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Old 04-13-2012, 10:50 PM   #1
the suicidal eggroll
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Default How Tuning Works

The fifth in the series:
http://forums.nasioc.com/forums/show....php?t=2339831


Tuning


Also see Unabomber's Manifesto on the topic:
http://forums.nasioc.com/forums/showthread.php?t=795608


Let me start off by saying that this is not a tuning guide, in any way, shape, or form. This is simply an overview of what tuning means, what it does, the options available, and how they work. If you're looking for a tuning guide, Bad Noodle has written a pretty comprehensive one on NASIOC, check it out.

So how does a modern ECU-controlled vehicle work? The simple answer is it uses a lot of sensors to measure what’s going on, and it uses a pre-programmed set of lookup tables (generally referred to as a “map”) to see how to respond to the input from those sensors. Everything from fueling, to timing, to boost is controlled by the ECU using these lookup tables. I don’t want to clutter this section with examples, so if you’re interested look at the fuel system section for a specific example of how these tables are actually used in practice.

“Tuning” on these cars USUALLY means using a piece of software to overwrite these lookup tables with new values. If you want the ECU to inject more fuel at a certain RPM, you modify the fueling table and lower the target AFR at that RPM, easy peasy.

There are two main choices for tuning, the Cobb AccessPort, and Open Source (RomRaider and ECUFlash). I will not go into which choice is better or why, since it is all a matter of opinion and I want to keep this guide as objective as possible. In general, both of these options do the exact same thing. They both use the same factory ECU, the same lookup tables, and they modify and flash them in the same way. A professional tune using AP will be exactly the same as a professional tune using OS. They are just two different paths to the same destination.

That’s not to say there aren’t differences though. While the end result is the same regardless of which path you choose, the path itself does differ. The AccessPort works by using your computer to download pre-existing (aka off-the-shelf, or OTS) maps from any number of sources (Cobb themselves, or other tuners). You also have the option of downloading the Access Tuner Race software from Cobb and modifying the map yourself (DON’T DO THIS UNLESS YOU KNOW WHAT YOU’RE DOING, YOU CAN BLOW UP YOUR ENGINE). Once you have the map you want to use loaded onto your computer, you load it onto the AccessPort, then plug the AccessPort into your car and flash the map onto the ECU. Once the map has been loaded, you can then use the AccessPort to monitor sensors to see how the engine is running. You can make “logs” of this sensor data, and then load the log onto your computer to look at a time series of data during your drive, to see how the engine was running and responding.

Open source is very similar. Just like with the AccessPort, you download pre-existing OTS maps from any number of sources (other users, other tuners, etc). You can also use the RomRaider or ECUFlash programs (both freely available) to modify the map yourself (AGAIN, DON’T DO THIS UNLESS YOU KNOW WHAT YOU’RE DOING). Once you have the map you want to use loaded onto your computer, you plug the laptop itself into the car using a Tactrix cable, and use ECUFlash to flash the map onto the ECU. Once the map has been loaded, you can use your laptop to monitor the various sensors and make logs, just like with the AccessPort.

BOTH AP and OS allow you to run off-the-shelf maps. BOTH AP and OS allow you to get professionally tuned. BOTH AP and OS allow you to tune the car yourself. A lot of people get confused here...they think that AP only allows you to run off-the-shelf maps, or OS only allows you to tune the car yourself. Neither could be farther from the truth.

The main difference between the two options is the device you use to flash and log. In the case of the AccessPort, this device is a little handheld box with a screen and a few buttons. In the case of Open Source, this device is your laptop with an OBDII to USB cable plugged into it. Beyond that, there aren’t many differences. The AccessPort has a little more functionality in regards to base maps vs real time maps, real time tuning (making modifications while the car is running, so you don’t have to shut the car off, flash the ECU, and start it back up), etc. The last time I checked, OpenSource had more lookup tables in the ECU defined and available for modification than AP. It’s a tradeoff, and a decision you’ll have to make yourself. Both choices are incredibly popular, and have almost a cult-like following. You will find no shortage of reviews, opinions, and heated arguments on the topic of which is better.

Beyond the two big dogs (AP and OS), there are several other choices as well. Ecutek works similarly (reflashes the OEM ECU). UTEC is a piggyback device that always stays connected to the ECU. It allows the ECU to control things like idle and cruise, and then it “takes over” at high RPM and high load. There is also a myriad of stand-alone ECUs, such as the Hydra, AEM, and others, which completely replace the ECU and control everything themselves. I’m not going to cover the different stand-alone options, because if your build is to the point where you need a stand-alone, you won’t be needing these guides to assist you.


Oh, and PLEASE don't turn this thread into an open source vs AP debate. There are hundreds of those elsewhere on the forum, so take those kind of comments elsewhere. That's not what this thread is about, this is about what the options are and how they work, not which one is better than the other.

FAQ


Q: Does the AccessPort need to be plugged into the ECU permanently to function?
A: No. It of course needs to be plugged in in order to log data from the ECU as you drive, but once you flash the map onto the ECU, you can unplug the AccessPort and toss it in your glove box or closet without the ECU reverting back to stock calibration. Same goes for Open Source, once the ECU has been flashed, you can unplug the laptop from the ECU and go on your merry.

