170 engine, oil pressure sender

[Gsav69]

Hey folks. I'm putting a sniper on my 1966, 170 and doing an intank setup. I'd like to add an oil pressure safety switch and ive only found the one port to grab oil pressure is where the oil pressure sensor is. I was under the impression the sensor was 1/4 npt to the block where i could add an extension of some sort. I didn't remove the sensor yet but did measure the threads sticking out of the block toward the body of the sensor and theyre measuring at 0.5 inch. Can anyone confirm the thread count for that hole and also let me know if theres another place on the block or way to get oil pressure? If theres another option, I'm inclined to leave that one there and not touch it, especially if I find it's been changed or repaired previously. Thanks as always.

 

[ntsqd]

Pipe is sized by it's ID, not it's OD. To further complicate things, all pipe sizes are "Nominal" meaning that none of them actually measure the name size that they're given.

For reference, the tap drill size for 1/4" NPT is Ø7/16" Your 1/2" measurement for the fitting sounds a bit small unless you're rounding down. However the tap drill size for the next pipe size smaller, 1/8" NPT, is ~Ø21/64" and the fitting would likely measure somewhere about 3/8" OD I think that the intel that you have is correct.

Was the safety switch supplied, or are you still in need of one of those?

 

[Broncobowsher]

1/4 NPT is the nominal pipe bore. Which is just under half an inch OD. So that is correct. NPT fittings are very common at any american hardware store. Just get a tee fitting and you can put multiple pressure sensors on the same port.

 

[Gsav69]

Pipe is sized by it's ID, not it's OD. To further complicate things, all pipe sizes are "Nominal" meaning that none of them actually measure the name size that they're given.

For reference, the tap drill size for 1/4" NPT is Ø7/16" Your 1/2" measurement for the fitting sounds a bit small unless you're rounding down. However the tap drill size for the next pipe size smaller, 1/8" NPT, is ~Ø21/64" and the fitting would likely measure somewhere about 3/8" OD I think that the intel that you have is correct.

Was the safety switch supplied, or are you still in need of one of those?

Great insight. Thank you. Company called tanks sells a kit FPSSK Tanks Inc. Fuel Pump Safety Switch and Relay Wiring Kits FPSSK which looks like a great option. Very little r&d required with the exception of an adaptor that allows me to add the switch to same source as the sensor. That's why I'm trying to learn about the thread pitch.

 

[ntsqd]

The switch at the core of that kit is sold by Carter (& others) https://www.summitracing.com/parts/crt-a68301 Been using them for decades, used to be able to ask for the "Chevy Vega fuel pump safety switch" and the counter guys knew what you were after. Sometimes they were even out on a a peg-board.

They are 1/8" NPT, so you will need a reducer bushing to screw one into a 1/4" NPT 'T'. Like this: https://www.summitracing.com/parts/sbc-9179k but buy it at your local hardware store for less than half that price when you're buying the 1/4NPT 'T'.

 

[DirtDonk]

Is it even necessary to have one with a throttlebody injection? Just wondering, because I thought that once the engine stops, the computer loses the tach signal, the injectors stop firing.
But I guess, depending on how it’s controlled, that wouldn’t necessarily stop the fuel pump.
Is that right? With this type of setup, the fuel pump is running anytime the key is in the ON position?

 

[ntsqd]

Of all of those pressure switches that I've used I don't recall any of them being on an EFI engine. The only way that I wouldn't install one with an electric pump would be if the system has it already as part of it's system, the vehicle already has an Inertia Switch, or something similar.

They have 3 terminals, Start (by-pass mode), Run, and Pump. Trigger pressure is pretty low, 5 psi or so.

 

[Broncobowsher]

As mentioned, EFI controls the fuel pump. Adding a pressure switch is going to cause starting issues. You will loose the system prime at key on. Crank the engine until you build oil pressure to get the fuel to start to flow. Long starts. Might even confuse the EFI as it will think it is squirting fuel that it really isn't getting.

 

[Gsav69]

I understand there may be a balance. Wiring the pump to be on whenever the key is on isnt optimal either. Im running a deadhead system with 1 line. In my perfect world, the pump fires when the sensor sees 15psi of oil pressure. I don't like these finicky key switches and in the event of an accident or loss of oil pressure, I may have some fail safes.

