18 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHWhat's that humming sound?
Leading reported evidence
Install between the air pump and the discharge valve
Performed · outcome unconfirmed
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
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Discussions that performed work without a confirmed outcome
1
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Performed · outcome unconfirmed
A pneumatic switching valve which is closed when the secondary air system is inactive thus preventing the flow of additional air is installed between the air pump and the discharge valve.
Leading evidence: 'Install between the air pump and the discharge valve' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, the most frequently mentioned possible cause is 'air pump' (1 discussions; 0 report identifying it and 1 suggest it). The most frequently discussed action is 'Check integrity of the vent lines and vapor recovery system.)' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that suspect a cause
1
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Suspected cause
Yep, as you describe it, it's likely the air pump.
Check integrity of the vent lines and vapor recovery system.)
Suggestion or failed attempt
No successful repair reported for this finding.
0
Reported fixes
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Unsuccessful attempts
1
Discussions
Read evidence and context
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Discussions that contain suggestions
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Suggestion
(In some cases it can be a pump (pressure or vacuum) running that is used to check the integrity of the vent lines and vapor recovery system.)
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
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Suggestion
It may happen when the DME does its continous monitor check of the secondary air injection system.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that contain suggestions
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Suggestion
Maybe that's used for the continuous monitor test?
Install between the air pump and the discharge valve
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Performed · outcome unconfirmed
A pneumatic switching valve which is closed when the secondary air system is inactive thus preventing the flow of additional air is installed between the air pump and the discharge valve.
Counts describe captured discussions, not unique people or a diagnosis. Author identities are not reliably stored. Exact duplicate evidence is counted once across matching discussions; one discussion counts at most once per action/state. Multiple repairs reported together remain a combination. Suggestions and failed attempts do not establish a fix. Matches cover whole discussions and can include related faults, model variants and incomplete threads.
18 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
0 evidence records excluded for query context · 0 excluded by outcome qualification · 0 adjusted by outcome qualification.
0 acknowledgements have no verified action link; they do not establish a repair result.
Generation: 20261027T075545Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
Upon starting a cold engine, there's a discernible humming sound that continues for, say, 45 secs. to a minute, and then disappears. The sound is definitely emanating from the engine compartment.
Occasionally the sound will briefly return for 5 secs. or so when idling for a stop light change, and the sound is then accompanied by a slight (50-100) rpm increase.
Could this sound be the SAI system operating? (How does that thing work anyway?)
relinuca
What DareDevil said.
Mostly likely the humming sound (with my cars it sounds more like a Hoover vac running in the distance) is the secondary air injection pump.
This runs at cold engine start to inject air into the exhaust system to cause the unburned gas to burn and heat up the converters quicker.
The pump runs from around 30 seconds to a minute, roughly. (By my observation when the pump shuts off the DME switches from open loop operation to closed loop operation.)
Anyhow, I have never heard the pump come on at any other times though.
If it isn't the secondary air injection pump, another explanation is that what you are hearing is not the secondary air injection pump but the gas tank vent system and the evacuation of the charcol canister. This can sometimes sound like a pump is running. (In some cases it can be a pump (pressure or vacuum) running that is used to check the integrity of the vent lines and vapor recovery system.)
(I've never heard any noises from my Porsches's tank vent/vapor recovery systems, but my 06 GTO's vapor system would emit 5 faint knocks -- like someone rapping a knuckle on the car's body -- in rapid succession when the DME was venting/evacuating the canister.)
If is it the gas tank vent/vapor recovery system that accounts for the noise, the engine can react a bit to this as it is being fed gas vapors from the canister which means that temporarily at least the engine sees a bit of a bump in the fuel in its fuel air mixture.
Sincerely,
Macster.
Yes -- that's what I've been hearing of late, too, and, although it's not that loud it is at an odd frequency that starts to get annoying...right about the time it shuts off.
-Eric
Most likely it is cooler now where you are. The onset of cooler weather always brings out these noise posts that most often turn out to be the secondary air injection pump that the new owner is hearing for the first time, or that the owner may have forgotten about since last time.
I sort of like hearing the sound, because when it stops I use that as a signal the engine is 'warmed up' enough to drive off, although of course I know very well it is not completely warmed up.
And it probably helps that at least to me the noise is not very loud and neither pleasant or unpleasant the ears.
Sincerely,
Macster.
Its sole function is to bring the cats up to temp, and keep them there, quickly. It sounds more like a table saw (cutting wood) when it starts to go bad.
I vaguely recall coming across some info that backs your statement up but I could not find anything in my sources on this so I hesitated stating that the SAI pump could run at other times.
It may happen when the DME does its continous monitor check of the secondary air injection system.
With my Boxster I do not recall ever hearing the SAI pump come on any other time other than at cold start. In fact, a few times I had to shut off the engine before the thing timed out and upon restart the SAI did not come on again.
There are 3 possible selections for the SAI pump's output: upstream of the 1st converter; downstream of the first converter's inlet; and atmosphere (off).
Upstream and atmosphere (off) I understand, but downstream? Maybe that's used for the continuous monitor test?
I have a data logger than I can set up to capture the commanded SAI status...
Sincerely,
Macster.
From
http://www.renntech.org/forums/topic...post__p__84676
courtesy Loren:
"Auxiliary air Pump
To reduce pollutants contained in the exhaust gas during the warm-up phase and to achieve the emission limits of the roll test in the USA, USA vehicles have a secondary air system. For this reason, an electric air pump has been mounted on the left-hand side of the engine compartment. This pump is activated by the DME control unit and blows the additional air through air ducts to the discharge valve. A pneumatic switching valve which is closed when the secondary air system is inactive thus preventing the flow of additional air is installed between the air pump and the discharge valve.
Functioning
If the engine is started in a temperature range between minus 10.5� C and plus 45� C, the secondary air system is activated for a period of time dependent on the start temperature (min. 50 seconds, max. 179 seconds).
The secondary air system is only activated if the following engine-related operating conditions apply:
- Engine load (TL) between 0.7 ms/rev, and 4.7 ms/rev.
- air mass (ML) not greater than 300 kg/h
- Engine speed between 680 rpm and 2,800 rpm
- Altitude adaptation factor greater than 0.76 corresponding to less than 2,400 meters above sea level."
I remember another post as well that explained the running of the pump after cold startup (example at stop light after warmed up), but my guess is in the functioning sections, if those conditions apply then it will run, as I and others have observed.
