Vss divisor information

[Tunedperformance]

I was wondering if any one has messed around with vss divisor setting on $8d or $DA2 or DA3. I have change the $8d to optical to run off of buffers and drac's but have never messed with the divisor. Is there a formula for a higher rear end ratio to calibrate the vss to run slower. I am trying to help a guy out and do not have the vehicle here for testing the values.

[Six_Shooter]

In $8D, you wouldn't use the VSS divisor to adjust for gear ratio changes, you would use the Vehicle SPeed Sensor Instrument Cluster Panel Pulse Divisor located at 0x14.

[Tunedperformance]

Sorry six shooter That is the vss divisor I had meant to state the Vehicle SPeed Sensor Instrument Cluster Panel Pulse Divisor.

[Tunedperformance]

I figured out the answer, sweeeeeeet ;)

[EagleMark]

So your not going to tell us? :nono:

I don't know if it is accurate for $8D but there is one in the $EE info thread...

[Tunedperformance]

pm sent

[JeepsAndGuns]

Working on $8D too, the other VSS scaler (0X15), can that be changed to match a non stock VSS?
Most stock bins I have seen are 4000 pulses per mile. I assume this means the stock vss is a 4 pulse one? So could this value be changed to 2000 for a 2 pule VSS, or 8000 for a 8 pulse VSS?

[Tunedperformance]

the magnetic vss input can be raised as a magnetic pulse input but not lowered starting at 4k. You can use 2k through a external vss buffer and into a 730 as optical or same thing with a drac

[JeepsAndGuns]

So if I have a 8 pulse hall effect VSS I can use it by simply entering 8000?

[Tunedperformance]

not with a hall effect.

[JeepsAndGuns]

So a hall effect vss is not compatable at all with 8d?

[Tunedperformance]

not that I am aware of. I sent you a pm. As far as I know just magnetic pulse and optical.

[1project2many]

If your Hall effect produces 5V out then it may be usable but it depends on the frequency. The signal could be connected to the optical input but you might not be able to adjust the vehicle speed properly since the optical signal is supposed to be 2000 pulses per mile.

[cmaje72]

I have it set to 8120 on $DA3 for an 8000 PPM sensor. Its right on with my speedo.
Jeeps - its the waggy one and I think it might work for the $8d ecu's. I just went out googling and found this:

Q: How do I tell the ECM I have a magnetic VSS instead of a optical VSS? Change bit 6 of the value at location $8018 to zero.

Its at this site:
http://www.diy-efi.org/gmecm/ecm_info/1227730/qanda.html#q10

So maybe $8d can support both types?

[RobertISaar]

a hall effect SHOULD be able to be used... but you may have to do a little tweak to the wiring first. the hardware in a 7727 wants to see an A/C signal that passes both above and below 0 volts. a normal 2-wire magnetic VSS will do this, hall effect goes from 0-5V(or something along those lines). well, you can make it swing from -2.5 to 2.5 volts using only a single capacitor. something i found out while making my testbench.

and 8D CAN use optical or magnetic, with adjustable PPMs with both. obviously magnetic needs to be at least 4000 pulses per mile for the divider to work correctly, but that's only for the instrument cluster signal.

[JeepsAndGuns]

The VSS in question is the factory one on my 93 wrangler, the one I am planning on swapping in a 7727 to run the 4.0. If I remember right, I read somewhere in the FSM, the factory VSS is hall effect. I know looking at the wiring diagrams, it has a power wire, a ground wire, and a signal wire. It recieves a 8 volt power supply from the ecm, and the signal wire splits of and 1 goes to the ecm, the other to the speedometer. I figure I can tie into a 5 volt refrence wire on the 7727 to power the factory vss, though there is one guy on jeepforum that did a engine swap and claims he is supplying 12 volts to his stock vss and it works fine, and has for years.
If I have to install another vss I will, The factory one goes into the transfer case and the gear is made on it. I can swap to the 91 and older speedo drive and use a standard thread on style vss like JTR has, however I will need to find a way to connect it to my factory vss so I can keep my speedometer.

