Fuel Pump Question/Ideas

[Chris P]

There is an extra unused wire that comes out of the back of the ignition switch. It is #85. I run my electric fuel pump off of it with no other switch. The fuel pump turns on and off with the ignition. I have a fuse behind the dash, near where it connects to #85. I suppose I could disconnect the pump at the fuse if for some reason I ever wanted the ignition on without the pump running. I also have a battery cutoff, which is a good idea to have with or without an electric fuel pump.

[sturmtyger380]

So tell us where you put your pressure regulator? Is it up near the engine?

Alan

[ZGjethro]

I am guessing we need a pressure switch which closes the contacts when you have decent oil pressure, maybe 20 lbs. Don't most switches do the opposite and open when you have pressure. The intent being that they turn on a light if oil pressure drops. Does anyone have a product number which I could order?

Never mind. Quick google search yielded lots of options

[carolinamv]

Ok ,

2 new questions. I replaced my oil pressure gauge with the correct one , it reads a little less than 30 PSI when you crank it and let it run for about 5-10 min. Is that normal ? Should it jump when you mash on the pedal?

2nd question ,
On the back of the Battery on off switch on the dash , there's 4 plugs I think I felt. Do you know which one the hot wires and the ground wires are? I wanted to ask here before I had to un plug them all to test them.

[F18hornetm]

I am guessing we need a pressure switch which closes the contacts when you have decent oil pressure, maybe 20 lbs. Don't most switches do the opposite and open when you have pressure. The intent being that they turn on a light if oil pressure drops. Does anyone have a product number which I could order?

Never mind. Quick google search yielded lots of options

Pressure switches can be normally open or normally closed. NAPA sells both although I don't have part # handy, if needed I can get it.

Dumb question, Why doesn't everyone just use the mechanical fuel pump they came with? If I had to install an electric fuel pump I would power off ignition switch and fuse it. Easy. No need to make any more complicated than needs be.

[just me]

I have a civilian fuel pump with sediment bowl. It provides more fuel than that tiny one hole can use. Easily. I do have a correct vacuum/fuel pump, but need to find a rebuild kit for it. The one place I knew had them is now out of business. The previous owner had an electric on it. (And a box with 4 more electrics and 2 civilian pumps) I put the good civvie on and no troubles. Gave away a few of the electrics so far.

[ZGjethro]

I am guessing we need a pressure switch which closes the contacts when you have decent oil pressure, maybe 20 lbs. Don't most switches do the opposite and open when you have pressure. The intent being that they turn on a light if oil pressure drops. Does anyone have a product number which I could order?

Never mind. Quick google search yielded lots of options

Pressure switches can be normally open or normally closed. NAPA sells both although I don't have part # handy, if needed I can get it.

Dumb question, Why doesn't everyone just use the mechanical fuel pump they came with? If I had to install an electric fuel pump I would power off ignition switch and fuse it. Easy. No need to make any more complicated than needs be.

Because after I crash into a telephone pole, and am knocked unconscious, your way of wiring would keep the electric fuel pump pumping gas. If the engine stalled, and oil pressure dropped to zero, a pressure switch would shut off the pump. My truck is wired like you suggested, with an additional switch in series.

[F18hornetm]

My dumb question wasn't WHY you would want a pressure switch or how it works. My question was why doesnt everyone use the original mechanical pump. It to would stop pumping if you run into a pole, your knocked unconcious and the engine stalls.

I dont disagree with safety measures and it would be easy to plumb in a low pressure switch or even an inertia switch. Since these ignition switches dont have a crank position, your going to have to come up with a way to run the pump while cranking, until oil pressure builds up. Especially if its sat for a while. There are time delay relays which would allow the pump to run in the ON position for 10 seconds, then the oil pressure switch would take over. Lot of first fuel injected vehicles used these type systems. You could also get a very low psi operating switch, so it would minimal cranking to build pressure. Or just use bypass switch.

[carolinamv]

Reliability of the truck is what id say.

Any ideas on the switch guys?

[just me]

Easy way to do what you are woried about.
Hot wire from ign to ctr pole of mom-off- on switch.
Wire from mom position to pump side of oil pressure switch.
Wire from ON position to other terminal of oil pressure switch.
Wire from pump side of oil pressure switch to pump.
Oil pressure switch must be open on low pressure type.
Now, you can boost the fuel for starting (MOM)
Have the pump run when the ign is on AND there is oil pressure.
Turn the pump off if you want ign on but engine not running.

[F18hornetm]

Reliability of the truck is what id say.

Any ideas on the switch guys?

Reliability of the truck? Your referring to why you would need an electric fuel pump? Do these trucks have issues with mechanical fuel pumps? This is my first M37 and have very few miles on it, but have plenty of other equipment with mechanical fuel pumps. Just wondering what the issues are. Heat, cost? etc


to give you some ideas
Napa # 701-1591 is normally open and normally closed depending on how you wire it, factory setting is 4 psi. 6-24 volt
Napa # 701-1577 is normally open and closes at 15 psi factory setting
Holley also makes oil pressure fuel switches for fuel pumps, normally open and closes at like 5psi or something like that
Napa ECH OP6624 is a fuel pump pressure switch, but don't have manuals near me to see details.

if you need more info, I can check with local NAPA guy and see what they have.

[Tuko]

Vapor lock, and the deterioration of the fuel pump innards leading to gas in the crankcase are concerns. A rebuilt pump with modern parts should solve the gas in oil problem some have success with shielding the fuel line from heat to solve the vapor lock.

[F18hornetm]

Thanks for the answer Tuko.
Mine has a mechanical fuel pump and seems to work fine. I haven't had it in the summer to see about the vapor lock issue so time will tell. But I did make a heat shield that was missing for it as well as routing new steel fuel lines[they were rubber] further away from the exhaust manifold than they were. The previous owner had the fuel pump rebuilt and believe it or not had all the receipts including parts list from the repair shop. He spent a fortune on this truck. I'll see how it goes this summer. I find it hard to believe the military used these in Vietnam [some as small gun trucks]with vapor lock issues that were not correctable. Just thinking.

[eagle4g63]

Sorry, to not check in faster....anyway in regard to your question about the factory ignition switch.....yes there are 4 contacts.....what you have is actually 2 pairs of contacts, hope that makes sense(called a dpdt switch). The 2 wires that are there now should be a positive coming into the switch and a the positive going back out of the switch....the other 2 spots are not in use and can be, that is why I said just use the factory switch.....you need to run a positive in and the positive out to the pump.....if you look at the back of your switch the 2 spots with the ribs on them(will make sense when you look) will be the positive in spots. You have 2 choices jump the one that is there onto the other one or run another positive to it, then come out the last spot and go to your pump.

[carolinamv]

I have a Pos wire for my fuel pump, and I can just take into one of the ribbed Pos wires on the switch and done?