ROM Tuning Primer
So, you are considering tuning your car’s ECU and you want to know where to begin or if you should attempt it in the first place. The first thing you should know is that tuning, while not insurmountable, is fairly involved and one should have a thorough understanding of engine management before beginning.A list of links will follow.
Once you have decided that you are up for the challenge, the next question is weather you have a DE or an E motor. Fortunately for the DE crowd there is a good base of knowledge and a very user friendly devise called a Bikirom that comes with everything you need to hook up to a laptop and tune away. There are also a number of tunes floating around for this motor. This devise comes with a daughterboard which is soldered into the ECU. There are a couple of very good write-ups with pictures that cover this procedure.
Those of us with the E motor have to deal with a slightly less user friendly situation. Our understanding of the ECU code is not as far advanced as the DE, but progress is being made. To add insult to injury, our ECU lacks consult capability (explained later)
E tuning will require removal of a chip in the ECU and soldering of a levered zif socket in its place. The socket will be used to inset an EPROM chip that will contain the tune you design. Once again, pictured write-ups are available.
Burning the Tune:
The chip mentioned above is created with a chip burner. This is a device that can be purchased for about $50 for a serial port type and $80 for a USB type – these link to a computer on which the tunes will be designed. The device comes with the necessary software for the file transfer.
An emulator is basically a chip with a cord attached that links to a laptop and will allow you to tune in real time rather than swapping and re-burning chips. These are nice but expensive.
There are a number of free tuning soft wares available. The only one I know of that can currently be used is one called RomEditor. This can be downloaded from the aforementioned site.
Once you have this downloaded, you will need to enable Japanese fonts to get it to display properly.
To use romeditor, you will need two files – an address file (adr) and a bin file (bin). The address file is basically a file that tells the software where everything goes and how to make sense of your bin file. The bin is the tune itself.
To begin, you will click “setup, are crowded reading address file.” Then you will select your address file. Now, select “file, load bin” and find your bin.
At this point I would take some time and get to know the features of the software. Although it is simple software and we are only using a handful of its features there is still too much to go into in detail.
Some key features:
A/F ratio does not work for us.
Graphic editing makes things a lot easier to understand
Function, replace VQ map allows instant MAF swap
Compare allows you to load another map and compare in graphic view.
Notice there are 4 maps entitled “low & high octane fuel and ignition.” The low octane maps are believed to be used in conjunction with the SCV or secondary butterfly valves. This can make tuning quite difficult as the ECU switches from low to high at 2500RPM under load and 3500RPM during cruising. The files I have included disable this function and only use the high maps.
When looking at there tables, you will notice an X and a Y scale – Y being RPM and X being load. The load scale is referred to as TP – it might help to think of it as throttle position although that might not be completely accurate. In the fuel map you will notice some numbers in the high 100s, these are areas of that map that are used for closed loop operation. The others are used to adjust the amount of fuel for the given RPM and load cell. The same is true of the ignition map except it is spark timing rather than fuel.
You will also notice that TP values can be changed. It was previously believed that these should be scaled in the same way K is. This is not the case and these values should be left alone. It might be the case that a few high load values need to be changed to prevent the ECU from running off the right hand side as air flow is increased by turbo. This is yet to be determined.
K is a base value used to determine injector pulse for fueling. K is adjusted according to changes in injector size and MAF. A good rule of thumb is to first adjust according to the ratio of old injectors to the new ones, say 270cc/460cc which gives ~.58. It is important to know that the K number is in Hex so a number converter (I use Quick Base) is needed to convert to decimal before doing the math and then back to hex afterward. MAF swaps also involve adjusting your K value. For a Z32 MAF this should be around 2.5.
So, .58 (injector) *2.5 = 1.45 – this is your multiplier.
6020 hex = 24608. 24608*1.45 = 35681 = 8B61 in hex.
Note this is ballpark. You will need to play with this number until you get it about where you want and then you will fine tune using the fuel map.
As far as we currently know, TTPmin should be scaled according to injector change. From the example above this would be .58
The other values should be left alone at this time.
This is straight forward but can be tricky. It is as simple as changing the numbers based on how you want your timing. The trick is knowing exactly where this needs to take place. For a turbo setup you should pull around .75* per lb of boost. Knowing where your turbo will produce boost and how much it will produce at any given point is the tricky part. I chose to avoid this situation and a lot of dyno time by using a BTM which I set to begin pulling timing after 5lbs and then 1* per lb after that.
A good N/A tune can be had by increasing the high load and RPM values by about 5* and leaning out your fuel to 12.5:1. The KA runs super rich in the high load high RPM range. You will need a wideband or some dyno time but it should pep it up quite a bit. Just be aware that this might shorten the life of your cat converter.
Turbo timing has been covered. The correct A/F ratio while boosting is between 11.5 and 11.9 with 12:1 being an absolute maximum. Many people suggest running very rich mixtures in the belief that this cools the intake charge and prevents detonation. While the cooling part is not true, it does decrease the risk of detonation but it does this at the cost of lost power and a mucked up engine. Under extremely high boost levels such measures or water or alcohol injection may be necessary. But, most of us should be aiming for about 11.9:1 and proper timing.
Hope this helps get things started.