An episode in the life of living with a TurboTweak ECU-GN

Last year I installed a TurboTweak ECU-GN in my Grand National. I had really reached the limit of what could be done with the original ECM. Even with a Powerlogger added on, I didn’t have enough inputs for all the sensors I needed. And mailing chips back and forth to deal with changes to the car was getting tedious.

I never did a full write-up on the ECU-GN install last year when I got it. Mostly because when I put it in, I was pressed for time and didn’t take any pictures. So I’ll summarize it here.

The TurboTweak ECU-GN is a plug and play standalone engine control module replacement for the Grand National and Turbo Trans Am. It uses the same MS3Pro (Megasquirt) core hardware you find in DIYAutotune’s version of their DIYPnP for the Buicks, but with a few added features:

  1. Additional inputs for sensors
  2. ScanMaster/ScanMaster-G compatible datastream output on the ALDL pin
  3. Anti-theft available
  4. A pretty blue anodized case with blinky lights
  5. A pre-loaded tune customized to your car by Eric Marshall. If you have a TurboTweak chip already and it works well in your car, he has all the data he needs to load a working tune on your new ECU-GN.
  6. A built-in 8GB SD card and realtime clock for on-board logging

The ECU-GN costs a bit more than the DIYAutotune unit, but the additional inputs and Eric’s service made the difference for me. He’s been responsive, even on weekends when I’m at the track and need some help. Not that I’ve needed a lot of help. I think I bugged him about a timing map change once, and had him consult on a VE autotune map in the upper RPM ranges after a track session. These are not situations the normal consumer of this product is going to be in.

When I got it, the car started on the first turn of the key. If you’ve dealt with FAST XFI or the Holley system on these cars, you’ll understand what a big deal that is. Auto-tuning the VE map took just two pulls on a deserted road. Since then, I’ve added enough sensors to enable traction control, launch control, an additional warning light in the dash to tell me if the transmission gets too hot, and various tweaks to make it run better.

The rest of this article is about a tweak to the VE map.

So, yes, this ECM had auto-tuning capability and closed loop based off a wideband O2 reading. The out-of-the-box tune from Eric was close, and the auto-tuning dialed it the rest of the way in.


Unless you take the car to a shop with a loaded dyno and run the car through every location in the VE map and tune it all scientifically, you’re going to run into situations where you need to tweak something. This was one of those days.

You see, coming back from a cruise-in tonight, I felt the car stumble on the highway. I was going about 70mph on level ground with a constant throttle. I glanced at the ScanMaster-G and managed to catch the AFR dropping to 7.4:1 for a moment. It’s not supposed to do that.

So, once I got home, I pulled the logs. Once dragging the logs into MegaLogViewer along with the current tune and searching for the lowest AFR reading (which happened to be that 7.4 I saw), I quickly found the spot where the AFR dipped:

If you look at the VE table on the right, you’ll notice it was right on the border between those cells at 45Kpa and at 40kpa, and there’s a dip in VE values going from 45 to 40kpa. That part of the map hadn’t been tuned. This is one of those things you deal with when living with an aftermarket ECM. The car just hadn’t spent much time cruising on the highway since I put the ECU-GN in, so I’d never hit this part of the map before. The values were wrong, and it went rich and stumbled.

So let’s fix it.

In MegaLogViewer, on the right side, pull over the panel that shows the VE tables. They might be blank. Just hit the “open tune” button and browse to your TunerStudio folder and load “CurrentTune.msq”. This will be the last tune saved off of your ECM.

Once it’s loaded, just hit “Run VE Analyze”. In my case, I had everything at 40Kpa and below blocked off so autotune wouldn’t mess with it. That’s because one time when I tuned the whole map, it had messed with those areas to the point where the injectors were getting shut off on decel. That’s not what you want on these engines. If you’re coming down from beating on it, you want the injector putting fuel in the cylinders at all times. At low MAP values/low load, the fuel acts to remove heat from the cylinder, which can extend the life of your pistons. This is also the part of the map you screw with if you want it to spit flames on decel (don’t make it do that, it’s hard on the turbocharger).

But in this case, I unlocked a few cells at 40Kpa near where my little stumble had happened. Locking/Unlocking cells is available in a right-click menu over the VE table. Hit VE analyze, and it does its thing.

Voila! New tuned table based on log readings. You can see here the cells where it stumbled changed quite a bit. This should take care of the stumble in this part of the VE map. Save this as a new MSQ file, go connect to the car, load the MSQ in TunerStudio, and burn it to the ECM. Boom. Done.

Other instances when I’ve had to do this? Race tracks. My little auto-tune pull on the deserted road only took me up to about 70mph. When I got to NCM last summer and ran the car up near 130, I noticed the AFRs were running ~9.8:1. Way rich. So rich it was bogging. So the first thing I did in the pits after the first session was pull the logs and run the analyzer on those high-speed areas. The next session, those AFRs were up around 10.9:1 and it ran MUCH better.

So there you have it, how to tweak your ECU-GN tune when you find a spot in the VE map that’s not quit right. If you have the DIYAutotune model, the procedure is exactly the same.






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