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My 1996 E-350 was running great all day yesterday. I started it up later in the evening and drove it about a block when it started making an extremely loud popping noise, in time with the engine. If I accelerate, the pop quickens. I shut the van down, removed the air filter, had my buddy start the motor, and with every pop came a burst of air out of the intake.

Is one of my intake valves failing to seal? Could that be a bent rod? Any other ideas, and what to do?

I have never worked on a 7.3 head before, but maybe now is the time to learn.

Most important, is it safe to drive it 2 miles back to my shop?