I'm looking to perhaps purchase an 89 iroc z. The body is in amazing shape no rust or dents, the interior is mint. This is a nice car. The seller has put a lot of money into performance parts into the vehicle and is now selling the car because he is disgusted at how much money he put into it just to watch it die.... The seller put in a new rear suspension, headers, exhaust and a supercharger. He took the car out a few times after the install of the supercharger and he started to hear a huge knocking sound. I just looked at the car today and it starts fine. The noise is so loud it sounds like there are a million nails in the combustion chamber. The noise appears to be coming from the back of the engine, closer to the driver side near the firewall. it is a rythmic knocking noise. The second the car is dropped into gear, the noise stops. You can rev the car up as high as you want and it sounds great. The seller said he checked the flywheel and didn't notice a crack. I figure there is no way it can be a rod knocking because even when the engine is reved up in neutral the knocking gets maybe slightly less noisy. any help please, this car is mint and i want it.

 

Sounds like a cracked flex plate (commonly erroneously referred to as a flywheel).
The crack would likely be at the crankshaft mounting bolts and extremely hard to see (but not impossible) without pulling the transmission. Usually caused by engine/transmission misalignment it, diagnosis can be confirmed by unbolting the torque converter, pushing it back, and starting the engine; the knock will go away.

Good Luck.

 

Thanks for the fast response. I'll make sure to use your recommendation to diagnose it. Any more ideas are welcome and i'll keep you guys updated.

thanks again,
ryan

 

check the torque converter bolts, even if they are still there they could be loose which could cause a knocking sound. as i recall when it happened to my car, it started like that, then would knock while driving at low speed ie 10-15 mph

 

thanks guys, keep the ideas coming. you guys are amazing for the help

 

wrist pin or lifter maybe

 

I have the same issue, I changed out the fly wheel and torqued everything to spec.

any other thoughts? Could it be the torque converter?

 

Id recommend starting a new thread, as this one is almost old enough to vote. That said, if you changed the flex plate and the noise remains, you can unbolt the three converter bolts and see if the noise is still present. If it is, it's very possible main bearing.