| Re: Fuel pump in but no pumpy [message #362880 is a reply to message #362854] |
Tue, 16 March 2021 22:18   |
Rick Staples
Messages: 126
Registered: May 2014
Location: Johnstown, Colorado, USA
Karma:
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Duce,
Since it worked before, and the only thing changed was the fuel pump, I'd start there. I'd disconnect the fuel line from the pump (suction side), attach a vacuum gauge, and crank the engine with the starter for ~30 seconds or so. The gauge should read at least 5 or 10 inches of vacuum, and should hold that reading for at least a minute or so. If it does not, I'd pull the pump off and recheck it.
Work the lever by hand and make sure it pulls vacuum. If it does not, you've got a defective pump. It happens!
If the pump works manually, look for scratches on the side of the lever. It is sometimes possible to install the pump a little cockeyed, so the lever essentially "misses" the cam in the engine, then no pump action. Reinstall carefully.
If the pump DOES pull vacuum when the engine cranks over, I would check carefully for any small leaks in the fuel lines from tanks(s) to pump. Any small leak in those lines will allow air to enter instead of fuel. (Been there, done that, although not on the GMC.) If you have access to a "Mity-Vac" or similar vacuum pump and reservoir, attach it to the fuel line and make sure you can draw fuel from the tank.
All the suggestions about electric pumps are generally good ones. I have a Carter 4070 pump in my auxiliary fuel feed, with a primer switch on the dash. It does help to overcome vapor lock on occasion. OTOH, the original mechanical pump is simple, safe, good enough for GM, and worked for 45 years. It should work now.
My 2ยข, HTH
Rick Staples
Rick Staples, '75 Eleganza, Johnstown, CO
"Advice is a dangerous gift, even from the Wise to the Wise, and all paths may run ill." -Tolkien
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