1994 Honda Civic Dx engine knock

Does the knocking increase in frequency when you speed up the engine? If not, does it increase with faster road speed? Again, if not, suspect something like a purge solenoid that cycles on and off about twice per second under certain conditions. They aren't terribly loud but you might hear them if their insulating foam cover or their rubber mounting insulators are deteriorated. I suspect it's more likely not a solenoid because you would have not noticed a change depending on which gear you were in. When it didn't make the noise when you pushed in the clutch, were you moving or standing still? If the car was coasting, you might suspect an engine mount. If it lets the engine sag enough, a half shaft could be hitting the edge of the inner cv joint housing. Normally you will feel that more than hear it. Have a mechanic listen to it. A loose timing belt can slap against the covers. If it jumps a few teeth the engine will run very poorly if at all and will lead to bent valves. That is a REAL expensive repair that you want to avoid. If you hear the noise while standing in front of the car with the hood open, that rules out cv joints. A mechanic should listen to it. If you must be moving to hear the noise, there is a tool called the "Chassis Ear" that will help. It is a set of six microphones, a receiver, and a pair of headphones. You listen while driving and you switch between the various microphones to zero in on the source of the noise.

Hmm. I don't think one nut on the engine mount would be a likely candidate but it depends on whether it lets the end of the engine sag. That would change the angle of the half shafts and the travel the cv joints go through. A split boot on an inner cv joint would be an additional clue. Outer joints can cause a clicking sound but you generally won't hear them when driving straight ahead. They are much louder when turning and moving slowly. I get the impression the noise is harder to hear in the higher gears because that's where there is less torque on the engine. Once the car is up to speed, the stress on the transmission, half shafts, and cv joints goes down a lot. What would not be affected is tires and engine belts. Since the boot is ripped, I think I'd look closer at that cv joint. You might try jacking up the front end and running it in gear to see if you can hear the noise. The car should be supported with jack stands under the lower control arms, not the body or cross member because allowing the control arms to hang down will put the cv joints and half shafts into unnatural angles and could likely cause them to bind and give a false observation.

If it's just one of multiple nuts, I don't think that's the problem. I was thinking of a really big nut on the top of the passenger side mounts on older Chryslers. That bolt could snap off in a crash and allow part of the mount to rotate and the engine would drop about an inch. If your half shaft sits at a fairly large angle, ... In other words, it doesn't go straight into the outer cv joint, that means it is going through a big angle change as it rotates. That would cause it to make the same clicking sounds, (if it is worn), as when you were turning. Outer boots are a real pain to replace on Hondas so you're better off with a rebuilt half shaft. The shaft is locked to the outer joint and can't be separated to slide the new boot on. The entire inner joint and boot has to be disassembled, then the outer boot is slid across the shaft, then the inner joint and boot are reassembled. Basically that means you're doing both joints to fix one.

Diagnostic equipment talks back and forth with the computers on the car. That won't help with noises. Sometimes emissions-related solenoids can be heard but that doesn't mean they're defective, just that they're working. Some of them cycle on and off a few times per second but they usually only do that at certain times. They might stay off at low speeds to prevent complaints about the noise. Often they would cause a rough idle so they only operate at higher speeds. From your descriptions I don't think you have a solenoid noise.

Bring 'em on.