Agreed, if you pull the relay there is no physical possible way for the pump to continue running. Pulling the relay means you've disconnected both possible power sources as well as one of the grounds.
Fuel pump doesn't quit
I have a 1990 buick regal and the fuel pump does not stop running, pulled out the relay and still stays running, doesn't stop until i take out the fuse and ideas?
1 - 8 of 8 Posts
Except if it's wired as a switched ground, which of course means you have a ground shorting out.
Doc here, 
imp:
Or you have a "Pump Bypass" for starting, to bring the pressure up before crank and run..That switch could be bad or stuck.
Docimp:
imp: Or you have a "Pump Bypass" for starting, to bring the pressure up before crank and run..That switch could be bad or stuck.
Doc
imp:That could also be true, except if it runs through the same relay, which I'm not sure.
It is a switched ground at the relay. The ECM controls the ground from the low side of the relay. If the ECM continues to ground it, it will stay running, but if you pull the relay you are removing all power sources to the fuel pump.
Here's how its wired in that car (and all GMs as far as I know)
Low side: switched power to fuse panel, fuse, low side of the relay, to ECM which controls ground and therefore activation of the relay.
High side: hot power to circuit breaker or fuse under the hood, high side of relay, to fuel pump, from fuel pump to constant ground somewhere near the pump.
I would believe that the relay is stuck on, but removing it would break the circuit. There almost has to be a short between the fuel pump supply power wire and another hot wire, but there shouldn't be any way for this to happen.
If you pull the relay, you are physically opening the circuit. Unless there is power arcing between the posts of the relay socket, it can't get power.
Here's how its wired in that car (and all GMs as far as I know)
Low side: switched power to fuse panel, fuse, low side of the relay, to ECM which controls ground and therefore activation of the relay.
High side: hot power to circuit breaker or fuse under the hood, high side of relay, to fuel pump, from fuel pump to constant ground somewhere near the pump.
I would believe that the relay is stuck on, but removing it would break the circuit. There almost has to be a short between the fuel pump supply power wire and another hot wire, but there shouldn't be any way for this to happen.
If you pull the relay, you are physically opening the circuit. Unless there is power arcing between the posts of the relay socket, it can't get power.
pump stills runs
sometimes there are diodes in a circuit to prevent feed back that would keep something running if one goes bad, it will lock up your circuit and keep stuff going when you don' want it
sometimes there are diodes in a circuit to prevent feed back that would keep something running if one goes bad, it will lock up your circuit and keep stuff going when you don' want it
found it
thanks everyone founfd the problem it is the oil pressure sending unit, it has a interlock in it which won't allow the fuel pump to run if there is no oil and when it screws up it shorts out grounding the circuit and making the fuel pump run when the car is off.
thanks everyone founfd the problem it is the oil pressure sending unit, it has a interlock in it which won't allow the fuel pump to run if there is no oil and when it screws up it shorts out grounding the circuit and making the fuel pump run when the car is off.
1 - 8 of 8 Posts
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