Top 17 Tuning Tips for every car

It's almost Xmas, so I decided to have a put a small gift under every tuner's tree, with a short list of tricks that people found useful at various times.
First, you want to make sure you do things in the correct order, as you want to make sure that you don't spend time doing something that will need to be redone at a later time due to related tables being modified.

1. Read your stock computer file and save it, preferably in multiple places, and on various types of media so you aren’t stranded without a known, functional tune. Email, USB thumb drives, multiple computers are all excellent ideas.
2. BEFORE you start changing anything, put it in accessory power mode and hit scan. You will get initial settings without the whole system under pressure. This is your base. Take notes, it might (and usually will) come in handy later.
3. Start up your engine, and start to log your idle. If you have an automatic transmission you might want to do it again the next day but in D not in P/N.
4. Check your Diagnostic Trouble Codes (DTC’s). You might find some problems with your car you didn’t know about before. Remember that tuning a car with mechanical problem merely band-aids the real problem. Don’t waste your time doing this, and don’t waste other’s time by asking questions about it on the forums.
5. Time to take a ride. You can take a normal drive through a neighborhood, but a mix of city and highway driving would be perfect. Log the car's behavior in these various situations. This time what you're looking for is older/lazy/faulty oxygen sensors, signs of knock, shifting patterns of an automatic transmission, rpm dipping/holding at coming to stoplights, and any other irregularities that you've been ignoring and living with for too long. Make sure you drive it long enough (a 15 minute drive usually does it) to bring the whole car up to temperature, not just the Engine Coolant Temperature.
6. Once you review your logs and decide there's nothing too scary or blatantly wrong, find a stretch of empty road and do a nice long Wide Open Throttle run. It's an excellent source of information as it provides you with some vital data (more on this later) as the whole system is under full stress, pressure, temperature, and load.
7. Organize your data! I cannot stress this enough. After just few weeks of tuning, you will be drowning in logs, settings, notes, and spreadsheets. Save yourself the pain and just make yourself a following structure:
   \HPTLOGS\NAME\DATEinYYMMDDformat\DescriptiveNameWithASerialNumber
   Why the funny date format? Because it goes from most significant to least, just like normal numbers, so it's easy to look at in series.
   The name of the file can be tricky, as you want to put info in it, but not too much, as it's going to make the name of the file awefully long and unmanagable. Usually what I look for in a name was the goal (VEtuning) and the mode (SD) and you want to know the order of things it all happened, so you want a serial number in here.
   So the example of the full thing would be:
   \HPTLOGS\Marcin\20050630\08_VEtuning_SD_smoothed.hpl
   This provides me with all the info I need. If I have few other attempts of tuning VE I know exactly in which order they happened, I know I'm also tuning in Speed Density, and I know I smoothed it. For more detailed information I'll have to dive into the file itself, but usually it's enough to just glance at the list of the files and you know which one it is that you want to investigate.
8. Check your hardware and see if your car computer is aware of it. If you changed displacement, you must change the "Cylinder Vol" field. If the EGR stealing gnomes did their deed, you have to disable it (EGR-Disabled) and then turn off codes in the DTC section.
9. One hardware setting is so important that I am making a separarate point of it: the Injector Flow Rate, popularly referred to as the IFR. Use a fuel pressure gauge to measure the idle fuel pressure and look up the flow ratings of your injection. With this data, use the spreadsheet I have in the "Idle tuning writeup" to create your new IFR table. Most fuel pumps will increase the pressure, Fuel Pressure Regulators might deregulate it in many creative ways, so you have to make sure you get it right. Boost-a-pump and vacuum-referenced setup are a bit tricky and beyond a scope of this post.
10. Undo the GM marketing department's lame attempts to keep the LS1 from a F-body lower output than the Corvette. Setting the Power Enrichment table universally to 1.15 results in a much more sane (than the overprotective stock) 12.7:1 air-fuel ratio.
11. Another day another dollar, only this time its relating to the timing tables. 01-02 cars are _notorious_ for this. They run about 19 degrees of timing at WOT, while 98-00 cars do 29. If you have no problems (read: knock) with the tables from the earlier cars, please flash your tables with them. If you do have problems with knock, or your car just doesn't benefit from the increased timing, go with a stock Z06 timing table. It should gain some power, but at the same time its not wild enough to induce knock.
12. If you have a cam but don't know how to tune the idle, the easiest way to make it easier is to raise the idle. Don't be shy, big cams need a big idle, and 1100rpm will make anything idle very smoothly.
13. Under Fuel_Control->Open_&_Closed_Loop there's a little section called LTFT Boundries. The RPM button has 3 settings, which cut up the RPM/MAP histogram used for VE tuning into logical clusters called the Fuel Trim Cells. On some cars, the GM settings are so asinine that they put the second and third value completely beyond the rev limit, making them useless. I like to use them to put the FTC's into logical pieces/clusters: idle, light cruise, passing, WOT. So if your idle is let's say 900rpm, you tool around town under 2500rpm , then i set them to 1200/2500/4000. This way the computer is using a very logically laid out FTC, facilitating quicker and more precise learning. This will make the car behave better in general.
14. Take a tape measure and measure the height from the floor to the center of your wheel. Double that, and use it as the height of your wheel for speedo calibration, NOT the advertised height. This is where Reality meets its arch-rival Marketing in a final battle ;) My tires are officially 17x315/35, which is 25.7" height, but practically it's more like 24.9" That's almost an inch off, a significant factor in calibration, and might be a difference between a ticket and a warning.
15. Get a lower temp thermostat and adjust your fan enable/disable temperatures for it. A car that runs cooler knocks less, making it easier to find the real levels of engine's comfort without random knock occurring too often. If you have aftermarket fans, make sure they are wired to work as advertised (pull or push) and that both of them do the same thing. It's very hard to diagnose cooling problems and they're potentially very destructive.
16. Monitor Dynamic Airflow and MAF(SAE) signals. It's best to just graph them on the same graph, same scale, but with two different colors so you can see how close they are. If you see discrepancies, you most likely need a VE or at least a MAF readjustment.
17. Now we're going to start looking at the data we've gathered earlier to help identify some potential problems.
    Shade tree mechanics often suffer from lack of patience, precision, and power tool happiness, resulting in leaks. The most popular leaks are by the throttle body (smooth bellows not completely going on the TB on the bottom), intake manifolds (FAST is supposedly very hard to seal properly), and of course the entire exhaust system (primarily headers, collector, and the Y-Pipe).

