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Unread 05-21-2013, 12:46 PM   #1
Rich Z
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Default The tuning chapter...

Figured I would just go ahead and move the latest work done on my car into a separate thread, since most of it has to do with tuning lately. I may go back and fill in stuff that was done earlier so I have a record of what I have fiddled with in case I need to refer back to it.

Anyway, the latest, first....

Did another data logging run yesterday. I've noticed that the short term fuel trims were fluctuating quite a bit, so I wanted to disable closed loop mode to see what was going on.



Car ran really well in open loop, but seems to be running a bit rich in most areas of the VE map. I disabled the fuel modifiers last night and will do another run today or tomorrow to see if that helps lean it up a bit before modifying the VE (volumetric efficiency - B0101) table.
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Unread 05-21-2013, 02:33 PM   #2
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Sounds like it's running just fine to me!
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Unread 05-21-2013, 04:52 PM   #3
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Yeah, it does sound pretty good!

What probably isn't evident from the video is that when the car is accelerating, I'm actually holding the gas pedal relatively steady, trying to get enough data points in each RPM cell. It's actually the turbos spooling up that are making the car go faster. The MAX I had the throttle was 42.7 percent, but rpm climbed pretty quickly to 5252. Something tells me that I'll be hitting redline REAL FAST when I actually try 100 percent throttle one of these days.
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Unread 05-21-2013, 05:33 PM   #4
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Did you retain the factory traction control? Or have a rev limiter programmed?
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Unread 05-21-2013, 06:26 PM   #5
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Originally Posted by 85vette View Post
Did you retain the factory traction control? Or have a rev limiter programmed?
Yeah, they both are still in the programming as best I can determine.

The rev limiter is set for 6900 rpm.

One puzzle I'm still trying to get an answer for is that EFILive shows a max value for engine torque of 640 ft.lbs. I'm sure my engine is producing significantly more than that at the crank, so I'm not sure what, if anything, the PCM does at that point when that value is exceeded. The PCM uses two methods to try to reduce power when it wants to. One is via reducing the timing advance, and the other via fuel cut off. If you've ever had a situation where you get REDUCED ENGINE POWER, you will likely have noticed that your gas pedal is effectively useless.

And I did not disengage traction control while driving the car doing these runs, but I didn't notice the engine losing power if traction control kicked in. Actually a couple of times it did feel like the rear tires broke loose under boost, though....
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Unread 05-21-2013, 07:32 PM   #6
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Yes, the traction control has a very generous limit on my CTS V also. I don't know what the perameters are but it will let the wheels spin quite freely. Only when I get really sideways does the gas pedal go away. Mine has the traction control and the stabil-trak, so if you get crossed up on a curve it will "brake" you out of it. Pretty amazing actually(not that I've used it alot) but these roundabouts up here can be a lot of fun! My car has a "competition mode" that shuts down both traction control and the stabil-trak systems. Part of that system encompasses the tire pressure sensors, and if one or more tires is low, or if the tps batteries are dead it won't let it go into competition mode. My rear tps sensors are dead so I can't get it into competiton mode. Probably a good thing.....
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Unread 05-21-2013, 08:17 PM   #7
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Yes, the C5 has pretty much the same thing. There are four states available when I click the button on the console that controls traction control and active handling.
  1. Both traction control and active handling ON
  2. Traction control ON, active handling OFF
  3. Traction control OFF, active handling ON
  4. Both traction control and active handling OFF

I can't remember which button press sequence does what right at the moment. Honestly, I haven't used that feature since before I took my car into Chris Harwood's shop. But the one I used most often was option 3. I don't mind the rear tires spinning, but not so keen on going sideways at the same time. I think this car would be easy to get away from me without some sort of nanny guards in place.

Anyway, I took the car out for another run today and did some more data logging. Results are inconclusive, I think. Some cells in my map display are showing leaner than before, but others are showing richer. So I'm not exactly sure those supposed fuel modifiers were really doing anything to the AFR.

I need to bone up on that volumetric efficiency table anyway, as it really doesn't seem intuitive to me at all just trying to figure it out on my own. It's supposed to be a representation of the relative efficiency of the engine's ability to fill the cylinders with air. It is used to predict the volume of air entering each cylinder under varying conditions. That's pretty much a direct quote from EFILive. But how it actually WORKS isn't very clear to me.

Some of the problem is that there are three ways of looking at the air fuel ratio in EFILive.
  1. AFR (air/fuel ratio, ei: 14.7:1 means 14.7 parts of air to 1 part of fuel)
  2. lambda (1.00 is stoichiometric. 0.98 would be richer, 1.02 would be leaner)
  3. EQ ratio (1.00 is stoichiometric. 0.98 would be leaner, 1.02 would be richer)

From what I understand, the GM PCM uses EQ ratio natively for it's internal calculations.

