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sprinkles08
sprinkles08, ASE Certified Technician
Category: Car
Satisfied Customers: 21592
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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Mazda B3000 4x4: we are working on a 1999 Mazda B3000 extend

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we are working on a 1999 Mazda B3000 extend cab. 3.0L. It caught fire and we have been working on replacing the parts that burnt. That consists of the fuel tank, fuel pump and wiring harness. We have put new fuel lines and fuel filter on. We tested the fuel pump outside of the tank and it works. However when we have the fuel pump in the tank it will not run. What may be causing this problem. the fuel pump is a brand new one along with the filter. We have no pressure on the fuel rail. When we turn the ignition switch on the truck the fuel pump does not run. Any suggestions on what to replace or test, please. Thank You

Hello and welcome to JustAnswer!

 

If there was a fire and melted wiring or the pump melted then the fuel pump power feed wire would have likely shorted to ground which would have blown the fuse. I don't see that you mention checking the fuse, this is definitely where you'll need to start. The fuel pump is fed power from fuse 9 under the hood, 20 amp.

 

If the fuse is good then you could have a bad fuel pump relay, try swapping it with another and see if that takes care of it.

 

Also check the inertia switch to make sure it hasn't tripped, this is in the circuit between the relay and fuel pump and will take power away from it.

 

It could also be a wiring problem on either the power or ground side of the circuit. Start by checking the fuse, switch and relay and we'll go from there.

 

 

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Customer: replied 3 years ago.

We have tried everything you have suggested. We switched out relays, we check the fuses they were all fine. The whole fuel pump and the top of the fuel tank melted down do to this fire. we had to replace the wiring harness from the cab to the rear of the truck. We got a used tank and a new fuel pump. we had to replace fuel lines and added a new fuel filter. We have pressed the button to the inertia switch. Could this have went bad? When we removed the new fuel pump we ran jump wires to a jump box and it clicked right on so we know we have a good pump. The fuel pump will not kick on when you try to start the truck. The truck turns over but just will not start. Any more suggestions. I appreciate the help. Thanks


 

It's possible the inertia switch is bad, you can check for continuity through it.

 

If the switch is good then we can do some electrical testing and figure out what's going on. I'm a full time tech and at work this morning and am away from my service information, but I'll be back to it this afternoon.

Customer: replied 3 years ago.

Thank You! My husband is also away today. I thank you for your help and will return a reply when I have more info. Have a wonderful day.


 

Customer: replied 3 years ago.

How do we test the inertia switch for continuity?

With the switch unplugged use an ohm meter set to the 200 ohm scale, probe each wire to the switch and make sure there is continuity. If there isn't continuity and the switch isn't tripped then it is bad.