Oil pressure gauge/sender on FJ45 with SBC (1 Viewer)

[avicenna110]

Hi all,

My car is a 65 FJ45, with a SBC 350. I want to use the stock gauge so I followed previous posts here on mud on how to make it work. I have a new Toyota sender unit plugged onto the block as shown below

I have a new oil pump installed. The needle does move upon start, but stays just above L, it doesn’t move when I rev it ( not sure if it’s supposed to). I know one way to test oil pressure is to install a mechanical gauge but hopefully I can avoid it for now. Here is what I’ve tested so far:

- resistance between yellow connector above (when disconnected from sender unit) and positive of battery is 47.6 ohms (this is really the resistance between the two legs of the oil pressure gauge at the instrument cluster)

- when I disconnect the yellow connector above and ground it (while engine is running) , the needle goes to H. I stop before it reaches H.

- the resistance between oil sender unit and battery ground when engine is off is high (inf)

- when engine is running, the resistance between oil sender unit and battery ground is 21.8 ohms. Revving the car doesn’t change it (again not sure if it’s supposed to)

So it looks like I have pressure as the resistance of the sender unit goes quite low but I’m not sure what to interpret the numbers above and how to proceed. Any help is much appreciated.

Thanks
Daniel

 

[ToyotaMatt]

- i think your SBC GM is NOT properly grounded to the NEG- of the battery ?

 

[avicenna110]

- i think your SBC GM is NOT properly grounded to the NEG- of the battery ?








View attachment 3147991

Ah good thinking. I am pretty sure it is but I’ll double check. But now I’m thinking the sensor might not be grounded well? I used thread sealer per suggestion of others since the thread of OEM Toyota sender unit is slightly different than SBC. Is the body of the sender unit supposed to be grounded? I saw some other non-OEM sender units with ground plugs on the body. I can measure the resistance of body of the sender unit to ground.

@ToyotaMatt you put me on a good path. But I’m curious to know if the ohm per psi of the sender unit is documented somewhere? Or some similar info.

 

[pb4ugo]

I think the only way to confirm where your gauge reads is to add a mechanical gauge. My guage is grounded by the threads. My sbc runs at the 1st line or a little more. Keep in mind generally stk gauges aren't the most accurate.

 

[avicenna110]

I think the only way to confirm where your gauge reads is to add a mechanical gauge. My guage is grounded by the threads. My sbc runs at the 1st line or a little more. Keep in mind generally stk gauges aren't the most accurate.
View attachment 3148130

Thanks. First line meaning L?

I checked the ground, both block and sensor body are well grounded with less than 1 ohm to the battery.

 

[B y r o n]

If you used Teflon tape around the threads of the sending unit then it may not have enough ground to get a proper reading. Threads are tapered so are supposed to seal without any sealer involved.

 

[avicenna110]

If you used Teflon tape around the threads of the sending unit then it may not have enough ground to get a proper reading. Threads are tapered so are supposed to seal without any sealer involved.

I used liquid thread sealer. I checked the ground of the body of the sensor and it’s ok, it has very low resistance to ground (<1ohm). I think the thread sealer was recommended because Chevy is NPT and Toyota is something else, but the threads are almost matching.