The way I always understood how to get a piggyback to work with the stock ecu was to send an artificial rpm signal to the ecu to trick it into thinking its at WOT so it runs in open loop and the piggyback settings would hold and not get undone by the ecu.
However I spoke with Church today and asked if the ecu needed to be tricked and he said no. It would run in closed loop most of the time. He seemed busy so I didn't ask him to elaborate on that and honestly if he did, I probably wouldn't have understood anyways.
So is my understanding completely wrong? If it is, how does the ecu running in closed loop not undo the EMU's settings by countering them?

There's another tuner around me that said he can tune the EMU also, but seeing how unliked it is by so many tuners, presumably due to lack of familiarity, my concern is he may not familiar with those intricacies to make the EMU work to it's full potential. But he doesn't seem to dislike it at all.

 

While in closed loop, any settings you do with the EMU, the ECU will fight it. If you have large fuel corrections in CL that you want to correct, you can use the EMU to bring those in check, but you'll also need to account for temperature corrections (which is pretty easy) under heat soak conditions. IE: I had large fuel corrections at idle. I removed fuel to bring them within +/- 5% and then after a few back to back AutoX runs, the car became heat soaked and it was running lean at idle. I corrected this with IAT vs. fuel so that it would add fuel as the temperatures started coming up which is similar to what you would do with any other ECU (add/remove fuel based of temperature).

Ideally, all the changes you're going to do with the EMU revolve around the ECU being in open loop, which is where your gain is going to be anyway. You can reconfigure a harness to allow you to force open loop sooner, if you're fighting CL conditions in boost. The directions on here are in the Greddy E-manage 101 thread, IIRC. It's pretty easy to figure out and any tuner should not have a problem with it. If you install it and not change anything on the map, you'll be running a completely stock program. If you make changes in CL, your ECU will try to combat these (fuel). If you make changes in OL, you'll see your changes make a big difference in the way your car runs.

 

That's what I thought which is why I was very confused after my slow brain processed what Church said. I guess I need to call him again to have him elaborate on the closed loop operation he mentioned.

 

What do you want to know? It can be answered here.

 

Thanks Jason. My main concern at this point is that my local tuner knows how to extract all the potential from the EMU. He seems very confident and said he's done 40 s2ks using the EMU, but his statement that the ecu would run closed loop has me confused. I'm 95% sure I'm going to get your EMU though.

 

The ECU will behave as it normally would for the most part. It will be aiming for the same targets in CL and will be clueless, for the most part, as to what is happening in OL as it will be ignoring what fuel is actually doing.

So, unless you setup the harness to be able to manipulate the throttle position, via the EMU, it will go in and out of CL as normal.

 

the str guys in the r&c forum have been playing with it. read there threads

 

all you need to do is change the throttle output to edu to over 73% and it will be in open loop constantly, or at least wherever you set that throttle in the map. use aux.. output and open that map, you can set throttle percentage vs whatever and however works for your setup if you get what i'm saying