[rfmaster]

Originally Posted by mcbassin

RF,
I am wondering if I tie truck A/C control wire(s) into the circuit that goes to the ecm for the a/c would that then control the relay to fire the a/c? What info about the truck is required to construct the harness you are talking about? Do you do this type of work? I am assuming you are a EE....is it just a hobby?

Regarding the VSS, it looks like this with the proper gear ratio and tire size would be a direct replacement:


It is pretty pricey at a $101 plus the shipping. I wonder if any of the early 90s
burb or blazer instrument panel with necessary wiring would solve the speedo issue? As always, thanks for the help!
Mike

Mike

The four pulse unit will not work very well with your car ECM. Assuming that 4 pulse VSS is a square pulse (On-OFF vs. AC) type will cause ECM to detect twice the actual speed and depending on ECM calibration fuel cut off will occur at much lower actual speed (around 55 MPH vs. 110 MPH). Not good.

Early 90's trucks & SUVs used the electronic vehicle speed sensor and DRAC module for electronic speedometer. That system is a kludgee mess as DRAC provided different frequency pulse signal to various sub systems (ECM, Spedo, Anti-lock brake computer). This simplest solution is to get 2000ppm inline VSS and non electronic speedometer gear housing.

Yes, I am EE - non automotive, but I have a lot of respect for auto boys since their environmental requirements exceed industrial ratings and probably on the par with mil specs.

AC wiring requires a bit of combining of truck controls with your new ECM.

//RF