My old motor was a 357ci 2 piece block that had provisions for the oil pressure that went to my Autometer gauge (top of the block behind the dist) and the lower pressure switch located in the oil filter housing. My new motor, roller 383 stroker, has a '98 Tahoe block. The provision for the oil pressure gauge is there but the hole for the pressure switch doesn't go anywhere. Theres nothing behind the hole where it mounts to the block. I jumped this connector with a paperclip to see if this was the cause my fuel pump wasn't turning on and as soon as I touched it with the clip, the pump started humming. What can I do to remedy this? Has anyone encountered this before? I was told to cut the connector off and loop the wires but won't that leave my pump on constantly? I've searched the boards and have come up with nothing that resembles my problem. Hopefully you guys can give me some insight on what to do as the days are getting shorter and the cold weather is coming. I'd like to get some driving time with this new motor before the bad weather hits. Thanks.

 

Correct me if I am wrong, but they both just sense oil press.
So you should be able to put a t fitting on the block and put them both by the filter. You will have to lengthen the wires to do so, but unless my thought is wrong, is will still read your min pressure to turn the pump on.

 

I have a 1989 Camaro FI Vin E (TBI). On my car the 'Fuel Pump Relay' is located on the driver's side and is located on a 'standoff' bracket. It is the second relay from the driver's side fender. The standoff bracket is bolted to the firewall. The relay has 5 wires that attach from the bottom. On my car that relay is energized by the ECM. I assume this circuit has a problem since you indicate that the fuel pump ONLY operates when the 'Fuel Pressure Switch' is jumped.

When I turn my ignition key from OFF to RUN the fuel pump should be energized for two seconds then it stops. When I turn my ignition key from RUN to CRANK then allow it to immediately return to RUN (without starting the engine) I hear the fuel pump run for another two seconds then it stops. Try these two tests and let us know what you hear or do not hear.

The 'Oil Pressure Switch' operates in 'parallel' with the 'Fuel Pump Relay' contacts. When the oil pressure reached 6 PSI or more then the 'Fuel Pressure Switch' is switched 'ON'.

The 'Fuel Pump Relay' and the 'Oil Pressure Switch' are completely independent on my car. However they do share the wire that attaches to the fuel pump and they share the fuse that operates the fuel pump.

The primary switch for the fuel pump is the 'Fuel Pump Relay'. So getting that working properly would be the first challenge to get you on the road.

 

Are you sure you're looking at the right hole? The reason for those holes to exist in the first place isn't for mounting sensors and switches, they're necessary to create the internal oil passages during the manufacturing of the block. Every block should have them.

 

Pretty sure its the right hole I'm looking at for the pressure switch. Behind the hold is absolutely nothing. I can feel the back of the sensor when it's in the hole. Now that the motor is in the car, it's a little hard to see things but I guess I'll have to get under it and check again but I'm 98% sure. Being that it's a new block, does that have anything to do with it? This is the ONLY thing preventing me from driving my car and it's pissing me off.

Would cutting the connector that goes into the pressure switch and hooking it up via a 12v source work? Maybe using a relay or something? It won't sense oil pressure though so I don't know how it would turn off lol, I'm thinking out loud here. I have my oil sending line that goes to my gauge on the top of the block, would making that a Y fitting or something work?

 

You can straight wire the fuel pump at the relay, and this will remove the Oil Pressure Sending Unit out of the picture for the purpose of running the fuel pump. IIRC, connecting the brown wire with the orange wire makes the pump run constantly. The one wire provides the 12v, the other runs it to the pump - so the wire that DOES NOT have 12v to it can be wired to a "hot-in-run" connection, so that your pump only runs when the key is on. Make sense?

Sorry about not being 100% sure on the wire colors - my Camaro has been in the paint shop since Feb. and I can't just go out and take a look for ya - but I believe I remember brown to orange connection at the relay to make pump run. I discovered this out of necessity - I installed a carbed 350, and took out the ECM, so I have no priming on my pump at all. It isn't an issue, unless the car sits for more than 2 weeks without running - at that point there isn't enough pressure reading at the OPSU to run the pump, and the car won't start without running the battery dead with the starter until the oil pressure comes up so I had to rig a jumper wire for these occasions that I keep in the console

Another thought: I happen to have moved my OPSU to the china wall location by the distributor, but I still get an oil pressure reading for the guage from the sensor in the driver head - the OPSU doesn't provide pressure info for the guage, just to run the fuel pump. Maybe there's another oil pressure sensor location on your block (or head) that you can tap into for your guage, and put the OPSU on the china wall like I did?

 

I'm going to run a T-fitting on the "china wall" for my oil pressure gauge and the pressure switch. Should work fine. Thanks for the info though.