Boost vs EcuLoad

For colts, I’ve found 160 load to equate to around 13-15psi.  But most of us are running higher? How can we reliably tune the car when ECU Load stops reporting load past 14psi? The answer is 2 byte load.

Colt Ralliart 2 Byte Load

Evoscan (and Tactrix SD card) logging can handle something called 2 byte load but to do that some changes are needed to your MUT table, and also your logging configuration. Before we get into that, some more background.
ECU Load is only 1 byte load. To log it, only one MUT request is required.  It maxes out at 159.375.  2 Byte load requires two MUT requests, one after the other, to retrieve the ECU’s internal master load value, which peaks at 200 load.  The two requests for 2 byte load can cause some rare strange results but more on that later.  For the most part, it is reliable and enables you to log up to 17-19 psi.  This sounds good but how does this impact on tuning?

Impact of tuning with only 1 byte load

If you tune a Colt Ralliart with only 1 byte load, maxing out at 159.375, then your ignition maps at 160 load, will end up being tuned to what doesn’t cause knock at your maximum boost.  Peak power might be the same, but when your car is actually producing 160 load, its ignition will be set as though it was producing 200 load and be too retarded, resulting in less power at that point.  It’s tricky to explain but a few graphs might help:

ECU Load 1 Byte tuning session:

ECULoad Logging

Based on this, a tuner would look to reduce timing at 160 load, rpms 3500 through to 6000.  They should also reduce timing in 180-260 load range based on this data.  Lets check out the 2 byte load version of the same logging session:

ECU Load 2 Byte version of same tuning session:

Based on this, a tuner would look to reduce timing at 200 load, rpms 4000-6000 (note the reduced range to before).  As with above, other cells would be adjusted too.  The key take away is that the tuner using 160 load max would be seeing a very different picture of when the car was knocking to the tuner using 2 byte load.

The different picture would result in a different, and inferior tune.   Peak power would be the same, but power at less boost than peak would be compromised.

OK so it’s important – how do I log it?

You’ll need to do two things. First you’ll need to modify your MUT table and then flash the changed ROM to your car’s ECU.

Colt Ralliart 2 Byte Load For AUDM and most JDM rcolts:

Set MUT00 to 0x804E90 and MUT01 to 0x804E91:

Save the changes then flash this onto your car.  Now you need to modify your logging setup.  If you’re using Evoscan check the option :

Then when in Live Logging, ensure the Load dropdown is changed to Load MUT 2 Byte Load:

Tactrix SD Card loggers need to edit their logcfg.txt to include the following two lines:

paramname=Load2Byte1Raw
paramid=0x00
scalingrpn=x,256,*
isvisible=0

paramname=Load2Byte2Raw
paramid=0x01
isvisible=0

paramname=LoadMUT2Byte
scalingrpn=Load2Byte1Raw,Load2Byte2Raw,+,0.3125,*

So that’s Colt Ralliart 2 Byte Load. Give it a crack and let me know how it goes. Hopefully this helps you, or your tuner, get your rcolt tuned as best as it can be.

Oh one more thing – in the Evoscan log used above you might have noticed there’s a data point past 200 load – 240 load @ 5500rpms. What’s that about?

As the 2 byte method needs to make two memory requests, it is possible that in the time between the two requests that the memory location gets over written.  So we have half of 1 byte of information read, then both bytes are changed, then we read the 2nd byte.  The result is an erroneous ECU load result, that should be ignored.

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The best way to do this that I’ve found is to graph knocksum with Evoscan.

This is how you do it:

1. Buy Evoscan from here.  They’re a small company, so go on do the right thing and pay the small fee

2. Download & Install it

3. Load it. You should see the following screen. Click the Graph / Logs button:

4. This will load the graphing screen (below). Note you can also do live logging from this screen. Anyway, lets set it up to read your Tactrix CSV log.

1. Set Data Values to Maximum
2. Set Load to ECULoad.  If you have logged 2-byte load (if you don’t know what this is, then you haven’t) select ‘Load MUT 2 Byte’, or Auto.
3. Use Load #1 Log button to load your CSV
4. Select ‘Knock Sum’
5. Your Max Knocksum graph should now be displayed

5.  By default evoscan will be displaying an ignition map from an Evo and axis’ from an Evo. You may find that this squashes up your knocksum data and you’re not getting quite the detail you were after.  To fix this, right click on the ignition map area, and select load ROM. Navigate to your car’s current ROM and load it. The axis will be redrawn using your ROM’s axis, and the correct ignition information will be displayed.  This is particularly important if you are adjusting the ROM based on the Evoscan graph.

Ok so now you have nice graph that looks something like the images below. Now what? What’s good? Whats bad? This is as subject of another (long) post. But to help, I’ll describe what I see in two example knocksum graphs.

Graphing Knocksum with Evoscan example 1:

Anything above 4.0 and >140 load I generally consider concerning. Where that 9.0 is, I would check out how many other knocksums were registered at this point in the graph (either by hovering over the cell, or by loading in Excel).  If it is clear that this is a troublesome area, and most are 9.0’s then I’d look at the main ignition map and consider taking one or two points off the ignition at that point. Note though, that the ignition at any point rarely fits exactly in the axis points, its usually slightly between two, or four other cells.. So consider if the ignition settings in the cells around areas of knocksum had any effect on the ignition used by the engine when it was knocking.  I tune my Ralliart Colt for zero knocksum at 140 load and above.

The 3’s and 2’s at 3000rpms, aren’t significant and could just be caused by bad driving. I’d watch here on other logs and if there was a trend, i’d consider a small ignition change, perhaps in the two cells that have 3’s, then flash, and log it some more to see its impact.

Remember if you tune down your ignition your car will go slower, so adjust carefully and over time. This will help ensure that you’re not reducing your performance unnecessarily.

Graphing Knocksum with Evoscan example 2:

This log doesn’t show too much. The car wasn’t boosting high at all, but there are quite a few 5’s.  If the entries at these points are consistently showing 5’s I’d look to make a small ignition change in this area (-1) and see if it improves knocksum in future logs.

Anyway please see this as just a soft intro intro the concept of knocksum tuning.  Don’t apply it without more reading (find one of the Merlin’s Guides for Evos). I’ll write much more on ignition tuning in a future post.

Comments, questions on Graphing Knocksum with Evoscan or on ignition adjustments? Hit me up below or find me on Rcolt.com, or the Rcolt.com Facebook Group.

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Things needed:

• Tactrix Openport 2.0
• Micro SD card (must be formatted to FAT32!)
• logcfg.txt file

Download my sample logcfg.txt from here (right click, Save As), then copy it to your Micro SD card. That’s pretty much it!  If done correctly your Tactrix device will now log to CSV files on the Micro SD card.  These can then be checked out in a spreadsheet program, or via Evoscan.

More advanced users may want to edit which MUT requests are being logged, you can do this by editing the logcfg.txt file with a text editor like notepad.   Also, note that not all of the MUT requests in this logcfg.txt will be correct. They key ones are though (rpms, ecuload, throttle is ok but inverted, speed, wgdc, ignition timing, fuel trims, knocksum etc).  I’ve used this logfile to help tune my AUDM 2006 Ralliart Colt, but it should work for the JDM variants as well as the Euro CZT & Ralliarts..

Hope this helps you get Tactrix OBDII Logging going on your turbo colt!  Oh and if you try this on a CZT/CZC or EUDM Ralliart Colt – let me know how it goes!

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