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I've read through all the 3rd gen fuel pump/fuel pump relay issue threads it seems and I can't find an answer to the problem im experiencing. My car ran 2 days ago then one day the fuel pumps wouldn't prime, checked all fuses and grounds, the issue seems to be with one of the relays or resistors. I use the diag box to jump the FP and it only works sometimes im confused, it wont work first try jumping it but if you repeatedly stick the wires in and out enough times the fuel pumps will finally prime. so would everyone say its a fuel pump relay and be done, or could it be the resistor or even egi relay?
Original pump? Aftermarket? Any mods to the fuel or electrical/pump system?
car has a full radium fuel system, 2 pumps wired to the battery on their own, the surge tank pump is wired to the factory wiring, but the key is that NONE of the pumps prime which tells me that the signal wire is not being triggered when the key is turned since even the hard wired pumps wont prime. and like i said the most confusing part for me is that if you spam the diagnostics box jump for the fuel pump it will prime intermittently, does anyone know if a bad relay cant intermittently work if continually activated?
also i will add that one of the previous owners installed a NA miata EGI relay on the car, they are known to be interchangeable online but not sure if that would potentially cause an issue?
You can use another relay to rule out the fuel pump relay. Relays either get stuck open or closed rarely are they intermittent unless the power source or wires/pins are damage that go into the relay. With only the aux power on check voltage to the pump, you should have 12V. If the car can be turned on you should have a minimum of 12V. I did the fuel pump relay relocation mod in the trunk bypassing the forwrad one in the engine bay.
According to the diagram, jumping the diagnostic connecter bypasses the just about everything and it runs the pump directly. it DOES have to go through the egi but you have ruled that out. why spamming it works i don't know and cant speculate. with your set up, the fuel pump resistor should be a non factor. if you still have it installed you can unplug it, cut the connector off the resister itself, strip the wires back and make a jumper plug out of it. after that, plug it back into the harness. that may or may not help but its worth trying.
i would need a diagram of HOW your pumps were wired to help any further....
According to the diagram, jumping the diagnostic connecter bypasses the just about everything and it runs the pump directly. it DOES have to go through the egi but you have ruled that out. why spamming it works i don't know and cant speculate. with your set up, the fuel pump resistor should be a non factor. if you still have it installed you can unplug it, cut the connector off the resister itself, strip the wires back and make a jumper plug out of it. after that, plug it back into the harness. that may or may not help but its worth trying.
I would need a diagram of HOW your pumps were wired to help any further....
Appreciate the effort trying to help, the 2 HP pumps in the surge tank are wired up with 2 of radiums fuel pump relay kits, same as most companies make to hardwire the pumps directly to the battery, ground is to the chassis in the trunk and ground is good as the car ran fine but just stopped working after sitting overnight randomly, obviously the aftermarket relays are spliced into the signal wire in the stock harness to tell the relays to activate when the key is turned on. The LP pump that fills the surge tank is just wired in using the factory wiring. Just to confirm the diagnostic jumper bypasses the fuel pump relay in the front of the car AND the resistor under the brake booster, so i can theoretically rule those 2 things out?
Well... the longer I look, the more I start to question it lol. It looks like yes but start with the resistor first. See if you have that still installed and jump the connector if you do. According to your description, your set up is wired independent of the car and is only using the factory trigger to energize the relay which turns everything on. If thats the case then you need only troubleshoot the oem side of the circuit. If you have a power probe you can apply power directly to the aftermarket relays and rule out the entirety of the circuit so you know for sure the problem is on the car side and not your pump side.
Lets isolate the issue first and go from there. Power your wired in fuel pump relay and verify everything back there works. This will tell us that the problem lies in the factory wiring. After that, check on the fuel pump resistor under the brake booster. If its there, cut the connector off of it and make a jumper with it and plug it back into the harness. We can move on from there after that.
Well... the longer I look, the more I start to question it lol. It looks like yes but start with the resistor first. See if you have that still installed and jump the connector if you do. According to your description, your set up is wired independent of the car and is only using the factory trigger to energize the relay which turns everything on. If thats the case then you need only troubleshoot the oem side of the circuit. If you have a power probe you can apply power directly to the aftermarket relays and rule out the entirety of the circuit so you know for sure the problem is on the car side and not your pump side.
Lets isolate the issue first and go from there. Power your wired in fuel pump relay and verify everything back there works. This will tell us that the problem lies in the factory wiring. After that, check on the fuel pump resistor under the brake booster. If its there, cut the connector off of it and make a jumper with it and plug it back into the harness. We can move on from there after that.
I know for a fact its there so ill definitely try and jump that, like i said the confusing part is why it will activate after spamming the diagnostics jumper, if it was bad ground the pumps wouldn't turn on no matter what correct? I don't have enough experience with failing relays but once a relay has failed is it dead or can it sometimes work if you continually try and activate it?
You can remove the outer case from a relay and manually squeeze the contacts together. If the coil on the inside is the issue then it wont magnetize and close the contact. YOU can be the magnet and close the contact yourself.
So just to update this thread I found out it was in fact the fuel pump relay, and to clarify it was the MAIN FUEL PUMP RELAY aka CIRCUIT RELAY the one next to the EGI RELAY not to be confused with the FUEL PUMP SPEED RELAY which is located in the front of the car. The big thing to note is that you should always double-check relays because when I test the relay it audibly clicks like a normal relay should but obviously was still bad, so a click doesn't always mean a good relay. Also apparently a bad relay CAN be forced to intermittently work like mine did when spamming the diagnostic terminal. Finally, I would definitely recommend bypassing the FUEL PUMP SPEED relay and just removing it and the resistor altogether which definitely helps simplify the system and leaves fewer failure points (shown in the attached pic from another user).
Yep, like i said i practically read through every fuel pump/relay issue thread from the last 20 years, including yours, before making my post so i know there will be many others in the future in the same situation we were in looking for information, so i try and document as much as i can to help haha.
01-17-23, 10:49 AM
