Here's why:
* Increased Fuel Delivery: Turning the fuel screw in (clockwise, usually) increases the amount of fuel injected into the cylinders. This leads to richer fuel mixtures.
* Potential Problems from Incorrect Adjustment:
* Excessive Smoke: Too much fuel results in excessive black smoke, indicating incomplete combustion. This isn't inherently damaging, but it wastes fuel and can contribute to clogged DPF (diesel particulate filter) if your truck has one (though 12-valves usually don't).
* Overheating: A very rich mixture can cause overheating due to incomplete combustion generating excess heat.
* Increased Wear: While not immediate, consistently running a very rich mixture can lead to increased wear on the engine components over time due to soot buildup and increased cylinder pressures.
* Runaway: In extremely rare cases, a severely misadjusted fuel screw could contribute to a runaway condition, where the engine runs uncontrollably at high RPM. This is usually due to other factors, but an excessively rich mixture can exacerbate the situation.
* Decreased Fuel Delivery: Turning the fuel screw out (counter-clockwise) decreases fuel delivery, potentially leading to lean running. This can cause damage through detonation or pre-ignition.
In short: Adjusting the fuel screw itself won't physically damage internal engine components. However, improper adjustment can lead to operating conditions that cause damage over time or result in immediate issues like overheating. It's crucial to understand the implications and ideally have a knowledgeable mechanic or experienced individual guide you through the adjustment process. Using a fuel pressure gauge is highly recommended for precise and safe adjustment.
