Scantools are used to pull fault codes and system data from vehicle computers. But most DIY and entry level scantools do not have the ability to reprogram the operating instructions that are already in the computer. They can only read it. Even professional scantools cannot change the programming unless they are J2534 compliant, and even then they only pass through new factory software settings to reflash the PCM memory.
People who want more performance from their engines used to have only one option: to replace the original equipment PROM (Program Read Only Memory) chip with a performance chip -- and then only on certain General Motors and Ford applications.
Aftermarket performance chips typically provided more spark advance, fuel enrichment, and allowed the user to bypasses the stock rev limiter and speed limiter. On applications where the stock chip could not be replaced because it was permanently soldered into the PCM main circuit board, the stock PCM could be fooled into delivering the desired ignition timing and fuel enrichment by piggybacking a second module into the vehicle's PCM wiring harness. This allowed the input and output signals to be modified to achieve the desired gains in performance.
With the introduction of EEPROM (Electronically Ereaseable Program Read Only Memory) chips in computers on OBD II equipped cars and light trucks, reprogramming become possible -- but only with a "factory authorized" reprogramming tool. This was to discourage emissions tampering and to protect the OEMs against unwanted warranty problems caused by someone fooling around with the calibration of the PCM.
Various aftermarket suppliers sell specialized "tuner" scan tools for tweaking the PCM to improve vehicle performance. Some of these are AmericanMuscle's BAMA tuner tool for Mustangs, Superchip's "MAX Microtuner" for late model GM, Ford and Dodge car and truck applications, Hypertech's "Power Programmer" tool for Ford and GM applications, GM Performance's "Granatelli/Diablo Sport Predator" tool for GM, Ford and Dodge, and Crane Cams "PowerMax" performance power tuner for Chevy, GM and Ford trucks plus Hummer.
These products typically sell in the $400 range depending on the model, application and where you buy it.
So what can you do with a tuner scan tool? You can recalibrate various settings in your engine's computer to increase Horsepower & Torque. The suppliers of these products say you can dial in 10 to 30 or more additional horsepower on otherwise stock gasoline engines, and 50 to 100 or more horsepower or more on many turbo diesel engines.
Most of these tools can be used to:
* Change the fuel mixture
* Change ignition timing and spark advance
* Raise or lower shift points of automatic transmissions
* Increase the rpm setting of the rev limiter
* Recalibrate the speedometer to match different tire sizes
* Recalibrate the speedometer for changes in axle ratios
* Match the speed limiter to the speed rating of the tires
* Download custom tuning profiles from the internet that have been developed for specific engine applications.
* Plus read diagnostic codes and clear codes like a regular scan tool.
Features vary depending on the product and supplier, but most do give you the opportunity to play around with the stock settings of the PCM. Such modifications are usually necessary if you want to increase the boost level of a turbocharged or supercharged engine (which may also require installing higher flow fuel injectors or other modifications). Recalibrating the PCM is also needed if the stock cam, cylinder heads and/or pistons have been replaced with aftermarket performance parts. Ditto for adding an aftermarket cold air intake system or performance intake manifold. Anything that changes the breathing characteristics of the engine will usually require retuning the fuel and ignition curves to realize the full performance potential of the upgrades.
Performance scan tools that can modify PCM calibrations are a great product, but they are not without risk. The main one is that modifying the PCM calibration in your engine computer with a performance tune may void your factory powertrain warranty.
For example, General Motors will NOT pay for any engine, transmission, driveline or exhaust system failures that result from doing a performance tune on a Duramax diesel. See GM Duramax Diesel Warranty Issues for more information.
Another risk is that you can screw things up rather easily. For experienced engine tuners who know what they are doing, using a tuner tool makes performance tuning relatively easy. But for a novice user who may not fully understand the implications of playing around with the PCM's fuel and ignition timing settings, you may make your engine run worse if you are playing around and making your own custom tune adjustments. The best advice is to NOT attempt a do-it-yourself custom tune until you have gained some tuning experience.
The best and safest approach for most users is to install one of the pre-programmed tunes that the tool manufacturer gives you when you purchase their tool. The tune will be based on detailed information you provide them about any modifications you have made to your engine such as installing an aftermarket cold air intake, low restriction exhaust, performance cam, larger throttle body or other such modifications. Most scan tool suppliers have already developed tunes that should work with any of these common modifications. And if you are not happy with the results, they can usually tweak the tune to suit your vehicle. You can also go back to the stock tune if the new tune does not achieve the desired results.
A richer fuel mixture makes more power up to a point (about 12:1 max), but beyond that point it only wastes fuel and increases exhaust emissions. You might also foul the spark plugs if the engine spends much time idling. The greatest danger is getting the fuel mixture too lean as this can result in detonation under load and possibly burning a piston! The safest way to modify the fuel mixture is to do so while the vehicle is running on a dyno and the exhaust temperature or mixture is being monitored to make sure it doesn't go too lean. Most download tunes have already been developed and tested on a dyno using a vehicle similar to yours with similar modifications.
