1993 Chevy P30 fuel pump help

If I recall correctly, the only wire that should have voltage is the fuel pump feed. The fuel pump ground is obviously a ground, and the sender measures resistance to ground so there's no voltage there either.

Unfortunately I can't help you with a wiring diagram. Mine's a carb'd 454 with a mechanical pump.

I didn't follow your post exactly. Are you saying you replaced the sender and pump and it still doesn't work? Or the trouble started after replacing the sender and pump?

Have you checked the fuel filter along the frame? Maybe try disconnecting the fuel line going into the fuel filter and see if the pump is pumping at all.

I'm not sure if they call it a relay but in the dog house mounted near the gas pedal there is a 3inch x 2inch black box that I changed on mine when I was having a hard start problem.

mike brez wrote:
I'm not sure if they call it a relay but in the dog house mounted near the gas pedal there is a 3inch x 2inch black box that I changed on mine when I was having a hard start problem.

Mounted on the plywood floor...under the fiberglass bubble thats the trans tunnel.....right next to your right foot. Fuel pump relay

When you are driving down the road power for your in-tank fuel pump is supplied through the oil pressure sending unit. That's at that the front left of the engine and down low of course.

When you turn on the key, power is supplied back to the pump through a relay for 2 seconds. To check for that pump running you have to have somebody back there laying down under the tank as you turn the key on.

When you turn the key to the start position the relay again provides power back to the fuel pump. As oil pressure comes up when the engine starts power is then picked up by the oil pressure sending unit.

That relay is likely located under the dog house over by where your gas pedal is. It is held by a metal clamp.

You may also have a multi wire connector at the top back of the tranny sort of down on the side a little through which that power goes back to the pump.

Good luck.

Fuel pump / sending unit was replaced as a whole. I can hear no pump while the key is turned on. I will open the line at the filter to verify but I believe the pump is getting no power. In the 3 plug wire is it the middle wire that supplies the power and do you know what volt is supposed to be supplied. My Dad has a 1992 p30 and you can hear the pump when the key is turned on as mine use to do. These seem to have pretty noisy fuel pumps which makes it pretty obvious when you can only hear silence. I will check for a box near the peddle in the dog house.

more to see - thanks for this information that will also help. Do you know what the voltage should be on these different plugs so I can check them?

Sully2 - thanks for the info

you guys are great with quick responses. I will stop and do some checking tonight if I can. BTW was running fine before and when I stopped I placed in park, and at the same time I put the parking brake on the engine died, not sure if that was just coincidence or not but I figure it is worth mentioning. Also while we are talking about oil pressure sensor, what should the oil pressure be at idle and while driving say 40mph?

If in fact the engine quit running when you put it in park that would eliminate the fuel pump relay. That relay is completely out of the circuit when the engine is running.

(So if you are ever out a hundred miles from nowhere and that relay fails all you have to do to get the engine started is to unplug it and temporarily jumper across two of the connector pins on the harness. Pin A is 12 V & Pin E supplies power to the pump. Only for a couple seconds though till you get the engine started. I'd be a bit careful in that connector. The computer is on Pin D to pick up and drop out the relay. Pin F is the relay coil ground.)

That entire fuel pump circuit is 12 V. The wiring diagram says it is picked up from the Ignition source by a 20 amp fuse and then sent to the fuel pump relay and to the oil pressure sending unit - on two entirely different wires. (I've never found that 20 A fuse on my rig, though. It must be picked up somewhere else.)

Back at the tank on the driver's side there is a gray wire in a somewhat small harness carrying that 12 volts to the pump.

If you want to check to see if that 12 volts is available when the key is turned on go down to the oil pressure sending unit and unplug the connector. One of the three pins should have 12 volts on it. I'd replace that sending unit just for the heck of it, too. They are cheap ($25) and that's all that keeps your pump running when out traveling around.

(The fuel pump start relay is a $10 item.)

Have fun checking things out. Better at home than parked out along some long lonely road - - at night in the rain.