Mechanical Fuel Pump not pumping
 

Small Block 350 in Project Heaven, thought fuel pump was bad because it was pumping but so slowly that the carb isnt getting any fuel. Im barely getting any to the inline fuel filter. But, there is pressure in the line as when I take one of the rubber lines off of the filter it blows the pressure off.

Replaced the mechanical fuel pump with a brand new one from the local auto parts store and same problem... I made sure that I got the pushrod onto the fuel pump lever properly, even double checked to make sure I had done the install correctly...

Any ideas????

Re: Mechanical Fuel Pump not pumping
 

you could have some blockage in the fuel line and the pump could be struggleing to pull fuel.

I had this same problem on the kids truck it ended up being the sock filter was clogged and half way up the sending unit reduceing the flow

Re: Mechanical Fuel Pump not pumping
 

Could be a bad fuel pump lobe on the cam. Not common, but it can happen.

Re: Mechanical Fuel Pump not pumping
 

I thought that to so I removed the pickup line and added a short (4 ft.) piece of 3/8 rubber line into a 5 gallon bucket and still no joy all the time. It is almost like it will pump a little fuel and then lose its prime and then pump a little and then lose its prime...

Re: Mechanical Fuel Pump not pumping
 

How would I go about checking that without yanking the camshaft?

Re: Mechanical Fuel Pump not pumping
 

So, you removed the line from the carb and little or no fuel came out of the line while cranking......before or after the filter?
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Re: Mechanical Fuel Pump not pumping
 

to completely rule out the lines I would attach a rubber line from your gas can directly too the pump then then another rubber line out the pump too another can and crank and see how much it flows then reconnect each line one at a time and note when the flow stops

Re: Mechanical Fuel Pump not pumping
 

Did the fuel pump push rod slide out? There are two bolt holes on the front pass. side of the block. The top one can be used to lock the pump rod if a longer 3/8" shank bolt is screwed into the threaded hole. Maybe somebody put a bolt that's too long in the hole and it's got the the push rod stuck..... maybe?

Re: Mechanical Fuel Pump not pumping
 

Lee H. -- I pulled the line between the pump and the carb, it is a metal tube up to just above where the intake manifold meets the block... Then it turns to rubber and in the rubber is an inline filter... I pulled the hose off of the filter on the pump side and I was able to get about 1/4 of a cup of fuel in less than 10 seconds and then it was like the pump lost its prime and it stopped pumping fuel all together. A few more turns on the key and she pumped again...

Midniteblues -- That is a good idea, I will try that tonight... I also called a buddy of mine that is the manager at the local parts store and told him that I think I got a bad fuel pump off the shelf, he has another one so I am going to take it out again and eliminate that as the issue.

Rustybucket -- There is a bolt in the top hole but it isnt long enough to hold the rod... I attempted to use it to hold the rod when I replaced the pump, to no avail...

Re: Mechanical Fuel Pump not pumping
 

You should make sure all the rubber lines before the pump are good. A small crack or pin hole may not leak fuel but can suck air, making fuel delivery spotty at best

Re: Mechanical Fuel Pump not pumping
 

Is the float bowl empty on the carb.? .... maybe the needle is stuck in the seat and won't let any fuel in. You said you had pressure at the fuel filter.
As far as watching the delivery, I've got a glass filter on the '66 Plymouth and it's always only about a quarter full when the car's running --- and it always runs fine. Fuel just kinda dribbles in but apparently it keeps up with demand.

Re: Mechanical Fuel Pump not pumping
 

Sounds like a bad pump, good luck! Just out of curiosity, can you blow through the line, has the rubber hose swelled up?

Re: Mechanical Fuel Pump not pumping
 

I had a glass one in there and could get a little fuel in there but not much. Maybe you are right and it isnt going to show much in the glass filter... I am going to take the carb apart tonight as well and make sure she isnt completely gummed up and not allowing fuel in and see if that is the problem...

Re: Mechanical Fuel Pump not pumping
 

Ignore that filter. My old truck did the same. Never looked like any fuel in it. Truck just kept on running on and on.
If it's running good leave it alone.

Re: Mechanical Fuel Pump not pumping
 

At this point I am trying to get the motor running after it sat for quite a while. So I am having to work to eliminate all the issues just to get it running again.

Re: Mechanical Fuel Pump not pumping
 

If the float is stuck in the up position (which I have had happen) just tap on the top of the carb to get it to fall. I repeat tap not bang lol

Re: Mechanical Fuel Pump not pumping
 

I have this problem now. New plastic tank, new sending unit with screen, new mechanical pump and the truck ran before rebuild. Tried bypassing the new tank by running a short hose to a gallon of gas. Nothing. Installed another new mechanical pump. Still nothing. Sucked gas up the lines to be sure they were not obstructed and getting fuel, they were. Removed second new pump and checked that the push rod was free and moving up and down, it was. Held the rod with a 3/8 bolt in the top hole, reinstalled pump still nothing. Bought a electric pump fuel tonight but I think I need to change my cam. I am hoping that the push rod is getting stuck and after I get the truck running it will be lubricated enough to function. Hoping!

Re: Mechanical Fuel Pump not pumping
 

I had a similar problem issue with my build "Ruby". I had installed a nw manual fuel pump, rebuilt the Q jet and had the truck running. Dad and I tore the truck apart for paint and 2 yrs later when I re assembled everything, the pump wouldn't pump. I installed a new pump and everything worked fine, The first pump had about 30 minutes of run time on it!

Re: Mechanical Fuel Pump not pumping
 

Well, it appears that a mechanical needs to be primed. I did not know this and swear I never have done it before. However, after 2 new mechanical pumps I bought a electric pump and plumbed it in series. Meaning that I have it pumping to and through the mechanical pump. It pulled from the poly tank, through 2 filters the mechanical pump and loaded the floats of the Edelbrock 1406 and my engine fired. Because I need to adjust my lifters and have my covers off, I did not start the engine and hooked up my under hood starter. While cranking the engine I noticed my fuel pressure gauge jump up to 7-8 lbs WITHOUT the electric pump! I let it rest a while and did some other tasks, came back and the pressure gauge dropped to 0, so I squeezed the remote starter trigger and the engine cranked, and the fuel pressure gauge jumped right back up to 7+ lbs!!!! Why would a mechanical pump need to be primed? Also, as I had sucked gas up through the line from 2 different sources to check for flow the mechanical pump did not build pressure. Anyone have any input?? This was very frustrating!! Guy

Re: Mechanical Fuel Pump not pumping
 

Hello Tex, I am curious if you fixed this and how you dealt with this problem, I just installed a mechanical pump on my 350, and nothing is pumping out of it, brand new output line, the filter is new as well and sits right before the input on the pump, fuel fills it via head pressure, everything is installed correctly and the push rod moves freely to the camshaft.

Re: Mechanical Fuel Pump not pumping
 

If there's no fuel in the line after sitting or when you run it out of gas, you have to prime the carb. The bowls have no fuel in them. The starter cranking will not be enough to prime the fuel pump but when you start the truck up by pouring a little gas in the top of the carb, it will prime the whole system quickly.

I have been doing this a lot recently after the engine rebuild, replacing old lines and such.

:gmc2:

Re: Mechanical Fuel Pump not pumping
 

Thanks hilandr, I have tried that about fifteen times, starts for about five seconds still no sign of fuel making it out of the pump, new line from pump to carb, disconnect at the bottom of tank and fuel pours out freely, I have purchased a second new pump and will try that right now, maybe its a faulty pump.