Oil Pressure Gauge and Idiot Light Wiring

[G3.Spiffy]

Hello, I have an 86 wagon with an in-progress SPFI swap from an 88. The donor car didn’t have a tachometer, oil pressure gauge, and a few other accessories. I’ve got it to start in the 86, although I need to make some idle adjustments, but figured I’d get the important gauges and warning lights to work before I ran the engine too much. 

The donor was was equipped with an idiot light for oil pressure which ran from what I believe is the oil pressure switch. The 86 wagon’s original engine had a larger unit which is just over from the plugged hole where the oil pressure switch would go, which I believe is the oil pressure unit.

In my attempts to get the gauge and idiot light to both work I ran the wire from the oil pressure switch to the idiot light and to the gauge, which made the light work fine but the gauge would go all the way up when the key was in IG and slowly fall to zero.

I then removed the oil pressure switch and installed the larger unit into the SPFI engine and connected the wire for the idiot light and gauge to it like before, and neither the light or the gauge worked.

I know the gauge and light both worked in the 86 wagon before the original engine was removed and I know the idiot light in the 88 worked before the donor engine was removed.

For me to have both the idiot light and oil pressure gauge working, can the larger unit  work both? If so how do I wire them? Do I need both of the units to be installed and have separate wiring for each? 

Any help is appreciated!!

-Will

[DaveT]

The 2 indicators operate on totally different systems.  The gauge and sender work together.  The switch and light work together.  If you want both they gave to be electrically seperate,  not combined.  As far EA82 powered cars go, they had one or the other, I have never seen one with both.  They used the same wire in the engine harness, but different sender, and different end point in the dash.

[G3.Spiffy]

2 minutes ago, DaveT said:

The 2 indicators operate on totally different systems.  The gauge and sender work together.  The switch and light work together.  If you want both they gave to be electrically seperate,  not combined.  As far EA82 powered cars go, they had one or the other, I have never seen one with both.  They used the same wire in the engine harness, but different sender, and different end point in the dash.

That makes a lot of sense. I plan to hook them both up, so I’ll run a second wire in the morning and see if I can get them working that way. Thanks!

[G3.Spiffy]

Update: Installed both of the units and both were working as they should hovering just above 45psi with normal response to throttle, until the engine began to warm up. Then the oil pressure dropped steadily to zero and didn’t give much response to throttle. Is this normal? It doesn’t seem like it to me. 

I’m pretty sure the engine still has oil pressure as it should because the idiot light doesn’t come on when the pressure on the gauge drops, and the engine sounds normal, no metal on metal. 

[DaveT]

Idle oil pressure at normal operating temp is low.  The built in gauge is not super accurate especially at low pressure.
Under the no load conditions of idle, the oil pressure doesn't have to be high.  Also, part of the reason to never lug these engines, they are made to spin fast. 

Cruising down the highway, it should be 40 -45 + / -.  But that's on the built in gauge.  It also has a fairly slow response time.

the light sensor switch probably doesn't indicate until a number under 5PSI.

 

[Crazyeights]

The EA series engines run very low oil pressure at idle. This is even stated in the owners manual. The factory gauges are not accurate at all either. What I would do if your concerned about it is hook up a test gauge and monitor the oil pressure from a cold start until the engine is warmed up. Once you know what the pressures really are you can train yourself to use the factory gauge.

[G3.Spiffy]

4 minutes ago, DaveT said:

Idle oil pressure at normal operating temp is low.  The built in gauge is not super accurate especially at low pressure.
Under the no load conditions of idle, the oil pressure doesn't have to be high.  Also, part of the reason to never lug these engines, they are made to spin fast. 

Cruising down the highway, it should be 40 -45 + / -.  But that's on the built in gauge.  It also has a fairly slow response time.

the light sensor switch probably doesn't indicate until a number under 5PSI.

 

 

2 minutes ago, Crazyeights said:

The EA series engines run very low oil pressure at idle. This is even stated in the owners manual. The factory gauges are not accurate at all either. What I would do if your concerned about it is hook up a test gauge and monitor the oil pressure from a cold start until the engine is warmed up. Once you know what the pressures really are you can train yourself to use the factory gauge.

Thank you both!

Based on what you’ve said it seems like my gauge is working as it should be. That brings peace of mind!

[el_freddo]

Install a quality aftermarket oil pressure gauge if you want an accurate reading. 

I’ve had one on my EJ22’d L series and I can tell when my oil is low or the engine is hot from the change in oil pressure. 

Mine’s mechanical, you can get electrical if you want too. 

Cheers 

Bennie

[Ionstorm66]

If you have no pressure warm, you could have too thin oil or bad pump seal.

 

I have a cheapo multi gauge in my Loyale. Does oil pressure/temp, water temp, vacuum, fuel pressure, and voltage.