[serpentang]

Help! I've got some knocking noise coming from the engine when you hit the throttle. It's fairly quiet when the hood is closed, but when you open it up, you can definitely hear it.

When it's not in gear (park/neutral) and I press on the throttle, the knocking starts. When it is in gear (reverse/drive), the knocking is significantly quieter.

The frequencies of the knocking rises and falls with the RPM.

I've got a few mixed opinions; Jarek thinks it's something with the injectors, and resetted some stuff on my ECU, while some other mechanic friends of mine think it could be a cracked flywheel or rod due to its behaviour when it's under load.

I think it might be the rod because when I manually shift, I don't feel anything

Any inputs would help! Thanks in advance

[BB_cuda]

Cut off a broom stick and place it in several spots on engine. Put your ear solidly against it in each spot and have a helper rev engine to reproduce noise trying to help find the source. If it is injectors like Jarek says, that would be good news. In my experience, a bad rod is something that wouldn't get better with load. You can buy automotive stethoscope at autozone too. Costs about $15. If it's flywheel, you would hear louder as you worked your way back closer to back of engine. I would listen on driver side where you have better access to side of engine block.
I used to work in machinery monitoring industry. If I had the equipment still, I would use an accelerometer with a bull nose tip screwed on to its base. You then FFT the data to see if noise is at running frequency of engine or something else.

You might look at the harmonic balance. PR's went bad but I don't know it it was making noise. Best of luck and pls let us know.

[Hoooper]

If youre working with Jarek, have him turn off injectors one at a time while trying to recreate the sound. If its a rod knock, you will most likely notice the sound get significantly quieter or disappear when the injector for that cylinder gets turned off.

[Mik325tds]

I remember seeing this before on this forum. Do a search. I think it turned out to be something with the pulley that drives the serpentine belt. Try to move the belt forth and back while engine is off. See if you have some play.

[BB_cuda]

Originally Posted by Mik325tds

I remember seeing this before on this forum. Do a search. I think it turned out to be something with the pulley that drives the serpentine belt. Try to move the belt forth and back while engine is off. See if you have some play.

Mike and I are referring to same thing. Harmonic balance has pulley on its end. Another guy had to get it replaced besides PR. I recall this other guy looking at it while it was running at seeing a forward/aft motion but unsure if he mentioned noise. Mike recalls the noise so do the search on pulley or balance or dampner.

A harmonic balance is really more for damping crank vibrations as the engine is internally balanced. Only some engines are externally balanced where weights are put on the harmonic balance and flywheel in different places to result of a zero out of balance for crankshaft, connecting rods, and pistons. My mopar 440 is internal balance with forged crank. My mopar 400 is external balance as it has a cast crank.