On my 91 454 TBI'd truck there are two coolant temp senders in the heads (one in each), both with what look to be green wires on them. There is a coolant temp guage (and no light), and you the CTS with it's yel/blk is on the intake. None of my wiring diagrams give any hint of what the second one might be. Anyone have an answer?.

Also, does anyone know for sure the PPM output of the DRAC (and where it is)?.

TIA

 

Doesn't it run the extra electric cooling fan?

 

on the 2 temp senders, i don't know. maybe the second sending unit is for a towing package?

chevy used 2 different setups on the trucks, on the first 1 the VSS signal went to the dash where they put the DRAC at & then to everything else. the other setup used an external DRAC, i think you will have the extenal setup which i think is the better system.

i think the trucks use 128000 A/C pulses per mile output from the speed sensor to the DRAC, the DRAC converts that into a 2000 & a 4000 pulse per mile square wave, it seems like there are 2 or 3 4000 pulse outputs on the DRAC. i believe the 4000 goes to the ECM, ABS, & dash with the 2000 for cruise control.

if you have the second DRAC system, you should find the DRAC in a small white box right around the glove box area.
i can post a picture of a DRAC if you want 1.

you can speed up or slow down the outputs by changing the jumpers inside the DRAC.

 

Ahh, could be.
I thought that ran off of the HVAC controller.
With that in mind, now, I can expect a result from tinkering.
Thanks.

 

So one is behind the dash, and the other by the glove box?.
I know what it looks like, was just curious about it's outputs, the 2,000 PPM is what I was hoping for...

Thanks

 

That is not exactly correct. The DRAC takes the 40 pulse per revolution VSS signal and outputs several signals to the various components. It outputs a buffered 40 PPR signal to the PCM for a tranny speed signal. Next, it puts out a 128,000 PPM signal to the ABS if so equiped. Next it puts out a 4,000 PPM signal to the cruise control. And lastly, it puts out two 2,000 PPM signals. One for the speedo and one to the ECM for vehicle speed. Check out a file called DRAC2.pdf at the diy-efi FTP site. It has diagrams and formulas for calibtating a DRAC. HTH

 

Finally, a question I can answer! Yippee!

The big block trucks, at least on the SS's, have 3 temp sensors. The one in the intake goes to the ECM. The other two, one in each head, go to the Temp gauge and the aux fan.

I think the passenger side sensor is for the aux fan, but I could have it backwards. Unplug the drivers side and see if the dash reading goes out.

Factory setting for the aux fan was pretty high. 220 or 230 or so, CRS acting up again.

Hope this helps.