ECOTEC ECM Tuning – Intro

Gone are the days of “burning a chip” for engine computers.  Modern Engine Control Modules (ECM’s) can now be monitored real-time and then modified based on readings done after driving down the road.  Pretty cool stuff indeed but it adds a whole new dimension to engine performance adjustments.

The factory install of the Ecotec in a Pontiac Solstice at its core consists of the engine, wiring harness, ECM and the Body Control Module (BCM).  The ECM reads and controls engine signals while the BCM controls such things as gauges, door locks, lights, etc.  In addition, the BCM supplies data used in the information center on the instrument panel showing fuel consumption, engine temp, outside temp, etc.  Furthermore, the ECM and BCM talk to each other via a digital high-speed bus integrated into the factory wiring harness.

So, one of the challenges in getting the Ecotec to run in bowtie6 was making all this work outside of the factory install.  After doing a ton of research and reading the Factory Service Manuals, we were able to figure out what wires actually control engine sensors and what goes to the BCM.  This enabled us to change the factory harness to fit our needs.  Since we did not run the factory instrument panel and did not need to control lights and such, we did not use the BCM.

A disadvantage of this approach is the lack of cruise control.  In the Ecotec the throttle body is electronically activated – there is no cable in the traditional sense.  Instead, the electronic “gas pedal” inside the car sends a signal to the ECM via a small wiring harness.  This gets accomplished by coarse and fine potentiometer readings of the throttle pedal position (Click here for my Drive by Wire article).  There is also no Idle Air Control (IAC); instead idle is now controlled by the ECM cracking the butterfly angle as needed.  This is very amazing stuff.  As a side note, it is interesting to pay close attention when turning the ignition to the “on” position:  there is a very short “click” heard from under the hood.  It is the throttle body going through its pre-check.  But I digress… Bottom line:  my goal is to be able to integrate the BCM into bowtie6‘s wiring and by doing so, have a fully operational fly-by-wire cruise control.

Among the wires going to and from the ECM is a group that end up in a special plug called an ALDL connector.  This special connector is normally found in production GM cars under the dash on the driver’s side.  It is by the ALDL that the GM TECII scanner/programmer gets connected to the car’s ECM.  In my case I use my laptop along with an interface made by HPTuners to read and change the ECM’s settings.

Enter HPTuners

HPTuners is a commercially available ECM tuning package.  It consists of a Windows-based software running on a laptop and an interface with a USB connector on one side and a matching ALDL connector on the other.  This software package is quite remarkable in what it does; equally remarkable is the lack of documentation.  Sure it has online help but it is very lacking in detail and content.  In the hands of a newbie it can spell disaster to the engine; in the hands of an expert it makes an already great engine even more remarkable.

HPTuners has two main software components:  the VCM Scanner and VCM Editor.  The Scanner is the means by which the engine’s parameters get monitored real-time.  There are a number of different ways to display data:  charts, a gauge panel and tables.  Scanning is accomplished by connecting the laptop to the ALDL connector via the interface, starting the engine and pressing the “Scan” button on the Scanner.  Then you drive down the road and start logging data – the more, the better.  This data can then be saved to a log file for further analysis.  Another feature of the Scanner is to load a log file and play it back – this is very helpful in determining what to change.

The tool used to re-flash the ECM is the VCM Editor.  The process is quite simple:  read the ECM, make adjustments and re-flash.  The hard part though, is figuring out what to change and in what order.  It has been my experience so far this is a bit of a black science.  Information on the interweb is vast about tuning.  However, discerning truth from fiction is the true challenge.  There are several books on the subject and then there are tuning courses available, however they are pricey.  HPTuners is the tool but what to do with and how to use it, is a very time-consuming task!

In the next installment I’ll go into more details about HPTuners…

10 thoughts on “ECOTEC ECM Tuning – Intro

  1. James

    Just uploaded a pair of photos of the Solstice shop manual to:

    Sounds like the key parts (beyond what I’m assuming you’ve already carried over) are the control panel for the cruise control and whatever’s needed from the BCM.

    I’ll need to dig into this some more, and I’ll upload more as I find out about it. The Vehicle Speed Sensor is, if I recall correctly, one of the two plugs connected to the manual transmission.

    It sounds like the only thing that really needs to be figured out is what the resistivity is of the three buttons (on/off, Res +, Set -) from the control panel. I still have the in-wheel control panel from the Solstice, so I may be able to transplant that over, or at the very least attempt to determine what the resistivity is.

    1. bowtie6 Post author

      The trick here is going to be figuring out what is a “must have” to run the BCM. The BCM is really the controller for the cruise control, from what I have read.

      Regarding the gearbox “plugs”: there are indeed two. If memory serves me correct, the plug on the passenger’s side of the gearbox (about midways down) is the backup light switch. The other plug is the VSS – from the wiring harness there is a yellow and purple pair going to it. There is a reluctor inside the tranny that generates the pulse.

      The buttons are the least of my worries – they are available from any of the aftermarket cruise control suppliers.

      Well – if you find out anything, do let me know!

      1. James

        Did a bit of reading over dinner, also talked with a friend who works at SnapOn and has a lot of experience with cars (particularly GM).

        What I’ve gotten out of it is roughly as follows:
        – the ECM handles the cruise control functions for the engine.
        – the BCM takes the signal(s) from the cruise control system as a set of voltages / resistances, interprets them, and sends a data signal to the ECM along a pair of wires that make up the GMLAN (essentially a data cable between the ECM and BCM)
        – the BCM also takes the brake pedal position signal and sends that along to the ECM through the GMLAN cables if you press the brake pedal
        – the clutch pedal sensor, which also can disengage the cruise control, is routed to the ECM directly
        – the signal between the BCM and the ECM over the GMLAN, according to my friend, is something that you’d have to find the baud rate and hz for, and would require a signal generator to replicate. However, GM has that information blackboxed, so there’s no easy way to try and find it out.

        That last bit came up from my asking my friend whether the was some way to remove the BCM from the picture. The BCM’s constantly sending voltage over the GMLAN cables as well (the signal is essentially tweaking that voltage).

        After digging that up, I’m going to look into the BCM itself and seeing if there’s some way to cut it down to just the bits needed for the cruise control, as it’s a somewhat bulky item. It’s obvious from your setup that it’s not needed for anything else on the car when put to our kind of use.

        1. James

          Quick look so far, the BCM’s all one board. The damn plastic box it’s in is being a real pain to open up. I think I’ll leave that be for now and read up on it’s power / other requirements for the system to work.

  2. James

    I’ll definitely be paying attention to this. Just finished pulling the wiring harness off the Solstice parts-car since we’re moving what’s left on the chassis out of the garage, and I’ll be starting to whittle the harness down to the needed bits soon enough.

    1. bowtie6 Post author

      Awesome! Great to hear this.

      Since you are going to “whittle the harness”, are you planning to keep the BCM? If you decided you no longer need it, let me know. I would be interested in it!

      1. James

        I’m a bit interested in the whole cruise control thing, actually. One of the units I was looking at that would pass info to newer gauges had some kind of signal-send that would enable cruise control.

        I haven’t looked through the system yet, is the BCM a large self-contained block like the ECM, or is likely that the cruise-control is some smaller part of it that could be split off?

          1. James

            I’ll have to take a look into the system and the Solstice’s shop manual. I’m doing an initial ‘cleanup’ on the wiring harness to whittle it down to what I need, so I’ll see what’s called out for the cruise control system.


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