Oil pressure lights stays on but gauge reads 40 psi at idle

[matrophy]

Z24 in '86 720 with oil pressure gauge. Just finished installing a kill switch to the fuel pump relay and noticed that the oil pressure idiot light stays on but the gauge reads 40-ish psi at idle. Thought it was the sensor but since I think they use the same wiring I'm wondering what it could be. Looks like both the idiot light and the gauge use the same #4 fuse.

[Thomas Perkins]

It should not read 40ish at idle.Should idle around 25,mine does and it is 48  on the high way.Been this way for 28 years.Why did you put a kill switch to the fuel pump relay.If you are running a Weber and it is dieseling and not idling properly.I stall a idle cut off solenoid.I have always used one on mine and it runs awesome.Blue and red wires from the 6 wire plug.I put a blue dot on the white choke so i know where the wires go,you never know.

Edited November 4, 2022 by Thomas Perkins

[matrophy]

The issue with my carb was that it wasn't starting easily without cranking a whole bunch. It's not dieseling and it idles fine once it's running. You might have me mistaken with someone else. Today I raised the fast idle a little bit to see if I had it too low. This is based on your recommendation of 2000 rpm from earlier with mine around 1500.  I'll try it tomorrow after it's dead cold.

 

The kill switch is because there seems to be a rash of 720 thefts in my corner of Oregon and I get guys asking me to sell mine all the time.

 

I decided to shut off the fuel pump because it is easier for a thief to bypass the ignition switch if I use the coils. Back to the oil idiot light, my point is that the oil pressure gauge is reading normally - mine has always been at 40 psi at idle - and it's mysterious why the idiot light comes on since they use the same wiring. This suggests to me that the sender is working like it should.

[datzenmike]

1 hour ago, matrophy said:

Z24 in '86 720 with oil pressure gauge. Just finished installing a kill switch to the fuel pump relay and noticed that the oil pressure idiot light stays on but the gauge reads 40-ish psi at idle. Thought it was the sensor but since I think they use the same wiring I'm wondering what it could be. Looks like both the idiot light and the gauge use the same #4 fuse.

 

Disconnect the kill switch from the pump relay. If the light goes out then that was the cause.

[matrophy]

26 minutes ago, datzenmike said:

 

Disconnect the kill switch from the pump relay. If the light goes out then that was the cause.

I hope that's not it. I hate gremlins

[datzenmike]

For the light to be on the oil pressure sender wire must be at ground. This normally happens if the pressure drops below about 8 PSI. As you haven't done anything but add a kill switch it probably is that.

 

Fuel pump relay plug....

 

All you need do is insert an on/off switch in the WB (white/black) line to the fuel pump. This will shut off power to the pump.

[matrophy]

7 hours ago, datzenmike said:

For the light to be on the oil pressure sender wire must be at ground. This normally happens if the pressure drops below about 8 PSI. As you haven't done anything but add a kill switch it probably is that.

 

Fuel pump relay plug....

 

All you need do is insert an on/off switch in the WB (white/black) line to the fuel pump. This will shut off power to the pump.

Update: I found oil inside the connector to the sender but the sender isn't leaking so that's odd but I cleaned the connector with contact cleaner and the light went off.

 

Right or wrong,  I was adivsed to add the kill switch on the white wire - before the relay - in case the amperage coming out of the relay is too high. Everything works so it's onward and awkward from here. Any tips on replacing the heater duct? Can't find the magical orientation to get it to snap back in.

[datzenmike]

The fuel pump determines how much current is drawn through the relay not the relay.

 

Yes the white fuse wire will also work but the relay can also be turned on by the L (Nissan for blue) accessory wire not that it likely would. In any case any possible failure of the relay can be prevented by a switch on the WB output. Off..... is off.

[matrophy]

I didn't see that diagram of the connector before with the Y/G wire going to the oil pressure sensor. I ran the engine just now with the kill switch closed and the oil idiot light was off. I wonder if the light comes on with the kill switch open? Maybe my cleaning the connector is a red herring. It's raining too hard to go look now. In a way that's a secondary deterrent to a thief that might not want to drive it with low oil pressure - maybe.

[datzenmike]

The only reason for theft is if you also have a 720 that needs parts or there's a $5k stereo in there... neither are too likely which leaves the third option... You aren't thieving for gain, just out for a hoon joyride. If that's the case part of the entertainment is hoping to see a rod fly out of the block.

 

Might be better to have a switch on the ignition so it never gets started.

[Crashtd420]

Matrophy are you using just a switch inline on the wire?

 

I never like to run a power circuit through a switch, I prefer the have the switch control a relay since they are usually rated for around 30amps. 

 

Yes there are switches that handle it so I hope you have a proper rated switch. If not think about adding a relay.

 

[Thomas Perkins]

.In November 2020, Oregon voters passed Measure 110, which decriminalized the possession for personal use of small amounts of all drugs, including cocaine, heroin, LSD, methamphetamine, and oxycodone. Oregon is the only U.S. state to have implemented this policy.Sep 7, 2022.Wow.ya'll don't need your drug dealer on speed dial.It's every where.That is scary.What happens if you go to get in your truck and some are sleeping in it...People don't steal stereo's no more,they are looking for guns.What would someone want with my stereo,people drive newer cars and my stereo is not what anyone want's.Even newer car stereo's are not stolen.Who in the hell would buy my stereo.It's grab and go and go to the next car.

Edited November 5, 2022 by Thomas Perkins

[datzenmike]

48 minutes ago, Crashtd420 said:

Matrophy are you using just a switch inline on the wire?

 

I never like to run a power circuit through a switch, I prefer the have the switch control a relay since they are usually rated for around 30amps. 

 

Yes there are switches that handle it so I hope you have a proper rated switch. If not think about adding a relay.

 

 

The fuel pump is on a 15 amp fuse. I would assume that the switch is thrown while the engine is off and before it starts??? if so, the pump isn't running and there's no current flow to interupt.

[matrophy]

Assuming that I remember to pull the switch before I turn the key, yes. Good point to remember.

[Crashtd420]

9 hours ago, datzenmike said:

 

The fuel pump is on a 15 amp fuse. I would assume that the switch is thrown while the engine is off and before it starts??? if so, the pump isn't running and there's no current flow to interupt.

But what about when the truck is running?

Wouldn't power be running through the switch at that point?

I didn't see how he actually wired the kill switch, so it was just a word of caution.... 

 

[datzenmike]

Oh I see. Yes power would be flowing when running. I was thinking only of the contact arcing when breaking or making the contacts. Yes overall power handling would be important 

[matrophy]

I have it wired after the fuse in the fuse box and before the fuel pump relay. Does that seem safe? A buddy suggested I wire it that way rather than between the pump relay and the pump  to avoid needing to add a relay.

 

Without blasting out too many details here, the switch I’m using is one that already exists in my vehicle that I believe is on a 20 amp circuit

[datzenmike]

Current flow is the same in all parts of an electrical circuit so doesn't matter where you interrupt it with a switch.

[matrophy]

Update: The oil idiot light does come on with the switch in the white wire to the pump relay off so I redid the wiring to shut off the power to the pump after the relay. 

Works perfectly now.

 

[Crashtd420]

5 hours ago, matrophy said:

I have it wired after the fuse in the fuse box and before the fuel pump relay. Does that seem safe? A buddy suggested I wire it that way rather than between the pump relay and the pump  to avoid needing to add a relay.

 

Without blasting out too many details here, the switch I’m using is one that already exists in my vehicle that I believe is on a 20 amp circuit

You should be ok if it's a 20amp switch.... after you drive for while check the switch if it feels hot then add a relay if not dont worry....