Hi Guys/Gals, I have a 85 Z28 with carb 305 4 speed auto. The engine runs quiet, I have listened all over and it seems very quiet. But when I sit inside the car and listen I can hear a knock sound from trans tunnel area. Almost sounds like something knocking on the floor. Any ideas?

 

May well be something knocking against the floor; an exhaust part for example.

 

Fuel pump. A weak spring can make a click sound on the fuel line that can be heard thru the line; seems to be directly under the center console because the fuel line passes from drivers side to pass side under the body 'tunnel' in that location. ( there's a long thin "brace" that holds the line against the tranny tunnel ) Could be a lot of other things too: cracked flywheel, bad lifter, rocker out of adjustment, exhaust leak, loose parts, etc......

 

I checked the fuel lines and brackets all seem tight, Checked the torque conveter bolts they are tight, I dont see where anything could be hitting the trans tunnel . But as I rev it and its coming down on RPM, I can feel it on the trans tunnel while sitting in the car . But I can't hear it outside the car.

 

It's not a matter of the fuel line being tight / secure....... the weak F/P spring causes a "click" in the fuel line itself that gets transmitted thru the fuel line itself and can be heard in the body because the line is touching the body. You probably would not hear this "click" in the engine bay, but might have a better chance hearing it under the car when it's running, just put your ear close the the fuel line where it runs down the body on the drivers side.


This description is just about exactly accurate to the problem I was dealing with. This might be your problem / it might not. Point is that I've dealt with a very similar knock/click/tick before and tried a lot of things to resolve it before finding out the cause. It drove me NUTS; I stripped the entire center console, re-adjusted then removed the roller rockers and so on. I was literally under the car preparing to remove the tranny to check the flywheel when my head happened to get close to the lines running down the drivers side & I noticed the 'click' in the fuel line. In my case the fuel pump was a NEW part,.... a cheap autozone of-the-shelf replacement that had a weak spring in it. ( I JUST changed the FP in my step-dads 86 Firebird about a month ago for the same reason. )



A block mounted pump is a cheap and easy fix compared to pulling rockers, separating the exhaust, or replacing the flywheel so keep it in mind before doing more extensive work to find the source.


Edit: if you disconnected the rubber fuel line at the pump and run the fuel lines from the pump into a bottle / bucket of gas and start the car; if the sound goes away,...... the FP is almost certainly the problem. ( might be a good idea to run the fuel return line into a second bottle / bucket just to be sure the FP is not connected to any of the body lines during the test. )