1993 Chevy P30 fuel pump help

[Tommy_U]

Hi All - I have a 1994 Fleetwood Southwind on a 1993 P30 chassis. Got back from 4th of July weekend and was pulling into storage the next day and just as I placed it in Park and set parking brake the engine died. After that it would not start and had 3/4 tank of gas. I used some starter fluid and it will start so it is a fuel delivery problem. Also I was not hearing the fuel pump. I am having a hard time locating the fuse / relay for the fuel pump. I have checked all fuses I can find any bad, all seem to be good. I have a Chevy service manual but it is terrible and has very little info. Does anybody have a wiring specs for a 1993/94 p30? I was having trouble with my gas gauge also so I dropped the tank and replaced the whole unit assuming it was a bad fuel pump but possible electrical. I need to start tracing the wires and checking them / possible bad ground or broken wire. The plug to the fuel pump has 3 prongs, I assume it is ground, power for the pump and sending unit signal. Does anybody know what the voltage should read for the 3 wires and which should have power when the ignition is on? Any help would be greatly appreciated cause I have a vacation planed Aug 1st and need to get this solved asap. Any suggestions on what else to check would be greatly appreciated.

[More_To_See]

I think maybe my oil pressure at speed is up around 55 or so but just idling with hot oil less than 40. I just sort of notice the general position of the dial and not exact numbers.

You first need to determine whether the 12 volt Ignition source (maybe from a 20 amp fuse) is being provided to your relay (and the oil pressure sending unit) when the key is on.

Just pop out the relay from its connector and check for 12 V on Pin A of the cable connector pins.

If you wanted to, you could then move down to the oil pressure sending unit. Same thing. Unplug the connector and look for 12 V on one of the 3 pins. But at this point that's not necessary until you get the engine started on the relay circuit.

Once you've established that you have Ignition voltage I'd then go back to the relay and jumper the 12 V on pin A over to pin E while somebody is back at the gas tank. Hopefully the pump will be running. If it is not running then the likely problem is either bad wiring back to the pump or the pump itself.

If the pump runs with that jumper installed but not when you plug the relay back in and turn the key on it comes down to perhaps the computer (Control Module - ECM) - - or a loose connection somewhere. It's not energizing the relay coil to switch the contacts to provide power back to the pump. That control voltage would appear on pin D for 2 seconds when you turn the key on.

You really don't care about that oil pressure sending unit at this point. Just whether you can get the pump to run off the relay for a couple seconds. That tells you the pump and pump wiring is ok. Then the engine should also start and run for a couple seconds (and if the oil pressure sending unit is ok it should keep running).

One tricky thing to be aware of when checking for voltage on high amp vehicle circuits is that a sensitive voltmeter could show 12 V since there is virtually no load on the circuit but with any load at all the voltage could go all to h*e*l*l. (Gotta keep the moderators happy.) A corroded connection or loose wire could make that happen. Sometimes a bulb type trouble shooting tester may be a more reliable indicator for voltage. It puts at least a little load on the circuit. Hope this gets you going without too much wasted time.

Have fun

[Tommy_U]

Looks like I will be busy this Saturday checking all this out and hopefully I will be back up and running. If the oil pressure sending unit if bad or going bad would it affect the oil pressure gauge at all? Oil pressure should be around 40 at idle correct and about what while driving? (just curious?)

[Sully2]

More To See wrote:
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.

The normal engine mounted pump cant "suck" gasoline the distance it needs to go...hence the AUX pump inside the tank....to help with that problem an it runs as long as the engine is running

[Sully2]

More To See wrote:
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 is supplied to the engine via the OP sending unit. That way if you are in a wrech or ?? and he engine isnt running ( No OP) the engine doesnt run and keep pumping gasoline

[More_To_See]

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.

[Tommy_U]

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?

[Tommy_U]

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

[Tommy_U]

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]

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.

[Sully2]

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

[mike_brez]

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.

[psa0298]

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.

[turbojimmy]

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?