A4 Corvette w/3.90s wont shift at WOT

[Chuck CoW]

Hey guys...:help2:

I could use alittle help on something. I'm having a problem with 3 different customers A4 Corvettes I built with 3.90 rear gears.

These cars are automatics and have NO motor work. Just Vararams exhaust...2 have headers. 2 have Pro torque converters. The common denominator seems to be a 3.90 rear diff ratio.

These cars run like crazy…..BUT, despite the fact that I’ve set the WOT shift RPM to 6,100. when at 100% full throttle….It seems the trans ignores the WOT shift rpm and revs right past the commanded shift point and hits the rev limiter. If you back off the throttle even the slightest bit it rocks into gear like a champion! One of the three cars (a 98 C5 auto) will sometimes shift great at WOT and then instantly the motor seems like it shuts off for 2 or 3 seconds and if I hold my foot to the floor, the motor suddenly “turns back on” and runs fine. For some reason…only at 100% throttle, it does not upshift and when the rpm’s exceed the WOT shift RPM the motor breaks up badly and continues to run like shit for about 30 seconds (even though the rpm’s are safely below the rpm limiter) ….at first it runs like it’s flooded….and then slowly “clears up” the more you continue to drive. Each car exhibits slightly different symptoms but bottom line is they (usually) don’t shift when commanded to at max throttle and if they do…the motor runs like garbage or “shuts off” while on the throttle . If you go 90% throttle they all BLAST into gear and run like wild. I’m lost and need some help…I’ve been staring that these tunes for 3 months now and despite the frustrated customers..I’m losing my mind.:bash:

I tune automatic cars and trucks every day and I do the same thing in every single tune…always works great…never a problem no matter what mods the cars have…..the problem seems to only occur when the car has a higher than stock rear axle ratio.

I have even thrown an original GM bin in the cars and only changed the rear axle ratio….and it does the same thing…..Additionally, I’ve even set the WOT shift rpm to like 5,000 where surely I’m not pushing the motor or running out of fuel and the same thing happens….So, I’m assuming it’s not the “tune”

But, I’ve been thinking…..could there be some issue with the 3.90 axle ratio and the other controllers in the car??? Or some Traction control/active handling/torque management nonsense not liking my WOT use of the 3.90’s and my tune or maybe the TAC module? I know very little about the background processing of the o/s and how values are passed back and forth between the controllers. As a programmer for 20+ years….I’m thinking there’s something happening behind the scenes that just isn’t obvious from what I see in the EFI LIVE editor.

As I said....I think the common denominator is the 3.90's with these 3 cars...Hopefully someone out there has got an answer for me....

:help2:
Chuck CoW

[Tordne]

When using EFILive to change the diff ratio did you use the adjust feature to raise/lower the shift points based on the difference between the old and new ratios?

[foff667]

does it do it in all gears or just the 1-2? usually I use mph as my tag for the 1-2 shift and a mix of mph & rpm for the 2-3 shift...basically im asking if it could possibly just be the computer not being able to keep up with the new gearing?

[Chuck CoW]

When using EFILive to change the diff ratio did you use the adjust feature to raise/lower the shift points based on the difference between the old and new ratios?


oh yeah....I've been doing this for a very long time....I kmow this software cold.....That's what buggs me....It's just these 3 cars....

All normal driving is perfect....all heavy throttle driving is perfect....it's just 100% throttle that messes up...not 95% or 98%.....ONLY 100% throttle the pcm ignores the "shift at RPM" I'm lost.....

chuck

[Redline Motorsports]

I have had a similar issue with the A4 as well. What about mechanical delays vs. the electronics???

[Chuck CoW]

does it do it in all gears or just the 1-2? usually I use mph as my tag for the 1-2 shift and a mix of mph & rpm for the 2-3 shift...basically im asking if it could possibly just be the computer not being able to keep up with the new gearing?

well, with an A4 you can only max rpm shift 2 times....or you're goin too damn fast....

Yes, it is primarially the max throttle 1/2 although it dosen't do it every time.

and it has happened with the 2/3 but it is less frequent.

