"Tuner" Scan Tools for Plug-In Performance Tuning

BY Larry Carley c2006

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Technicians have long used scan tools to pull fault codes and system data from vehicle computers. But most scan tools do not have the ability to reprogram the operating instructions that are already in the computer. They can only read it. Consequently, the only way you could recalibrate the PCM was to replace the original equipment PROM (Program Read Only Memory) chip with an updated chip -- and then only on certain General Motors and Ford applications.

People who were interested in making performance modifications found that the PCM really limited what they could do. The solution here was to replace the stock PROM chip with an aftermarket performance PROM chip that provided more spark advance, fuel enrichment, 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 many late model 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.

Several aftermarket suppliers have now introduced what are essentially specialized "tuner" scan tools for tweaking the PCM to improve vehicle performance. Some of these include 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 and where you buy it.

So what can they do? By recalibrating the PCM, it's not unusual to realize gains on the order of 15 to 30 horsepower on otherwise stock gasoline engines, and 50 to 100 horsepower or more on many 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. The question is, do you really want to play around with the PCM?

If there's a valid reason for doing so (like your customer is clamoring for MORE POWER!!), these tools will certain provide the means for modifying the PCM. Such changes are usually necessary if the boost level of a turbocharged or supercharged engine is increased (higher flow injectors may also be necessary). Recalibrating the PCM is also needed if the stock cam, cylinder heads and/or pistons have been replaced with aftermarket performance products. Anything that changes the compression ratio or 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. For experienced engine tuners who know what they are doing, they make performance tuning much easier. But for a novice user who may not fully understand the implications of playing around with the PCM, he may end up making things worse instead of better.

Too much spark advance increases the risk of engine-damaging detonation and preignition. Raising the rev limiter increases the risk of valve float and damage if the stock valvetrain can't handle the increased rpms. Raising the speed limiter with no consideration for the speed rating of the tires is asking for trouble. These are the main risks that I see with misusing these kind of products. But in competent hands, a performance scan tool allows you to do things no ordinary scan tool can do.