Hello all,

I am working on a fuel injection project and had a quick question concerning customizing a TBI ECM. Taking into account all of my project requirements I will be utilizing the 1228746 ECM found on the 1989 to 1992 F cars with the V8-305 engine. This set-up meets all of my needs and I am pleased with how my project has progressed so far. There is one area that came up over the weekend I had a question on.

I finished putting together the wiring schematic for my project this weekend. During this process I noticed that the 1228746 ECM does not have an output for a WOT (wide open throttle) signal for the air conditioning compressor cut-out. The 1228746 ECM does have an input for when the air conditioning system is functioning (and I am assuming that this is to raise the idle speed to prevent the engine from stalling at idle).

Here is my question, the 1228746 ECM does have a few pin-outs that are not utilized (at least according to the documentation I have found, pin-outs A2, B4, B9, B11, B12, D3, D8, D9, D10, D11, D12, D13). Is it possible to re-program the 1228746 ECM to provide an output on one of the before-mentioned pin-outs for when a WOT condition is achieved? This could take the form of providing a ground path I can use to trigger a relay, much like the logic used for triggering various solenoids in the 1228746 ECM (i.e. pin-outs A3, A4, C1, C2) or providing control voltage to trigger a relay much like the logic used for triggering the fuel pump relay (i.e. pin-out A1). FYI I cannot re-purpose any existing mapped pin-outs in the 1228746 ECM as all existing pin-outs are interfaced to various engine components.

Please let me know your thoughts if my question is doable. Thanks in advance for any input and help with my project.

-Andy

 

A non-computer-tuning bonehead like me would put a momentary switch somewhere on the throttle linkage. Could be power or ground, depending on how it's wired--whichever worked better for the application.

When you go to WFO, the linkage taps the momentary switch, giving you your + or - as needed.

 

The pin A2 output is commonly used for A/C control on these C3 ECMs. It provides a ground to activate a relay that runs the compressor clutch. As for changing the ECM code, the PROM holds all of the calibration data and a little code. The remaining code is in masked ROM (in 2 chips soldered to the board).

What you want to do in modifying the code can be done. Just takes a little finesse.

Quick and easy is what Schurkey posted.

RBob.

 

Thank you both Schurkey and RBob for the insight and solutions for my problem.

I am at a point where it makes the most sense to modify the ECM as the solution. FYI I have already completed fabricating the throttle linkage for my project and have now just started working on preparing the ECM. Also, I am planning on re-capping the ECM and also replacing the fuel injector drivers as well. I am also starting to build my new wiring harness.

As I will be working on the ECM anyway, I do want to modify my ECM to use the A2 pin to control the A/C compressor as RBob has suggested. I have experience in working with soldering PCBs and some scripting experience as well, however I believe that modifying code on ROM chips is a bit outside of my skill set. RBob, do you have any suggestions on how I can proceed on modifying the code in my ECM? If you would like to discuss this via a PM please let me know. Thanks.

-Andy