Q: Will resetting the ECU cause it to revert back to stock calibration?
A: No. With either AP or OS, the ECU is completely reprogrammed with the new settings. There is no copy of the stock calibration on the ECU for it to revert to, the only thing it knows is the new map. Now with the AP, there is one “gotcha” here. When the AP is first installed and a map is selected, the above is correct. It is completely reprogrammed, a reset will not bring you back to stock. However, when you go to change maps on the AP, there are two ways to do it. You can flash the new map as a base map, or as a real time map. Base maps overwrite the programming in the ECU, so it is persistent through battery disconnects or resets. Real time maps are only temporary, they will stay in effect until the battery is disconnected or the ECU is reset, at which point the ECU will revert back to whatever base map was last used.

Q: Can an AccessPort be used on multiple vehicles?
A: No. You must “marry” the AP to your ECU when first setting it up. This pairs the ECU with the AP, and the AP with the ECU. In order to use the AP on another ECU, it must first be “divorced” from the previous ECU, which will flash that ECU back to stock in the process. If you ever buy a used AP, make 100% sure that it has been divorced from the previous owner’s ECU, otherwise you won’t be able to use it on yours.

Q: Can tuning be used to disable CELs?
A: Yes, almost any code can be disabled with AP or OS, including the resulting limp mode caused by several of the more “serious” codes. Just because they can be disabled, doesn’t mean they shouldn’t be though. Only codes that you are 100% certain do not matter should be disabled (such as the TGV codes if you’ve deleted your TGVs). Other codes, even the “annoying” ones, can be critical in debugging problems you might run into down the road.
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Last edited by the suicidal eggroll; 04-20-2012 at 11:44 AM.
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Old 04-16-2012, 11:06 AM   #2
d_r0ck
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Can you go a little deeper into the benefits of me tuning my own car with AP/OS vs. having it professionally tuned?

Also, I understand that tuning the ECU can give you power gains, but what about aftermarket ECUs? Are there any ECUs that are 'better' than the stock ECU, or does it 100% depend on the tune?

Last edited by d_r0ck; 04-16-2012 at 11:22 AM.
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Old 04-16-2012, 11:32 AM   #3
the suicidal eggroll
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Default

The professionals have access to the same tuning software you have (they might have a little bit more power than you do in the AP domain, but in OS it's the same), so it really just comes down to experience. While each car is different, the professionals know what generally does and does not work, and can get you to maximum power much faster than you can on your own.

That said, it's not their car, most of the time they're trying to get you out of the door and will often take shortcuts with the tune (not every tuner, but a lot of them). If the engine blows, 99% of the time they won't pay for it. Also, it's impossible to get a complete tune in the few hours your car will spend with them. You need to accept the fact that either you'll be going back to them for touch ups probably every few months for the first year, or you'll have intermittent problems like cold weather overboosting, bad AFR in the summer, etc. The closer to stock you are, the less of a concern this is, but when you start getting into big MAF intakes, aftermarket turbos, EWG, E85, etc., you're going to be going back to them quite a bit (unless you live in California where the weather never changes). This isn't their fault, they just aren't able to tune the car for anything other than the weather conditions at which they do the tune. They can guess how things will change as the weather changes, but if you're far from stock they won't necessarily be right.

It's just a tradeoff between having to learn how to tune and taking days/weeks/months to dial your car in yourself, versus getting in and out of the door in a few hours, having to go back a couple of times for touch ups as the weather changes, and putting 100% faith in the ability of your tuner.
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Old 04-16-2012, 02:08 PM   #4
d_r0ck
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Quote:
Originally Posted by the suicidal eggroll View Post
Perfect, awesome answer
Thanks!
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Old 09-15-2012, 12:32 AM   #5
SubWrx13
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Default

Great article and it does shed a lot of light on the topic. Thanks!

Now my only question is does accessport allow for several interchancheable maps during driving such as better mpg, racing, winter, summer etc.

My understanding was you could have several maps programmed that you can change while driving with the push of a button on the screen. So instead of running to get retuned for summer, winter, etc. you can just pick the maps that fit the conditions and revert back when conditions change as long as your programmed without visiting the tuner shop.

Or... Does visiting the shop for several retunes eventually allow for the tuner to get to where one map will be smooth regardless of conditions?
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Old 09-15-2012, 10:43 AM   #6
the suicidal eggroll
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Default

Yes, both AP and OS allow you to hold multiple tunes on the flashing device, and swap them out at will. You can't do it while driving though, you would need to pull over, shut off the car, connect the green test connectors, flash the ECU, disconnect the test connectors, start the car back up, then start driving again.

As you pointed out at the end of your post, there is no need to have separate maps for winter, summer, etc. though. If your map has issues in winter that it doesn't have in summer, you need to go back to the tuner to have the low temperature compensation tables adjusted. Unless you're actively tuning the car or switching between fuels, you should be reflashing the ECU very, very rarely.
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