Sbc Knock And Fuel Pump Questions

I've been trying to track down an ever more noticeable 'knocking' sound in the sbc. For awhile, I thought it was exhaust leak, but after checking various exhaust leak spots, that doesn't seem to be it....plus, that typically is more of a 'clack' than a knock, often gets better as the engine warms up, and typically is most noticeable when you let off the throttle (I think?). This knock sound happens in the engine, not associated with transmission, and varies with rpm. You hear it most noticeably with light acceleration, and it goes away entirely when you let off the throttle completely. Its more noticeable when the engine is warm to hot (oiling related?). Unfortunately, for as noticeable as it is cruising around in the 1500-2000 rpm zone, I never hear it when running the engine with vehicle parked - it seems to need some load to occur. I am starting to get hesitant to drive it around much....

Concerned it could be rod knock, I broke out the stethoscope and started listening all over the lower end and then the upper end/valve covers etc - no distinct knocking sounds... at least not until I put the scope on the fuel pump....I am pretty sure I hear the sound in the fuel pump (mechanical). I've never listened to the pump before, so not sure if it should have a distinct knock sound under the stethoscope - but it most definitely does. Jen listened too, and as she said, if you just made it louder, it would be the exact sound heard when driving. I pulled the pump wondering if there was a broken spring or something obvious, but not that I can tell...


is there something I should check? I pulled the pushrod too - it seems okay - length is correct. The pump arm has a significant section of soft travel that just compresses the spring before engaging the diaphragm. Going past that point it gets really stiff, and seems to operate the diaphragm fine. I assume this section of 'soft' spring travel is supposed to be permanently out of its typical range of motion once the spring is compressed when installing? Is there a way I can check the lift on the pushrod from the cam? Kind of a scary thought, seems possible the cam lobe is flattening and getting some knock/slap between the pump arm and the pushrod? so far there has been no indication of limited fuel supply when driving....I did buy a cheap replacement pump from NAPA seeing if swapping the pump would tell me anything, but I forgot how many different fuel line fittings and orientations sbc pumps have, and it requires getting some fancy fittings to get everything back together with the new pump....

 

not sure I am comfortable driving around at 30mph with such a set-up....

 

Yes....can't hear the knock without load on the engine

 

its definitely rpm and engine related, not wheel speed related....