2.3L ('83-'97) Input On Knocking Noise

[esmith84]

I’ve finally got the Ranger timed properly and the carburetor rebuilt. However, once warm I’m noticing some knocking noise. Wondering if anyone could provide their thoughts on what it could be or how to troubleshoot what it could be.. Goes away with RPM. Doesn’t sound like an exhaust leak or a ticking. Any input is helpful. Thanks!

(84 2.3L)

P.S I just noticed when I unplug spark plug wire four it goes away.

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[franklin2]

Ok, so it's #4 cylinder. How long have you run the engine? Till it got fully warmed up yet? The reason I ask, a engine with some wear in it can have some piston slap when cold. But it will go away once the engine heats up. Or the skirt could be collapsed, in which case it will never really go away, but may be less when warmed up.

Another thing you can do, is get a aftermarket oil pressure gauge. One with the plastic tube, not a electric one. Hook it up, get the engine warmed up, and see if the oil pressure gauge flickers with the knock. If it does, that is not a good sign. It's a sign of a rod bearing that has spun or is worn out.

 

[RobWigglezz]

#4 being unplugged means there is minimal cylinder pressure and minimal exhaust pressure. I know you said it's not an exhaust leak, but I believe it is. When the motor is cold, the exhaust manifold is sealed up. Once the manifold is warmed up, it expands enough to allow a small leak around #4 exhaust port.

 

[RobWigglezz]

#4 being unplugged means there is minimal cylinder pressure and minimal exhaust pressure. I know you said it's not an exhaust leak, but I believe it is. When the motor is cold, the exhaust manifold is sealed up. Once the manifold is warmed up, it expands enough to allow a small leak around #4 exhaust port.

If your exhaust manifold studs and nuts still look like nuts and studs, you could try tightening them up with the motor warm. Don't force them if they feel tight though

 

[esmith84]

It happens when the engine is warm. I’m not sure about cold I can check in the morning. It goes away when the rpm’s climb instead of getting faster and louder. I suppose I shouldn’t rule out an exhaust leak it just doesn’t totally sound like one to me but I’ve only ever had a Jeep TJ exhaust manifold leak before. Oil pressure on the dash stays consistent. I did confirm the timing was 10 degrees. Seems the slower the rpm’s the more prevalent the knock.

 

[RobWigglezz]

Any chance #4 plug is loose? I drove for weeks with 2 plugs loose before.

 

[esmith84]

Any chance #4 plug is loose? I drove for weeks with 2 plugs loose before.

I took all the plugs out and re-sat/retightened them. I’ve never really heard of a noise like this that goes away with rpm haha. I’ll post tomorrow after a cold start and record it too

 

[RobWigglezz]

Unplugging #4 is the confusing part. Piston slap and a lifter tick can go away with rpm but simply removing combustion shouldn't affect it. Interesting