Chuck:nixweiss:

[Chuck CoW]

I have had a similar issue with the A4 as well. What about mechanical delays vs. the electronics???


please explain


what it seems like to me is not a malfunction of the "shift at rpm" parameters, but the engine cruises right past the "shift PRM" and hits redline.....

and usually the engine in the 98 car just "shuts off" with my foot to the floor and then resumes afew seconds later.....the 2000 C5 begins to break up at the shift rpm.....hits the rev limiter and then begins to run like it's flooded or something i have never seen and slowly recovers...it sometimes takes 1 min to "clear out" and then runs fine......

chuck

[SinisterSS]

Here's something to try - Set the WOT shift speed in D0910 through D0922 at some rediculously low numbers that you know are easily attained in each of the gears (see example of 20, 38 and 60 mph). Next, set the WOT shift rpm where you want it to shift (5600 was used in this example). With these settings, it'll bang home a shift like clockwork at 5600 rpm. What ever rpm is set in the rpm table will control the shift point. 6500, 7000, 4500, etc. as long as the mph threshold has been exceeded.

To shift at WOT, both the speed and rpm must be "true". Think of the shift speed values as enablers that put the PCM into WOT upshift "mode" and the shift rpm values as the actual trigger that makes a shift happen.

[Chuck CoW]

Here's something to try - Set the WOT shift speed in D0910 through D0922 at some rediculously low numbers that you know are easily attained in each of the gears (see example of 20, 38 and 60 mph). Next, set the WOT shift rpm where you want it to shift (5600 was used in this example). With these settings, it'll bang home a shift like clockwork at 5600 rpm. What ever rpm is set in the rpm table will control the shift point. 6500, 7000, 4500, etc. as long as the mph threshold has been exceeded.

To shift at WOT, both the speed and rpm must be "true". Think of the shift speed values as enablers that put the PCM into WOT upshift "mode" and the shift rpm values as the actual trigger that makes a shift happen.


So far, I have actually set the WOT shift rpm to like 5,000 to make it shift..and it dosen't.....I see what you are saying.....I'll check it....

I use the same shift tables in almost every tune I write....NEVER a problem.....but, with the 3.90's installed....it's screwed up....Hopefully, it's something with the 3.90's messing with some internal calculation and not me losing my mind.....I do this every day for a living with out a hitch...Just these 3 cars.........Maybe it's time for me to retire?????

uh
Chuck
:Eyecrazy:

[GMPX]

Chuck, did you get anywhere with what was sent via Email from Paul?

Cheers,
Ross

[joecar]

Chuck,

Have you checked that the downshift WOT MPH is lower than the upshift WOT MPH (say 10 MPH lower)...? Try making it even lower.

Joe

[Chuck CoW]

Chuck, did you get anywhere with what was sent via Email from Paul?

Cheers,
Ross

Hey man...I'm gonna try it later today....

Chuck

[Chuck CoW]

Chuck,

Have you checked that the downshift WOT MPH is lower than the upshift WOT MPH (say 10 MPH lower)...? Try making it even lower.

Joe


Hey Joe.... Yeah....In fact, I have loaded the bone stock tune in the cars and they do the same thing....That's why I believe it is some wierdo issue with the 3.90 gear set.....Messing up the ecm's calculations.

Chuck

[Chuck CoW]

Chuck, did you get anywhere with what was sent via Email from Paul?

Cheers,
Ross

Yeah man...I think we got it fixed.....I have to test drive it for myself in the morning.....but, looks promising.....all i think i have to do now is the speedo and hope that the same fix repairs the other two cars.....

I think that by changing the axle ratio and some of the other parameters
Paul suggested we fixed it. You can not rely on just inputing the new axle ratio and press the recalculate button. I think this issue is specific to the corvette...Maybe the editor could check the vin for the "Y" in the fifth position and then manage the "recalculate" differently than other cars. After inputing the new Axle ratio (which was 3.90 or 4.10) I believe that the pcm calculated a rear axle torque far in excess of what the operating system was equipt to process and the motors sort of shut down or went into some sort of "torque managment overload"...Wierd thing was all three vehicles seemed to ignore the WOT shift RPM when the TPS was maxxed....any other time it was working fine....

I'm still kinda not sure of EXACTLY what went wrong, but.....the 30 min conversation I had with paul seemed to put some of the pieces together. I'm not sure any of us totaly understands it..but from what he told me, GM ust sorta fudged alot of that speedo stuff....Wonder why it seems so confusing?!?!?:nixweiss:

:master: Thanks ROSS AND PAUL!!!:master:
and I was gettin ready to sign up for EFI 101!!! sheesh!

Chuck CoW

[driver456]

I had something like that,The car wouldn't shift 2nd to 3rd.I raised my BASE PRESSURE for 2nd to 3rd shift,Worked like a charm:D ..................................Paul

[Chuck CoW]

I had something like that,The car wouldn't shift 2nd to 3rd.I raised my BASE PRESSURE for 2nd to 3rd shift,Worked like a charm:D ..................................Paul


yeah.....we did that too.....and it only worked for 2 days....


then it screwed up. for 4 months.

