Wiring the electric fuel pump

[Unregistered Guest]

I am confused with the wiring of the electric fuel pump. The diagram in the manual shows that the fuel pump gets its power from something called the oil switch. I don't seem to have one. Would you please advise how I should wire it up?

[Don Moyer]

The purpose of an oil pressure safety switch is to deactivate the electric fuel pump any time that the engine is not actually running (and producing oil pressure). These switches are a Coast Guard requirement to protect against the possibility of someone accidentally letting the ignition switch in the "On" position, which (without an oil pressure safety switch) would let the fuel pump pressurize the fuel system while the boat is left unattended.

Primary power for an electric pump normally comes from the positive terminal of the coil. From the positive terminal of the coil, a 14 gauge wire is connected to either side of the oil pressure safety switch. This power lead should be protected with a fuse between 5 and 10 amps. The fuel pump connects to the other side of the oil safety switch.

On late model engines with Delco starters, there is an "R" terminal on the rear face of the starter solenoid which functions as an auxiliary contact, meaning that it is energized only during the time the starter is engaged to start the engine, and becomes de-energized again when the starter is disengaged. Universal used this terminal to supply power directly to the fuel pump while the engine is being started, by running a lead from it (the "R" terminal), to the same terminal on the oil safety switch to which the pump connects.

Early model engines with Prestolite starters do not have an "R" terminal, and their fuel pumps work fine without this feature. As it turns out, oil pressure raises above 10 psi (to close the pressure switch) within seconds following the start of cranking, making the connection to the "R" terminal somewhat redundant.

Many customers (both early and late model) connect a switch across the terminals of the oil safety switch and locate it in some convenient location so as to provide a manual bypass feature. With this switch in the "On" position, the pump will run any time the ignition switch is turned on.

Such a bypass switch can be used during maintenance and troubleshooting activities, first start up in Spring (when fuel level is usually low in the carburetor), etc. The oil safety switch should not be bypassed routinely, however, as to do so would violate Coast Guard requirements.

[pdecker]

Also, make sure your fuel pump is fused! The fuel pump on my 1982 Catalina 27 failed last year, and the insulation on the hot wire melted before the wire broke. Lots of smoke. I then found that the fuel pump was not fused. That is not the kind of excitement you want on the water.

[Moby]

R connection on solenoid

OK, this is what happened to me. I have the exact set-up Don described. A wire going from the + terminal of the coil to the oil pressure switch. The other side of the switch goes to the fuel pump and to the R terminal on the solenoid. This is really just a direct connection to the S side which goes to the ignition key start terminal.

I'm pretty sure that is the way it was connected before I upgraded my engine and installed all new wiring.

So when I go to start the engine, I turn the key, it cranks over but when I release the key it continues to crank until I turn the battery switch off. Then when I turn the battery switch on it does not crank over (not stuck solenoid).

My theory is that when I start to crank the engine, the oil pressure switch closes after a few seconds like Don said, this then connects the +12 from the coil to the pump but also to the R terminal on the engine. This energizes the solenoid and keeps it going even after the key is released. Why did this not happen before and why does it not happen on every engine wired like this?

I remove the wire going to the R terminal and everything works fine. I did have to run the pump manually before starting the engine to fill the carb bowl.

Two years idle and the engine starts and runs great. I did turn it over by hand a few times and lots of fogging oil in the cylinders. Not bad considering I upgraded a lot of things (new fuel pump, all new wiring, new electronic ignition, rebuilt the carb, new thermostat, new cooling cover plate, stripped and painted the engine).

Moby
Miss October 2009

[rigspelt]

That's a puzzler. The R terminal only has power during cranking. If the lead to it was continuous with the ignition circuit, then presumably there would also be power to the R terminal when the key was in "run" as well as "start", but I don't see how that would keep the starter cranking. But then I'm not a mechanic. If I've got all that right, then could there be an electrical fault inside the starter solenoid between the R and S terminals?

Sounds like one does not need the R lead anyway with the new MMI oil pressure safety switches.

[ndutton]

I realize safety is the reason for having the oil pressure switch for an electric fuel pump and I believe it's an ABYC requirement but considering what it protects against, under what circumstance would the ignition switch be left on without the engine running? I've never had that situation on my boat and can't conceive of it ever happening. Am I missing something?

