Oil pump switch for fuel pump 2.8 Vs. 3.1

[Geyservillebob]

Hi,

Long story but I've a 1986 Camaro with a 3.1L long block but most of the electronics is 2.8L. The 1986 wiring harness has two connectors at the oil filter housing, from the shop manual it seems one is for the oil pressure idiot light and the other is for the fuel pump. The manual says the fuel pump switch is there as a back up in case the fuel pump relay fails, this switch will power the fuel pump (short across the relay?) whenever there is engine oil pressure.

On my motor the fuel pump switch connector is dangling. On the oil filter housing there is no place for this switch. There is a blind cavity but no hole and no switch.

I'm thinking the filter housing is off the 3.1L motor and this motor did not have this switch. Is that correct?

Frank

[geoffinbc]

First off the oil pressure sending unit is what powers the pump as soon as the engine builds presure. The relay is only for priming. In the event of oil pressure loss the vehicle will not run. This is a safety feature.

You need to revert back to your 2.8L oil filter housing and the 2.8L oil pressure sensors.

[Geyservillebob]

Not according to the 1986 shop manual. The manual says the fuel pump is run (under control of the ECM via the pump relay) for 2 seconds when the key is turned on and then it is run whenever "references pulses" are received from the distributor (again by the ECM via the relay). These pulses would provide the safety feature. The following is a quote from the 1986 manual...

"As a backup system to the fuel pump relay, the fuel pump can also be turned on by the oil pressure switch. ... If the fuel pump relay fails, the oil pressure switch will close and run the fuel pump"

My car runs fine. I believe this is evidence that the oil pressure switch is not controlling the pump relay. However, maybe the DPO has placed a short across the connector. I'll check and see... Nope, no short found on the connector. Anyway the 1986 manual description appears to be in contradiction to your comments. I'm just trying to figure out what I really have.

Frank

[geoffinbc]

Ok back in 86 I guess they did things differently.

Although on some S-trucks this same situation exists where there is an extra plug with no place to go.

So I would just leave it if everything runs right.

[Geyservillebob]

Although on some S-trucks this same situation exists where there is an extra plug with no place to go.

Ahhh... so now a piece of the puzzle. Yeah it is kind of weird because there is this blind hole on the filter housing where a switch could have been equipped on other models. I do not know where my 3.1L long block came from, perhaps a truck?

I think your advice is best, I'm just trying to make sure I understand this stuff so I can fix it if I need too.

Thanks.

Frank

[geoffinbc]

Nope no 3.1L's in trucks (except Isuszu but it has the starter on the drivers side). Must have come from a 1990 to 1992 Camaro

[packardbell]

Nope no 3.1L's in trucks (except Isuszu but it has the starter on the drivers side). Must have come from a 1990 to 1992 Camaro

I have an issue with the fuel pump still running after the key is out. I pulled out the fuel pump relay but the fuel pump is still running, i pull out the plug from the oil pressure switch (1 terminal) and the pump is still running, I pull out the 20amp fuse besides the fuel pump relay and the fuel pump stops. Is there another switch i am missing that is keeping 12volts to the fuel pump? I find it cumbersome to always have to remove the fuse under the hood when i park and install the fuse when I go.

[Guest]

To address the old posts:

The operation of the fuel pump was not changed all the way through OBD1 equipped vehicles for sure (up to 1995), and I'm 99% sure that OBD2 is the same way. The ECM triggers the fuel pump relay, the oil pressure switch is a back up.

There are only the two controls, the ECM controlled fuel pump relay and the oil pressure switch. It is pretty common that a fuel pump will run for a couple seconds after key off, since oil pressure needs to bleed off. If the pump continues to run for more than about 15 seconds (Some vehicles have an after shut off fuel pump run time to attempt to eliminate vapour locking), you have an issue elsewhere, that you need to find.

[packardbell]

To address the old posts:

The operation of the fuel pump was not changed all the way through OBD1 equipped vehicles for sure (up to 1995), and I'm 99% sure that OBD2 is the same way. The ECM triggers the fuel pump relay, the oil pressure switch is a back up.

There are only the two controls, the ECM controlled fuel pump relay and the oil pressure switch. It is pretty common that a fuel pump will run for a couple seconds after key off, since oil pressure needs to bleed off. If the pump continues to run for more than about 15 seconds (Some vehicles have an after shut off fuel pump run time to attempt to eliminate vapour locking), you have an issue elsewhere, that you need to find.

I have a 1988 oldsmobile with a 2.8MFPI and it has two oil pressure switches, one close by the oil filter housing that is a one terminal for the oil gauge. then the second oil pressure switch which is a 2 terminal beside the coolant temperature sensor of all places. My issue was this oil pressure switch leaking oil and also the wires melted the insulation.