Chuck CoW

[Doc]

Yeah man...I think we got it fixed.....I have to test drive it for myself in the morning.....but, looks promising.....all i think i have to do now is the speedo and hope that the same fix repairs the other two cars.....

I think that by changing the axle ratio and some of the other parameters
Paul suggested we fixed it.

What other parameters?


You can not rely on just inputing the new axle ratio and press the recalculate button.

So what can you rely on? Are you implying checking what VIN code EFI Live is reporting via the main calibration page to make sure the change took hold?


I think this issue is specific to the corvette...

I have a customer with a 98 a4 Z28 that originally had 2.73 gears and has ugraded to 3.73 doing the same thing(s) you described. Maybe this is a 98 thing?



I'm still kinda not sure of EXACTLY what went wrong, but.....the 30 min conversation I had with paul seemed to put some of the pieces together. I'm not sure any of us totaly understands it..but from what he told me, GM ust sorta fudged alot of that speedo stuff....Wonder why it seems so confusing?!?!?:nixweiss:

So did you confirm the fix yet this morning?

[Chuck CoW]

I had something like that,The car wouldn't shift 2nd to 3rd.I raised my BASE PRESSURE for 2nd to 3rd shift,Worked like a charm:D ..................................Paul

I was thinking about you....The problem you had was definately not the same....likely your trans was not holding....and the pressure helped out....I've seen it before.....It's alot to get into here, but.....Now I realize what's been happening.


Chuck CoW

[Chuck CoW]

What other parameters?



So what can you rely on? Are you implying checking what VIN code EFI Live is reporting via the main calibration page to make sure the change took hold?



I have a customer with a 98 a4 Z28 that originally had 2.73 gears and has ugraded to 3.73 doing the same thing(s) you described. Maybe this is a 98 thing?


:nixweiss:

So did you confirm the fix yet this morning?


Yup....FIXED. it is not a 98 thing. The reference to vin number was a suggestion to Ross to possibly modify the editor (when the corvette "Y" vin was present) to manage the "recalculate" button differently. I don't think that your Z28 was having the same problem. It's posible, but the Vettes manage the whole speedo/ pulses calculation crap differently than all of the other RWD vehicles.


Chuck CoW

[driver456]

Hey Chuck,Glad you got it fixed.I just checked on mine in calibrations "SPEEDOMETER" Where it shows tire size and below that it says "Trans output shaft revs/mile,Since I have 3.73's it says 2893.6860 then below that {H0104} should have the same number,But it didn't.And in the description it says"FOR AUTOMATIC VEHICLES,IT IS USED BY THE PCM TO DETERMINE THE TRANSMISSION SHIFT SPEEDS.I don't know if that causes to much of a problem,But it doesn't hurt to check and make sure those numbers match,Also PULSES MILE with {H0101} and VSS pulses/rev with {H0102} those should match too.I know you have been at this for a long time and know this stuff inside out:D ,But other people should check also:cheers: ..................................Paul

[Redline Motorsports]

please explain


what it seems like to me is not a malfunction of the "shift at rpm" parameters, but the engine cruises right past the "shift PRM" and hits redline.....

and usually the engine in the 98 car just "shuts off" with my foot to the floor and then resumes afew seconds later.....the 2000 C5 begins to break up at the shift rpm.....hits the rev limiter and then begins to run like it's flooded or something i have never seen and slowly recovers...it sometimes takes 1 min to "clear out" and then runs fine......

chuck

Chuck,

I have seen many 4L60E's with broken 1-2 accumulator pistons that will cause this same effect. Even though the PCM is commanding the shift, mechnically it is not following through. Would be real odd on three cars but it is a common problem. This is why Rodney at RPM transmission custom fabricates a billet one for his trannys.

[Blacky]

Based on lots of research and hard work work by Chuck, and by some number crunching here at EFILive, we believe we figured out what is causing the problem, and how to "solve" it.

EFILive's speedo calculator already has a "corvette" specific mode. It is the Transaxle check box. That checkbox will be checked automatically if the VIN indicates a corvette. That checkbox will be cleared automatically if the VIN indicates otherwise.

The speedo calculator must operate differently for a corvette because the pickup is on the rear axle not on the trans output shaft (TOS).

However, the problem is not "corvette specific", maybe the symptoms are specific to a corvette but the same problem could occur in any LS1/LS6.

