That lifter tap at cruising speed is called pinging...

One of the problems with vacuum controlled emissions is they are a pit of snakes and it is hard to know if anything is operating properly. Can you imagine working on a 72-74 car? Talk about a nightmare! You don't see any of those vehicles on the road anymore, -emissions killed them. If you have a working EGR leave it alone. It is hard to put one back on line tho. You need a working truck to get the whole system from.








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