E38 - Speedo Calibration

[ben_att]

Hi all,

This may be a silly question, however I was wondering if it's possible to modify the no of pulses that the E38 sends out on X1-57?
I have fitted a VF ECU to a VZ the ECU details are
Main OS 12656930
System 92271525
Speedometer 92271528

Now that I have set the diff and tyre ratio correctly in the ECU, the readout from the ECU seems spot on when measuring to a GPS device or driving along side another car comparing speeds but the cluster is saying 50km when doing 60km.
I have set the PPK in the cluster as low as it allows which is 3000, I did it with the Tech II and also tried out of curiosity to force a lower number into the eeprom directly but it doesn't seem to make a difference.

One thing I've noticed in HP Tuners is that on the VZ OS, there is an extra variable on the speedometer page that is not there on the VF OS called 'PCM Output Calibration' (photo attached).
I was trying to avoid introducing a pulse adjuster between the ECU and dash, but looks like it may be my only option.

Thanks

[Tre-Cool]

your using a 6l80 too yeah?

if you read the trans/ecu out togethor it might not be showing u all the options for just the ecu.

[ben_att]

Sorry, that was silly of me to leave that out, yes running the 6l80.

Do you mean take a read of the E38 on its own without the TCM?
I’ve got a read of the E38 on its own, E38 with TCM and another one with E38,TCM & FPCM.
I’ve just had a look and all of them look the same on the speedometer page in HPT.

Maybe I misunderstood what you meant?

[In-Tech]

Tre-Cool brings up a good point.
I always make the ECM and TCM match on speedo correction because I can control that much. Maybe it doesn't matter except to the ECM or other modules as long as the TCM is correct. It would be nice to know. Also, the ECM has a switch to only listen to the ECM for speed control as well as ignoring the other modules. I dunno, all I know is what has worked for me.

[Tre-Cool]

yeah i meant seperate read from the controllers. hpt does some wierd shit were options disappear/get added when they are a combined read.

tends to happen in the speedo area since both the trans & ecu have similar table settings.

My experience with auto combo's is get the speedo working correctly/accurate in the auto, then you should be free to play/fudge the output pulse from the ecu. in efilive for instance i always log the vss pids for ecu/tcm. u can tweak the internal pcm calculations by adjusting tire size or ecm pulses per km.

basically 6l80 uses the diff ratio/tyre size-revs per km to work out the speed. ecu then picks this info up, then can manipulate it for internal calculations & or the output pulse.

just gotta play with it.

easy peasy on a dyno

[ben_att]

yeah i meant seperate read from the controllers. hpt does some wierd shit were options disappear/get added when they are a combined read.

tends to happen in the speedo area since both the trans & ecu have similar table settings.

My experience with auto combo's is get the speedo working correctly/accurate in the auto, then you should be free to play/fudge the output pulse from the ecu. in efilive for instance i always log the vss pids for ecu/tcm. u can tweak the internal pcm calculations by adjusting tire size or ecm pulses per km.

basically 6l80 uses the diff ratio/tyre size-revs per km to work out the speed. ecu then picks this info up, then can manipulate it for internal calculations & or the output pulse.

just gotta play with it.

easy peasy on a dyno

I finally got a chance to play with this today. So my starting point today is as I had it working nicely and the VCM speedo was correct auto shifts properly but the dash cluster speedo was reading slow.
So I did a read of ECU only without T43 and changed the wheel/tire rev and the ratio and wrote it in, speedo on cluster now good and shifts are still good, drives well but the VCM Speedo is now 25km over. Does that matter for any other calculations in the ECU? Or have I not understood what you meant and done that wrong? Not sure if related or not but after doing this, my cruise control didn’t work, when I tried to activate I got a message on the cluster I’ve never seen before that said something like ‘press the brake pedal before activating cruise’. Would the cruise be comparing auto/ECU speed and be unhappy? The last time I drove this car the cruise was working, I could also see on VCM scanner that the brake pedal state was changing, so I’ll put the original values back in and check to see if it’s that or if something else has happened while it’s been sitting there for the last 5 or 6 months.

[Tre-Cool]

ideally you want the tcm values to read correct since the ecu gets that as the incoming speed.

what os & cal is in the tcm