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Buzzing noise from fuel cap area

Locosaki

Well-known member
Joined
3 Jul 2016
Messages
409
Took the car out today for a run and pulled over after 100+ miles, I turned the car off and was away for 10 minutes when I came back the car wouldn't start, it was turning over but nothing else.

I gave it another 5mins and tried again, this time it started but didn't spring to life as normal it took a couple of blips of the throttle to get it going.

I've got the car home now and just plugged my reader into it, I've got 2 faults, P1571 something to do with immobiliser and tank vent as well.

The car drove home perfectly but I didn't turn it off again, now I've got it home I can't get it to start.

What would the buzzing noise likely be ?
 
Looks like your tank vent could be blocked or not functioning correctly. The tank needs to be able to let air in as the fuel level drops or the vacuum created could eventually cause fuel starvation. The noise you could hear was probably the hissing/buzzing from the vacuum pulling air around the fuel cap seal.

Edit. I believe a certain level of vacuum is acceptable for omission control reasons but too much may cause problems with fuel delivery. Alternatively, a leaky fuel cap seal may be letting in air when the car expects to see a vacuum and this may be detected by your fault codes. First thing I would do is to check the filler cap and seal for obvious signs of damage.
 
Cheers mate I'll check it out.

I just gambled and took the car for fuel, there were no issue's filling the car up at all, I read that there could be a problem if the vent was at fault.

Again I get the car home and it cuts out, struggles to start again same symptoms as before, buzzing near the filler cap was noticeable this time but doesn't happen all the time, also when i turn the car off there seems to be a screech/howl from the filler area again
 
Locosaki said:
Cheers mate I'll check it out.

I just gambled and took the car for fuel, there were no issue's filling the car up at all, I read that there could be a problem if the vent was at fault.

Again I get the car home and it cuts out, struggles to start again same symptoms as before, buzzing near the filler cap was noticeable this time but doesn't happen all the time, also when i turn the car off there seems to be a screech/howl from the filler area again

When it does that, immediately undo the fuel cap and see if there's a big (more than usual) inrush of air.

Can you hear the fuel pump under the front when you first turn the ignition? Should get a good 30 seconds of prime cycle on the pump, even if you then turn off the ignition..
 
I'm definitely not getting the fuel pump when I turn the ignition on as I had a listen for that earlier, I'll check the fuel cap also. Cheers
 
Locosaki said:
I'm definitely not getting the fuel pump when I turn the ignition on as I had a listen for that earlier, I'll check the fuel cap also. Cheers

That sounds quite like the issue then. The buzzing and howling might well be the fact the pump isn't generating any meaningful pressure and is internally leaking.

Quickest way to check is slacken off a fuel line on the fuel rail as it doesn't involve jacking the car up to get to the fuel filter.

[edit] it's a C4, of course, where the fuel filter is near the engine. If your diagnostics is more than a simple code reader, use it to drive outputs on the ECU and drive the fuel pump relay, you can then hear if the pump is running..
 
Unfortunately my tester is quite basic. So this could be a fuel pump issue, if it makes any odds the car go's good when it's going, no signs of fuel starvation when it's going
 
The C4 has a scavenge type fuel system to get the fuel out of the saddles .. if the tank is lowish on fuel say quarter of a tank then you might have a problem with the pickup on one of the scavenge pipes .. its kinda a valve .

All the above posts though cover pretty much anything i could say .

The immobiliser fault though would certainly stop the car from starting .. its a coms issue between the alarm cu and the dme .. always worth checking the alarm cu connections if this is a current fault.
 
Dermot thanks mate, I was hoping you'd see this. I reset the fault codes and now there is nothing stored, car continues to make the same noises and struggles to start.

I'll try and get time to give it a good look over tomorrow.
 
Non start .. standard checks ... do you have spark , injector switch and fuel pressure.

Noid light on injectors .. nothing here and its crank sensor or alarm fault .. which you have a code for .

Rig up a coil and plug if needed to test for a spark .

Fuel pressure and really you need a gauge on it to check , cracking a pipe and seeing fuel come out is not good enough .

Fuel pump is not a noticable noise as such .. i would tend to have my hand on it whist cranking to feel if it was running .

The noises are a little odd , if a fuel pump aint running then its not going to make any noises , hence tank vents , tank going vacum as air cant enter are all good calls from other posters .

The alarm fault will stop spark and injector switch but i dont think it stops the fuel pump .. if no injector switch then it doesnt need to .

Atm the most obvious does seem to be fuel pressure .


There are no fault codes or actual values for a fuel pressure fault on a car .. the car is unaware of why its not starting .. hence a non start car with no codes leads us to fuel pressure .
 
Would the fuel pressure account for the buzzing/humming noise on the right wing at the fuel cap, I've not heard that before today. I've always had a EVAP fault code flag every now and again but I put that down to low fuel level and didn't give it a thought before today.
 
Short answer .. no it wouldnt .. you either have a pump working or you dont .. the noise is a strange one and something im unsure of .. its a lot easyier when i have the car in front of me lol .

If you can then try and get a sound clip .. anything helps in situations like this and unfortunatly we are at opposite ends of the country .. if closer i would happily come and have a look .. you have not had the best of luck so far and i for one feel bad about that .

Ill be mulling it over tomorrow .. i just know i will lol .

Fuel cap off will sort any vacum .

Stupid idear but the fuel lid lock solinoid is there .. buzzing perhaps , and the start issue is something else .. ie fuel pump .

EDIT .. hmm low fuel lvl .. that takes us back to the scavenge system fault , not herd a noise before but it can stop a car from starting .
 
This may give a little more insight into the complexities of the fuel delivery and vent systems. The symptoms are not the same though. What was the adult code relating to the vent issue?

https://www.renntech.org/forums/topic/10045-cel-code-is-p0455/

And this

http://www.pelicanparts.com/techart...-FUEL-Replacing_Your_Fuel_Line_Vent_Valve.htm

Here's an extract that looks a bit like your problem. Charcoal canister?

Comments: My 2000 Porsche Boxster S will start and run but after turning it off occasionally It just turns over and doesn't fire/start or even sputter. Hours later it will fire and start like there is nothing wrong. I do hear a howling sound while driving occasionally. Replaced fuel pump relay, same deal. Would bad fuel pump or pressure regulator explain symptom?
July 19, 2015
Followup from the Pelican Staff: Very common...99% sure you have a faulty charcoal canister purge valve (aka fuel regeneration valve?!). The purge valve is located in the engine compartment on the left side beneath the intake. Part number: 996-110-129-06-M100 - Casey at Pelican Parts
 
Dermot, I thought after the rebuild my luck might change, hopefully this will be easily resolved. I'll listen out for the noise and checkout the locking mechanism, I didn't think of that I'll also try and capture the noise if possible. Again thanks for the input

Gurmot, cheers mate I'll have a look over the links. I'll post the evap code up when it appears again as I've since erased the codes. Cheers
 

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