set at 255 mph from the factory (WS6) so that tells me there are other table we do not have access too.
Gary
Gary
Re: What parameters are needed to initiate a WOT downshift? I'm not positive on the use of the "Performance Mode" table. I've read that it's only used on vehicles that have Sport Modes (C5's). I believe the trucks use this table when in tow/haul mode.
FWIW my '00 SS also has the Performance Mode table set to 255. I really don't think the fbody cars access this feature (although it would be cool
).
Richard
FWIW my '00 SS also has the Performance Mode table set to 255. I really don't think the fbody cars access this feature (although it would be cool
). Richard
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From: Raleigh, NC
Re: What parameters are needed to initiate a WOT downshift? Performance mode is not used unless you have one of those switches some LT1's had that gives you more aggressive shift points. It should be disabled (255 values).
