VSS with 5.101 code

A forum for discussing applications and implementations of the MegaShift transmission controller code for the GPIO from B&G. This can control up to 8-speeds and 6 shift solenoids (plus a 16x9 table for controlling a PWM line pressure valve). It has manual and fully automatic modes (16x9 load x speed table), with under and over rev-limit protection, and full data logging of all inputs and outputs (among many other abilities). A TransStim to test your completed board is also available.
gui67
Posts: 134
Joined: Tue Oct 05, 2010 11:58 am
Location: Strasbourg, France

VSS with 5.101 code

Post by gui67 »

Hello Lance,

I switched from 4.145 to 5.101 code. I put all the parameters to the same as what was before.
Now when I started to drive, i saw that the speed on the log and on speedometer was much smaller then reality.

after looking at the logs, it seems that it is half of the real speed:
at 2300RPM, in 4th, TCC locked, the speed was normally 98km/h, the log shows 2012HZ for VSSHz
now with the new code, I only have 1022Hz, 50km/h.
I attached the tune. Do you know what the problem could be? I first thought about a problem with the intermediate ratio parameter, or unit problem : inch vs cm, but now that I see that the frequency has changed, I don't understand. I used the same parameters( input masking, smoothing factors as before)
thanks
Guillaume
Bernard Fife
Posts: 1696
Joined: Fri Apr 04, 2008 1:28 pm

Re: VSS with 5.101 code

Post by Bernard Fife »

Guillaume,

Did you re-start the GPIO board after changing VSS settings or loading the MSQ? Not doing that is the most common cause for what you are seeing, and this has tripped up many (including me) before.

Are the frequencies you mention the known and measured frequency input from a function generator, or are they only what you are seeing reported from MShift? If they are only what MShift is reporting, there may be an error in the INI (either for 4.145 or 5.101) and this might not actually affect the actual speedo reading.

When I load the default values, I get 59.6 mph at 1583 Hz input (from a known good func. gener.), which is the correct value. The VSS Frequency gauge shows 1584.8 Hz. What do you calculate the actual input frequency should be for your tire dam, gear ratio, etc. at a given speed - say 60 mph?

However, it's certainly possible there is something wrong in the code. Could you post a datalog as well, as this will help narrow things down?

Lance.
"Never wrestle with pigs. You both get dirty and the pig likes it." - George Bernard Shaw
gui67
Posts: 134
Joined: Tue Oct 05, 2010 11:58 am
Location: Strasbourg, France

Re: VSS with 5.101 code

Post by gui67 »

Hi Lance,
The frequency is what I saw on Mshift.
When I calculate the theoretical frequency, with 2300RPM, and 0,75 transmission ration, I get 3066 RPM at output shaft, which, with a 40 teeth wheel is 2044Hz (3066*40/60)
So I think what the 4.145 code was certainly OK.

I loaded the 5.101 code last sunday. I tried the car this evening and did not change the parameters. I stopped and restarted the car several times, so I don't think this is the problem.

I will send a datalog tomorrow andI will check all parameters again.
Thanks
Guillaume
gui67
Posts: 134
Joined: Tue Oct 05, 2010 11:58 am
Location: Strasbourg, France

Re: VSS with 5.101 code

Post by gui67 »

I just saw something else strange on the datalog:
normally, on the 4L80e, the IS speed does not change between 3rd and 4th gear (the sensor is after the overdrive)
In 3rd and 4th, the IS and OS are the same. It is the case in the "old" datalogs.
Now with the new code, there is a difference between the IS and OS speed. and when shifting from 3rd to 4th, the IS decreases which is mechanically impossible.
I will make some short logs tomorrow, the ones I have are way too big (more then 40 minutes drives)
Guillaume
gui67
Posts: 134
Joined: Tue Oct 05, 2010 11:58 am
Location: Strasbourg, France

Re: VSS with 5.101 code

Post by gui67 »

OK, I just understood the reason the IS Schanges, this is because of the new parameters: he code divides the IS signal by the ration (0.75) to get the true IS speed.
When I check the IS values, they are correct: same RPM as the Engine, but the OS is half the value it should be.
Bernard Fife
Posts: 1696
Joined: Fri Apr 04, 2008 1:28 pm

Re: VSS with 5.101 code

Post by Bernard Fife »

Guillaume,

I calculate your VSS at 118884 pulse/mile (40 teeth, 25.26 inch tires [= 64.16 cm] and a 3.73 axle ratio). This is 1981 Hz at one mile per minute (= 60mph or 96.6 kph).

When I check using your setting (MSQ) on my bench and an input frequency (measured) of 1981 Hz (± a percent or so), MShift's speedo shows 95.8 kph and the 'VSS Frequency' gauge shows 1980.2 Hz; which all seems correct to me.

It may be the 50% VSS masking you have set is causing one half of the VSS pulses to be missed. You might need to change the VSS masking to 75% or higher.

Lance.
"Never wrestle with pigs. You both get dirty and the pig likes it." - George Bernard Shaw
gui67
Posts: 134
Joined: Tue Oct 05, 2010 11:58 am
Location: Strasbourg, France

Re: VSS with 5.101 code

Post by gui67 »

Hello Lance,

Sorry for taking so much time to answer. I made changes to the car, so I did not drive it.
I tried it yesterday with your advice:
I put the input masking to 75 and then to 80.
at 75, the speed read is still the half but at 80% it is OK. But the speedometer is more "bouncy" then before. It made a lot of "jumps" to a lower value. what is strange is that I can see it on the speedo: needle going to 0, but I don't see it on the datalog... and it does not affect the transmission, it does not downshifts or anything.
So I tried a higher value: 90%, then it was a bit more stable, but made jumps to higher speeds: 200km/h... but again, it is nearly not possible to see anything on the datalogs, only on one point, i can see a small jump from

that was with the Old VSS ISR setting.
then I tried the new beta, but the speed remained on 0.The IS was working but not the OS or the speed:
http://g.scheidt.free.fr/4l80/2015-07-27_19.00.48.msl
Do you know what could cause that?
Bernard Fife
Posts: 1696
Joined: Fri Apr 04, 2008 1:28 pm

Re: VSS with 5.101 code

Post by Bernard Fife »

Guillaume,

If it isn't visible in a datalog, and I can't reproduce it here, it is hard for me to comment.

Lance.
"Never wrestle with pigs. You both get dirty and the pig likes it." - George Bernard Shaw
gui67
Posts: 134
Joined: Tue Oct 05, 2010 11:58 am
Location: Strasbourg, France

Re: VSS with 5.101 code

Post by gui67 »

Yes,
I can undestand for the speedo jumping.
but for the last part of the message:
where the speed stays at 0 with the beta vss ISR:
the datalog in the link is with this setting and I was driving, the settings are the same as with the old isr, I just changed this parameter: new instead of old and speed stayed at 0.
I restarted the car between to allow the changes to take effect.
Bernard Fife
Posts: 1696
Joined: Fri Apr 04, 2008 1:28 pm

Re: VSS with 5.101 code

Post by Bernard Fife »

Guillaume,

On my bench I don't see the effect of the zero speed in changing between the old and new VSS code. For me the new beta VSS code works okay (bear in mind that you might need to experiment with the masking).

I need a datalog taken with the new beta VSS code to see what is happening for you.

In the meantime, I would suggest that you use the old VSS as it appears to work better for you.

Lance.
"Never wrestle with pigs. You both get dirty and the pig likes it." - George Bernard Shaw
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