It's a knocking that happens under the following circumstances:

* light load
* rev high then completely let off throttle
* it gets really fast when it is about to change gears

Isn't noticable at idle. I just pulled off each spark plug one by one and the knock was still there. The sparks tickled a little when it grounded on me.

Known issue ... got a used eha and it is junk. Leaks fuel out the bottom just like the other.

Can I rule out rod bearings at this point? I just changed out my belt tensioner and tensioner shock. The belt went loose. I verified it was bad by putting it in a vise and rotating it. It stayed where I put it which indicates a bad tensioner. I went with febi. The one that came off was FAG which I assume was oem.

Somebody has suggested lifters. Just still troubleshooting.

is it a heavy knock or a tapping noise

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1990 190E 3.0L

Heavy knock.

I went around with a stethoscope when the car was up on ramps. The sound is most pronounced next to the transmission. Not much noise from the oil pan.

Other known issues, coolant is leaking from the breather hose that goes to the air cleaner. No coolant in the oil or vise versa.

Hmm, doing a little more research. I'm going to torque the torque converter bolts and see if that's it. The car does shudder on acceleration from a stop.