I have always wanted to make my ECM control the second cooling fan in my engine. After reading the sticky post about adding a WB O2 into one of the spare inputs on the ECM I figure it is possible to have the ECM ground a pin at a certain temperature if a little code is added. I would hook this pin up to the second fan control relay.
I currently use the 730 ECM.

Here are my questions:
- Are there any spare pins that the ECM has the control to ground?
- I have never disassembled and recompiled source code before; I assume I am going to have to do this right?

 

I am not able to reply fully, but I am currently attempting the same thing.

At this time, I have changed my Intake and since I no longer will be using the EGR, I will use that lead.

But, as for "spares" I think there may be a few on the 7730. I've been studying the pinouts for the V6 version and I noticed that the V6s use a couple of inputs and outputs that are not on the V8s. So, it should be no problem incorporating those drivers with the $8D code since the "hardware" is already there.

Also, with the V8s, if you have an auto, you can use the pinout for the Shift Light OR if you have a Manual, you could use the pinout for the TCC.

Good luck on the Source Code. Please read all the stickies we have about relating to Source Code, Programming plus a few others. RBob has graciously provided his S19 Converter to the people of Thirdgen and in one of those "stickies" regarding source code, there is links and downloads to everything you need.

I currently am not able to provide copies of those, but if you look through the stickies you will find them.

Also, for "quick code changes", you can also "bit twiddle". I do this occasionally for changing a "test" condition like from "Greater than" to "Not Less Than". I found that if you "twiddle" the hex code and then "read the bin" with TunerCat that TunerCat will automatically fix the Check Sum for you. Before I actually got the Asembler etc, I did all my code changes by "bit twiddles".

 

This might help you but it might just confuse you.
I've got a crappier ecm, the 8746 for TBI. I don't have EGR and my air pump system is gone. I also am getting rid of the a/c. My extra pinouts are as follows; can purge solinoid, egr, air diverter valve, and air select valve. There is also an a/c on input that I could use for something strange. When I say strange...just imagine flames coming out of the tailpipes .
My eprom doesn't have much if any room for extra source code so I have to remove all the egr, air diverter and a/c code to make room for some things I want to do. My "want" list includes having a shift light along with the tcc control, rev limiter along with the mph cut off (super valet mode ), count miles driven along with time to tell me when to change oil or a ruff 1/4 mile estimate, wide band o2 input along with some code to keep the car in closed loop under WOT (this is going to be tricky), and last but not least, fan temp/speed control.
It's a lot of work and the only thing that's holding me back right now is finding some stupid crappy wiring harnesses so I can finish my test bench.

 

I have found a TON in the local wrecking yards. In fact, I have found the early 90s 3.1 SD V6s wiring harness is the CLOSEST to an F-body. You will have to swap a couple of pins (because the V6s do have a few minor differences) but it is the closest that can be readily adapted to the SD TPI V8s.

As for the ECM ends, again, most wrecking yards where I live don't give two hoots about those. I have cut a number of the connectors off, and the guy didn't even charge me for them.

Just learn how to "pick the lock" on the connector pin and you are all set. Again, grab a couple of connectors with wires attached and play with it. I "ripped" the first wire/pin out just to see how it looked so I could figure out how to "pick it".

 

When at all possible you want to lessen the thermal loading on the ecm, not increase it.

IMO, adding a fan or addition fan load to the ecm isn't a good idea.

I like using a GN radiator fan switch, and then adding a manual override.

 

Well if the electrical engineers who made the ECM put the extra pins there with the option of having the ECM ground them why would the ECM not be able to handle it? Don’t some cars that use the 730 use these extra pins? Wouldn’t they not have put the extra pin outs on the ECM if they felt it may be a problem?

I am not a electrical engineer and I am not claming that it will work at all I am just trying to figure out why they would design the ECM to control these extra outputs if there would be a problem using them.

Grumpy, you know a great deal more them me when it comes to this so I guess I will just have to take your word for it. Would it help if I added thermal compound between the metal “heat sink” inside the ECM that contacts the ECM frame to cool things down?