[Moby]

The R and S terminals are shorted inside the solenoid. So what happens is that when I crank the engine, the oil pressure switch closes and connect the + terminal of the coil to the R terminal on the solenoid. This keeps +12 on the solenoid even when the key is released from cranking. The engine will continue to crank until I turn off the battery.

Even if I remove the key it continues to run. This must mean that power going to the engine on the purple wire is there all the time, not just when the key is in and on.

Good thing I am figuring this out now and correcting it. I am also following ABYC wiring rules and creating a schematic so it is documented!

Moby

[Figment]

I realize the safety reason for having the oil pressure switch for an electric fuel pump and I believe it's an ABYC requirement but considering what it protects against, under what circumstance would the ignition switch be left on without the engine running? I've never had that situation on my boat and can't conceive of it ever happening. Am I missing something?

My fuel gauge doesn't read anything unless the ignition circuit is active. Many is the time I've powered the circuit to check the fuel level and then forgotten about it for hours. Or days.

[ndutton]

Many is the time I've powered the circuit to check the fuel level and then forgotten about it for hours. Or days.

The scenario you describe could be avoided with an oil pressure and temperature alarm system, the buzzer would serve as an audible reminder. Did your coil suffer any damage?

[rigspelt]

solenoid gremlins

A slave starter solenoid on another boat developed a cold connection that took me 3 seasons and hundreds of dollars to locate. The tach would flicker and finally the engine would simply stop running after about an hour, then I could restart it in 20 minutes. Searched all over for that gremlin. Turned out to be a $30 part.

[thatch]

R clarification

Moby,
Great looking engine,.... now on to the business at hand. I have read and re-read your posts and and I believe you may be missunderstanding the R terminals function. It is completely isolated and only becomes hot (+12v.) when the start switch is engaged. It's use in automotive systems was to bypass the coil "resistor" during starting for a hotter spark and would become disconnected when the start switch was released. If during your rewiring you have connected the R and S terminals together, then the R terminal is now acting as a "holding circuit" and will continue to keep the solenoid energized after the start switch is released. When you turn the battery switch off, you are killing all power to the starter allowing the circuits to open. Actually, current thinking is to "not" use the "R" bypass terminal but to go to a momentary contact (spring loaded) switch wired to a fused, hot 12volt source to prime the fuel pump.
Tom

[Figment]

The scenario you describe could be avoided with an oil pressure and temperature alarm system, the buzzer would serve as an audible reminder. Did your coil suffer any damage?

Of course, but I positively LOATHE those beeper/buzzer things.

I used to have the blower direct-wired to the ignition so that it would run constantly. That was certainly audible.
I conventionally-wired that though when I installed the PCV system and no longer needed the blower to rid the cabin of blowby odor.

No coil or other damage that I can detect. Runs like a top.

[Moby]

Tom,

I looked at pictures of a solenoid that was taken apart and the R and S terminals are hard shorted inside the solenoid. In fact, kind of funny, I have a white wire and a yellow wire with a red stripe. White is connected to the S terminal, yellow-red connected to the R terminal. Both go to the start terminal on the ignition key. I can disconnect the yellow-red and the engine still cranks. Redundancy is the best policy of redundancy.

The big puzzle for me is how did it work correctly in the first place? I can only guess that the connection to the R terminal from the pressure switch/fuel pump wire was bad. The other puzzle is that the engine would continue to crank after the key was removed. The purple wire going to the + of the coil should lose power when the key is turn off. I verified that with the volt meter. So what kept the solenoid energized when the key was turned off?

Moby

[hanleyclifford]

defective solenoid

If your "R" and "S" terminals are shorted together, you have a defective solenoid.

[thatch]

Hold on to your hats!

Moby,
Bear with me while I walk through this very interesting circuit phenomenom. Your explanation of the white and yellow/red wires acts just like it should for the way the wires are run. In this configuration with the two wires run together to the start switch the solenoid in addition to energizing the starter is sending an internally supplied 12volt signal, back to the start switch via the now energized R terminal and back to the solenoid through the white wire, this type of wiring is called a "holding circuit", which is good in certain cases just not here. The only thing that would disengage the starter at this point would be to shut off all power (the battery switch) or to disconnect the red/yellow wire which of course you are aware of. The yellow/red wire from the R terminal, belongs on the fuel pump side of the oil pressure saftey switch, if you choose to use it but is not absolutely necessary.
Tom