I am working on making a circuit to simulate the flex fuel sensor output (0-5V square wave ~50 to 150 Hz) to utilize the additional timing / fuel tables in the L59 OS's. I have a board made, and tried to see if I could see it using EFI Live. I started with a 2000 Blazer 0411 PCM (happened to have it laying around). I started up the Scan tool .... neither of the flex fuel PID's showed up. Makes sense, the OS in there isn't looking for it

Flashed a 2002 L59 (5.3L) Silverado tune into the PCM ... changed the VIN # to make what is in the OS ... then started up the scan tool. Validated the PIDs and low and be hold, there are the flex fuel PID's .... yeah!

Now, I tried to plug in a square wave generator to the flex fuel sensor input wire (C1 (blue) pin 56) to see if I could watch it on the scan tool. Didn't work.

I am using a bench harness (not a full wiring harness), so I thought maybe I didn't have a ground hooked up. LS1B PCM bench harness only hooks up a couple of ground wires. I grabbed all of the grounds that I could find (ECT, TPS, MAP, etc...) and hooked them up to the same ground as my bench harness..... still didn't work. I verified that the square wave generator is putting out a signal by hooking it up to an oscilloscope, but the PCM doesn't show anything.

Has anyone used the flex fuel PID's on a 512 kB 0411 PCM??? Were the L59 PCM's different than the rest of the 0411 PCM's? I am actually planning on using this on a 1 MB PCM, but I don't have the vehicle available to play with. That is why I was hoping to get this working on my bench setup 1st.