Brucato acu

[Wild Bill]

I have a 01 SVS Drag that came with a A-13 box, I was having problems and sent it to Brucato to test. They said it had some problems which I am skeptical about, so I got an ACU. Now my problem, it has a flat spot between 6-7000 rpm it accelerates hard until it gets there then there is an almost imperceptible taper off of acceleration. I have tried to adjust the midrange pot a little but nothing changes. I talked to Brucato and they said they could check it out or put another curve in it, I figured they put the A-13 curve in it. I am not well versed enough to know what curve it needs other than the original Has anyone herd of this problem? Itis a little unsettling when it does this. The piston tops look ok.

[Jim Speros]

I have installed a number of them without issue. I suggest you give them the chance to make it right.

[CI STV]

Are you sure its not an ignition issue? Does it go flat in that rpm range and then run fine above that rpm?
I have the Brucato tuning cable/tool and a bunch of curves, but I’m too afraid to mess with it too much.
But my motor (ported Drag with a Diamond manifold and 17cc heads) runs fine with an A13 curve in my ACU, so I can’t see a Drag motor going flat in midrange with an A13 curve in the box.
I have noticed that when I’m loading a tune in the box it can sometimes glitch and some cells end up with whacked numbers or blank, which is why I read every curve after I load it into the ACU.
Maybe something like that could’ve happened when they loaded the tune?
BTW: I only bought the tool so I could see what tune Diamond had in my ACU and it was a standard A-13 curve with the only modifications being a 10K limiter and the enrichment on the 2 bottom pairs of cylinders being slightly lean than the stock Merc A13 tune.

[rjdubiel]

I have a 01 SVS Drag that came with a A-13 box, I was having problems and sent it to Brucato to test. They said it had some problems which I am skeptical about, so I got an ACU. Now my problem, it has a flat spot between 6-7000 rpm it accelerates hard until it gets there then there is an almost imperceptible taper off of acceleration. I have tried to adjust the midrange pot a little but nothing changes. I talked to Brucato and they said they could check it out or put another curve in it, I figured they put the A-13 curve in it. I am not well versed enough to know what curve it needs other than the original Has anyone herd of this problem? Itis a little unsettling when it does this. The piston tops look ok.

What is your compression? We have found that more compression (to stay on pump gas) will really make the brucato run better if you dont mess with the curve. If you dont try to get 145-150ish compression then you have to start leaning out the curve but be careful. The mid range is not a spot to pull fuel out if you river run at all.

[Wild Bill]

I will certainly work with them; ignition problems started me down this rabbit hole. It turned out to be switch boxes. it has new stater, trigger, switch boxes, rectifier. Compression is stock 170-180 psi. I put the stock box back on and am going to try it tomorrow or Thursday. It is just a slight drop of acceleration for about 1000 rpm then picks up again. The thing runs great other than that except it doesn't get the primer shot of the old box which makes it harder to start. I don't know how that will work on those 40-degree days.

[Wild Bill]

Well, the wind finally quit blowing so hard and I went out and tested the old bad Mercury A-13. Guess what, the engine ran like its old happy self. Started right up and no flat spot between 6-7000 rpm, everything is right with the world again. So, I guess the ACU is going back to Brucato to let them figure out what is wrong with it. Hopefully they can figure it out. Rite know I feel like I was taken for a 1600-dollar ride. We Will se.

[PanRonnie]

Well, the wind finally quit blowing so hard and I went out and tested the old bad Mercury A-13. Guess what, the engine ran like its old happy self. Started right up and no flat spot between 6-7000 rpm, everything is right with the world again. So, I guess the ACU is going back to Brucato to let them figure out what is wrong with it. Hopefully they can figure it out. Rite know I feel like I was taken for a 1600-dollar ride. We Will se.

It would be logical that they provide you with a curve that is on the rich side and up to you to fine tune that to what you want
if they would go on the edge from the start and you end up with a piece of molten metal, you would also not be a happy camper
The brucato unit is not an out of the box solution then you need to buy factory stuff
but investing in a EGT and AFR setup would be the next step in working with the brucato

[CI STV]

Since it seems to be running fine elsewhere in the RPM range, I would bet it’s a glitch in the fuel curve.
I’ve seen that myself a couple of times, after I reload a tune, where a cell or two gets corrupted somehow and that leaves a “hole” in your fueling map whenever your RPM + MAP conditions references that cell/those cells, and then the injectors don’t get the right amount of fuel and the engine bogs or leans out until that corrupted part of the fuel map is no longer referenced.
As far as I know, Brucato only uses the Merc fuel maps for each type of motor (per Mercury’s specs) as their “base tunes” and then the end user can tweak the fueling using the potentiometers or their Steam Wheel. There are other differences between the ACU and the Merc ECUs, like the ACU doesn’t reference throttle position but uses MAP to determine what the throttle position is (pure speed density fueling).
These ECUs are the crudest/most basic of “speed density” controls, since they only control fueling (so they’re actually an “FCU”) based on MAP and the fuel graphs themselves are very basic.
In fact, if you look at the A6 (horn manifold Drag) and A13 (2001 slider Drag) fuel graphs side by side, you’ll see that the only differences in fueling is the amount of offset on the bottom pair of cylinders, as below:
IIRC, both of these fuel maps came from Brucato after I bought their tuning cable and software, so I stand to be corrected if anyone has somehow read a stock Merc fuel graph.

[CI STV]

In any event I think that if you send the ACU back to Brucato, they will figure it out and fix it. From the few times I’ve interacted with them, they seem to be decent folks to deal with.

[Wild Bill]

It sure sounds like a corrupted bit in the curve. If they can give me a little more prime and get rid of that flat spot I will be happy. I really like the idea of cleaning up the idle, those long idles tend to load it up and it has to get a breath before it takes off. I will call them Monday.

[CI STV]

It sure sounds like a corrupted bit in the curve. If they can give me a little more prime and get rid of that flat spot I will be happy. I really like the idea of cleaning up the idle, those long idles tend to load it up and it has to get a breath before it takes off. I will call them Monday.

IF it’s a corrupted or incorrect fuel map, they will easily fix that.
BTW: there’s no prime for the midrange at WOT, the Brucato ACU has 5 potentiometers, but none of those can address the middle of the curve at WOT. That would have be taken care of by changing the map, which could be disastrous if you don’t know what to tweak. I don’t know myself, so I haven’t really been brave enough to change anything in the fuel map itself, except for the fuel offset for the bottom cylinders, which I reduced by 1% above 10K rpm. The reason I did that is that my manifold doesn’t have different length runners like the Merc blue SVS slider did from factory, AND, I flow tested my injectors and put the highest flowing pair on the bottom cylinders.
For ease of reference, here’s the ACU setup and basic tuning instructions:

[CI STV]

Also note that you can lean out the idle, but that might make it hard to start in colder conditions (which I will never have to worry about myself, since it’s always hot here).
With the ACU, since it fattens the pulse width up to deliver more fuel for cold start enrichment, rather than pulse the injectors using the “choke” circuit, like the Merc ECUs do, you also need to connect the yellow with red stripe to the starter solenoid so that it will tell the ACU when you’re cranking the motor. My motor struggled to start cold before I figured that out, thanks to some advice I got from folks on these forums.
This wire: