Posted by Paul Cook on Monday, September 24, 2001 at 1:12PM :
In Reply to: M-37 fuel pump switch -- how does it work and posted by Robert on Friday, September 21, 2001 at 0:14AM :
Many owners installed an electric pump to prime the fuel system when their trucks aren't used often. Use the pump when starting and then shut it off. You may not even need to use the choke.
Or, bypass the mechanical pump and just use the electric. They work well if you make sure of several things.
Some electric fuel pumps have higher working pressures than others. The correct pressure for the M-37 is not less than 4 psi and not exceed 5 1/4 psi (TM 9-8030, Para 138) If you use the electric and the mechanical pumps in series, each adds pressure. Some performance shops have adjustable fuel pressure regulators you can put in-line if your pump pressure is too high.
Check to see that the electric pump is the right voltage for the power you are using. It is possible to use a 12v pump briefly for priming but it might not be safe for full time use. It also might create higher pressure than when used at the correct voltage.
Because the electric pump creates pressure even when the engine is not running, the float valve must be in good condition or the pump will flood the engine. Also, having the float level set correctly is important.
The best locat1on for an electric fuel pump is near the tank. It is important to have a filter BEFORE the pump. Also, this locat1on pressurizes the entire fuel line so all components must be in good condition. Any leaks in a pressurized system will show up. Minor leaks may not show up when the system is under suction and these minor leaks may allow foreign material to be sucked in.
Another advantage to a pressurized system is rubber hoses don't collapse when you have had to use a piece that is longer than usual.
You can use an electric pump in the engine compartment but this puts most of the system under suction as discussed above.
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