help understanding the oil pressure / cutoff circiut (1 Viewer)

[PERUVIAN]

Guys..
A few quick questions-
My oil pressure sending unit has 2 terminals.. a round center tap and a spade terminal.. Are they both the same.. How does the cutoff work.. When you have no oil pressure does the switch have high resistance or low ( or does it ground or go open ) ? If I could understand the unit a bit more.. maybe I could design my own circuit that worked with the fuel solenoid on my rotary inj pump.. in the 3b manual it seems to keep talking about an EDIC that I do not have.. it seems to describe a unit that actuates linearly a rod that controls the fuel flow.. I have no such device -

my oil pressure goes immediately to full when I start it.. both with the 2F and 3B motors.. it seems to not matter which sender I use.. they could be both bad.. or something else entirely..

ideas?
Todd

 

[Kynot62]

There are two sending units on my 3B with an inline injection pump. The one on the filter housing is for the pressure gauge on the dash and the one just forward of that sends a signal to the EDIC that shuts off the motor if there is no oil pressure (I think it has an 8 second delay or so) It's the motor that controls the inj pump.

Since you don't have the EDIC (which shuts off the fuel or puts the pump in run or start position) the cutoff circuit won't do you much good. I don't know if the rotary pumps had an automatic cut off or not. What you could do is wire the cutoff to an alarm or light that shuts off once you have oil pressure. Diesel boats are set up like this but you may find the alarm irritating.

Can't say much about how the electrical part works as wiring is my weak point.

Bottom line is that you don't need the cutoff circuit for the truck to run, its a safety device to avoid cooking an engine. Nice to have, yes. Just make sure you have an oil pressure gauge you trust and you will be fine.

Tony

 

[cruiser_guy]

As Tony says, two separate senders. The sender goes to ground on low oil. If you want it to work on your swap then you'll need a relay and a timer to over-ride the relay until oil pressure is sufficient.

 

[lostmarbles]

This pic shows the difference in appearance between the switch and sender Todd:



And the switch and sender normally receive their earthing via their screw-in threads. But some actually have an earthing tab (spade terminal) on the body too.

The switch opens on oil pressure rise (at about 2-5psi) and recloses on loss of oil pressure.

 

[cruiser_guy]

Todd you're will look a little different as the pic is a "B" not a "3B" but the senders are the same.

 

[jake2far]

[A few quick questions-
My oil pressure sending unit has 2 terminals.. a round center tap and a spade terminal.. Are they both the same..]

The oil pressure sending unit center terminal is for the gauge, the spade terminal is for a ground connection, the sending unit will work with or without the ground terminal hooked up.



[How does the cutoff work.. When you have no oil pressure does the switch have high resistance or low ( or does it ground or go open ) ?]

The oil pressure switch makes contact to ground when the pressure falls below a set point which I think is around 4 psi (not sure, doing it by memory)



[my oil pressure goes immediately to full when I start it.. both with the 2F and 3B motors.. it seems to not matter which sender I use.. they could be both bad.. or something else entirely..]


Not sure what you are saying, your gauge pegs to full pressure when you run the rig? Have you put an actual gauge on the pressure port to get a PSI reading? This will tell you if you have high oil pressure or a gauge sending unit problem.


Jim