Fuel smell

Themoog2 · Post by **Themoog2** » Sat Sep 16, 2023 2:12 pm

My 01 V8 has a petrol smell inside the car. Not strong and not all the time. My daughter noticed it the other day after I had started it from cold and today I was going along the A14 and when I opened the window for fresh air I could smell petrol.
Any ideas? I can’t see any leaks underneath and fuel consumption is ok. I haven’t lifted the rear seat yet though.

X5Sport · Post by **X5Sport** » Sat Sep 16, 2023 2:30 pm

Check points are going to be: fuel lines, fuel cap (check if the tank is venting as there is a pressure relief valve in the system), injectors and fuel rail pipes, fuel filter/pressure regulator assembly (underneath behind covers, but can’t see which side - diesel are near side, midway back) fuel pump/level sensor gaskets on the tank (below back seat as you surmise).

Can’t think of anything else. You might need diagnostics for the pressure relief system as it uses special tooling and access to DIS. If you can only smell it when running that points at a small leak or overpressure in the tank. Even a tiny leak smells strong and in these temps will evaporate very quickly.

If you are hunting for it, make sure you stay ‘bonded’ to the car (in contact with metal) so no chance of a spark.

Themoog2 · Post by **Themoog2** » Sat Sep 16, 2023 7:29 pm

Ahh. Now I do have a fault on the scanner that says something about fuel vent or something. What’s that mean then..

X5Sport · Post by **X5Sport** » Sat Sep 16, 2023 8:21 pm

It depends what the actual error is.

Petrol engines pressurise the tank slightly and we know petrol evaporates at a much lower temp than diesel (so it needs no valve)

The fuel tank has a pressure control valve system built into the fuel cap. It might be that is leaking (as in not holding pressure). The only way to check that is with DIS and a special toolset that connects to it. You also have to pressurise the tank by 0.3Bar (4.2psi) and see if the pressure holds. Not possible to diy safely. Changing the fuel cap would prove/disprove it.

If it’s a tank leak then the below applies:

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If you don’t have a warning light in then it should not be the tank, more likely the fuel cap valve.

X5Sport · Post by **X5Sport** » Sat Sep 16, 2023 8:27 pm

Technical description of petrol fuelled tank system…..

Petrol engine fuel supply systems

Fuel system

The fuel pump in the fuel tank generates pressure in the fuel system, which is set by the electronic pressure control valve to a certain level.

Tank-venting system

The tank safety valve is a closed system that is bled via a carbon canister. The carbon in the canister is stored as granules. The large surface of the granules traps the fuel vapour, that occurs in the fuel tank. The carbon canister needs to be refreshed regularly in order to be able to continue to store fuel vapour. This is done by flushing it with fresh air from the intake pipe. This process is controlled by the engine control unit.

henrym3 · Post by **henrym3** » Sat Sep 16, 2023 8:31 pm

There is a fuel vent valve on the front right cylinder head (as you look at the engine) has an inlet and outlet pipe plus an electrical plug. The valve is cycled by the ECU to vent the tank fumes into the inlet manifold. Check one of those pipes isn’t disconnected from the valve or got holes. Also that the plug is in good nick, maybe needs a squirt of electrical contact cleaner. The valve could be knackered but that should show on diagnostics. looking at X5Sport answer I could be talking s%!t.

henrym3 · Post by **henrym3** » Sat Sep 16, 2023 8:36 pm

: IMG_1245.png (146.77 KiB) Viewed 10024 times

I am talking about item 1

Themoog2 · Post by **Themoog2** » Sun Sep 17, 2023 12:07 pm

Ok so I’ve checked that valve and it’s ok. Under the rear seat is clean and no odour. The filler cap however, was wet around the rubber seal. I haven’t used the car since yesterday. Maybe it’s worn out? I’ve cleaned it all up and put it back so we will see.
I do remember having to buy a new filler cap for our other X5 years ago but can’t recall why.

X5Sport · Post by **X5Sport** » Sun Sep 17, 2023 12:11 pm

henrym3 wrote: ↑Sat Sep 16, 2023 8:31 pm There is a fuel vent valve on the front right cylinder head (as you look at the engine) has an inlet and outlet pipe plus an electrical plug. The valve is cycled by the ECU to vent the tank fumes into the inlet manifold. Check one of those pipes isn’t disconnected from the valve or got holes. Also that the plug is in good nick, maybe needs a squirt of electrical contact cleaner. The valve could be knackered but that should show on diagnostics. looking at X5Sport answer I could be talking s%!t.

That was another thing I looked at but couldn’t be certain if it was a ‘US Only’ thing, as they have tighter fume control. You definitely weren’t talking

henrym3 · Post by **henrym3** » Sun Sep 17, 2023 12:41 pm

I looked up checking the valve and it should show 28 Ohms resistance +/- 1

Themoog2 · Post by **Themoog2** » Tue Sep 19, 2023 3:19 pm

I think cleaning the fuel filler cap and rubber seal has sorted it as I’ve not smelt anything since.

X5Sport · Post by **X5Sport** » Tue Sep 19, 2023 4:54 pm

Sounds like good news, and a simple fix.

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Fuel smell

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Fuel smell

Fuel smell

Fuel smell

Fuel smell

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Fuel smell