Old, New guy, with Old Problems

[ChevyTech]

Definitely check the fuel pressure.

Take a test drive with the EGR disconnected.

When a cam lobe is going flat it is hard to diagnose until the lobe has a lot of damage.

If an exhaust lobe gets flat, it will pop back through the intake when the throttle is cracked wide open for a split second, while in neutral, with the air cleaner removed.

I had a friend that asked for some ideas on his truck after he did a full tune up replacing all ignition parts. After I heard it run, I told him to remove the air cleaner and start it. The popping out the intake was extreme. He had not run it with the air cleaner off to notice the popping. One of his exhaust lobes was so flat the rocker arm had almost no movement.

If an intake lobe is getting flat it is not as easy to find and a flat lobe does not show up well when doing a compression test.

It is so easy to take the rocker covers off on these TBI trucks, to me the easiest way to check for a flat cam lobe is to remove the rocker cover and check the rocker movement. You can disconnect the ignition coil primary wires and unplug the injectors so it does not start and squirt oil everywhere or supply fuel.

If there is valve-train noise, the knock sensor can detect this a pinging, and cause the timing to retard.
Something loose rattling on, or in, the engine, like lifters, cam, rod, crank and piston noises all have the potential for causing false knock signals to be produced.

When these truck have head gasket failure, a compression test shows the problem. Usually these trucks ping, when the engine is hot, when the head gasket fails between the center cylinders.