Heres one for thought.......

I have converted a 93 GMC truck ECM to run on a boat. This ECM has the integrated transmission controls within the ECM. Most are disabled. The system runs fine, and I am happy with all settings, except.....

Before EFI, idle was approx 700 - 800 rpm, and when you put the boat in gear, idle would go down approx 100-125 rpm due to load. With the new system, IAC compensates and keeps the idle at 825 regardless of in gear or not.....I am flying through the marina and getting dirty looks.

I have found the IDLE IN GEAR matrix, and changed the numbers that I want. Its burned and ready to go. The problem I have is how do I trick the ECM into thinking it is in gear? Since the transmission controls are within the ECM on this one, I would need to ground something or energize, but I dont see anything that would work..... Shift Sol A, Shift Sol B, Mode A, B, C. do these have any relavence?

Once I have a way to trick it, I will wire in a way that when the boat is in gear, it will revert to these settings.

Thanks in advance,

fallflight

 

You would have found it easier to start with a $E6 manual transmission bin file for this project. You didn't say what size engine? I don't think there was one for 5.7L but there is for 4.3L and constants can be changed, VE tables etc... you could find bin files at link in my signature. It may also be possible to run a differant mask on this PCM, I am running an $OE manual bin file and mask on a 16197427 $OD PCM which are all from same family of PCMs.

825 RPM is high for a bin file I looked at for it? Warmed up should be closer to 600 RPM. You may have other issues. Like probably no O2 sensor? So would need to tune open loop idle paremeters.

One thing is boats usually run much cooler thermastats like 160 do to the cooling systems of fresh water whether enclosed or not. Trucks are higher at least 180 possibly 195... so you could still be in choke mode.

There are so many things to change in $E6 for idle it would be some trial and error.

EFI boats also usually have a ignition blip switch for when they are put into gear to momentarily stall ignitionwhen going into gear as there is no clutch or tourque converter. You could add a P/N - Drive wire here but I don't beleive this PCM has such a wire like older ECM.

HTH!

 

Thanks for the reply.

Most of your concerns below were addressed. lower cooling temp is addressed and it does have an O2 sensor. I cut my manifolds through water jacket to get O2 sensor installed correctly. I will check when I get home this weekend, as I may be incorrect on idle RPM. Either way it is too fast for "in Gear with no throttle" activity.

The transmission tells the ECM that the vehicle is in gear, correct? this way the idle doesnt force the car down the road when the operator has is foot on the brake. Does the brake play any part in this? what is the trigger? Maybe no actual trip wire per say, but something has to direct the ECM to the "Idle in Gear" matrix when on the vehicle.

We' ll get to the bottom of this.....its my last bump in the road for this project, other than this, it runs AWESOME.

Thanks,

fallflight

 

The brake wire is to unlock TCC.

The PCM does know when in gear, but manual trans does not. You could avoid all these problems by going to a manual trans bin. There are litterally 100's of things differant between the 2. IAC logic and idle is most apparent.

I don't know exactly how to solve this issue with your auto bin, but again I don't think it would be an issue with a manual trans bin.

Bigger issue is idle spark/fueling and off idle/spark fueling calculated by TPS% and VSS. You need to remove VSS from the equation somehow because you obviously don't have VSS...

I'd really like to see how you did the O2 sensor?

Your obviously recording data so you would know if it is getting hot enough to go closed loop/BLM enable. I've done a few boat conversions and always tuned them open loop, no O2 sensor as most EFI boats are or were. One aftermarket system... IIRC Holley had an O2 sensor but it was only reading from one rear cylinder.