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What is known and tried with 0MPH speedometer when a stall converter is installed?

17K views 80 replies 28 participants last post by  CHEVY6000TBSS 
#1 ·
I would like to know what is known about this and what has been tried and failed.

I am going to take a crack at solving this issue with a black box that modifies ECM inputs. Tricking computer if you will. If you have seen my chime kill mod you know how hardcore it will get.

It will be fun to try and give me an excuse to install that Yank...

:cheers1:
 
#12 ·
State law requires an accurate speedo.

Who doesn't drop the throttle from a standing start? You really need to know when you hit the speed limit so you can back out.

Um, nothing better to do? :biggrin2:
 
#4 ·
I think its deeper than most think. I know some of the tuners took some stabs at it. I don't know if HPT or EFI has access to the tables required. I really dont think they would.

I suspect it will take some custom OS work. I think input and output shaft speeds run pretty deep into the system.
 
#7 · (Edited)
I'm thinking it has got to be something with the relationship with the input speed sensor as related to engine RPM thats throwing it out. While standing still and stalling up, the ISS and VSS both read 0. But shortly after launching the ISS will rise sharply to eventually come relativly close to engine RPM. The relation ship between the ISS and the VSS is a given value depending on what gear ratio is selected. The TCM knows what to expect as far as the difference between the two goes. It the TCM sees a deviation of that, then slipping trans DTCs get thrown. So I doubt it has much to do with the relationship between the ISS and VSS but has more to do with how fast the ISS rises in relation to the engine RPM. When you add a stall the rate that the ISS rises vs. RPM is the only thing that has changed compared to a stock vehicle. What y'all think?

If I had a stall, I could also plot it with my Tech2 to see if the VSS signal actually drops out for some reason. Or the VSS could be tapped into with a DVOM to see if for some reason the sensor is actually dropping out or is it a fluke with the TCM calculating the VSS signal. If its an error within the TCM, then there will be no fixing it.

BTW, does the speedo on the dash drop out as well when this occurs?

Jay
 
#10 ·
I dont know why they need to make it so complicated for anyway. All you need is the tailshaft speed from trans. Like they have been doing for over 75 years.

I am sure they are using that calculation for something and just decided to pull the pulse out somewhere else.
 
#11 ·
GM cares about something they should not. The difference between Trans and converter and converter clutch slip. I figure the input sensor is for sensing trans slip under hard acceleration when the converter clutch is off. Perhaps it was intended to back off the throttle if the trans started slipping badly at WOT? This would be an improvement over the older trans and converter combined slippage code.

Well guess what the trans is going to be toast before the code is thrown and by walking you will know that yes the damn thing is really slipping! Converter clutch or trans slipping? Who cares! The entire trans has to come out and both get serviced during the rebuild. Does it matter if it was the converter or the trans clutches? Point of interest maybe.

Maybe they need a code to justify transmission repair as part of cost cutting?

Anyway I figure to tap the front trans sensor and make it follow engine RPM within factory stall of 1900 RPM. This will look like huge trans slippage, but as I point out that code is useless.

What would happen if the front sensor just flat quit? Limp mode?
 
#13 ·
i think luis may be on to something with the wheel sensors....that is a viable work around that could be tapped into with HPTuners or EFILive and ploted in a scan log file, this would help me at the track with ACTUAL speeds and rpm to do my tranny tuning with....
 
#17 ·
leftcoast joe just clued me into a possible LOGGING fix.....

log the tranny output shaft rpm.....with that log you can create a guage that takes that and create an equation to multiply the tranny shaft rpm X gear ratio X tire height to calculate MPH......

I WANT MPH in my logs....and i could careless how i get it......
 
#18 ·
The only other thing I can think of is doing a code segment swap with the same PCM model different car. Like GTO, Vette, to TBSS. This would be for the transmission code and VSS only. Just to bypass the TBSS specific issue via cutting support for the 'new' sensor.
 
#21 ·
Food for thought on this discussion, here is the description and operation of the ISS from the service manual.

The Automatic Transmission Input Speed Sensor (AT ISS) Assembly is a hall-effect sensor that produces an input speed signal as the turbine shaft rotor teeth pass in front of the sensor tip.

The AT ISS is made of a permanent magnet with an iron pole piece and an integrated circuit (IC) chip with a two-element transducer molded into a plastic housing. The two-element transducer functions as an on/off switch by sensing changes in the magnetic field strength. The dual element design greatly increases the sensor's switching accuracy.

