C5 convert A4 cycling hum issue
Thread Starter
Race Director
Joined: Nov 2000
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From: Beverly Hills (Pine Ridge) Florida
C5 convert A4 cycling hum issue
My 2003 A4 convert. with 25K total miles has a cycling hum that I have not been able to locate it's source.
It is present when ever the engine is running, and is the same low/high "hum" that cycles up & down about every second or 2. Does not matter if the Vette is rolling or not, or even if in gear, just that the engine is running (no noise when engine is off).
At first I thought it was maybe the A/C blower, but it still makes the hum when the A/C and blower is off.
Only other item I can think of is the Fuel Pump, but that should not be cycling up and down (never heard one do that). And there are no performance issues.
Only mods are a Calloway intake, and Corsa Touring Cat back. And this is a Mag. selective ride Vette.
Any ideas?
If I put the radio on at "normal" level, I can just barely hear the cycling hum. So the obvious answer is to turn up the volume.
Thanks,
Plasticman
It is present when ever the engine is running, and is the same low/high "hum" that cycles up & down about every second or 2. Does not matter if the Vette is rolling or not, or even if in gear, just that the engine is running (no noise when engine is off).
At first I thought it was maybe the A/C blower, but it still makes the hum when the A/C and blower is off.
Only other item I can think of is the Fuel Pump, but that should not be cycling up and down (never heard one do that). And there are no performance issues.
Only mods are a Calloway intake, and Corsa Touring Cat back. And this is a Mag. selective ride Vette.
Any ideas?
If I put the radio on at "normal" level, I can just barely hear the cycling hum. So the obvious answer is to turn up the volume.
Thanks,
Plasticman
Last edited by Plasticman; Oct 23, 2009 at 10:39 PM.
Thread Starter
Race Director
Joined: Nov 2000
Posts: 10,340
Likes: 664
From: Beverly Hills (Pine Ridge) Florida
I will look at the Mag. selective section, and yank a fuse to see if that can be making the hum. As for an idler pulley, I would expect any noise related to the engine would change with engine speed.
Battery voltage is rock steady.
Thanks guys, and keep them coming!
Plasticman
Battery voltage is rock steady.
Thanks guys, and keep them coming!
Plasticman
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Things that I can think of that can RUN/Cycle are:
-- Seat Bolster motor. If the bladder is bad, you wont feel it change pressure.
-- Passengers seat motor running and shutting off. Trying to maintain its position. The seat motors are on a circuit breaker and if the motor is STUCK and power is applied it will try to run and shut off, run, shut off.........until it kills the battery.
-- A. I. R. Pump. Could be running when it shouldn't.
-- Head light motor trying to maintain its position. Raise the lights and see if the noise changes.
-- The fuel pump does cycle so,,,don't rule that out. Get the cyclic rhythm down and have someone pull the fuse (the engine will continue to run for a little bit) and see if the cyclic rhythm changes.
EBTCM/BPMV Motor. The BPMV motor runs when the EBTCM senses that it needs to apply brake pressure to one of the caliper/wheels. Could be running on its own. Remote possibility but the motor still runs and could be an issue. It did it on my 02 Z.
Had to replace the EBTCM.
Hope this helps
-- Seat Bolster motor. If the bladder is bad, you wont feel it change pressure.
-- Passengers seat motor running and shutting off. Trying to maintain its position. The seat motors are on a circuit breaker and if the motor is STUCK and power is applied it will try to run and shut off, run, shut off.........until it kills the battery.
-- A. I. R. Pump. Could be running when it shouldn't.
-- Head light motor trying to maintain its position. Raise the lights and see if the noise changes.
-- The fuel pump does cycle so,,,don't rule that out. Get the cyclic rhythm down and have someone pull the fuse (the engine will continue to run for a little bit) and see if the cyclic rhythm changes.
EBTCM/BPMV Motor. The BPMV motor runs when the EBTCM senses that it needs to apply brake pressure to one of the caliper/wheels. Could be running on its own. Remote possibility but the motor still runs and could be an issue. It did it on my 02 Z.
Had to replace the EBTCM.Hope this helps
Thread Starter
Race Director
Joined: Nov 2000
Posts: 10,340
Likes: 664
From: Beverly Hills (Pine Ridge) Florida
Bill,
Thanks for all the ideas/things to check!
What ever it is, is not shutting off, it just hums soft then increases in volume, then soft again. I checked it again this morning briefly (but did not have time to do any indepth checks - honey-do list takes priority), and it is about a 1 sec. freq.
Plasticman
Thanks for all the ideas/things to check!
What ever it is, is not shutting off, it just hums soft then increases in volume, then soft again. I checked it again this morning briefly (but did not have time to do any indepth checks - honey-do list takes priority), and it is about a 1 sec. freq.
Plasticman
