fuel pump won't pump
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fuel pump won't pump
I am making good progress. The engine runs great but i am continually having fuel pump problems. I finally bought a new one from Macs. It worked for a couple weeks but now it won't suck fuel. It is definitely the pump - there is no suction. Everything looks good. Are these pumps really that bad?
Hotshot
Joined: Oct 2004
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From: Durham NC
Sounds like you have trash in your tank/fuel line that is getting under the one way valves in the pumps. Fuel pumps are rather simple design. Rocker arm moves diaphragm in and out pumping the fuel, two one way (usually disk) valves only allow gas to go from tank to carb. If it doesn't pump it must be either the rocker arm pivot pin fell out (check, they some times work themselves out, especially on rebuilt pumps) the arm or cam is worn/broke, or the diaphragm is ruptured, or a one way valve is stuck open (trash or broken spring) Since the pump is new and did work my money is on the open valve.
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thank you - problem found
Your note got me thinking. You are right this pump is a simple device. I took it apart blew everything out. As i stroked the pump lever manually i could see it had great suction. I reassembled and as i was putting it back on the engine i noticed that it is possible for the push rod to be out of the pocket which operates the pump lever. I was careful to make sure it was retained in the pocket on the lever. Hooked everything up and it worked great. Then as i left it running in the driveway while i swept out the garage it killed and wouldn't restart. It looks like the pushrod worked its way out again. In watching the pushrod i notice that it has a bend in it and that it rotates as it strokes. I am guessing that is why it works its way out. I'll get a new pushrod unless someone notices this post and tells me that pushrod should have a slight bend in it. Thanks again for the quick reply. That was the trigger to make me look further.
Phantom of the Phorum
Joined: Jan 2011
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From: Kentucky
I assume this is your '48 w/Flathead V8. The fuel pump push rod should be straight.
You should also check the stamped steel clip on the end of the rocker arm in the pump. Sometimes they will work their way out of position but still be attached. If this happens they won't hold the push rod in place.
In the first picture it is correct, in the second it is not:
You should also check the stamped steel clip on the end of the rocker arm in the pump. Sometimes they will work their way out of position but still be attached. If this happens they won't hold the push rod in place.
In the first picture it is correct, in the second it is not:
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Good idea
Thanks very much for the pictures. There is no question my pushrod has a gentle curve in it, so I'll have to replace that but after looking at your pictures I do need to check that clip on the end of the arm - I think it might have been damaged by the eccentric action of the bent rod.
Hotshot
Joined: Oct 2004
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From: Durham NC
There are several fueling problem topics going, here is an illustration Number Dummy posted in one of the others: 
Pin# 9378 sometimes backs out of one side of the housing due to worn bore and the arm ***** That can bend the pushrod and or allow it to fall out of the cup. Spring #9380 keeps the cup onto the pushrod by acting like a shock absorber. Parts #9352 are the one way valves.
Pin# 9378 sometimes backs out of one side of the housing due to worn bore and the arm ***** That can bend the pushrod and or allow it to fall out of the cup. Spring #9380 keeps the cup onto the pushrod by acting like a shock absorber. Parts #9352 are the one way valves.
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That's why the pushrod is bent
This diagram and explanation is really helpful. The original pump - or at least the one that was on there when I took it apart - did not have the spring and it had the bent pushrod. Mind you it is not much of a bend - but it is definitely not flat. So I am assuming that this happened along the way - presumably we got the spring out of the engine when we tore it down and rebuilt it but it has been a while. That probably contributed to the pushrod problem. Then when I put the new pump on with the bad pushrod - it can work its way out of the clip on the end of the fuel pump arm. In addition I am pretty sure the pushrod is worn some making it even easier to come out of place. I ordered a new pushrod from Mac's and I am sure this will solve the problem.
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