Because the turbine shaft is splined to the torque converter, it spins at engine speed. As the turbine shaft spins, the rotor teeth pass in front of the sensor tip, changing the magnetic field. As a result, the transducers are sensing high and low magnetic signals. The IC chip will then amplify and filter the high and low signal. Therefore, whenever the engine is running, the sensor will produce high and low signals proportional to turbine shaft speed. The more rotor teeth passing by the sensor's magnetic field in a specific amount of time, the faster the turbine shaft is spinning.

The ISS assembly is attached to the pump cover with the tip of the sensor passing though the stator shaft and sleeve. The ISS mounting bolt passes through a steel insert and into a threaded hole in the pump cover. The ISS wiring harness is routed and secured to the pump cover with clip-on brackets. At the transmission control module (TCM), the signal is electronically converted and is interpreted as transmission input speed. The TCM uses transmission input speed together with the transmission output speed to provide shift energy and torque management capabilities, improved shift quality (feel), increased TCC function, gear ratios that are more accurate and enhanced transmission diagnostics.
Here is what is mentioned about the VSS:

The vehicle speed sensor (VSS) assembly provides vehicle speed information to the transmission control module (TCM). The VSS assembly is a permanent magnet (PM) generator. The PM generator produces a pulsing AC voltage as rotor teeth on the transmission output shaft pass through the sensor's magnetic field. The AC voltage level and the number of pulses increase as the speed of the vehicle increases. Output voltage varies with speed from a minimum of 0.5 volts at 100 RPM to more than 100 volts at 8,000 RPM. The TCM converts the pulsing voltage to vehicle speed. The TCM uses the vehicle speed signal to determine shift timing and torque converter clutch (TCC) scheduling.
 
#22 ·
Ok, apparantly the flow of information is as follows on how the vehicle determines vehicle speed and displays it on the IPC.

1st the TCM calculates the A/C voltage signal frequency from the VSS (pulses per mile). It then sends that data to the ECM via GM LAN communications. The ECM will then command the IPC on what to show on the speedo via a discrete circuit between the ECM and IPC's logic module (internal to the IPC). The IPC then reacts and drives the motor on the speedo gauge to display what is commanded.

In HPT, do you guys know if when your logging the VSS pid, is the pid actually coming from the ECM or the TCM? I was asking because both modules actually recieve the VSS signal, the TCM directly from the module and the ECM via data communications.

Jay
 
#24 ·
I understand that going WOT from a standing start puts the ECM/TCM in abuse mode where going WOT from a roll doesn't. One more factor to look at?

DashHawk working indicates speed data is available. I think the ECM is where the ball (speedo) gets dropped.

I recall asking Vectormotorsports on Dave's, from Yank, recommendation. The person on the phone said that the drop out condition approached the clock speed of the ECM. Perhaps the sensor pulses can be divided by 2 and rescaled in the ECM tables? Over clock the ECM? :biggrin2:

Is it possible to flood the GM LAN or run the ECM or TCM out of computing power? If it does run out would the ECM start dropping non-critical calculations?

I mean computing "shift energy... etc." Must take a lot of computing power for all these items. Esp when the SS accelerates fast enough stock + tune to out run some Radar signs. Or maybe it is going off (or under) the table for input speed VS engine RPM. This may add one more calculation for a trouble code and be the overload.

What would happen if this trans input sensor failed? Limp mode?
 
#27 · (Edited)
After working on my T-56 swap, and talking to Jay, I think I have a solution for this issue. I currently have my speedo wired this way and it is working. Here is a brief explanation of how the VSS works in the TBSS. The raw AC voltage from the VSS goes to the tcm, the tcm compares that voltage with the iss signal, and then sends a buffered signal out to the ecm, which in turn generates a 4000 pulse per mile signal and sends that out to your IPC (speedo).



I think the the reason for the 0 speedo at launch is because with a stall, it throws the ISS signal out of range of what the TCM is expecting based on the VSS signal it is receiving, so it defaults to 0.

What you need to do is install a 2nd ecm (E67), loaded with a tune from an 07 CTS-V which uses a manual trans. (I have both HPT and EFILive versions and can send them out upon request.) The CTS-V tune is designed to accept the raw AC voltage straight from the VSS, since there is no TCM or ISS, and generates the 4000 pulse per mile signal and sends that out to you IPC. The only change you will need to make to the CTS-V tune is to copy your tire size, pulse per mile, and gear ratio settings over from your original tune. Here are the settings for STOCK wheels, tires, and rear gears.




