vss issues..killed my diffs and a prop!

[zen]

thought i had it all sorted...

zf24hp gearbox, now the vss was unuseable just running into gpio, but i made the lm2907 crt on this forum and i thought it was ok...but..alas no..
on my cars first proper outing i hit 60mph and the trans went into oscillation between 4th and 2nd gear...ripped apart diffs and prop before i could slow down..still drivable but now need replacing due to fecked uj.s and massive backlash in diffs..bugger (NOTE..was right foot down with 450hp..)

it appears thart at 6omph the gpio loses vss signal to such an extent that tuner studio shows speed drop from 60 to 10-20mph..but why??and how to cure..?

vss settings are as follows..input capture edge =falling (tried rising, it is worse)
vss input masking 70..(any less speedo to slow in reacting, higher its jittery)
input smoothing factor 12 (lower i set it, worse the drop out)
max vehiche speed 100
min vehicle speed 3
max errors to reset 1000..(have tried various, no real difference)
reset filter off 2secs

have tried various passive filtering..ie one side sensor to gnd, other 10k resistor in series then 0,1uf to gnd then into lm2907 crt..
and then.. lm2907 side of sensor 10k in series and 0.1u to gnd, other side 0.1 to gnd then grounded via 10k..no change..
plus other variations of..could 0.1u be too hig a value? i dont think it is..
gearbox to gpio runs a good gnd to correct pins etc..gpio pcb was washed lots with ipa 99%..its not sealed as of yet

its upseting me now, as i dont really want to kill another set of diffs..but am rather concered about driving car till sorted..

any thoughts please, before i junk the gearbox vss sensor and go buy speedo cable type sensor...thanks

[Bernard Fife]

zen,

Do you have rev-limiting enabled? I would enable that, and set it conservatively, while sorting the VSS issue out (and before doing anything near full throttle).

You need to get the VSS sorted before doing anything else. Have you tried setting the VSS input mask to 0? There are more VSS tips here: http://www.msgpio.com/manuals/mshift/vss.html, have you tried these?

Do you happen to have an oscilloscope?

Lance.

[zen]

Hi Lance

Yes i have over revving enabled,i will lower it!

I have a scooe yes,but quite tricky to check ,i will remove both props and try it like that
And post up pics of scope display

Will set madking to 0 and try it on way home.

At the moment this is my daily drive as i destroyed the clutch on the orher
Range rover and am waiting for a replacement(bespoke)

Thinking of using the speedo takeoff from a later range rover that goes in transferbox
Output where traditioal speedo cable goes,this is magnet and reed type micro switches..
This may be an easy solution (if all else fails)

[zen]

Hi Lance

well i scoped the VSS input to the lm2907 conditioner crt..all was well. nice sine wave in (no real noise, but more than enough to take out the gpio without the lm2907)..BUT output from lm2907 voltage droped from 5v square wave to 1v at 60 mph..TEST done with transfer box in neutral, running though gears.)

investigation on crt ....i had a small smoothing cap across the 5.6v zenor diode acroos the output (ecu protection) to elimate noise created by zenor diode..it was only 10nf, but once removed voltage stopped droping..prehaps it was not 10nf after all, but marked incorrectly..as 10nf sholud not have effected output..

so..now same test in neutral all is good with speed reading on TS upto 120mph which is where i stopped..(thought of car dropping into gear at that speed was enough to think enough!)

so i hope that is now sorted, but over revving is still enabled very at a safe level for now..

BUT..i dont see how it will work, DOES not over revving rely upon vss speed input to decide what is over revving??..ie if gpio thiknks its doing 10mph then it wont think its over revving if it drops into first EVEN though its doing 60mph??

NEXT to sort TCC as it oscillates on off on off at aroud its cut in speed... see post.(though about to do major search on forum before said post)

regards Simon