Fuel pump or fuel percolation

[Doug&Deb]

I’m trying to determine whether my fuel pump is going bad or if heat is the problem. When going up hill at temperature my Coronet sometimes acts like it’s not getting fuel. Kicking on the electric pump cures the problem. This only happens when the temperature gauge shows 200 degrees. The mechanical pump is 2 years old and the pin isn’t coming out. There are no leaks that I see. Any thoughts?

[Dan Hiebert]

Sounds like vapor lock.  Especially since the problem goes away when you kick on the electric pump.  Fuel vaporizes in the line due to heat.  The weather doesn't have to be hot, engine heat itself will do it, but it's more prone to happening when it's hot out.  Mechanical pumps work on a vacuum principle, which cannot overcome the vapor in the line.  Electric pumps don't and easily push / pull the fuel through. 

[greg g]

Any air infiltration on the suction side of the pump will have a negative effect on pumping efficacy.  Slight cracks, loose flare connections, clamps can be culprits.  Or opposite that would be insufficient  venting, causing  impared flow under high demand situations. 

[Sam Buchanan]

3 hours ago, greg g said:

Any air infiltration on the suction side of the pump will have a negative effect on pumping efficacy.  Slight cracks, loose flare connections, clamps can be culprits.  Or opposite that would be insufficient  venting, causing  impared flow under high demand situations. 

 

Or a restricted filter in the tank.

[keithb7]

A fuel pressure/vacuum gauge is cheap and will tell the story. Hook it up. If needed tape it to the windshield and go for a drive.  Won’t say I’ve never done that. ?

 

 

Edited November 6, 2022 by keithb7

[Doug&Deb]

Good idea on the gauge. I’m not able to drive it as much as I’d like. The deer are in rut and I have no desire to hit one. I assume you plumb the gauge between the mechanical pump and the carb? 

[keithb7]

Yes. That’s where to plumb it in. 

[Doug&Deb]

Thanks everyone. I’ll check for leaks first then try hooking up a gauge to check pressure.

[greg g]

There is also a flow quantity test in the service manual. Easy to do but needs an assistant or a remote for the solenoid.