1998 Volvo v70 xc - awd fuel pump issue?

[Ozark Lee]

When I get another chance, I'm going to jump the fuel pump relay again, and measure the voltage in the back.

That should put voltage to the connector at any time the key is in position II. A reading of 4 volts at the connector is a problem, it should be in the 12+ range.

...Lee

[reggie1364]

Well, it appears that I made a mistake in reading the voltage in the rear access hatch. It should have been 0.09 volts briefly when key was turned to pos II, then down. When cranking it moved up to 0.04 volts. This is much less than the expected 12+ volts.

I get 12.2 V at the fuel pump fuse, so somewhere I'm losing all voltage before it gets back to the rear access hatch.

Any thoughts?

[reggie1364]

Well, it appears that I made a mistake in reading the voltage in the rear access hatch. It should have been 0.09 volts briefly when key was turned to pos II, then down. When cranking it moved up to 0.04 volts. This is much less than the expected 12+ volts.

I get 12.2 V at the fuel pump fuse, so somewhere I'm losing all voltage before it gets back to the rear access hatch.

Any thoughts?

Looks like I'm having the same problem as this:

https://www.matthewsvolvosite.com/forums ... 49#p342949

[holler1]

reggie,
As Lee suggested, when you check voltage on the red wire at the rear hatch, try connecting the black voltmeter lead to a good bare metal ground on the frame or chassis, and see if that makes a difference. If you get 12 volts relative to the frame, but not relative to the black wire, the lack of a good ground connection might be the problem. If you're disconnecting the fuel pump connector at the hatch to connect the meter, make sure you're connecting it to the wires from the main bundle, not the ones going on to the pump. I'm looking at a picture of those connectors now, and it's easy to confuse them. If your meter has a a resistance (ohm) setting, check the resistance between the black wire and ground. It should be zero. I don't recall how the wires are routed from the fuse area to the rear hatch, but you may want to see if you can trace the wires and check voltage at some intermediate location to try to find the break.

[reggie1364]

reggie,
As Lee suggested, when you check voltage on the red wire at the rear hatch, try connecting the black voltmeter lead to a good bare metal ground on the frame or chassis, and see if that makes a difference. If you get 12 volts relative to the frame, but not relative to the black wire, the lack of a good ground connection might be the problem. If you're disconnecting the fuel pump connector at the hatch to connect the meter, make sure you're connecting it to the wires from the main bundle, not the ones going on to the pump. I'm looking at a picture of those connectors now, and it's easy to confuse them. If your meter has a a resistance (ohm) setting, check the resistance between the black wire and ground. It should be zero. I don't recall how the wires are routed from the fuse area to the rear hatch, but you may want to see if you can trace the wires and check voltage at some intermediate location to try to find the break.

Thanks. Yes, I was using ground to make the measurements, as many as I could try. I have not tried checking the resistance for the black wire to ground - will do so soon.

[Ozark Lee]

You are to a place where you are going to need to start tracing the wiring which is a huge PITA. You can download the schematics from this site:

http://www.volvowiringdiagrams.com/

The pagination on the schematics is a mess but they are very detailed and they show all of the junction points and ground points. You will essentially need to start at one end or the other and work it in segments between junction points until you find the wire segment with the problem.

...Lee

[abscate]

Whenever you are trying to measure resistance make sure you don't have voltage on the wire in question. Disconnecting negative battery cable is the safest way to make sure you have done this.

[precopster]

I loath these situations when one train of thought is to replace a common failing item without adequate diagnosis. The mechanics that first dealt with you sent you on a goosechase and now you're questioning your wire repairs and your own fault -finding logic.

Instead of trying to trace a faulty loom I would simply call it quits and work out which element is missing here; ground or positive. The resistance check with battery disconnected is good enough.

Once you've worked it out simply run a new wire from the relay or replace the groumd wire. This is what auto electricians actually do most of the time unless fuses are blowing.

[abscate]

I'm with a Mike on this one.

Once you have the wiring diagram in hand, and make sure you understand everything that is connected, you can cut the wire from the fuse box out of the circuit and replace with your good, new wire.

You can just pull the connector off the load end of the fuse and tape it off ( good practice) and move on.

[reggie1364]

Thanks for all of your help and suggestions - they've kept me calm as I try to work through this problem.

I'll disconnect the battery and rerun my resistance/continuity checks.

Before trying to cut wires, I decided to check continuity from fuse to relay pin 15 - everything OK. I then checked my fuses, both visually and with the ohmmeter - all OK. Before tackling the wiring/electrical issues, I decided to jump the relay and verify that the pump was working. The car still didn't start. I checked the power at the relay pin 87, then the pump - both OK. Since I have a hole where the pump is located, shouldn't I be able to hear the pump when operating? I certainly did not hear anything. I've taken the pump out. Is there anyway to safely (to the pump) apply power to verify the pump's operation? Would I need to immerse in water, so that the pump has something to pump?

What does the fuel regulator have to do with this? Could this be my problem?

For the wiring/electrical issues - is there anything ignition related that could be not allowing the power from the fuse to the relay?

Thanks again!