3.0 knocks intermittently

[SamC777]

Hey y'all, got a question! My '94 has an occasional knock when idling, but all I have to do is rev the engine for a second and it stops. I change her oil every 3-4k miles and there's no leaks I can see. No engine lights on, despite sitting at >340k miles. What could be causing this, and why would revving it silence it? Could this be an oil pressure issue?

 

[broncc]

Maybe? Does it sound like its happening at engine RPM or at half engine rpm? Maybe the top end has a soft lifter that gets noisy at low pressure.

I would look into renting/buying an oil pressure test kit to see whats going on. New engine is like 40psi at idle but Internet wisdom typically repeats that engine RPM/100 is good enough.

If its not low, try a few oz of mystery oil for a few hundred miles. If it is low, go up a weight in oil. Maybe consider taking the truck out of daily service if the knock comes back after.

 

[rusty ol ranger]

Yeah dont trust the factory oil pressure gauge. My 460 showed good pressure even with cooked mains.

Once you rev it up and it goes away does it come back once you get to idle? Does it do it more warm then cold? Hows it sound when you put it in gear?

If you have an automatic sometimes a loose/broken flexplate can sound like an engine knock.

 

[broncc]

Something I was thinking about today; when was the last time your timing chain was changed? At 340k you're due for a new chain and tensioner.

 

[SamC777]

Something I was thinking about today; when was the last time your timing chain was changed? At 340k you're due for a new chain and tensioner.

Man, you're right, but I'd really like you not to be. I'm not in the mood to put my daily out of commission for awhile to do that lol. I'm no expert, but I think I have to pull my 3.0 motor out just to do it.

 

[broncc]

This is a problem for after you discover where the knock is coming from, but its not that big of a job. Radiator fan and harmonic balancer are blocking the timing cover but that can be removed if the radiator is out of the way. Should be a one day job if its your first time and have the parts ready.