hi,

I have an issue with fuel pump harness.
Basically when i start the car, sometimes the fuel pump doesnt start.
i've tried to change the main relay and the big fuel fump resistor behind the headlight but nothing worked.

but if i fiddle with the harness portion in the trunk, it usually starts.
i think one of the wire is cut somewhere. Can this harness be replaced or it is directly link to the engine harness with no plug in between ?

 

do you have a copy of the factory wiring?

Foxed.ca - Mazda RX-7 Manuals

 

Yes I do, but i dont know how it is supposed to be read...

 

the wiring diagram has a section in the beginning that explains how it works, once you get it its pretty simple

 

Have you thought about wiring your fuel pump to a switch? Easy defloods, proper voltage to the pump, not worrying about obviously unreliable 30 y/o wiring.

 

Fuel pump harness is short and can easily be repaired if needed. If I were you, I would remove the fuel pump and inspect the wiring inside the pump for burnt spots on the ground side. I have seen the connector melted several times inside the pump. If so, I would suspect that the pump is failing and pulling excessive amperage.

 

Well I don't think the pump is at fault here. Basically when then car is not starting. I just have to move back and forth the harness portion in the trunk under the carpet, and then usually the car starts and nothing else seems to occur during the drive.

 

Also consider that a fuel pump can fail much like a starter motor in that it will stop in a "bad" spot. Jostling the wires and sometimes banging on the pump or tank like you do with a failing starter motor can kick start it. Try unplugging the entire harness, jumper 12v through each wire one at a time to a headlight bulb and a good ground to the other side of the bulb. See how bright the light illuminates on the two main wires (black and black with white stripe?? If I remember correctly the other two colored wires are for level sensor). This is testing the wires ability to carry a load. A wire can still carry 12v or ground with one strand still intact under the insulation, but can't carry a load big enough to power the part it goes to. In this case the fuel pump.

Think of an electric wire as a garden hose and one of your wires has a kink in it due to corrosion or an anvil cut. Water may still flow through the kinked hose, but won't be enough to do what you need to to.

 

I dont think the pump is at fault, cause only moving the harness makes it works.

when i first encounter the issue i was at work and could test things as i had colleagues around. basically the voltage arriving at the pump was a bit weird (sometimes 12v sometimes nothing).

so i didnt know wether the wire was at fault or if it was something else that blocked the current.

i changed already the fuel pump resistor and the main relay.

It could be my alarm that is messing things up but i dont think so.

For me it can only be the harness... but i dont like the idea of cutting and soldering new wires...

 

so basically i'm looking for this :


except that this one is for a FD, does somebody know the part number for this on a FC ?

 

Most likely it is NLA, meaning you will need to make your own or buy used.

 

I think it's this part :

could be the good one, but i think it's the one that goes from the fuel pump to the first disconnect socket.

I suppose the harness might come with the sheet metal part that goes above the fuel pump...

 

The harness in question is no longer available. I would remove the harness and check for corrosion in the pins and for any breaks in the wiring. This would be the first place I would start if I suspected the harness to be at fault. You can even do a continuity test to ensure you have good continuity between the each end.

 

is there a particular method to find break in the wiring (cause i think this is the probleme), i suppose you clamp your multimeter on both end of the cable and move the cable and see if you have continuous contact or not ?

 

Yeah that could work. Inspecting the harness and the insulation is key. Ensure there is no corrosion on the pins. I would suspect the issue to be a the pump side of the connector. You may also have a grounding issue as mentioned above. Inspect the top of the pump hanger that bolts to the tank and see if there is any corrosion on the top of the hanger.

 

i've removed it this evening.

I'm a bit confused... it doesnt look good, there was missing shrink wrap after testing the wires there seems to be not breaks (even the resistance is fine, less than 0.5ohms per wire).

I will have it reworked anyway.

I don't think there is corrosion on the top of the fuel pump hanger, i'll check when i replace the harness.

 

Ok so the black wire with grey striping has a small break when it reach the connector on the fuel pump side. To have a clean repair, I'd like to change the complete connector or at least one of the pin. Trouble is I don't know what is the model of the connector. I suppose it's a sumitomo one but I cant pinpoint which one. Any idea?

 

Any chance you can post a pic of what you're looking at?

 

the faulty one is the lowest one relative to the picture ( the most rounded one)