[1project2many]

Does the Jeep ecm supply voltage to the HE sensor? I probably wouldnt use the 5V line without knowing how much current usage the sensor adds. Look around the net and youll find circuits for 12V to 5v DC converters. Somewhere in Jeep FSM there might be a note about how many pulses per mile the trigger wheel generates. Might need to use a DRAC in between but DRAC might not like DC voltage pulses either. Prolly need to build a "voltage level shifting circuit" to drop signal level from 0 - 8V to -3 to 5V. That way signal could be sent right to ecm. Or maybe use GM sensor in back of Jeep Xfer case.

[JeepsAndGuns]

From what I can find, the stock jeep vss is 8 pulse, however I can not find exactly what kind of signal it actually outputs.
The power wire to the vss come straight from the ECM. The same power wire powers the stock crankshaft and camshaft position sensors, and the vss.
The ecm pinout calls that wire a 8 volt refrence, but the fsm also shows to check for atleast 5 volts at the vss plug.
Only reason I need to keep the stock vss is for my spedometer. I dont know what type of signal the jeep vss outputs, and I dont know if any other type of vss could run the jeep speedo. Worst comes to worst, I can just piggyback the jeep vss on a compatable "passthrough" vss.

[RobertISaar]

grab a multimeter, set to DC volts, watch the reading as you slowly rotate the wheels/driveshaft. if it goes signficantly positive to signficantly negative, you can use it directly with the GM ECM. if it goes from positive to ~0 volts, then you can run a capacitor in series with the GM ECM and it will work.

[JeepsAndGuns]

I will have to give that a try. Hopefully my cheapie craftsman multimeter is fast enough/up to the task.

[RobertISaar]

keep in mind you'll need to get these readings with the unit powered up, so it may take some stripping to do so. otherwise, it should be fairly simple. some of the FWD units with a really high PPM can easily read down to 1MPH, but i couldn't guess how low you'll be able to go with this unit.

[JeepsAndGuns]

Well I couldnt figure out a way to test the one on my YJ with it still hooked up, and I didnt want to poke a hole in my wire with the tip of my tester. But I did score one of these at the junkyard today. For $6 it was worth it, and it never hurts to have a spare. Got the pigtail too.
I set it on the bench and hook it to a 9 volt battery, set my multimeter to vdc and started slowing spinning it. It would go from 0 volts then jump up to around 1.68-1.69 volts, then back to 0.
So is it useable? Tell me more about this capacitor if I can use this.

[RobertISaar]

assuming it's not directly usable(meaning only goes from 0 to positive voltage), then this will create an A/C signal(thereby providing the zero crossing signal the ECM wants to see) out of a 0-9 volt(in your case) signal.

i've done this with 12 volts on my testbench and it works great, down to ridiculously low MPH.

http://i.imgur.com/w6lcm.png

the actual size of capacitor needed is pretty open... i used a .01uF ceramic cap, the larger you go, the longer it will take to make a stable A/C signal, so ideally, the smaller, the better, as long as it can handle the current and isn't polarized.

also, not sure if you're hooking directly to the PCM or a DRAC or what, i just generalized the name.

[EagleMark]

Hey Robert, why don't you build some of these VSS simulators for our benches?
http://lukeskaff.com/?page_id=305

[RobertISaar]

name your price and requirements?

VSS sim is easily done with a simple 555 circuit and a potentiometer to adjust speed.... price on the parts is extremely cheap, it's assembly time that can take a while if you don't have etched PCBs laying around... i do all mine on prototyping board. MAF, RPM and a couple of other signals can be simulated the same way.

EDIT: okay, i see what you mean in the link now.... still probably really easily, but i'll look into it.

