Trouble understanding Tacoma Instrument Clusters VSS Input/output

Hello everybody.

I performed the Tacoma 3.4L conversion into my 1988 Pickup, and all is great so far except for one last detail, the VSS Input (SP1) to the ECM.

The reason I'm asking is I have a set of custom gauges that is NOT Tacoma but are 2004 Carolla (they were what was available when I started the conversion) and they don't have a source from the gauges to the ECM similar to Tacoma.

Can one just tap the pulse from the VSS circuit that does go to the Speedo and provide input to the ECM?

Do I even need a SP1 signal to the ECU if the 1988 Pickup truck is a Manual with standard (non-ABS) brakes?

I'm trying to understand the magic that occurs inside the speedometer cluster regarding the way the combo meter "converts" the 4-wave pulse into a more refined waveform. I have attached the 2001 Toyota Tacoma (the year/make/model of the donor) explanation here in this thread below. (I apologize if this topic has been addressed before as I wasn't able to find anything.)

Anyone with an explanation or diagram/ circuit would greatly be appreciated...thanks in advance.

 

Maybe I missed it, but why are you not using your stock instrument cluster? Why switch to a Corolla?

 

My understanding is that the 1st Gen trucks and the 2nd Gen trucks operate essentially the same.
The manual trucks go from VSS to Combination Meter to ECU.

The ECU signal doesn’t have to be there for the combination meter to work.
I would think, as long as the combination meter from the Corolla uses the same square wave pattern, it would work.
You will still have a P0500 code, even if the speedometer works.

@Dm93 captured the signals out of the speed sensors and out of the combination meter.
They looked identical. So far, no one has bypassed the combo meter to the ECU to see if the signal is “clean enough”.

 

Yea here is the 2nd gen vehicle speed signal, they are essentially the same.
I don't see why you couldn't tap the PCM speed circuit into the same source as the speedometer.
Vehicle Speed Signal Input & Output (aprox 0-5-0 mph)

 

This is all great stuff. Thank you all for your posts.

The reason I went with the Corolla gauge set was for the fit into the smaller foot print of the 1988 dash space. The 3.4L requires a digital input verses the analog 1988 gauge set. The 2004 Corolla gauge set came with all the needs I was looking for and they're digital not requiring the traditional speed cable.

I was thinking of tapping into the Junction Block 3 where the VSS ties together (input from the VSS transmission sender and out to the speedometer) and there are two additional spaces on the same tie. I could share one of these ties with this VSS circuit and send the signal also to the ECU, thus sharing the transmission VSS signal to both the speedometer and the ECU.

I didn't want to tie the three parts together if there was some sort of difference that could cause damage to the ECU.

The reply with the scope image helps a great deal.

 

Do you have the diagrams for the Corolla meter?
If not, I can see what I can find.

The year the model would be nice if you know it.

 

I actually do have the 2004 Corolla instrument diagram abs used it to rewire the cluster. I've rewired the connectors to suit the Tacoma harness, and fitted the cluster into the space of the old 1988 cluster so it appears factory looking. Turned out pretty cool.

I do have a small concern regarding the tach that I'll post later...I think it reads double the actual value but I'm not too sorting this issue out yet. (I did change the resistor value on the circuit board to the 10K ohm resistor and it works but I think it's double the actually speed of the engine.)