THINKING OF making any tuning mods to your bike? Then chances are you'll be needing to have a tweak of the old fuelling. In days gone by, that meant swapping out brass jets from inside carburettors - a fiddly job indeed. But nowadays it's all about the electronics – so we're tweaking ones and zeroes inside the fuel injection ECU instead.
There are a few ways to do this these days - ECU editing, entire replacement ECUs and various piggyback modules, but perhaps the most ubiquitous one is the Power Commander (PC). Produced by US firm Dynojet, this add-on piggyback ECU module has been making fuel injection tweaks easy on bikes for a couple of decades now. We've been fitting and using them for most of that time, and have had really good results over the years.
So we wanted to get one onto our long-term Suzuki GSX-S750 to make some changes. These are twofold - firstly, to try and improve the stock fuelling, which is a bit messed up these days to comply with Euro 4 emissions regs. The firms are compelled to keep exhaust gasses super-clean, with even microscopic amounts of pollutants being verboten. As a result, many modern bikes can feel a bit jerky and on-off in terms of power delivery, with random peaks and troughes in torque at part throttle settings in particular. A good PC setup will let you tune these hiccups out of the standard bike, while still keeping the engine very clean and efficient - win-win.
The second reason fo fit a PC is to adapt to any changes. We've not gone mad with the GSX-S - just a GPR end can so far. But we'd still like to get the fuel injection optimised to suit, and see if we can get any extra ponies out to the back tyre.
The top folks at Dynojet UK sent us a unit out to try, and we fitted it today at DM Performance Motorcycles in Wallington. Our top mate Dan Miles has fitted more Power Commanders than we've had McDonalds breakfast muffins (and that's a lot), so he whistled through the fitting in about half an hour. We made some video of the job, which we'll put up once we've edited in some more swearwords.
In the meantime - it's fair to say the GSX-S750 is one of the easier bikes to install the PC onto. The hardest part is actually getting the plastic surround off the fuel tank so you can remove it. Pillion and rider seats come off in seconds, as do the black plastic sidepanels, and then you unclip and unbolt the plastic tank surround. Unbolt and remove the tank and you've got all the access you'll need.
The Power Commander works by intercepting the fuel injector signals from the ECU, altering them, and sending them on to the engine. So you have to unplug the injector connectors, inserting the PC wiring harness in between, and connecting the PC plugs onto the injectors. There's also an earth connector that goes onto the battery, and a connector that goes into the stock Throttle Position Sensor connection on the bike.
There's also a replacement oxygen (lambda) sensor with the Power Commander which replaces the stock sensor wiring under the tank too. This fools the ECU into thinking the stock oxygen sensor is still in place and sending a 'clean' signal. Without this, the ECU would see unusual signals from the oxygen sensor, and it would try to cancel out the Power Commander's fuelling changes - causing all sorts of trouble and poor running.
Refitting all the panels and fuel tank took ten minutes tops, and we were out of Dan's hair in under an hour. Next we have to get the bike to a dyno so we can check out the fuelling, and remap the injection to suit our exhaust. Stay tuned...