Fuel pump out of power

[Felson]

Hello everyone.

I have 2001 1.0 Micra (coilpack) for 15 years, strong runner with no problems until recently. I parked it two days ago and suddenly it will not work now. I traced it down to fuel pump not receiving power.
When I turn ignition to ON position there is 0 volt at the fuel pump plug. My guess is there should be 12 (or so). Obviously there is no noise from pump building pressure. When I try to start the engine it shows about 9 volts there, but it still does not pump (the battery is ok, shows 12,7 volts)
When I connect the pump directly to 12 volts supply it works fine, you can hear it and it pumps fuel (engine starts).

I checked the fuel pump fuse - it is ok.
I suspected the relay, so I swapped it with one from the engine compartment (fan relay), but to no avail.
I removed the fuel pump fuse and measured voltage in the fuse socket. There is about 5 V when the ignition is in ON position, and about 10 V when it is at START position.

I have run out of ideas. Is it some short circuit somewhere? Or is ECU broken?

Please help.

 

[MattInARedMicra]

Before it went had you noticed any loss of power?

A fuel pump that runs (even slowly) should be able to achieve enough fuel pressure for the car to idle because that takes very little fuel, you'd just notice it hesitating if the voltage drop was too much while it was running.

The only thing I can think of is a blockage. The fuel pump cuts out when the correct pressure is built at the engine when you turn to on (but not start), then you start the car and it begins running again while you idle/drive. Some fuel pumps are designed to run at a range of voltages giving more volts for higher revs but I'm 95% sure that's not the case with the micra. The micra fuel pump has a return line where fuel cycles back from the engine if it isn't needed and maintains constant pressure at the engine.

So if there was a blockage, the pump might be shutting off because it thinks it's fully pressured the lines but in reality it's only pressurized up until the blockage. But when you turn the car over it hasn't built the pressure so it doesn't start. I'd probably start with the fuel filter if that's not been done in a while, and give it a quick check for any crushed lines anywhere. Do you have any way to test fuel pressure?

If that doesn't seem to be the issue then I'm stumped as to what it could be, but someone with more knowledge could probably have more advice

 

[Felson]

Hello and thank you for the answer.
It's my wife's car, she drives it daily and didn't notice anything before it happened.
Unfortunately the fuel pump does not start at all.
However when I applied 12V from an external power supply directly to the pump then it worked fine and I was able to start the engine.

That's why I think the problem is not with the pump itself.

 

[MattInARedMicra]

Hello and thank you for the answer.
It's my wife's car, she drives it daily and didn't notice anything before it happened.
Unfortunately the fuel pump does not start at all.
However when I applied 12V from an external power supply directly to the pump then it worked fine and I was able to start the engine.

That's why I think the problem is not with the pump itself.

if the signal comes from the ECU to cut the fuel because operating pressure is reached, this may be why the voltage is dropping to 9, although you would think it would be zero

I'm not very good with the electrical side, I would check for continuity and ground, but beyond that I'm clueless. It could be a short within the pump? I'd just be hesitant to fit a new fuel pump first because they're quite expensive and from what I've heard it's difficult to get the old one out

The AA have told me that the diesel ones do get fuel blocks as a fairly common issue, rarer on petrol ones

 

[fuzzy-hair-man]

if the signal comes from the ECU to cut the fuel because operating pressure is reached, this may be why the voltage is dropping to 9, although you would think it would be zero

Afaik there is no electrical fuel pressure cut out just goes into the rail and is returned to the tank if not required using the mechanical fuel pressure regulator on the end of the rail. What I think you're confusing is the cut off after you turn the ignition on the fuel pump primes and will then switch off, this is a timer that switches off after a set time if the car is not started.
Given the symptoms I'd be checking the fuel pump fuse then that the fuel pump relay is clicking on and finally that there's a signal from the ECU to the relay, I think out might be switched on earth similar to the injectors so there should be 12v at the signal but the pump won't run as it's not earthed via the ECU.

 

[MattInARedMicra]

Afaik there is no electrical fuel pressure cut out just goes into the rail and is returned to the tank if not required using the mechanical fuel pressure regulator on the end of the rail. What I think you're confusing is the cut off after you turn the ignition on the fuel pump primes and will then switch off, this is a timer that switches off after a set time if the car is not started.
Given the symptoms I'd be checking the fuel pump fuse then that the fuel pump relay is clicking on and finally that there's a signal from the ECU to the relay, I think out might be switched on earth similar to the injectors so there should be 12v at the signal but the pump won't run as it's not earthed via the ECU.

oh it's a timer? I couldn't figure out how that worked to stop the flow I figured it might work the same way as the hot water switch on a combi boiler. But a timer makes more sense, sometimes the simple solutions are the best lol

I can't figure out how it would still be getting 9v - possibly a hairline crack in a fuse? somethings adding resistance

 

[Felson]

It works!

To be honest I don't know what helped. I opened the ECU but there was no apparent damages inside. There was some dust inside so I removed it.
I did all of the troubleshooting according to diagnostic procedure from the service manual - all the harnesses, relay and fuses were OK.
So I put everything back together and it started. Now it works.

Thanks for all the suggestions.

 

[jonny hSL]

hi, i have this exact issue, those 3 blue relays above the fuses, can someone lease tell me what controls what?
it's a right hand drive micra if that makes any difference

 

[.Maarten]