A place for more technical discussions. Please make sure you post in the correct section on the site, this way it keeps the site tidy AND ensures you get a more relevant answer.
To alter the performance in an ECU you need to change the mapping. The map is basically a 3d grid which allows the ECU to determine how much fuel to inject, to retard or advance timing etc. based on what its sensors tell it. Changing the map (remapping) can be done on all Jimny ECUs.
When Suzuki made your ECU they designed the software (map) to keep everyone happy. The map they installed is a kind of balance between best performance, torque and fuel economy. They also have to comply with emission and noise regulations.
When you have your car remapped, the remapper can improve performance, torque or fuel economy but its at the expense of something else. If you remap a car on a rolling road you can change the map to meet your requirements. If you are having your car remapped by a guy with a van/local garage/Dave's mates brother they will load a map with a few tweeks but in order to acheive this there can be side effects. Increasing performance may decrease fuel economy. Increasing torque may increase noise. How effective the remap is and how minor the side effects are depends on the programmer who supplied the file to the 'remapper'.
Early Jimny ECUs can be rewritten relatively easily. Rhinopower has explored this extensively as mentioned above (its a really good website, well worth a look!)
Gen 4 ECUs can be re-written thru the diagnostic plug, in otherwards the remapper can plug his computer in and upload his 'map' directly into the ECU without removing or unplugging anything. Companies such as max-tune.com sell the kit for doing this. However, the remap is only as good as the supplier of the remap files.
Gen 3 ECUs can be remapped too but they need to be removed and 'reflashed'. This means the chip containing the existing map has to be identified. When its been identified it may have to be unlocked and have the existing file removed. After this the remap file can be uploaded. I have not personally done a Jimny one but certain Japanese makes are sneaky and use a different procedure for unlocking than for uploading. In effect you can wipe the info from the ECU but initially cant upload the new map rendering the ECU scrap!
Given the amount of good and bad places offering 'remapping' its difficult to justify the cost of the kit you need to do your own ECU.
If you have built something unique and feel the way to get the best from it is to design your own performance map perhaps onsider changing to a DIY ECU like the megasquirt kits. You can make your own, buy a ready made one etc. There are loads of forums swapping maps and tips etc.
Thanks for the advice! You were very clear and I now know what I'll do.
I'll just buy a megasquirt or some good ECU and have my mechanic or somebody I can trust and has experience fiddle with it.
What is your ultimate goal with this? You don't get big gains just by tweaking the ECU on a normally aspirated engine. The manufacturer has spent huge sums of money on the standard tune to give the best combination of emissions, power and economy. There are only two parameters you can realistically change, fuel and timing. If you increase fuel you get a small increase in power but fuel consumption goes way up and you risk failing emissions testing and/or damaging the catalyst. If you always use premium fuel you can increase the timing advance a little which gains you a small amount of power. Go too far and you cause detonation which can destroy the engine. If you are looking for power, Jackonlyjack's suggestion is a much better way to go.
Going for a standalone ECU such as a Megasquirt gives you lots of control but again you aren't going to gain much. Tuning takes a lot of practice. Doing it yourself without a rolling road is hard and you are unlikely to beat the standard ECU. I have had a Megasquirt on my trials car for well over 10 years. This is running a modified Peugeot 205 GTI engine. After much tweaking it still doesn't run as well as a stock ECU. I fitted Megasquirt for two reasons. First to prove I could and second the stock Peugeot EFI is unreliable and parts are hard to obtain.
Another thing to keep in mind if you want to go the Megasquirt route is that it can't control VVT. Losing VVT will negate any gains you could achieve by playing with the fuel or ignition maps.
An aftermarket ECU only makes sense on a normally aspirated engine when combined with engine upgrades, such as porting, a hot cam or a turbo. These days cylinder heads are so well designed that even porting doesn't really give much improvement.
Re mapping turbo engines, both petrol and diesel, can give big gains. Basically the re maps increase turbo boost while tweaking other parameters to keep emissions roughly legal. Go to far and emissions go through the roof and/or the engine eats itself.
Another thing to keep in mind if you want to go the Megasquirt route is that it can't control VVT. Losing VVT will negate any gains you could achieve by playing with the fuel or ignition maps.
That may not be good news for me either. I was looking at getting a megasquirt to manage my swift sport engine when I eventually get time to swap it out amongst other work to be done to it.
I don't know much about it all, but the megasquirt specs for the MS3+MS3X does mention VVT control within it's medium current outputs. Perhaps the VVT control is not suitable for the M13/M16 engines?
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