The differential ratio {H0103} is NOT used to calculate the speedo value or the trans shift points in any LS1. It is only used by the PCM to calculate axle torque. Setting it to higher values will cause much larger axle torque values to be calculated by the PCM - maybe pushing the PCM's shift point calculations into the twighlight zone (at WOT, i.e. max calculated torque).

So, just leave the {H0103} value as 2.73 (usually what the corvettes are set to out of the factory) and all should be well.

The only problem with that is, EFILive needs the diff ratio to be correct in order to figure out the TOS. So put the correct diff ratio in the calculator, calculate all the values, save them back to the calibration, then manually re-edit the {H0103} value back to 2.73 before reprogramming the PCM.

Regards
Paul

[spdnman]

Based on lots of research and hard work work by Chuck, and by some number crunching here at EFILive, we believe we figured out what is causing the problem, and how to "solve" it.

EFILive's speedo calculator already has a "corvette" specific mode. It is the Transaxle check box. That checkbox will be checked automatically if the VIN indicates a corvette. That checkbox will be cleared automatically if the VIN indicates otherwise.

The speedo calculator must operate differently for a corvette because the pickup is on the rear axle not on the trans output shaft (TOS).

However, the problem is not "corvette specific", maybe the symptoms are specific to a corvette but the same problem could occur in any LS1/LS6.

The differential ratio {H0103} is NOT used to calculate the speedo value or the trans shift points in any LS1. It is only used by the PCM to calculate axle torque. Setting it to higher values will cause much larger axle torque values to be calculated by the PCM - maybe pushing the PCM's shift point calculations into the twighlight zone (at WOT, i.e. max calculated torque).

So, just leave the {H0103} value as 2.73 (usually what the corvettes are set to out of the factory) and all should be well.

The only problem with that is, EFILive needs the diff ratio to be correct in order to figure out the TOS. So put the correct diff ratio in the calculator, calculate all the values, save them back to the calibration, then manually re-edit the {H0103} value back to 2.73 before reprogramming the PCM.

Regards
Paul

Thanks Chuck and Paul for all of your work. I am one of the customers with the A4 and 3.90's that does not shift correcty. Chuck will be tuning my car in a few days and my question is does any of this affect the speedometer calibration on the guages or should it all function correctly? Again thanks for all the help. :cheers: :)

[Chuck CoW]

Chuck,

I have seen many 4L60E's with broken 1-2 accumulator pistons that will cause this same effect. Even though the PCM is commanding the shift, mechnically it is not following through. Would be real odd on three cars but it is a common problem. This is why Rodney at RPM transmission custom fabricates a billet one for his trannys.


Thanks pal, tried that already....pluss a new Pressure control sol....and also wanted to look for evidence in the pan....If the accumulator was cracked (which we suspected so I always use Aluminum pistons) then The foward clutch would have smoked and left dirt in the pan....Thank god it wasn't....

Thanks for the advice
Chuck CoW

[Chuck CoW]

Based on lots of research and hard work work by Chuck, and by some number crunching here at EFILive, we believe we figured out what is causing the problem, and how to "solve" it.

EFILive's speedo calculator already has a "corvette" specific mode. It is the Transaxle check box. That checkbox will be checked automatically if the VIN indicates a corvette. That checkbox will be cleared automatically if the VIN indicates otherwise.

The speedo calculator must operate differently for a corvette because the pickup is on the rear axle not on the trans output shaft (TOS).

However, the problem is not "corvette specific", maybe the symptoms are specific to a corvette but the same problem could occur in any LS1/LS6.

The differential ratio {H0103} is NOT used to calculate the speedo value or the trans shift points in any LS1. It is only used by the PCM to calculate axle torque. Setting it to higher values will cause much larger axle torque values to be calculated by the PCM - maybe pushing the PCM's shift point calculations into the twighlight zone (at WOT, i.e. max calculated torque).

So, just leave the {H0103} value as 2.73 (usually what the corvettes are set to out of the factory) and all should be well.

The only problem with that is, EFILive needs the diff ratio to be correct in order to figure out the TOS. So put the correct diff ratio in the calculator, calculate all the values, save them back to the calibration, then manually re-edit the {H0103} value back to 2.73 before reprogramming the PCM.

Regards
Paul


Hey Paul....So far, of the 3 cars with problems....You nailed the first one with your calculated values.....The Second one didn't work that way though.....AGAIN, more heartache! It took almost a whole day to do it. And you won't believe the answer!!! UH! and I'm gona have at the third one which is a 98 A4 vette this weekend..I'll let you know how it goes.

Before you modify the editor or anything like that....Give me another call as I have some new "insights" for you. You'll die when I tell you what I discovered!

Chuck CoW