# Cant hear the fuel pump today and the car is hard to start.



## snowwy66 (Nov 5, 2017)

If you could hear the fuel pump before. It was already bad. 

I can't hear mine and it has 2 pumps.


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## Barry Allen (Apr 18, 2018)

The only time I hear the fuel pump (low pressure, back by the tank) was when I was in a quiet garage and it was after I changed the fuel filter. I did the procedure for priming the pump, where you hold the start button without engaging the clutch, and I could hear the pump run and change pitch as it filled the new filter.

How old are you? I have good hearing. The fuel pump is a high-pitch whine sound, and if you are older that's the first frequencies of hearing that usually disappears.


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## 6speedTi (May 18, 2018)

I can hear my fuel pump running if there is no loud outside noise, the radio is off, windows closed and the vehicle is not moving. At first it's a steady humming sound then after a while it has a pulsating humming sound. It's not loud and you can't hear it under normal driving conditions because of road noise. Is this normal? Probably.


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## JLL (Sep 12, 2017)

I've always been able to hear my fuel pump since it was new to me at 9,000 miles.


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## Cruz15 (Mar 17, 2016)

I have always heard my fuel pumps in my 2015 and 2018 diesel Cruze s during start up and shut down. Im mid century and have Very good hearing.


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## Cruz15 (Mar 17, 2016)

If I prime the fuel system it will start normally, after shutdown it will be a hard start again without priming.


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## Cruz15 (Mar 17, 2016)

Any Diesel Mechanics have any comments? I am taking it in early this week.


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## Barry Allen (Apr 18, 2018)

Sounds strange because once the fuel system is primed by the low pressure pump, it's full of fuel all the way from the tank to the engine. Normally starting the car will give you a brief hesitation where the LP pump turns on and maybe that system is about 30-40 psi: just enough pressure to push fuel forward to the engine so the HP pump isn't sucking a vacuum and causing more wear that way. From that point the HP pump is doing the 30,000 PSI thing for the HP rail that feeds the injectors and then returns overflow (used for cooling the injectors and the HP pump) back to the tank somewhere.

I had an old Subaru with a leaking O-ring around one of the fuel injectors. That caused some long starts if you left the car sit for a while, because the fuel would leak out and would take some air into the fuel lines that would have to be purged out on the next start. But that was an older gasoline engine where the total pressure in the fuel injection system was maybe 40 psi.

The symptoms you describe are similar, like there is a leak somewhere that is letting air into the fuel system that has to be purged. But if there was a leak on the high pressure side you would get diesel fuel spraying out at very high pressure, so you would definitely notice that! My Subaru had a whiff of gasoline smell when parked and running because the fuel was a slow drip out of the injector O-ring onto the exhaust manifold, so it instantly evaporated from the heat while driving or when the engine was running. Once I replaced all the O-rings (8 total; 4 upper and 4 lower) as preventative measures, everything was fine.


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## Cruz15 (Mar 17, 2016)

Im along this way of thinking except I think the leak may be in the tank as I cant smell fuel anywhere. I have tried to get my nose into everything and cant smell fuel at all.


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## Barry Allen (Apr 18, 2018)

Cruz15 said:


> Im along this way of thinking except I think the leak may be in the tank as I cant smell fuel anywhere. I have tried to get my nose into everything and cant smell fuel at all.


I don't know what kind of pressure relief valve are on the fuel system.

The ideal setup is where the HP fuel pump is cooled by diesel fuel that is then routed back to the tank so that any metal particles from wear are caught by the fine filter. A few places sell a kit to retrofit the fuel pump in the Ford 6.7 engine for this reason, because that HP pump setup has the fuel used to lubricate/cool the pump going through the HP fuel rail. This means a catastrophic failure of the pump ruins all of the HP fuel rail and all the injectors are destroyed by metal contaminants.

Otherwise, the setup is that the HP fuel exits the pump and flows through the common rail to all the injectors. The injectors use some fuel for combustion and the rest flows through the injectors to cool them and is then routed back to be dumped in the fuel tank. This allows some cooling of the fuel for the next cycle through the LP and HP pumps, but it also has the benefit in winter of dumping some waste heat into the fuel tank to keep the fuel flowing if it were on the edge of gelling. I don't know the exact amount of fuel flow but on some Duramax message boards I have read that the entire contents of the pickup truck fuel tanks will cycle through the fuel system about 5-6 times per hour. That's a good amount of fuel flowing through the fine filter to keep it all clean, and that's a good amount of waste heat returning from the engine to keep fuel from gelling in very cold weather.

If the Cruze engine system is like the PowerStroke from Ford, 100% of the fuel coming out of the HP pump is going through the fuel rail, through the injectors, and then returning to the tank from some outflow that presumably has a pressure valve to release the return fuel flow. If that outflow valve is leaking even slightly, it could cause longer cranking because the HP pump has to build up pressure to start the engine.


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## Cruz15 (Mar 17, 2016)

Yes I was going the ask the mechanic this as well. Where is the outflow valve and is it easy access for them.
Thank you.


