This little fitting sits on the very far back of the intake manifold, right next to the distributor. It looked like a vacuum fitting but when I looked some more I saw three wires coming out of the end of it all chopped off and going nowhere. I'm thinking this is a vacuum sensor of some sort...any confirmations on that?

Btw car runs great its a carbed 400 so this is basically just out of curiosity was this an intake manifold for a computer controlled carb or something like that?

 

That's your oil pressure sender. Senses oil pressure and sends that info the the ECM and the oil pressure gauge in the dash.

 

That's the Oil Pressure Sending Unit. Is your oil pressure guage working? There may be another one just above the oil filter - I'm not familiar with the 400's, the 305's and 350's sometimes have one above the oil filter. If the wires are cut, then maybe someone cut them to rig the wiring for the intank fuel pump to run - this is what I've done with mine. Out of the 3 wires going to it, the smallest one is just the sender wire for the oil pressure guage.

 

Hey so thats why my oil pressure guage doesn't work...geez its a mess cleaning up somebody elses terrible engine swap

 

Might want to double check that tidbit.

 

You know - that would be a great idea - to send oil pressure info to the ECM, so that a code could get set, and let the teens, wives, non-car savvy folks know that they NEED OIL!!! Maybe the new cars have 'em - I have nothing newer than 1997. But they need a big flashing light and a siren!

Case in point - my brilliant 19 year old son. While in Afganistan, he bought a car from none other than an ebay seller ... from the Bronx, and had it shipped to his base in Ga. so it would be there when he returned. Not bad enough? The story continues ... When he returned, he drove the car home to NC, when he arrived I asked him if he'd checked the fluids - he tells me yeah, it's all good. Next day, his car died on the highway. Can you guess where we're going here? That's right - NOWHERE - there was not a drop of oil in the car, and it completely seized. I asked him why he told me the fluids were fine when they obviously were not, his response was "the seller told me he had just changed and filled the oil"

 

As you requested.

 

That leg is a fuel pump power signal, not an oil pressure signal.

 

Actually, it functions as both. It sends a signal to the ECM telling it that there is oil pressure and the ECM turns the fuel pump on. As long as there is at least 3psi of oil pressure, the ECM will turn the fuel pump on.

If the ECM fails or is disconnected, the oil pressure sender provides a separate ground path for the fuel pump relay.

 

As your own diagram states, the ECM will turn on the fuel pump for 2 seconds, and keep it on as long as it sees ignition pulses. It doesn't use oil pressure as an input.

 

See, this is what I get for trying to post while at work. Yes, the diagram does state that. I think I'm mixing up my diagrams in my head.

It also shows a connection from the oil pressure sender to the ECM. If it's not to report pressure to the ECM, then why is it connected to it?

Also, in the interest of accuracy, I should mention that the oil pressure sender provides a separate POWER supply to the fuel pump if the ECM dies, not a ground as I mentioned in my last post.

 

About all I can figure is it will trip a trouble code if both the fuel pump relay and the oil pressure switch fails. But, I don't know that for sure.

At any rate, this apparently doesn't affect the OP, as he says his car runs great. Hard to say what the PO did to get the system to work. My guess is mechanical fuel pump on the engine with a unpowered electric pump in the tank.

 

thats correct

 

You might want to drop the tank, remove the electric pump, and modify the pickup per the sticky. The electric pump isn't doing you any good, and could be hurting you.

 

thanks for the tip, i'll look into that