• The bellows leak is characterized by having a lower than average airflow. If you know your car used to flow 40lb/min and suddenly you can barely see it crack 32lb/min, you can bet the air is getting out by the bottom of the TB.
• Intake leaks can be spotted by low MAP pressures during WOT runs. This is where it pays off to know what the pressure would be with the engine off. If you know it was a 100kPa day and you can't go past 85kPa then there are some bad gaskets underneath that need to be replaced.
• Headers are notorious for leaking because they are metal expands and contracts in relation to heat, thus expanding and collapsing in size. The general consensus is to go over the header bolts after a week of driving after you installed them to them on as tight as possible. Its easy to pick out a header leak by using a scanning program, as you're going to see a repeatable pattern of one side's O2 reading consistantly leaner than the other.
  For those who are not afraid of Excel, dump the data from a few WOT runs into a spreadsheet and run Tools->DataAnalysis->DescriptiveStatistics on the O2 readings. Even if it's been a while since your last statistics course and you don't remember what specific values mean, just look and see if both of the banks have a similar descriptive parameters, or if one of them is significantly different from the other. If it is, re-torque the header bolts and check again.
  
• In the scanner, collector leak looks similar to a header leak, but both banks are off instead of one. Of course there's a possibility of a regular header leak, just with both sides leaking. Either way, start re-torquing.
  

Here's an example of an interesting header leak, you can see both O2's go crazy, but one much more than the other:



The real story here turned out to be a TWO overposed leaks. One was a traditional 'need to retorque one side' leak, but the other was a small collector leak.

That's all for now, I'll try to make some pictures demonstrating some of these things.
As always, feel free to add, comment, correct and point out anything you think can use an improvment.
Happy Holidays!