Valve Noise 2.7

Just bougth a 98 Taco 2.7L with 67000 miles. Truck makes a valve like ticking sound only when under load and throttle. If you lift, all noise goes away. Also in Park it is not present. It is definitely in time with engine speed and sounds like valve noise. I brought it back to the dealer and they replaced the heat shield, gaskets and inspected the manifold. Any Ideas?

Sounds like you have pre-ignition/spark knock. If you are using regular grade fuel try a tank of premium grade fuel. I believe your truck should have a knock sensor to retard ignition when spark knock is detected. It may be defective or it may not have enough spread to prevent knocking.

Clifton

This definitely does not sound like detonation. It is also constant and runs great. Im leaning towards an exhaust leak somewhere. Maybe in the crossover pipe.

the earlier taco 4 cylinders with the cast iron exhaust manifolds have a habit of cracking , check the manifolds top and bottoms , look for black carbon , replace if cracked