[Six_Shooter]

Hey Robert, why don't you build some of these VSS simulators for our benches?
http://lukeskaff.com/?page_id=305

Interesting, I'll have to study that later, in more detail.

I plan to buy a TransStim from DIYAutotune, to add VSS and E-trans testing abilities to my test bench. http://www.diyautotune.com/catalog/transstim-pcb-p-494.html

[RobertISaar]

total cost for 4046 ICs: $.70
total cost for 7404 IC: $.18

so it basically costs $1, plus pots(another ~$1 or so), plus a couple of resistors and small caps (another couple cents), plus sockets and board...

literally, under $3 in parts to sim both RPM and MPH.... i may have to do this myself.

in the higher RPM and MPH ranges, a tap of the pots can be the difference of ~1000RPM or 20MPH. :laugh:

[Six_Shooter]

Yeah, I keep meaning to set up VSS with one of my breadboards. The sad part is that I basically had it set-up when I was building a VATS bypass module on a breadboard, but need parts of it for something else.

[RobertISaar]

and some more investigating, and hopefully my last off-topic post....

the 7404 will support up to 6 pulse generating signals... so you could feasibly run 6 4046 ICs making pulses for whatever reason, tie them all through a singla 7404 and have more signals than you'll ever need.

[EagleMark]

Six I was looking at that trans stim too...

Robert, what ? Why don't you just build us all a nice simulator, we will start a group buy and put you in business...

[RobertISaar]

maybe i should post pics of my bench.... :laugh:

more or less self-contained unit(minus the ATX computer power supply i have powering it and the ALDL cable connecting to the laptop), all within a radioshack project box. http://www.radioshack.com/product/index.jsp?productId=2062285 that one i think.

currently have 17 pots, 28 LEDs, 6 switches sticking out of the top, and 18 switches sticking out of the side. full powertrain simulation.

[EagleMark]

There's no way you fit all that in that little box?

[RobertISaar]

way. it's all in there, with room to spare.

8 X 6 X 3".

if i had to do it all over again, i would actually mount stuff on the bottomside and make the top a removable lid, rather than how i have it now with almost everything mounted to the lid.... makes it a pain to open up.

[JeepsAndGuns]

Actually the signal was 0-1.68 volts, not 0-9. I need to unplug the one on my wrangler and measure how many actual volts its sending to it. ECM pinouts says 8 volt, but the test in the fsm say to check for atleast 5 volts.
The stock signal wire Y's off and one goes to the stock speedo, while the other goes to the ecm. I would only add a drac/buffer/whatever if I have to, otherwise I would hook right to the pcm (with your capacitor). Whatever I do, it will be between the Y and the ecm, as I need the vss sending the stock signal to the speedo for it to work.

[RobertISaar]

if i had to guess, i would say signal magnitude is proportional to the speed of the VSS... so at higher speeds, you'll see closer to 9 volts.

[JeepsAndGuns]

Ok, checked, and I get 9.56 volts key on, engine off, and 9.57 engine running. This is just what the ecm is sending to the sensor to power it, not what the sensor is sending back to ecm.

So is it typical for hall effect sensors to vary voltage as they speed up? I am kinda dumb on sensor signals and differences. If it does, will it still work? If worse comes to worse, I think I know a way I can run the stock vss and a JTR passthrough vss.

[gregs78cam]

Hey Robert, why don't you build some of these VSS simulators for our benches?
http://lukeskaff.com/?page_id=305

It works pretty well. RPM and VSS in one unit.

http://www.gearhead-efi.com/Fuel-Injection/attachment.php?attachmentid=2602&d=1340062904

[RobertISaar]

So is it typical for hall effect sensors to vary voltage as they speed up? I am kinda dumb on sensor signals and differences. If it does, will it still work? If worse comes to worse, I think I know a way I can run the stock vss and a JTR passthrough vss.

that's how it works with the magnetic ones, at least.... can produce up to 100 volts AC.