I have a 2.8L V6 in my 1986 Chevy Camaro. I have fully rebuilt the engine but when I plug the oil temperature sensor/pressure sensor in the fuel pump turns on without the key in the car. How could this be, and how could I fix it? I did do a air pump delete and was thinking of jumping the connector to the pump.

 

Your car has an oil pressure switch, the contacts are stuck closed. Get a new one

 

Congrats on the rebuild, glad to see someone showing a 2.8 some love! As far as the pump running when you hook up the oil pressure sender, I'm not entirely sure why it would trigger the fuel pump without the key on... If I recall correctly, the fuel pump circuit wants to see at least some kind of signal from the oil pressure sender before it powers the fuel pump... could be misremembering, and could be different on an '86, but I do believe that it was built in as a safety feature for the motor. I wonder if your car is thinking that the key is rolled forward for some reason.... hopefully someone with a bit more knowledge on the wiring can chime in, but figured I'd at least put forward an explanation for why the oil pressure sender would even be affecting the fuel pump.

As for the AIR pump delete, you don't have to worry about doing anything with the wiring. I deleted my AIR pump about 6 years ago, and have jut left the connector for it kinda tied up with a zip-tie. Hasn't caused any CELs or issues with how the engine runs.

 

I wouldn’t consider the ops to be a safety feature. It’s backup for if the fp relay fails.

 

Ahhh gotcha, that makes more sense. I remember it being explained to me as being a failsafe so your pump wouldn't run if you had no pressure, but yeah if you think about it, that'd definitely cause issues trying to start the car

 

The fuel pump still runs with the ignition on without the oil sensor plugged in which I found strange and the engine was running fine too for the break in period. I was thinking a fault in the ecm but that went out the window when it was running fine and I hooked up the engine code reader and it was blinking with a no engine faults found.

 

So if the fuel pump relay has gone bad how come the engine starts and runs with 45 psi just fine without the sensor plugged in? I would've thought that would keep it from running

 

Yeah, it's an old wive's tale. I believe the myth started because mechanics knew that there were some 70's GM cars (the H-body I think) that had a helper electric pump in the tank that ran when the engine had oil pressure (which meant the engine was running) and they never bothered to actually look at the diagram of how GM wired the pumps on the later FI cars. Then the internet came along and that old wive's tale ran rampant. Still to this day, there's knowledgeable mechanics that think it's a safety feature to turn off the pump when the engine loses oil pressure. Including that "car wizard" toolbag on youtube.

 

If i'm understanding correctly, does that mean that there are 2 fuel pumps and one of them is just a help pump? That would make since with the connector plugged in the fuel pump is much quieter than with it running.

 

No, there's just one fuel pump. It gets power via the fuel pump relay. But it also gets secondary power from an oil pressure switch, so the car will still run in the event of a pump relay failure. The teletale for that would be an extended crank time.

But as was mentioned previously, your oil pressure switch is stuck closed.

However, I didn't think that circuit should have constant 12v supply. I could be wrong though.

 

Okay I understand what you're getting at now. So since the relay is okay can I just leave the switch unplugged in the meantime and roll around with it like that?

 

You can. An oil pressure switch should be very cheap though.

 

Alright sweet. I appreciate it a lot. Thank you so much!

 

Here is a little more information.


As you can see in the diagram the oil pressure switch contacts are wired in parallel with the fuel pump relay contacts and they don't require a key on to start the fuel pump if the oil pressure switch contacts are welded closed.

 

This explains it.

GM Port Fuel Injection Training VHS by AVI - 80s / 90s How-To Tape

 

This is very helpful! Thank you!