More fuel pump relay fun!

V
Protege5
Question: does power have to pass through any fuse before going to the fuel pump relay?

When I have my lovely assistant try to start the car, I'm reading zero volts to the fuse box connectors for the signal side of the relay, and zero volts across the connectors for the power side of the relay. So I suspect juice isn't flowing to the relay.

Background:
Previously I "fixed" a no-start by swapping a fuel pump relay (the black one labeled Circuit Or SPV on the cover chart) from my parts car. Car ran great after that.

Now I'm working on the car after an unexpected tow truck ride last week, shut off after leaving a gas station.

Because the fuse box relay spot is noticeably charred, I swapped the entire fuse box from my parts car (which ran beautifully before the rust rendered it inoperable and I sold the motor), as the parts car box has mere discoloration. Still no start.

I tested both relays with some leads and my spare battery, both go click when juice is applied to the signal spades.

When I apply 12v to the fuel pump I can hear it whirr, but it's not loud. I had Lovely Assistant try to start the car like this but I couldn't hold the leads on steady enough due to mosquito swarms LOL.
 

pcb

The Diagram Dude
V
2002 mazda protege 5
Question: does power have to pass through any fuse before going to the fuel pump relay?...
No, the power goes through the main relay then to the pump.
There is a fuse for the main relay but if that was blown, you would have nothing.




Check Your Ignition Switch...

It's common for them to wear out.


 

pcb

The Diagram Dude
V
2002 mazda protege 5
..., and zero volts across the connectors for the power side of the relay...
That doesn't sound right...
Try measuring from each connector to a ground somewhere.
One of them should be +12 V
 

pcb

The Diagram Dude
V
2002 mazda protege 5
EDIT: If your car starter motor is turning over then the ignition switch probably isn't your issue.

This is a picture of the the fuel pump and relay.



You should get +12 V going to two terminals in the relay socket.
Measure between the terminals and a good ground.

If you don't get +12 then the power isn't getting from your main relay to your fuel pump relay.
 
V
Protege5
Update:
Readings across rearmost signal connector in fuel pump relay mounting spot in fusebox to chassis ground:
0.8 to 0.9ish volts at rest,
1.15ish volts during cranking.

Reading 11.3 to 11.5 volts across the two pins for the fuel level sending unit with key on, which makes gas gauge read either zero or super low even though the tank is topped off.

Battery is probably weakening from repeated cranking tests.

I hate electrical stuff.
 

pcb

The Diagram Dude
V
2002 mazda protege 5
OK, I'm confused..

The power comes from the battery, through the INJ fuse then through the main relay when the ignition is turned to ON (which must be working because nothing would turn on if the fuse was blown or the main relay wasn't working.)

Then it goes to both connector pins in the relay socket.
Number 7 with the arrow head.



You should +12 V between each of the terminals and ground ( maybe use the negative battery terminal)

Don't measure the voltage across any two terminals in the socket... That yields erroneous results.

You don't need to be cranking your engine over to do the reading, just have the key in on position to kick in the main relay.

The +12 V will always be on waiting for the ECU to provide aground path for the control circuit that kicks in the fuel pump relay the the big "switch" in the relay turns on to deliver the +12 V to the fuel pump.

You may have a problem with your ECU not kicking in the relay or the wiring from the relay to the ECU.

Make sure you've got +12 V getting to the socket on two terminals first.
 

pcb

The Diagram Dude
V
2002 mazda protege 5
How was it to swap out your fusebox ??

Isn't there a butt load of wires and connectors that needs to be spliced in ??

Doesn't it tie into every harness ??
Did it just plug right in ??
 
V
Protege5
0.9 volts to relay terminal

Fuse box: three 10mm bolts for hold down, two 10mm bolts for power and ground on main fuse thingy.

On top of box is one small connector to unplug.

Under the fusebox are 2 big, 2 medium, and 1 small connectors that are easily unplugged. The big ones are held in with green slide clamps in their mounts, kinda BMW-ish style.

Of the two big connectors, one is orange and the other white. The white one is probably the one with the fuel pump wiring because A) It's on that side of the fusebox, and B) Both parts car and the Blue Lemon have scorch marks on some connections.

I'm taking the fusebox back off the car now, will post pics.
 

pcb

The Diagram Dude
V
2002 mazda protege 5
I just checked this again and realized you might not have your main relay operating. I thought it operated more things but only supplies power to your fuel injectors, fuel pump, purge solenoid valve and speed sensor.

Check your INJ fuse and see if plugging that fuse in and out makes the main relay click ( the fuel pump relay may click as well you should be able to feel it clicking)
Fuse #10..
Do this with the ignition in on position.

 
Last edited:

pcb

The Diagram Dude
V
2002 mazda protege 5
You can test your main relay for power too.



Unplug it and check for +12 V between each terminal and ground.

One terminal should be live all the time (it comes from the battery, through the INJ fuse to the terminal)

One of the other connectors should turn to +12 V when the ignition is turned to on (the control circuit)
 
V
Protege5
Fuse checks perfect continuity.
Plugging fuse in with ignition on, no click in relay.
Still only have 0.9 volts to relay terminal, ignition on.

Fuse box pics being uploaded soon, Blue Lemon has very little discoloration on large white plug - in fact it looks like old dialectric grease and there's no melting at all.
 
V
Protege5
Fuse box:
Pop up the coolant reservoir and lay it aside, otherwise you can't turn the box over:


Use little flathead screwdriver to depress locks on green sliders to free the big connectors.


Old grease?
 

pcb

The Diagram Dude
V
2002 mazda protege 5
Try swapping your main relay with the parts car.

But both relays should click when the fuse is plugged in and out.

See if there is power in the socket for the INJ fuse.

There should be power to one of the terminals.
 
V
Protege5
Main relay is green, right?

Both the green ones I have on hand go clicky when given 12v.

There's 11.5 volts going to the INJ fuse.
 

pcb

The Diagram Dude
V
2002 mazda protege 5
Its looking like the power isn't getting through to the INJ fuse.
Look for the fat black wire going into the fusebox and check for+12 V in the connector.
Try to follow the fat black wire through the fusebox., checking for +12 V along the way.
 

pcb

The Diagram Dude
V
2002 mazda protege 5
Fuel pump relay is #2, main relay is #4. (I don't know about color.)

 

pcb

The Diagram Dude
V
2002 mazda protege 5
Main relay is green, right?

Both the green ones I have on hand go clicky when given 12v.

There's 11.5 volts going to the INJ fuse.
The power goes from the INJ fuse right to the main relay.

Try to trace the connections between the two, looking for a bad connection.
 
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