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Mechanical Fuel Pump **Pump Replaced, Noise Getting Worse**

nemesis_pyros

nemesis_pyros

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My big block is sounding like it has a loose rocker but I double checked and adjusted all the rockers so its not that. What I was wondering is would a mechanical fuel pump thats on its last legs sound like a loose rocker arm. ever since this noise got worse the truck does kinda stumble on hard acceleration but other wise runs fairly well. Also if its improtant I put in a new cam but it was making this noise before.
 
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describe the sound in more detail. Is it a clacking, clanking, ticking?

Is the sound intermitant or does it constantly do it? Any times worse than others?
 
Sorry for the late reply been busy all weekend.

I have replaced the fuel pump this weekend and there was no change in the sound but the truck does run better now, the stumble is gone and infact the truck runs awsome. But this noise is getting really loud and its starting to really bother me.

The sound is more of a clacking. It almost completely goes away when its idling and its the worst when crusing at 2000 rpms. Its also gotten worse over the weekend, but in the begining it was only apparent after the motor warmed up.
 
was the fuel pump push rod damaged in any way, did you notice when you changed the pump? That or have you check your valve lash? maybe it is a valve out of adjustment.
 
Ya I made sure to inspect the fuel pump push rod and it looks in good shape. The new pump didn't make any difference regarding the noise.

Yes I adjusted the Rockers 3 times and I'm pretty sure the noise is not coming from any of the valves.
 
Does your oil smell fuelly? If the pump went bad they sometimes leak gas into your oil thinning it down and causing noise/bearing failure.
 
To completely rule out the fuel pump and pushrod as the source of the noise, take the pushrod out so the pump is not pumping. The carburetor should have enough fuel in the bowl to run. Give it a few revs...
 
It might sound stupid, but have you checked to see if you have any exhaust leaks?
 
Hmmm Maybe I should check the exhaust again. I did tighten up some bolts and that got rid of them. It really sounds like something clacking, I've never heard an exhaust leak sound like this before. We did take a mechanics stethoscope and try to find the noise but with no luck.

And to the other responses. No the oil is fine the pump wasn't leaking any fuel in the oil. Taking the fuel pump off and letting it run sounds like a good idea although I don't think it will run long enough.
 
When it starts stalling out just spray that starting fluid stuff down the carb.
 
Chevy305 said:
When it starts stalling out just spray that starting fluid stuff down the carb.
Click to expand...

spraying starter fluid or pouring gas in the carb while trying to make it run or keep it running is not a good idea. i have seen a few carbs backfire with huge flames coming out the carb when they did this, which resulted in fires and lots of damage:eek1:.

also , could your timing chain be slapping the cover when you rev it up ?
 
How many miles on the engine?

Could it possibly be a collapsed lifter? Flat cam lobe? Main bearing?
 
Brand new cam and lifters, timing chain has less than 5k miles on it and was in great shape when we took out the old cam. I'm sure its not a main bearing going sounds more like valve train noise.
 
Sure you got the right fuel pump?

A smallblock pump will bolt up and work, but the arm is different and will leave a gap between it and the pushrod, resulting in a knocking noise. And, with the extra clearance between the pump arm and rod, the pump doesn't travel fully resulting in reduced pumping capacity, which can affect full throttle operation (read: the pump can't supply enough fuel when the secondaries open, the carb gets sucked dry and the engine stumbles)

Fwiw the smallblock part # is 40987, and I've had more than one parts store tell me their catalog listed it for a BB also. It isn't the right pump for a BB, ime.
 
test...

You could rig up a "gravity feed" fuel tank to run it longer than the carb bowl will allow...an old lawnmower gas tank works well--we used one at the boneyard to start carbed motors,we'd put it up on the cowl,higher than the carb..but it will run on whats left in the carb bowl for at least a minute or two,long enough to diagnose most noises..

You could have a collapsed or cracked piston skirt,I've seen quite a few on BBC motors..or a rod bearing thats loose..they rattle the most at about 2500 rpms,and when you let off the gas suddenly,its a metallic rattling sound...main bearings are more of a "thud" under load,they dont usually make noise at idle unless they are really wiped out--and you'd see the drop in oil pressure,if you have a gauge....a collapsed lifter is a possibility too..

Also mke sure the flexplate isn't cracked,and the torque converter bolts are tight...noises can "travel" and sound like they are in one place,but actually originate in another--a mechanics stethascope could be helpful in your diagnosis:crazy:
 
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