Hello to all, here is my first post for help. I posted in the fuel section because I am leaning toward the fuel pump being the source. Anyway,  I have bought a low mile 78 Coupe. After filling the tank up and driving it about 150 miles home, there was no issue except typical anti freeze drips from the hose edges etc....The next morning, after some clamp tightening and what not, I took it out for a spin and after drive 10 miles, returned home. As I was pulling into the garage, low RPM, I heard a rat tat tat noise from the right rear. I did not hear this as I was driving the speed limits. At idle, in the garage, the noise continued. So, I blocked the car and got out to inspect. I narrowed it down to the right rear wheel area. As the noise continued, I banged on the catalytic converter (thinking something had broken loose inside the converter) but it didnt change the sound. Baffled, I put my fingers on the fuel lines that sit on top of the frame in the right wheel well. The pulsation of the rat tat tat sound could be felt. So I proceeded to take the car out for another spin to trouble shoot this. Again at high RPM, I didnt hear the noise. Upon finding a flat stretch of road, I pushed the clutch in and let the engine idle down and I could hear the rat tat tat noise again. I shut the engine off and coasted down the road. No rat tat tat noise. So,  and Thanks for bearing with me, I am leaning toward the fuel pump being the culprit. If I am off base, please input your thoughts. I really appreciate it. Jon  

|UPDATED|4/27/2014 11:07:45 AM (AZT)|/UPDATED|

Jon, you might check your exhaust pipe and muffler for a loose clamp or baffle in the muffler.  I had that happen to mine and had a rattle like you describe.  Good luck.

What does it sound like up on the lower right side of the engine block where the fuel pump is?  The rat-tat-tat could be the short rod that drives the pump.  I replaced my pump last summer.  Mine was spraying gas out the vent hole....removal-replacement was not the most fun I've had.

|UPDATED|4/27/2014 11:46:45 AM (AZT)|/UPDATED|

Thanks for the response. When checking it out, it was louder on the back end of the car. My first thought after I felt the fuel lines was the same - the fuel pump was giving it up - and since the pump is not in a great spot, I didnt get a chance to put a hand on the housing. But I am certain I felt the percussion of the tat tat on those fuel lines, or something was knocking against the lines somewhere on the frame bottom. I did look from the top side to see if he pump mounting bolts were loose or coming loose but all was tight against the block. Ugh. I will try to troubleshoot it more. Thanks. Jon

Take a long piece of metal (crowbar or similar) and rest it on the fuel pump, then to your ear.  I doubt the fuel pump internals are making that much of a noise, but it may be the pump pushrod that's driven by the engine cam.  If you need a new fuel pump, PM me...  I have a brand new stock Corvette pump (with the built in vapor return) that I'll make you a hell of a deal on. 

I bought an Edelbrock pump and was convinced it wasn't working so I bought another stock one.  Turns out you have to have enough fuel in the tank for ANY fuel pump to work, and once I put enough gas in the tank the Edelbrock pump worked fine. 

Thanks for the reply. I actually was trying to find my Texas screwdriver (about 3ft long) to do just what you said, put it against the pump, but I will be damn if I can find it. (its hard to lose) I appreciate the offer and will contact you about the fuel pump when I get a chance to find that screwdriver and then fire up the Vette and do further diagnosis. I guess when I am thinking the internals are failing- it also means the fuel pump rod maybe part of that equation as well. I dunno. Been working on cars a long time, never came across this scenerio before. Jon  

I'd find it hard to believe a fuel pump noise would travel all the way back to the rear of the car.....the pump is connected to the fuel lines with rubber hoses. The only way a noise could travel like that would be if the hoses are rock hard....in which case ya need to change them anyway! A fuel pump can certainly make a rat-a-tat noise like that, either from an internal failure, OR the pump rod wearing....I've seen/heard both....but never from the rear of the car. If the pump or pump rod is creating the noise, you would be able to hear it at the front, and you could put your hand/fingers on the pump and feel it.
Check those hoses!
Another thought is that possibly the sock filter on the pick-up tube on the fuel sender is collapsed, or otherwise damaged. If so, it could allow the fuel pump to create pulses back there that would possibly transfer to the line by the tire, but it would not indicate a problem with the pump itself.



dam spel-chek....


|UPDATED|4/28/2014 10:03:33 AM (AZT)|/UPDATED|

Joel, excellent response. That is an angle I didnt think about. Yes, the rubber hoses are there of course so maybe checking the fuel tank area is a more viable option. I was double thinkin g my routine from that day and it seems that this noise started after the tank got to quarter level. Up to that point it was quiet. Not sure if theres a connection there or not. Anyway, great response and some more fuel for the thought process, I really appreciate the help. Jon  

I believe the '78 up cars also had some sort of roll-over valve in the tank, since the fuel sender comes out the top. Could be something with that thing, too. Try loosening the fuel cap while the noise is happening, and see if that makes any difference....might lead us to a different solution.