Clicking behind driver seat -Resisitor fuel pump relay

Hi,
"I have a clicking sound like a relay opening and closing quickly behind the left seat. It sounds like some is tapping Morse code."
"Just randomly stared one day and it happens at idle or while moving always when motor it operating temp not am Start when Engine cold. Have inspected the main relay which was fine no cracks and replaced both 4p relays on the bulkhead just to be safe. The car starts and drives fine but its an annoying sound. There are no codes and no other symptoms just clicking at various RPMs and drive states but nothing else correlates.
I suspect that the relay or wires, connector is not the cause of the problem.
That is definitely strange behavior. That relay should not be operating at low engine outputs. If you confirmed that you don't have some sort of intermittent ground on the red wire between the fuel pump relay and the ECU, then the ECU must be applying errant grounds causing the relay to operate (the ECU connects the red wire to ground to operate the relay). The ECU uses an internal transistor to switch the relay on and off; but when transistors fail they usually stay failed and most commonly as an open circuit. It might be possible that the ECU is getting some erroneous input signals causing the relay to engage and disengage.
There were 3 cases described on Prime.
I'm surprised by the solution:
1. Replacing the alternator
2. Repairing the engine-chassie ground (alternator replacing did not help)
3.Replacing ignition switch (this case probably concerned the Main Relay)
There is a verification procedure written in ETM. He suggests replacing my ECU with a functional one - confirmed from another car. I talked to R1 Motion, our friend from the forum. He has 37820-PBY-N01 Japan spec - mine is 37820-PBY-A01 US spec. It is not a cheap part (and there is no exact match) and the way the fault was solved on Prime means that I did not solve the problem. The common feature in solving the problem was power supply. (Alternator, ground). I noticed that these posts (errors) are from recent years. Our cars are getting old and knowing how to solve the problem can help others in the future. I encourage you to take action... I serve as an example.

Have you actually confirmed that it is the fuel pump relay that is making the noise? If you drive the car and keep the RPM below 3000 RPM the fuel pump relay will stay open. This means that you should be able to carry out a test by driving the car with the relay removed. Do that and if the noise is no longer present then the problem likely originates from the fuel pump relay. Confirm that the noise returns by plugging the relay back in. If the noise does not go away when you unplug the relay then it is originating some place else.

If it is the fuel pump relay I have no further comments on what might be causing the noise.

I found another entry on Prime from 2017 that describes identical issue. This means that the symptom is the same clicking noise and occurs when the engine is warm. The next step I will take is to remove the alternator and send it to a specialist service.

have you isolated the unit making the clicking noise? if so, what happens if you unplug it?

of the initial 3 options, the alternator overhaul is the most expensive!

Asas I wrote in the first post. I'm sure about the part that makes the noise. This is fuel by pass resistor pump relay. If I unplug it, the noises disappear

Fuel pump resistor by pass
the relay coil is constantly powered by the plus and controlled by the minus via the ECU. More specifically, with a transistor inside the ECU

yup, the fuel pump has a resistor to slow it up, then the relay short circuits the resistor when the car decides it wants the full pressure..... and, yes, its switched earth (which makes the electronics easier, but can do your head in when sorting thru many logic gates :) )

quite common for people to just short the resistor connector when their fuel pump is getting tired

so the alternator rebuild is a separate issue?

have you monitored the supply voltage across the relay?

I monitored the supply voltage as well as the signal from the ECU. i.e. ground. The problem is internal in the ECU. But I don't know what makes it. I can only guess from the cases described on Prime. The fault lies in the voltage.

I don't think its the vehicle voltage causing the problem otherwise all the other relays would develop similar clicking noises.

Under light load operation the relay should be de energized. Did you confirm that you are getting an intermittent ground connection for the relay at the ECU terminals? If so, I would expect that it is more likely that you are getting a short to ground which is causing the relay to energize rather than the ground switching transistor in the ECU actually energizing. That would require some odd firmware problem that most other people don't have or a short on the board that is energizing the transistor.

Any short to ground at any point on the wire between the relay and the ECU will cause the relay to operate. The definitive way to locate the source of the short would be to de pin the relay control wire from the plug on the ECU and just let it hang. That way it is impossible for the ECU to cause the relay to operate. If the relay continues to click then you have a wiring problem between the ECU and the relay. If the relay stops clicking then the problem would be in the plug or internal to the relay. You would have to pop the cover off the ECU and examine the solder connection between the plug and the board to start looking for a failure point unless you just want to hand over the money for a replacement ECU.

I will note that the generation of micro controllers in use by the NSX are most likely 5 volt CMOS logic. The ECU will have an on board voltage regulator to drop the 12 V car voltage to the 5 V logic voltage and that regulator is most likely a low drop out regulator. That means that the ECU should continue to function just fine down to DC input voltages of around 7 volts. If that was happening there would be lots of other things happening on the car that would make a voltage induced problem obvious - this would include an engine that was seriously misbehaving because the injectors and the coils, which operate at 12 volts, would not be functioning correctly.

I'm not willing to spend money on a second ECU. I diagnose my case according to the Manual. The control cable from the ECU to the Fuel bypass resistors relay, as you know, is very short and does not pose any risk of abrasion. As I mentioned in the first post, I am sure that the fault comes from the ECU. This is confirmed by connecting the oscilloscope with the recorder directly to the ECU by disconnecting the pin. I am as surprised as Old Guy by the way of solving the problem described on Prime. Old Guy was making his voice heard there. Maybe there is a capacitor in the internal +5V stabilizer system that is failing due to the passage of time?