4 Cylinder Knocking?

[shado40]

This one has me scratching my head. My friend has a 86 2m4 with an auto. The guy he got it from said that the crank bearings were shot. When we start it there is a rather obvious knocking, clunking sound coming from the engine area, but this is where I am confused. When we put it in gear or otherwise put any load on the engine the knock goes away and it sounds like any wonderful fiero should. If the bearings really are shot why would the sound go away when the engine is under load? If not the main bearings what else could it be?

[Namtraf]

Sounds like you could have a clutch sticking in the transmision.When in neutral a clutch isn't fully disingaged making the knocking sound. This happedn to my friends Eagel Talon before his transmission went out. If its not an automatic, it could be the throw out bearing.

[shado40]

Yes it is an automatic trans. I thought it might be trans related too, but When we drive it it seems to shift just fine. Could it still be a tranny problem if the shifting is still pretty tight?

[Namtraf]

Once you put it in drive the clutch becomes fully engaged. Therefore, it's not free and able to move around. You might want to check out the torque converter.

[shado40]

ok, thanks for the help.

[feduke]

I had an '86 S-10 2.5L with the exact same problem ,sounded like a diesel with 4 bad rod bearings at idle. I never figured it out, drove it that way for 5 years and finally sold it as is.