Buzzing sound from engine when ignition half on

[ChrisD]

I should probably start by pointing out that I crashed the car a couple of weeks ago - but it was nothing too major. Front end body work damage, crash bar, passenger side wing and chassis leg, washer bottle, etc etc, but nothing further back in to the engine bay than that.

Anyway, while I'm repairing everything I noticed that when I turn the ignition half on (i.e. press the Start button twice but without the clutch pressed in, so the engine doesn't start but the electronics all come on) there is a weird buzzing sound coming from the engine. Its not very often that I start the car like that without actually starting the engine at the same time, so who knows maybe it has always done this... but it seems unlikely that I would never have noticed it before.

It isn't the fuel pump or anything else that you normally just hear starting up for a few seconds, you still hear those and they stop after a while as normal... but this other sound doesn't stop. It is like an electrical buzzing sound.

I took a video to try show what it sounds like:

[ame="https://www.youtube.com/watch?v=8pcZCCaCnLE"]GT86 Engine Noise - YouTube[/ame]

You can't tell very well from the video but it isn't a single constant sound, it kind of shifts pitch ever so slightly all the time and almost crackles. I did notice there are two battery terminal like connections on the first part of the gearbox bell housing that you can see, pretty close to where the noise is coming from. But they look to be in normal condition and nothing is loose.

Any ideas?

[RustySocket]

Is it possible that it is your ac/heater fan?

[ChrisD]

Originally Posted by RustySocket

Is it possible that it is your ac/heater fan?

It doesn't sound like a fan at all when you hear it in person, much more like an electrical buzzing. I guess it could be something to do with the AC, as the AC condenser is currently not there (old one got damaged and waiting for replacement to arrive, so I figured as long as I don't turn the AC on it will be fine to run it like this for now). I can't see how the condenser being missing would end up with that kind of noise coming from all the way back there though.

[chaoskaze]

My car always have buzzing sound from alternator or some electric stuff when it's half on.

Yes it's very loud. I can hear it inside the car too if my music isn't on.


Note: now I think about it, the noise is there whenever my headlight is on.

[humfrz]

Since you suspect it may be related to the A/C ...... you may consider pulling the A/C fuse to see if the buzzing stops.


humfrz

[Tcoat]

Originally Posted by ChrisD

It doesn't sound like a fan at all when you hear it in person, much more like an electrical buzzing. I guess it could be something to do with the AC, as the AC condenser is currently not there (old one got damaged and waiting for replacement to arrive, so I figured as long as I don't turn the AC on it will be fine to run it like this for now). I can't see how the condenser being missing would end up with that kind of noise coming from all the way back there though.

The relay could be trying to activate it and since it isn't there it just sits and buzzes.

[ChrisD]

Originally Posted by humfrz

Since you suspect it may be related to the A/C ...... you may consider pulling the A/C fuse to see if the buzzing stops.


humfrz

I actually meant to pull that fuse earlier anyway just in case I accidentally put the AC on some time while there's no gas in it. So yeah I'll definitely give that a go tomorrow and see if it makes any difference

[ChrisD]

Originally Posted by chaoskaze

My car always have buzzing sound from alternator or some electric stuff when it's half on.

Yes it's very loud. I can hear it inside the car too if my music isn't on.


Note: now I think about it, the noise is there whenever my headlight is on.

I think that's different to my issue then if its only when the headlights are on. Your noise is probably just the ballast of the HIDs. I get that as well when I put the headlights on, but this other noise happens even when I didn't have the headlights connected to the car at all.

[RustySocket]

Originally Posted by ChrisD

It doesn't sound like a fan at all when you hear it in person, much more like an electrical buzzing. I guess it could be something to do with the AC, as the AC condenser is currently not there (old one got damaged and waiting for replacement to arrive, so I figured as long as I don't turn the AC on it will be fine to run it like this for now). I can't see how the condenser being missing would end up with that kind of noise coming from all the way back there though.

I was just tossing it out there as an idea. I've seen a piece of paper or a leaf get into the fan box on other cars and drive people nuts trying to figure it out.


Pulling fuses isn't a bad idea to eliminate things.


A piece of tubing can be used like a stethoscope to start listening around the engine compartment and may help you locate exactly what is making the sound.

[Ultramaroon]

It's the throttle body servo. No biggie. I've heard others that loud.

IIRC it's a micro-stepper motor so depending on its commanded position in relation to the natural cogging, you'll hear lots of noise while it maintains those in-between positions.

I'm not describing it very well but it's ok.

[ChrisD]

Originally Posted by Ultramaroon

It's the throttle body servo. No biggie. I've heard others that loud.

IIRC it's a micro-stepper motor so depending on its commanded position in relation to the natural cogging, you'll hear lots of noise while it maintains those in-between positions.

I'm not describing it very well but it's ok.

Ahh ok, that makes sense. When we first heard it that was our first thought too - that it was the throttle body. But then we thought there's no reason for that to be trying to move when the engine isn't even running... I could understand it moving briefly as like a quick test or prep for the engine starting, but this noise doesn't stop even after 5 minutes of the ignition being half on.

The throttle still seems to work as normal when the engine is running, so I guess I should just assume its ok... but it really doesn't sound healthy when its not running and there's this constant buzzing lol

[Ultramaroon]

Originally Posted by ChrisD

Ahh ok, that makes sense. When we first heard it that was our first thought too - that it was the throttle body. But then we thought there's no reason for that to be trying to move when the engine isn't even running... I could understand it moving briefly as like a quick test or prep for the engine starting, but this noise doesn't stop even after 5 minutes of the ignition being half on.

The throttle still seems to work as normal when the engine is running, so I guess I should just assume its ok... but it really doesn't sound healthy when its not running and there's this constant buzzing lol

We have some pretty awesome subject matter experts in our 86 gang here in Portland. @johan was generous enough to perform an experiment for us last month. Here you can see a Honda K20 throttle body being controlled by the FA20 ECU.

[V_86]

I have the same sound that I just noticed recently, I don't think its anything to worry about. More than likely you are used to starting the car before the sound starts, or have the radio on, so never noticed it before.

[ChrisD]

Originally Posted by Ultramaroon

We have some pretty awesome subject matter experts in our 86 gang here in Portland. @johan was generous enough to perform an experiment for us last month. Here you can see a Honda K20 throttle body being controlled by the FA20 ECU.

Ah thanks for the video - its good to hear the exact same sound in that I guess I'll just stop worrying about it then.

Thanks!