For some reason my fuel pump stays on. Originally car wouldn't start at all and pump wouldn't prime when turning key so I checked the oil pressure sensor and it was discontented. After reconnecting it, the fuel pump stays on and when I crank car it won't fire up. But when I disconnect sensor, car fires up but does not run properly and eventually dies. I checked the inline fuse between battery and radiator and it was blown. After replacing it, pump won't turn off and again engine won't fire up. I disconnected pump relay and it still stays running. I'm at a loss as to what to try next? Could it be ecm ? Anyways it's a89 305 firebird formula tpi. Any help is appreciated this is my only car to get to work. Also I tried jumping the wires at the relay and pump did not react.

 

Either the fuel pump timer circuit in the PCM is bad or you have a shorted wire somewhere, disconnect the computer and see if the fuel pump stops running; if that stops it, it verifies that the PCM is bad.

 

I disconnected ecm and fuel pump continues to run... Does this mean the circuit is shorting out?

 

Yes, the pump is getting power and a ground from somewhere; are you sure you disconnected the correct relay? Either way, I'd disconnect the relay again and do a good shake down of that circuit to find the short.

 

Yea I'm sure I disconnected the right one but I tried disconnecting them all to be safe. If the pump is getting power w/ relay disconnected does that mean short Is most likely on the circuit after the relay?

 

The oil pressure switch is bad, replace it. This switch runs in parallel to the fuel pump relay. So if the relay fails the oil pressure switch will run the pump. In your case the oil pressure switch has failed with the contacts in the closed position.

RBob.

 

There you have it, parallel circuit................

 

There you have it, parallel circuit................

 

If I disconnect the oil pressure switch, the pump stays on .

 

The pump is getting a ground from somewhere, you are going to have to inspect for a short.

 

That isn't what you stated in your first post:

Not sure what to tell you, maybe a previous owner wired the fuel pump to always run at key-on.

RBob.

 

Hi Caitnop, perhaps this diagram may help. If you are sure about pulling the correct relay, then as others have mentioned, there is a short but it is 12v's feeding into the pump not GND. When you first turn the key on to before actually cranking the motor , you should hear the pump running for about 2 seconds. If the pump doesn't stop, it means that fuel pressure is not being maintained. Check the flow chart below in my next post to trace out the problem.

This diagram is typical of TPI systems.

 

This diagnostic flow chart may help also. Keep in mind that it doesn't detail the specific locations of the harness wires and modules for a certain vehicle - just a basic guideline of where/how to isolate the problem. Also, insure that all connections are as normal - meaning to not disconnect anything while performing flow-chart diagnostics unless instrcted to do so.

 

I replaced the oil pressure switch and the pump no longer stays running. However , when I turn the key the pump does not prime. I can get car fired up but only for a few seconds till it dies out. Relay doesn't click on when I turn key so I'm suspecting bad relay

 

You need to look at the flow chart, and the proper tools to diagnose. You will need a fuel pressure gauge to do this correctly. When you turn the key on ( this would be on a cold start - pressure in the fuel line must be below operating range.), you should hear the pump go on for about 2 seconds. If not, it may be the relay or open circuit to it. If it does go on, but the engine dies after it is started, it could be that the fuel pressure is not being maintained. Need a gauge to determine this. If no gauge, it's just a guess.

 

As for the pump relay, the ECM provides +12 volts to power it. It is pin A1 at the ECM, GRN/WHT wire. This goes to terminal C on the fuel pump relay socket.

You can pull the relay and measure for voltage there. Can also check it at the ECM. It will only be powered for those 2 - 3 seconds at key-on. To power it again tap the ignition for a short cranking of the engine. The ECM will respond (or should) with powering the relay again for 2 - 3 seconds.

Terminal B of the relay socket is ground.

RBob.