I have a 91 TPI unit installed in my 61 Vette with a painless harness. If I understand the operation of the oil pressure switch right, this should work.

Please give me your thoughts.

I want to NOT use the oil pressure switch at the block, but instead run the two wires to a hidden switch to operate the fuel pump that also acts as a security device. I do have the relay installed for ignition on before start-up for the short run and that works. Any problem with what I want to do you can see?

 

The oil switch is to kill the pump in the event of a wreck so you don't get burned up. which happened in the early days. Eninge is dead and the fuel just keeps pumping, comes out busted engine parts and poof, BBQ no one wants to eat.

 

Not correct - the oil pressure switch is to keep the fuel pump running in the event that the ECM stops working - that's why there is a direct connection between the battery and the OPSU - the OPSU will run the fuel pump if the relay or ECM stop working. Remove the fuel pump relay, and the car will still start and run - may take a few cranks to get the oil pressure up, but it will crank and run. That's why folks swapping to carb don't have to do anything wire related to start and run a carbed car if using the in-tank pump - because the OPSU will kick on the fuel pump as soon as it gets oil pressure.

Some very new cars now have a fuel pump kill switch associated with the airbag system, but not 3rd or even 4th gen cars.

OP - if you are running a straight forward TPI wiring harness, the fuel pump will still run as long as the ECM gives the relay the signal to run it - so putting a switch at the OPSU wires won't do it for you.

But you could put a kill switch anywhere forward of the pump itself but after the ECM/relay & OPSU circuits combine if that makes sense - then unless your hidden switch is turned on, the fuel pump would not prime or run regardless of the relay, ECM, or the OPSU.

 

After 25 years people still believe the fuel shut off MYTH.Pops up on here at least once a week

Only have to look at the pump circuit diagram to see how it all works

 

Thanks for the input, guys, being a newbie to TPI.

I installed the hidden switch in the wire that feeds the pump coming out of the ECM- it's a gray wire in painless. That works to suit my needs.

The reason for deleting the OPS is that the sender associated with it is not compatable with my gage, and I only have one port open at the back top of the block. If I read your comments/schematic correctly, I can just not use the OPS and all I lose is the backup function it serves for the fuel pump relay- Is that correct?

 

People in the know like some of us on there could easily jump the relay to make pump work.
Much better to cut the line to pump itself ( harder to find ) as camaronewbie suggested above.






Early TPI's used a seperate ( smaller ) OP switch on a log manifold at rear of block along with a separate gauge sender unit instead of the combined unit you have

Do you have the threaded hole into oil gallery above oil filter ? Another place to install the OP switch

 

I looked into using that hole above the filter, but it appears to have been blocked off or not drilled out. Since the engine did not come out of the car, I couldn't try to open that port.

I thought about the "t" like you show in the pic. The problem is available space between the engine and firewall in a C1 Vette. That smaller switch may provide some more room, so I will look at that...

I also am considering have a high pressure line about 12" long with NPT fitting on the end, so I can get over to an area where I have some space to mount the sender and switch...

I appreciate your input, Vetteoz

Mark

 

Oh, by the way- I would take someone a while to find both the ECM and the fuel relay- they are prety well hidden...

 

Sorry to hop in here but I was asking similar questions awhile back and I'm wondering if the small pressure switch you show in the picture will be compatable with the 7730 ECM if I'm also using a Painless harness. If so do you have a part number? I'm not worried about having a Sender Switch because I run a mechanical guage. I just need some sort of a tee at the hole in the top of the block for the 1/8" plastic line to attach to.

I also plan on installing a kill switch in the gray wire heading to the fuel pump like McGivern did.

Thanks...

 

In the pics above, neither the smaller or the larger OP units have any connection to the ECM, so that's not an issue. The ECM doesn't get or use oil pressure readings for anything.

The larger 1-wire unit in pic above just feeds the gauge, nothing else.

The smaller 2-wire unit in pic above just senses oil pressure above 2psi, and connects the two terminals together anytme oil pressure is above 2psi. There was a fuel pump circuit wired to it, a direct wire to battery on one terminal, and a direct wire to fuel pump on the other - switch senses 2+psi oil, closes, and sends 12v+ to fuel pump - nothing more elaborate - just turning on fuel pump.

Not sure if taht answers your question sch151, but now you know what they do, and that neither is connected to the ECM in any way.

 

Thanks but let me clarify...I incorrectly called it a Sender Switch so just to be on the same page, the Guage Sender is of no concern to me because I'm running a hard line mechanical guage. That said I know the Painless kit has wires (two I think) that are labeled oil pressure switch. If I were to use the factory (tall round) style switch which has three terminals in it I have to attach the adapter (supplied) and wire it accordingly. What I want to do is use a smaller pressure switch for less clutter and an inline tee to attach the guage to. So my question was will that smaller switch in vetteoz's picture work for whatever it needs to do. If so does anyone have a part number.

Sorry to be so wordy...

 

Yes , if all you are looking for is to run the pump
Check out OP switch listings for early TPI cars ( pre '88 )

 

But as shown in the circuit diagram there is a pump input to the ECM ( on a '165 at least )

There is disputed published documentation around
Exp ;http://www.corvettebuyers.com/c4vettes/l98.htm

that the ECM uses this input signal to determine that the engine has oil pressure while cranking ( only ) before it will pulse the injectors.
If you agree with that then , in effect the switch serves two purposes ;
as a direct power supply to the pump in parallel with the relay and as a OP indicator ( while cranking only )

 

vetteoz:

Hmmm - I never looked at the wiring diagram that way before - I just always assumed that the orange was simply a hot-all-times wire that fed the ECM & the fuel pump switch, not that it fed the ECM through the fuel pump switch. I've always looked at the www.austinthirdgen.org wiring diags, which look a tad different than what you have shown above. In them it shows orange wire from hot-all-times that splits, going to fuel pump switch, ECM, fuel pump relay, burn off relay & mass air relay - all kind of 'concurrently' if you will. Interesting.

 

The small switch is a D1818. Hard to find now. I found one on Amazon about a month ago.

 

When you datalog there is a value recorded for fuel pump voltage ; which would be achieved from said input as it is linked to pump side of both OP switch and relay

There are stories on here where guys have said the engine would not fire with a faulty OP switch and others who say theirs is disconnected and engine starts fine

 

Thank you everyone....