It takes a lot to engineer a car well. Everything has to be balanced. Aftermarket modifications can easily screw that up. And Ford knows that.

Modifying cars can be a lot of fun. Sometimes all you have to do is bolt on a supercharger or re-calibrate the engine tune, and voila- instant power! Sometimes cars can handle it; other times they can’t (or won’t for very long).

Consequences of bad mods can range from decreased longevity to catastrophic failure. Your head gasket can only take so much pressure. Your driveshaft can only handle so much torque. You should always consider supporting mods when looking to upgrade your ride.

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These are important things to keep in mind, especially if you like to do all of your own wrenching. But what if you still take it to the dealer from time to time? They also need to know what’s been done to the car, especially if it’s still under warranty.

Some things don’t affect a car’s warranty; but some do, and it’s important to understand how parts can influence other components. Besides, it’s not just about determining whether or not to deny a warranty claim; it’s about identifying the root cause of the problem and preventing future failure.

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So Ford has issued the “Gas Engine Performance Modifications Job Aid” document to help technicians spot common problem areas susceptible to aftermarket mods. This isn’t exactly a new thing. The current 29-page document released earlier this year is version 3.0 and urges the tech to look for both hardware AND software mods:

Aftermarket calibrations are used to increase engine performance by altering calibratable parameters such as rev limit, spark advance and air-fuel ratio. Most aftermarket tuners advise the customer to reflash the PCM back to the stock calibration when bringing the car in for any warranty work. Refer to Section B to help determine if an aftermarket calibration is or was present in the vehicle.

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So think twice before making your new car’s first mod a nitrous kit, m’kay? Your “improvements” have nowhere to hide, baby.