Basically all you need to do is run power and ground to the 2nd ECM, split both raw AC voltage wires coming off the VSS between the two ECMs (this can be done very easily just before the wires go into the TCM), and disconnect the wire that comes out of the TBSS ECM and goes to the IPC and connect it into the same spot on the 2nd ECM connector. What this does is, sends the raw AC voltage to both the 2nd ECM and the TCM. This way the TCM will still know how fast the vehicle is going. The TCM will still send the buffered signal to the TBSS ECM (when the ISS and VSS are in the correct range). The TBSS ECM will no longer be connected to the IPC. That wire will be removed from the TBSS ECM connector and installed into the 2nd ECM connector. Now the 2nd ECM is sending out the 4000 pulse per mile signal out to the IPC your speedo is working. Here is a hand drawn schematic. (Some of the power feeds into the 2nd ECM may not be necessary but I wasnt sure so I listed them all)



The E67 ECM connectors can be purchased here and come with all the pins as well.
 
#28 ·
After working on my T-56 swap, and talking to Jay, I think I have a solution for this issue. I currently have my speedo wired this way and it is working. Here is a brief explanation of how the VSS works in the TBSS. The raw AC voltage from the VSS goes to the tcm, the tcm compares that voltage with the iss signal, and then sends a buffered signal out to the ecm, which in turn generates a 4000 pulse per mile signal and sends that out to your IPC (speedo). Here is my ghetto, hand drawn version of that.



I think the the reason for the 0 speedo at launch is because with a stall, it throws the ISS signal out of range of what the TCM is expecting based on the VSS signal it is receiving, so it defaults to 0.

What you need to do is install a 2nd ecm (E67), loaded with a tune from an 07 CTS-V which uses a manual trans. (I have both HPT and EFILive versions and can send them out upon request.) The CTS-V tune is designed to accept the raw AC voltage straight from the VSS, since there is no TCM or ISS, and generates the 4000 pulse per mile signal and sends that out to you IPC. The only change you will need to make to the CTS-V tune is to copy your tire size, pulse per mile, and gear ratio settings over from your original tune. Here are the settings for STOCK wheels, tires, and rear gears.




Basically all you need to do is run power and ground to the 2nd ECM, split both raw AC voltage wires coming off the VSS between the two ECMs (this can be done very easily just before the wires go into the TCM), and disconnect the wire that comes out of the TBSS ECM and goes to the IPC and connect it into the same spot on the 2nd ECM connector. What this does is, sends the raw AC voltage to both the 2nd ECM and the TCM. This way the TCM will still know how fast the vehicle is going. The TCM will still send the buffered signal to the TBSS ECM (when the ISS and VSS are in the correct range). The TBSS ECM will no longer be connected to the IPC. That wire will be removed from the TBSS ECM connector and installed into the 2nd ECM connector. Now the 2nd ECM is sending out the 4000 pulse per mile signal out to the IPC your speedo is working. Here is yet another ghetto, hand drawn schematic. (Some of the power feeds into the 2nd ECM may not be necessary but I wasnt sure so I listed them all)



The E67 ECM connectors can be purchased here and come with all the pins as well.




:wtf::doh::shocking: I have no idea what was just said:eek::confused1:
 
#30 · (Edited)
LOL it looks much more complicated than it really is. All you're doing is splitting the VSS signal between both the 2nd ECM and the TCM, and then swapping the output wire to your speedo from the original ECM to the 2nd ECM.
 
#32 ·
Why Not Just Take The One Output That Still Works (A or B) And Parallel Them Into The ECM On 66 & 67 ?
 
#34 ·
The VSS induces AC voltage and sends it down both wires to the TCM. The TBSS ECM OS was not designed to accept the raw AC voltage from the VSS. It wouldnt understand it. It accepts the buffered signal from the TCM on X3-66. Plus since the TBSS ECM OS isn't programmed to use X3-67, it would ignore any signal on that pin.
 
#33 ·
"Run a bypass." For those wondering what is being done this is how you remove the Input Speed Sensor (transmission input shaft speed) from the MPH calculation. Many have maintained ISS has no business being used for a MPH calculation.

The HPTuners folks wouldn't work with Alvin on the fan delay issue, and I can't watch the ECT on my diesel as the table corrupts in the logs. They got their hands full and are not making much progress (on the diesel.)

Now that the way is shown maybe someone can do the patch like Alvin does for the fan issue? Some sort of motivation to do this may be needed.

Otherwise this 2nd ECM in kit form after someone attempts and proves it would be cool.

Awesome solution, thanks for sharing!!! :coolthumb:
 
#36 ·
I wish. I still don't have the throttle working yet. Gotta get that fixed before I put the trans in.
 
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