I think you can see where confusing lambda with EQ ratio will have the opposite effect you are striving for. So the problem I have is figuring out whether the map function I am viewing is using a lambda or EQ ratio equivalency when applied to the VE table. Since the VE table is NOT in any sort of AFR units, just some sort of relative value concerning "efficiency", I'm just not sure if making the values smaller in the VE table makes the FINAL AFR leaner or richer. What does it mean if the cylinder is made to appear LESS efficient by lowering the number? It's little details like this that are not self evident but can have a BIG difference in reaching your goals with this tuning stuff.

AFR seems so much more intuitive to me, but to really get into this tuning stuff, you have to abandon that way of looking at the air/fuel mixture. And of course, there is no real consensus on whether working with lambda is better or worse than working with EQ ratio, so some tutorials and help pages will use one, and others use the other. Then you combine this with some tutorials using metric values, and others use SAE, and you REALLY have to keep your eyes on the ball to make sure you are putting apples in the apple bin, and oranges in the orange bin.
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Unread 05-22-2013, 02:05 AM   #8
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Well, I think I've got a better handle on this VE table now. First off, here's what a VE table (B0101) might look like in EFILive..



The values in each cell are a representation of how much air is PREDICTED to be able to fill the engine cylinders at the intersection of the manifold vacuum/pressure and the rpm of the engine, as shown in that table matrix. The PCM uses that value to determine how much fuel to inject into the cylinders when the engine is actually at the rpm level that corresponds with the intake manifold vacuum/pressure. This is pretty much the basis of what's known as a SPEED DENSITY tune.

What a MAP file is, therefore, is just a representation of the VE Table set up in the scan tool, set up to capture the DIFFERENCE between the commanded AFR and the actual AFR as determined by the wide band controller in the exhaust. This is done via a calculated PID that generates these values on the fly while the scan tool is capturing data. What this map file then represents is a correction factor for each cell of the VE table that sufficient data has been captured during a data logging run. That MAP file will look something like this:



The values shown in the above are AVERAGE values of each cell with data in them. Cells that have had hits between zero and ten(10) are excluded from the MAP display so that the average value is more realistic of the actual differential.

So, now with that information captured in the MAP, what EFILive allows you to do is to cut those values in the MAP display from the scan tool, and then paste those values into the VE Table in the tune tool and at the same time also MULTIPLY those map cell values to the cell values in the VE table. This CORRECTS the values in the corresponding cells of the VE Table based on the difference determined in the MAP data. The values less than one (1) will therefore reduce the cell values in the VE Table cells, which will make that cell command a leaner value. Cells in the MAP that are greater than one (1) will increase the value of the VE Table cells, which will command the AFR to be richer. So a smaller value tells the PCM to expect LESS air and therefore inject LESS fuel into the cylinders. A larger cell value does the opposite, telling the PCM to expect MORE air in the cylinders, and therefore inject MORE fuel to compensate accordingly.

So increasing the numbers in the VE Table indicate a richer AFR, and decreasing those numbers indicate a leaner AFR. So this cut and paste of the MAP display values is a very quick and easy way to do what used to be manually capturing data from such cells, figuring out the percentage of difference needed, richer or leaner, and then manually multiplying EACH CELL in the VE Table by that percentage of difference. Yeah, I'll bet THAT was tedious!

Of course, the issue is trying to get enough "hits" in each cell of that MAP display to cover the entire VE Table. Which is why this sort of thing is certainly much easier to do on a dyno where you can control the RPM of the engine and the loading (on a load bearing dyno) of the engine in order to capture ALL the cells needed for a complete VE Table correction. Unfortunately, I have to do this the hard way on the street, which means I most likely will not be able to capture all the cells at the higher RPM range, under all vacuum/boost conditions.

Whew! That had me scratching my head for a while, but I think I understand it now....
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Unread 05-22-2013, 08:01 AM   #9
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SEE! I told you..............another career is just around the corner!
You're getting it all worked out, and will be able to put out the "Tuning
by Rich" sign soon!
Andy
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Unread 05-23-2013, 06:21 PM   #10
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Quote:
Originally Posted by navy2kcoupe View Post
SEE! I told you..............another career is just around the corner!
You're getting it all worked out, and will be able to put out the "Tuning
by Rich" sign soon!
Andy
Nope, not going to happen.

I'll quite likely learn how to tune MY car, but that doesn't mean I will be able to tune anyone else's. Mine is so far from stock that likely everything I am learning won't apply to any other cars anyway. Besides, in the area I am located, someone specializing in tuning Corvettes would quickly starve to death. If I wanted to do this as a business, I would be learning how to tune pickup trucks.
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