Howdy Y'all,


At the prompting of Mike, 46yblock,

Here's a little info on how you should wire up your electric fuel pump.

All new cars nowadays and any boats with electric fuel pumps require a way to cut off the fuel if there's an accident or the key is left on with the engine not running etc.

So there's always an oil pressure switch that will prevent the fuel pump from running if the engine is not producing oil pressure.

Some marine applications have a solenoid operated fuel valve at the tank that will also close the fuel valve to prevent fuel from siphoning out of the tank when there's no power supplied.

For our trucks it's an easy operation to hook your electric pump up to only run when oil pressure is being produced.

You always want fuel pressure when cranking so you have to connect the fuel pump to the starter switch to power the pump during cranking only. After the engine starts an oil pressure switch keeps the pump powered.

To do this, use an oil pressure switch that "goes to ground" when oil pressure is present. Most of them are exactly opposite (so they ground when you lose oil pressure to illuminate the idiot light)

Your oil pressure light is wired such that one side of the light is connected to 6/12v + power when the ignition is on. The other side of the light is grounded to complete the circuit..... To do this it's connected to the pressure switch so that when there's NO oil pressure the pressure switch completes the circuit to ground and lights the light.

Using this concept for a fuel pump you would need to use an oil pressure switch that closes (grounds) when there IS oil pressure present.

The fuel pump "+" wire would be connected to the ignition A+ (6/12V) so that it would be powered any time the key is on.

The fuel pump negative lead would go to the pressure switch and only be grounded when there's oil pressure.

Since you would need to ground it when cranking also, you would either use a connection in your start switch that only grounds when you press the button/turn the key, or you could use a simple Radio Shack 12v relay to gound the connection while cranking. (the relay coil could be connected directly to the starter solenoid and be powered when starting)

You could even put a little LED idiot light in circuit to indicate when the pump is being powered.


The key here is that you only want to power the pump (ground the NEG lead) during cranking and after wards, only when there's oil pressure. This would greatly increase safety in case of an accident...... just having the key on wouldn't pump all the fuel out of that broken fuel line under the car for stray sparks to ignite!

Oh, by the way, a mechanical fuel pump does all this stuff without any electrical power or switches ...... "kiss"


Merry Christmas (can we still say that?)


Rick

 

Rick,
Thanks, nice post and very helpful. One thing comes to mind though. Making a guess that half of the Y trucks are running with the older style oil pan, and that they are prone to oil pressure dropping during hard stops or moderate downhill stops, I wonder if a fuel pump would quit running creating a stall and problems. Just thinking aloud here not arguing.

I sure hate loosing some of the convenience of my current wiring. Like being able to shut off the pump while the motor is running thus emptying the carb for winter storage, and likewise disconnecting the fuel line at the carb, turning on the pump and draining the gas tank.

Merry Christmas!

Mike

 

Mike,

I suppose that could be a concern... but if you lose fuel pressure in a closed throttle condition the engine would probably not quit since it would probably take a little longer to drain the bowl.

Also. We're probably talking about a momentary oil pressure drop to 10 psi or so maybe? Those oil pressure switches only take about 3 psi or so to close.....You may not even see enough of a drop to cause the switch to open (killing the pump)

Also, it would be a simple thing to add a simple switch to defeat the oil pressure switch operation or add a switch to run the pump with the engine off etc.

If I had a pan that allowed the oil to migrate away from the pickup long enough to produce zero oil pressure, I would pull it and weld in a baffle (like I did with the one I got from you!!)

On trucks where this is a problem does the oil pressure drop completely to zero and stay there for any period of time or does it just fluctuate?

 

I can only speak regarding my truck and pressure. But on a hard stop, or a moderate stop on downhill grade, the pressure gauge goes to zero. I can actually watch it going down in direct proportion to the foot pressure on the pedal. Currently have no baffle with 15W40 oil. Cruising oil pressure is 50. Gauge and sender are high quality Autometer. A baffled pan is due to go in place with the new motor so most or all of the problem will go away.

Yes you are probably right on the fuel bowl not emptying soon enough to cause stall in most instances.

 

Yeah....I would fix the pan so it doesn't do that. I wouldn't want my oil pressure going to zero for ANY length of time!!!

 

Good post for safety. A lot of times when we improve our older vehicles that is one point that is over looked. BUT (there is always a but, isn't there?) I would suggest using a crash relay switch to shut off the pump like most of the new cars have instead of a oil pressure switch. What if your engine continues to run after the accident? You still have oil pressure and you still have fuel pumping...

And Mike that would solve both of your concerns, low oil pressure and installing a switch so you can shut the fuel to "being able to shut off the pump while the motor is running thus emptying the carb for winter storage, and likewise disconnecting the fuel line at the carb, turning on the pump and draining the gas tank."

Y-Blockhead

p.s. Mike, how's my rear main side seals working out?

 

Forgot to mention, I was almost up in your neck of the woods to visit the in laws in Roseburg, OR this past week but the family got sick and the weather wasn't looking too good going over the hill from CA to OR.
So we're still in Southern CA.

Y-Blockhead

 

Today I began the breakdown process leading to the pulling of the old motor and putting in the new. I was under the truck looking at or for something and noticed some RTV that I had applied to one side of the clutch dust cover. It was JELLY. Oh crum! That was the same brand of RTV used to install the side seals, and oil turns it to JELLY. So I need to pull them and try and clean them up for reinstall. It is good the RTV problem was discovered before putting the motor in place.

Mike

 

Mike, If you don't mind sharing, what brand and/or type of RTV did you use so others including myself doesn't use it??

The side seals fit pretty tight though so maybe you won't have a problem?

I, personally am not a big fan of RTV as I am an ex-motorcycle mechanic and I've seen sealers destroy top ends on high dollar racing engines because of plugging of oil passage restrictors.

Y-Blockhead

 

I will look and see if I still have the tube tomorrow. Seems like there was still some left. Yea I agree about not liking RTV. You can find it in areas it isnt supposed to be in, like floating in your radiator. Plus, it is very difficult to clean a gasket surface previously sealed with the stuff.

 

Yblockhead, Where can you buy a crash relay switch, and how basically does it detect a crash?

If you are up here sometime stop by and say hello ! Give me a heads up and I will send directions.

The RTV was NAPA brand, number 765-1469, RTV Blue Silicone Gasket Maker.

 

Mike,
Crash relays are what newer cars have to prevent fires in a collision by detecting ah, well a crash... I have to admit I don't know how they work because they are self contained. I know they have been around for a while, my '89 Super Coupe has one. Thankfully I've never had it tested.

There is a reset button in the trunk if it ever gets "tripped".

The one I have on my '55 Ranchwagon I got from Ron Francis www.ronfrancis.com part #CR-92. Altho a little on the expensive side ~$89.00, I figure the car and my families lives are worth it for the added safety it provides. I'm sure others offer them.

We probably won't be up in Oregon to visit the inlaws in Roseburg now until spring break from school, takes about 13 hours straight through driving from where we are at in SoCal. (But thats hauling azz in the T-Bird Super Coupe, wife doesn't like the sound of the Eaton Blower on boost for that long, ha,ha).

Your outside Grant Pass, aren't you??

Anyway maybe we will hook up sometime,

Y-Blockhead

 

Mike, Did a little more research. I guess the more common name is Inertia Shutoff Switch, Do a search for more info if interested??

Y-Blockhead

 

Thanks. That should help a parts guy from going DUH .