 

[Broncobowsher]

But with a sniper the pump isn't on whenever the key is on. It is only on when the computer calls for it. You are adding extra complexity and failure points. You will be making it hard to start. And nearly impossible to start after doing an oil change where the engine needs to get up to speed to get the oil pump primed and pumping.

The pressure switch is fine for carburated applications where the engine can run long enough on the fuel bowl to get the oil pressure established. EFI can't do that. No fuel bowl, the moment the fuel pump isn't running, neither is the engine.

 

[ntsqd]

This particular switch has a start mode by-pass as I stated above. During cranking the fuel pump will run regardless of the oil pressure.

That said, most EFI systems have control of the fuel pump thru their own sensors and software. Adding this switch may or may not be a good idea depending on how the pump is controlled.

 

[Gsav69]

It's an in-tank setup controlled through a relay. As this isn't my strongest area, i welcome any ideas on how to wire this thing so the pump will not always be running with the key on. I have an American autowire harness with a fuel pump circuit and all roads i have found bring me to the pump running with the key on. The sniper for autolite 1100 is not controlling the pump and I dont believe it has the capabilites to do so unless I missed it. Thanks for all this info. I'm definitely open to suggestions.

 

[73azbronco]

yeah, use a pressure guage you can see vs cuttof switch. One more link to failure you don't want. I know of no one who blew up a 170 because of no pressure. I know for a fact it gives an audible clacking when top end starts to lose oil

 

[Gsav69]

This dialogue has prompted me to call Holly again today. There's a dude who did a sniper Auto like 1100 on a Mustang named mecatrician on youtube.

 

[Gsav69]

yeah, use a pressure guage you can see vs cuttof switch. One more link to failure you don't want. I know of no one who blew up a 170 because of no pressure. I know for a fact it gives an audible clacking when top end starts to lose oil

I was hoping to use both lol.

 

[Gsav69]

Quick call to holley demystified this. In short, if you wire the autolite 1100 unit using the blue wire for the fuel pump to the relay, the pump primes and won't fire unless there is a tach signal. If i was to use the American autowire circuit, which is constant 12v, the pump would run anytime the key is on. Thanks to those who helped me see the light and for saving me from unnecessary parts, wiring and failure points. Grateful for this forum.

 

[Broncobowsher]

What you will likely need to do is find the front side of that fuel pump wire and splice the Holley fuel pump relay into it. That will change the always on fuel pump labeled wire into a computer selected fuel pump wire.

 

[Gsav69]

What you will likely need to do is find the front side of that fuel pump wire and splice the Holley fuel pump relay into it. That will change the always on fuel pump labeled wire into a computer selected fuel pump wire.

This is where my wiring expertise will be challenged. There is a wire under the dash, likely buried that goes to the fuse box. Im gonna sniff it all out and decide the best path forward. THANK YOU. And I hope I can share and teach back some stuff after all this.

 

[DirtDonk]

Maybe just to be on the safe side, you should call Holley back and ask them if the Blue wire is a ground trigger or a positive trigger.
Unless somebody here knows that first.

If it’s a negative trigger, then you simply unhook the #85 terminal of the relay from a direct ground, and attach the Blue wire.
That way, your AAW switched 12V wire stays on the #86 terminal, your battery remains on the #30 terminal and your fuel pump remains on the #87 terminal.
As long as that’s the type of relay you’re using…

 

[Gsav69]

Maybe just to be on the safe side, you should call Holley back and ask them if the Blue wire is a ground trigger or a positive trigger.
Unless somebody here knows that first.

If it’s a negative trigger, then you simply unhook the #85 terminal of the relay from a direct ground, and attach the Blue wire.
That way, your AAW switched 12V wire stays on the #86 terminal, your battery remains on the #30 terminal and your fuel pump remains on the #87 terminal.
As long as that’s the type of relay you’re using…

From the installation guide...

4. Blue Wire (Optional) = +12v Fuel Pump Relay Power Output - Used to directly power a fuel pump (max current 15A). Make sure to terminate blue wire properly if not utilizing blue wire to provide power to the fuel pump.