Does anyone know what this is

[Ricko1966]

Bucket did you look at that diaghram I put in That last post?

https://images.app.goo.gl/ASQhzMYCBLvTkwq38

That link I put up was for a 1976 Chevy Monza. If you look at that diaghram the oil pressure switch is the trigger for the fuel pump relay.As a teen v8 Vegas and v8 Monza were my favorites and so that was the first GM fuel pump circuit I learned , and obviously the only one I remembered.After you posted your diaghram that's when I posted I learned this, meaning your diaghram around 2000 but obviously forgot it.Then posted son of a bitch I think I learned it on the acheava. Just like if you learned B.O.B on drum brakes it's always your go too, even when it's not right.I gotta keep in mind when posting that all cars are not the same

 

[bucket]

Thanks for posting that diagram, I keep hearing that it is just a secondary power supply to the pump, but couldn't figure out what the purpose would be until seeing that diagram. I wonder what pressure the switch is set to? My take on this is that it is there to prevent the truck from just shutting off while driving due to a failed relay. It keeps the fuel pump running as long as the engine is running. So, if you are driving and the relay fails mid drive you would never knw until yo uget to your destination and shut it off. Once oil pressure bleeds down, the switch disengages and the pump turns off. Then when you go to start it back up again, you have a failed relay, you will get the fuel prime on key-on, but wouldn't get fuel pumping when you go to start(unless maybe it cranks fast enough to build enough pressure to engage the switch).

What do those relays look like on a TBI truck? Is there a bunch of them like a modern car? Its pretty common to have a fuel pump relay cause a car not to start, you can usually just swap it with the horn relay that is almost always right next to it(and easy to test) to verify the problem.

I don't know the pressure that the switch will trip, but it's low enough that even a high-mile engine will build enough pressure during cranking. Although the crank time will obviously be extended.

Bucket did you look at that diaghram I put in That last post?

https://images.app.goo.gl/ASQhzMYCBLvTkwq38

That link I put up was for a 1976 Chevy Monza. If you look at that diaghram the oil pressure switch is the trigger for the fuel pump relay.As a teen v8 Vegas and v8 Monza were my favorites and so that was the first GM fuel pump circuit I learned , and obviously the only one I remembered.After you posted your diaghram that's when I posted I learned this, meaning your diaghram around 2000 but obviously forgot it.Then posted son of a bitch I think I learned it on the acheava. Just like if you learned B.O.B on drum brakes it's always your go too, even when it's not right.I gotta keep in mind when posting that all cars are not the same

I guess I missed it somehow. So that was carbureted, with a helper pump then? Was there also a mechanical pump on the engine?

All the ones I have experienced are later models with FI and an ecm.

 

[Ricko1966]

It's been so long.Im. pretty sure they were just electric, because they wouldn't run with no oil pressure or bad switch.some bucks were that way too. Can't remember them all. I just assumed they kept doing it that way. But I vaguely remember that achieve throwing me for a loop because it was like that square body diaghram.

 

[Poppy 87]

Thanks for posting that diagram, I keep hearing that it is just a secondary power supply to the pump, but couldn't figure out what the purpose would be until seeing that diagram. I wonder what pressure the switch is set to? My take on this is that it is there to prevent the truck from just shutting off while driving due to a failed relay. It keeps the fuel pump running as long as the engine is running. So, if you are driving and the relay fails mid drive you would never knw until yo uget to your destination and shut it off. Once oil pressure bleeds down, the switch disengages and the pump turns off. Then when you go to start it back up again, you have a failed relay, you will get the fuel prime on key-on, but wouldn't get fuel pumping when you go to start(unless maybe it cranks fast enough to build enough pressure to engage the switch).

What do those relays look like on a TBI truck? Is there a bunch of them like a modern car? Its pretty common to have a fuel pump relay cause a car not to start, you can usually just swap it with the horn relay that is almost always right next to it(and easy to test) to verify the problem.

There are not a bunch like a modern car. It is mounted on the upper firewall just right of center on my 87 R10. My truck has a similar relay next to it for kick down on the TH400 transmission

 

[bucket]

It's been so long.Im. pretty sure they were just electric, because they wouldn't run with no oil pressure or bad switch.some bucks were that way too. Can't remember them all. I just assumed they kept doing it that way. But I vaguely remember that achieve throwing me for a loop because it was like that square body diaghram.

It makes a lot of sense on those cars then, to me anyway. The pump doesn't need to run to start the engine due to having a carb with a fuel bowl. It just needs to keep the bowl full when the engine is already running.

 

[Ricko1966]

It makes a lot of sense on those cars then, to me anyway. The pump doesn't need to run to start the engine due to having a carb with a fuel bowl. It just needs to keep the bowl full when the engine is already running.

They could still do that IDK why they quit.Trigger the pump for 10 sec with ecm then use O.P. switch on the road.It would save a couple of engines.i assumed that's how they were doing it