No power to fuel pump
My car has 165000 miles.
My car has a manual transmission.
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The ECU is the brain of the operation. It uses engine RPM and signals from different sensors to meter the fuel. It does this by telling the fuel injectors when and how long to fire. The ECU often controls other functions like the fuel pump and ignition timing.
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The first thing I would do is to connect a scanner to the car and see if you can communicate with the PCM. As a technician, I have access to communities of technicians where repeat failures are reported. In these reports, it is most common when the PCM fails in this fashion, that you will not have PCM communication. If you do have communication and the Check Engine Light turns on with the key on, I would be leaning away from the PCM being the problem.
However, this is by no means conclusive. You could be correct in your thoughts about a wiring problem mid vehicle. On most GM vehicles, there is a connector along the frame rail for the wiring harness that services the fuel module in the tank. This has problems with corrosion because it sits under the vehicle exposed to the elements. But why am I doubtful of this, and this will require you to confirm where the power starts and stops, is you stated you didn’t have power from the fuse box. This would be before this connector and the fuel pump. If this is the case, I wouldn’t be thinking of a wiring problem mid vehicle anymore.
I am wondering if you confirmed the fuse box was getting power? It is a very common problem that when we move wiring we inadvertently move the damaged wiring and fix the problem for the short term. You may have done this when replacing the fuse box. Not to mention you seem to have an intermittent failure on your hands. This compounds the process quite a bit.
I’m not sure how you are confirming you have power at the various points, but I highly recommend a test light over a multi-meter. A test light draws current and a multi-meter does not. There can be voltage present but not a good enough connection to carry current. This is a very important distinction when you are battling bad connections. The problem with a test light though, is knowing when it shouldn’t be used. Some test lights draw too much current and can damage computer modules. Even us technicians perform tests on modules at our own risk.
The best way to test a relay is to simply use a jumper wire to bypass them. If I suspect there is a problem with the power supply to the fuel pump, this is the first thing I do. This way I can be sure it isn’t the relay or the PCM that turns the relay on. If the fuel pump does not run, use the before mentioned test light to find where the power stops. This requires you to methodically track the wire back to the fuel pump. I usually start at the central connector, if it has one. Not all of them do. I go directly to the pump if I can, but this is often not easy to access without dropping the fuel tank down. If you successfully confirm power to the pump, it maybe a bad ground, in which case the easiest way to confirm this is to add a ground yourself.
If this circuit checks out good, a few other things to check are power and ground to the PCM. Locate the wire from the PCM that powers the fuel pump relay. This can be done at the relay connector while you are testing the fuel pump circuit without the relay. When you turn the key on, on of the four terminals should receive power from the PCM for a few seconds. It will turn off after a couple of seconds if the PCM doesn’t see a signal that the motor is running. This is normal operation.
As for the air pump, I wouldn’t think this is an indication of the problem unless this occurred at the exact same time as the fuel pump failure. If so, I would suspect a wiring harness is shorting to ground somewhere. If they didn’t occur at the same time, this is most likely a separate issue.
The challenge you have here is isolating each part of the system. The PCM, the fuel pump relay, or a wiring issue. The PCM is actually fairly easy to check. Is the Check Engine Light on with key on and does it communicate with a scanner? Then follow the fuel pump relay test I outlined above. If it is a bad connection somewhere in the system, you will need a good wiring diagram and a well thought out plan to isolate where the problem is. This can be the most difficult to diagnose, especially if the problem is intermittent. Find a wiring diagram and study it carefully. If you’d like help, you can have a qualified technician, such as one from YourMechanic, to inspect your car’s loss of power and make the correct repairs.
Good luck. I hope I have been of assistance.
If you detect no power at ANY time to the pump (including during key on), your only recourse is the Factory Service Manual wiring diagram. With the diagram in hand, you have to trace the fuel pump circuit from the power source to find the interruption. There may be a fusible link in the circuit; also check the pump ground. Obviously check the wiring harness and plug connections as those were handled during the repair. You can probe the new motor terminals to see if they are open. If the motor is good, you should find a small winding resistance of maybe 3 ohms or so (varies from pump model to pump model).
If you desire a mobile repair for this, simply request an electrical diagnostic and the responding certified mechanic will get this taken care of for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.