Hello, If you unplug the oil pressure switch that is in the fuel pump circuit, will your vehicle still start and run? thanks

 

Yes, the engine should run just fine with the oil pressure switch disconnected. If it doesn't that means your fuel pump relay is bad.

The ECM controls the fuel pump relay both to prime it (before you start it) and afte rthe negine is running (which it determines based on if it is recieving distributor pulses.) The OP switch is a redundant supply for the fuel pump in the event of relay failure.

 

Hello again, I saw an article at chevythunder.com on the trouble-shooting link. It said, if the oil pump or oil pressure switch fails, the fuel pump won,t work. That is a TPI site, are they wrong? I saw an article in a book titled how to tune and modify chevy fuel injection, under symptom, starts and dies, it said to check the oil pressure switch. Where is that statement coming from? I used to think, the oil pressure switch was the safety shutoff for the pump on a chevy, guess I was wrong. I guess it is the no RPM signal shutoff. thanks

 

Yes they are completely wrong. Below is the relevant part of the wiring diagram from helms (factory service manual)

The fuel pump power wire is the line that says "to fuel pump" between the OP switch at the bottom and the relay. Now notice that both the OP switch and the relay feed it. The line back into the ECM is a sense wire (if you've ever look at a scan tool you know FP voltage is a reported/monmitroed parameter).

Now besides the facotory wiring diagram, we've also beatn this topic into the ground on here before several times. It always ends with the naysayers shutting up when we make them go out and try unplugging the OP switch with the car running only to find it doens't shut off.

 

I can imagine that answering the same questions over and over can get aggravating. I don,t have TPI, but I did have a question about the oil pressure switch in the pump circuit on chevy fuel injection. My old chevy has MPFI. About two weeks ago, I went out and unpluged that switch just to see what it would do. The car started and ran just fine. So I wondered about TBI and TPI. I,ve talked to a lot of people and can,t find anyone that says that switch will kill the engine. But , I have seen written articles. I e-mailed the person at chevythunder.com about this question. May not get an answer. I think I got Roy at batauto.com aggravated with me about this subject, also. No offense, but I do find sometimes, when experienced or trained people are answering questions from novices, they seem to have a dogmatic attitude. Like their answers are gospel and a person shouldn,t ask questions. Well i,m a novice and I do what novices do, I ask questions. That,s how I learn. Thanks for your answers. I,m sorry if I aggravated you.

 

No, you didn't aggravate me. I gave my answer in such a firm tone because i am 100% sure i am correct. Like i said, not only can i (and did) produce factory documentation showing the wiring for the pump, but i also know from collective experience and past arguments that it is the way it is.

The problem is, if i don't assert the correct answer in such a tone, then inevitably some bonehead comes in the post and gives incorrect and misleading information. And THAT is what i find aggravating.

There are a lot of myths out there regarding these cars. Hell, i just looked in a haynes manual that i have laying around to reference trouble codes and the wiring diagram in there is incorrect, showing the OP switch in series with the relay. Doesn't change my answer because i am sure thats not how it is wired. But you can see how seeing that would lead someone to argue a point, even though they really didn't know for sure what they were talking about.