Fuel pump?

STUMPED99

MEMBER
1998 MAZDA B3000
2.5L
4 CYL
2WD
MANUAL
239,000 MILES

I have replaced every harness except one in the floor of cab on the truck listed above. I have no power to fuel pump whatsoever and truck has good ground touch anywhere on frame with test light it lights up. Sometimes get power to pump at 5-9 volts or nothing. I have bypassed inertia switch same thing new pump same thing ran wires through a relay to pump and ignition same thing no power. If go directly to pump from battery pump works but still won’t start. Also, the relay in fuse box under hood for the pump has two hot wires constantly? And no ground shows when test for ground the thick blue/orange is hot and thick red wire is hot constantly? Did nothing but plug n play all new used harnesses no splices. So, if have any suggestions I’m open and listening Thanks Is it possible that the computer is partially out or not getting proper signal?

Sunday, February 26th, 2023 AT 4:42 AM

3 Replies

JACOBANDNICKOLAS

MECHANIC
110,055 POSTS

Hi,

I need clarification. Is this the B3000 or B2500? The B3000 only comes with a V6. The 2.5L 4 cylinder is in the B2500.

Please confirm.

Joe

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Sunday, February 26th, 2023 AT 9:24 PM

STUMPED99

MEMBER
2 POSTS

B2500 has the four cylinder looks like a straight six used to.

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Monday, February 27th, 2023 AT 3:01 PM

JACOBANDNICKOLAS

MECHANIC
110,055 POSTS

Hi,

I attached the relay schematic below. First, in the engine compartment fuse box, fuse 13 provides power at all times to the relay. That power reaches the relay's primary side via a red wire. For power from the red wire to flow through the relay, there is a light blue wire with an orange tracer. That provides a ground path by the PCM to complete the primary side of the relay circuit. This causes an electromagnet in the relay to close the power supply portion on the secondary side of the relay sending power from fuse 9 to the pump.

So, here is where I would start. First, remove the PCM power relay and make sure there is no corrosion or any issues in the box and that the relay itself is good. If that relay doesn't close, you get no power to the fuel pump relay and fuel injectors which would explain why running power directly to the pump with it running, the truck still wouldn't start.

Actually, to make that test easier, check the red wire at each injector to see if there is power with the key in the run position. Do that and let me know what you find.

Also, try switching the relays with others having the same part number. If there are none, here is a link that explains how to test one:

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Take care,

Joe

See pic below.

Image (Click to make bigger)