More initial spark advance helps low end torque, throttle response and off-the-line acceleration. But too much total spark advance increases the risk of engine-damaging detonation and pre-ignition. The more advance an engine has, the higher octane fuel it requires. Most engines run best with about 6 to 10 degrees of initial spark advance, and 32 to 34 degrees to total advance.
Some downlaod tunes are marketed as "87" octane, "91" octane or "93" octane tunes based on how much spark advance they dial into the PCM. If you opt for a 91 or 93 tune, that means you'd better fill up with premium fuel, not the cheapest unleaded.
This mod can really bump up power and torque. The more boost pressure the turbo develops, the more air it can cram into the engine's cylinders to make more power. But there is a limit on how far you can dial up a stock turbo/engine combination before things start to break or before you exceed the fuel flow capacity of the fuel injectors. Too much boost pressure can blow head gaskets, cause rod failures, transmission failure (automatics in particular), break driveshaft U-joints and halfshaft CV joints, even differentials. When you crank up the power, sooner or later you will find the weakest link you your vehicle's powertrain.
On most light truck turbo diesels, you can dial up the boost pressure 4 to 6 PSI and add another 100 to 150 hp without harming anything. Beyond that, the driveline is usually the weakest link.
On passenger car turbo motors, the fuel injectors usually have to be upgraded to higher flow injectors if you add more than a few extra pounds of boost. Most engines can safely handle 50 to 100 extra horsepwoer before things start to break (unless other upgrades are made to increase strength and durability).
If you go crazy with boost pressure and want a turbocharged motor to make 800 horsepower on the street, you'll have to make some major engine and driveline upgrades such as a forged steel crankshaft, forged steel connecting rods, forged aluminum pistons, a stronger clutch, and maybe beefed up drive axles and transmission/transaxle changes.
The stock rev limiter kills the ignition if the engine is revved too high to prevent possible valve float that could result in piston-to-valve contact and valve damage. Raising the rev limiter beyond the capabilities of the stock valve springs is asking for trouble. You can usually bump up the rev limit 500 RPM with no problems, but beyond that may be risky unless you are also installing stiffer valve springs.
This is a built-in safety feature to prevent idiots from driving faster than the speed rating of their tires. Tires have speed ratings for a reason. They can explode if they are driven at sustained speeds beyond their speed rating.
WARNING! If you raise the stock speed limiter setting on your vehicle, make sure your tires have adequate speed rating to safely handle any changes you have made. For more information about tire speed ratings and tire safety, see Why Tires Fail.
Performance tires generally are speed rated for 130 mph or faster. Look for the letter speed rating on the sidewall to make sure it is high enough if you increase the speed limiter on your vehicle:
H = 130 mph (210 km/h)
V = 145 mph (240 km/h)
Z = 149 mph (240 km/h)
W = 168 mph (270 km/h)
Y = 186 mph (300 km/h)
Changing the PCM calibrations on your vehicle may also create a problem is you live in an area that requires emissions testing. The EPA does not like this because to them it is "emissions tampering" which is illegal. The EPA has confronted at least one vehicle manufacturers who was selling an aftermarket tuner module kit for increasing power. The manufacturer is no longer offering that module.
Some tunes are emissions-legal and will not cause any problems, but some performance tunes are really designed for off-road or racing only because they disable the downstream oxygen sensors. This prevents the OBD catalyst monitor from running, which will cause your vehicle to be rejected when you take it to the emissions test station. All of the OBD monitors must have run and completed before your vehicle can be tested, and there must be no faults found to pass the test.
One option is your vehicle has to undergo an annual emissions test is to temporarily reinstall the stock settings until the monitors run, then get the vehicle tested. Once it passes, reinstall the performance tune.
When you use a tuner scan tool to install a tune over the stock calibration in the PCM, the tool becomes married to your car. The tune in your car cannot be changed without the tuner scan tool that installed it. If you make additional modifications to your vehicle, or are having problems passing an emissions test because the tune disabled the OBD oxygen sensor monitors (which is a common modification with tuner programs), you will need the tool to make the necessary tuning changes. If the tool has been lost, your only option is to take your vehicle back to the car dealer and have the PCM reflashed back to its stock calibration. This will also require removing any add-on modifications such as a cold air intake, custom exhaust or other parts and replacing them with the stock components.
Custom tuning a PCM using a laptop and a plug-in interface requires special software that can hack the original calibrations in the PCM and overwrite them with new values. This is a job best left to those who have dyno tuning experience and the know-how to do it successfully. If you don't know what you are doing, you can really screw things up!
The safest way to retune your PCM is to buy a tuner scan tool and download a custom tune from the tuner tool manufacturer that is calibrated specifically for your vehicle and what ever modifications have been made to it. Download tunes like these are not as good as doing a custom tune on a dyno, but they are pretty good and usually work quite well.