fire350tpi

Was there a pulse change in the vss 86-89 vs 90-92?

i have heard it was 2k to 4k, thanks!

fire350tpi

No Ideas guys?

Grim Reaper

You are correct. The VSS in MAF cars was 2000 ppm and the VSS in SD cars is 4000 ppms. If a person converts from MAF to SD, they can reuse the VSS by setting a switch in the SD eprom to use 2000 ppms instead of 4000 ppms.

Comp788

As a rule of thumb a cable driven VSS is 2000 PPM and electronic ones are 4000 PPM.

Grim Reaper

If you have a cable driven speedo, you can be assured that the VSS is 2000ppm.

However, because 1989, I tend to use MAF vs SD because in 1989 they used electronic speedos but still used the 2000ppm because they also used the '165 ECM. The "speedo buffer" was located externally for the 165 ECM while it was "internal" for the 730 ECM. But, I admit it's been a long time since I reviewed this.

And I have no idea about TBIs.

fire350tpi

Well thats good that i know now ( still havent installed it have it sitting at work)

is there any good wiring diagrams of the buffer box - to - vss because i think the previous owner hacked it up

also i had heard that the VSS itself was always 4k but the 165's external buffer turned it to a 2k pulse any idea?

Other wise i can just get a quick chip burned for 4k and go for a 89 maf code anyhow while im at it

Grim Reaper

You can make a 2000ppm VSS work in an SD eprom, but I don't believe the 89 MAF eproms have a switch to make a 4000ppm VSS work on them.

fire350tpi

that sucks, Because i cant find a 86-89 sensor for a t-5 for the life of me, lucky i even found the 90-92 one.

And i certainly dont wanna pay 300 bucks for the Signal change board or w/e it is

Grim Reaper

I have difficulty believing you cannot buy a 2000ppm VSS from GM or a Parts Store. But if you are, go the the "online junkyard" in the Parts For Sale forum board. Or send a PM to RCAR7395.

Those VSS were used on a large variety of cars that used the 700R4.

RBob

iTrader: (1)

I'm not sure which ECM you are using, as that helps define what hardware is required for the VSS.

The VSS sensors that go into the trans are all 4 pole magnetic units (4000 PPM).

The VSS sensors that go into the speedo cluster are all 2 pole optical units (2000 PPM).

The MAF TPI & SD TBI ECMs require a 2000 PPM input. These ECMs were used with both the optical VSS and the magnetic VSS. When used with a magnetic VSS a 4-OUT Buffer box was also used. This box buffered the VSS signal and presented it to the cruise, ECM, and speedo (when required). It generates the 2000 PPM signal for the ECM to use.

The SD TPI & SD MPFI ECMs (the '7730) require the 4000 PPM VSS signal. The ECM acts as the 4-OUT Buffer and sends pulse streams to the speedo & cruise. And uses the signal internally.

The optical VSS unit is a digital output.

The magnetic VSS unit is an A/C signal output.

The 4-OUT Buffer converts the A/C VSS signal to digital signals.

RBob.

fire350tpi

Well, 700r4 sure i grabbed that but it is to large and i need a specific one for the T-5 and for some reason, Autozone, Standard motor parts all dont have it anymore ( d9e ) Code, Now of course i didnt try ac delco but...

I snagged a used one of a t-5 on ebay for cheap money and was hoping it would work.. According to Rbob i think itll do nicely as long as the buffer box isnt hacked

Artic-Trans am

hi
You look like you are up to date on this VSS tech!
I have T/A with digital speedo. Now I have changed the trans from a 700R4 to a 4L60E (with a TCI controller) the new trans have a magnetic VSS and the 700R4 have a optical VSS.
As you might know I can't run the VSS signal to both TCU and speedo! so I did try to use the buffer box that have two output with 2000 pulses and two output with 4000 pulses.
But this ended with faulty readings for both spedo and TCU.
At the moument I run only with signals to TCU. Do you have any idea how to fix this so I can use the speedo too?
and why did not the speedo read the signals from the 4-out buffer? It should convert the AC signal to digital pulses! I did belive also the TCI box could read digital pulses, but it look like it does not!
Have anyone try this?

69firemaro

I am running an 87 TPI with a TH400 and a 96 firebird dash unit in a 69. What do I need to make my speedo work? I am told that late 80's early 90's chevy trucks with th400's used vss.

Dyno Don

iTrader: (7)

Those are two different animals, one is a magnetic generator (700R4) the other is a reluctor (4L60E) they do not interchange. They produce different signals.
----------
The late truck unit might work for your speedo but the TPI ECM won't understand it's signal.

69firemaro

What does the vss signal tell the ecm to do? Is it only for the purposes of locking up the torque converter? If so I don't have that with the th400. Can it be eliminated? What else does the vss signal do in the ecm?

Artic-Trans am

ok.. so is there any solution, so I can get the speedo to work?
Or do I have to start looking for a new transmission controller (TCU) that have a digital pulse output. I do belive that is what the speedo need. If the "4-out" buffer give digital pulses. I did not check this. (I know I should)!
But if Mr. "RBob" is correct it is so.

I can get a controller from HGM COMPUSHIFT that have the output. But it is expensive. Is there any other solutions?
I thank you for clearing out my problem "Dyno Don"

to you "69firemaro": I do belive it is only for the lock up. so if you use Th400 then ECM don't need the VSS,
exept: if you'r ECM is controlling your cruise control, or do any speed recording(aftermarked ECM)

Dyno Don

iTrader: (7)

The ECM needs to know the vehicle is moving to correctly make adjustments, besides the TC. lockup.

Dyno Don

iTrader: (7)

I just looked at the 4L60E I have, and it looks like you could use the early VSS (mounting looks the same) but not sure if it would be compatable with the TCU.

Artic-Trans am

I did try. the housing is the same, but the gear wheel on the tail shaft is diffrent. on the 700R4 the tooth are like this // and on the 4L60 it is ||. Mounting is the same.

So I have to change the gear on the shaft, then it might work. If my TCU can handle the signals.
I have never tryed to change that gear inside the tail shaft, is it possible? easy?

Dyno Don

iTrader: (7)

Yes, the steel one you have is a little tight but it will knock off.
The one you will need is plastic and requires a metal clip that fits into a hole in the shaft. You will need the correct gears depending on your rear end ratio.

Artic-Trans am

oki. I was not sure if I would get the "steel one" off. The other VSS sensor I have. so Iwill try to change this when I got time. Right now I have a lot off tuning to do on the stelth ram and computer, before "sreet legal" next weekend. Have some problems geting the RPM's up when accelerate under hevy load.... BAD TAKE OFF...
Thank you very much Dyno Don! you have helped me much here.

69firemaro

What else does the vss tell the ecm?