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## Barry Allen (Apr 18, 2018)

If it's under warranty, maybe let them do it.

If it's not under warranty, an important question to ask is: "Can I live with this?"

There is always the chance that the repair is expensive, and the mechanic could break more stuff or cause more problems down the line if things are taken apart and put back together. If the only symptom of this is putting up with the engine cranking a couple seconds longer than usual to start, can you live with that? If the problem is what it is (something you could live with) and it won't get worse, consider that.


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## Snipesy (Dec 7, 2015)

Barry Allen said:


> I don't know what kind of pressure relief valve are on the fuel system.
> 
> The ideal setup is where the HP fuel pump is cooled by diesel fuel that is then routed back to the tank so that any metal particles from wear are caught by the fine filter. A few places sell a kit to retrofit the fuel pump in the Ford 6.7 engine for this reason, because that HP pump setup has the fuel used to lubricate/cool the pump going through the HP fuel rail. This means a catastrophic failure of the pump ruins all of the HP fuel rail and all the injectors are destroyed by metal contaminants.
> 
> ...


Make of this what you will. Drawn by yours truly. The orange output of the fuel pump is the excess/leakage but also some dedicated lubrication stuff as well.


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## Barry Allen (Apr 18, 2018)

Snipesy said:


> Make of this what you will. Drawn by yours truly. The orange output of the fuel pump is the excess/leakage but also some dedicated lubrication stuff as well.
> 
> View attachment 289905


So the diesel dedicated to lubrication/cooling of the HPFP goes straight into a return line, and doesn't pass through the common rail or injectors?

PRAISE THE LORD there is some common sense in this design! Whoever thought the Ford PowerStroke design was just OK to push all that fuel through the HP fuel system should get their head on a pike as a warning to newly graduated engineers.


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## Snipesy (Dec 7, 2015)

Barry Allen said:


> So the diesel dedicated to lubrication/cooling of the HPFP goes straight into a return line, and doesn't pass through the common rail or injectors?
> 
> PRAISE THE LORD there is some common sense in this design! Whoever thought the Ford PowerStroke design was just OK to push all that fuel through the HP fuel system should get their head on a pike as a warning to newly graduated engineers.


The only difference I see is instead of the ‘cooling’ output going to the rail/regulator. It just goes straight into the return hose. Or more specifically, it is the return hose.

I don’t know what difference this makes. But I’d imagine the merging is easier if it’s done right at the relief valve. See this picture of the CP1.



https://dieselnet.com/tech/images/diesel/fi/cr/control/~cr_valve_bosch.jpg


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## Barry Allen (Apr 18, 2018)

Snipesy said:


> https://dieselnet.com/tech/images/diesel/fi/cr/control/~cr_valve_bosch.jpg


I wondered about the return to the tank and it looks like it's got something to do with the fuel filter similar to what VW does or did. They had a valve arrangement on top fo the fuel filter where there was a T or something. Upon a cold start, fuel returning from the fuel rail and injectors had been warmed by the engine and it flowed through the T. A thermostat in there let the warmer fuel flow back through the filter and then be immediately returned to the HPFP instead of taking that warmed fuel and dumping it into the tank. The thermostat would keep a steady temperature of warmer fuel going into the filter to keep it from gelling up and stalling the car.

I was under the impression that our fuel filter housing had a built-in heater. I thought there was something in there like an electric heater that turns on any time the fuel is below about 50-60ºF?


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## Snipesy (Dec 7, 2015)

Barry Allen said:


> I wondered about the return to the tank and it looks like it's got something to do with the fuel filter similar to what VW does or did. They had a valve arrangement on top fo the fuel filter where there was a T or something. Upon a cold start, fuel returning from the fuel rail and injectors had been warmed by the engine and it flowed through the T. A thermostat in there let the warmer fuel flow back through the filter and then be immediately returned to the HPFP instead of taking that warmed fuel and dumping it into the tank. The thermostat would keep a steady temperature of warmer fuel going into the filter to keep it from gelling up and stalling the car.
> 
> I was under the impression that our fuel filter housing had a built-in heater. I thought there was something in there like an electric heater that turns on any time the fuel is below about 50-60ºF?


No that image isnt our Cruze. Thats just a generic image. The drawing I made is based off the real engine.

Our Cruzes have electric heated fuel filters. I am not sure if the return line goes through it or not. But I highly doubt the line loops back to the engine.


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## Barry Allen (Apr 18, 2018)

Snipesy said:


> No that image isnt our Cruze. Thats just a generic image. The drawing I made is based off the real engine.
> 
> Our Cruzes have electric heated fuel filters. I am not sure if the return line goes through it or not. But I highly doubt the line loops back to the engine.


OK, gotcha.

VW's design wasn't the greatest in the world. If the thermostat stuck open you could get fuel that was too hot going back to the engine. A lot of VW owners who switched to a CAT 2-micron filter would entirely eliminate the thermostat T and just return all the fuel to the tank, and rely on good anti-gel to make sure the filter doesn't clog.


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