AEM UEGO rings at 14-16khz and it is driving me nuts. - Miata Turbo Forum - Boost cars, acquire cats.

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Old 05-29-2016, 09:52 PM   #1
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Default AEM UEGO rings at 14-16khz and it is driving me nuts.

I have no idea where to even put this thread. This is the only free weekend I have to try and get all this stuff in and get the car running on the MS3x for a long time to come.

Ok, I just installed an AEM UEGO in my car and it rings audibly. The frequency is somewhere in the 14-16khz range (sounds like the flyback on an old CRT if any of you have heard that). It rings louder through the stereo, but is audible even with the stereo off. I have spent the last two hours trouble shooting.

Things I have tried that made no changes to the sound:
Grounding in various places in various ways
Power from various places (tried grounding/power right to the battery, no change).
Ferrite chokes on RCA cables
Ferrite chokes on speaker cables

These two made a change in how much noise came through the speakers (duh) but the ringing was still there, just not as loud.
Speakers dissconected
Amp powered off

There were two things I did that made changes:
Putting a ferrite choke on the ground cable for the AEM UEGO made it LOUDER. I mean super loud, the choke itself was ringing.

Putting a capacitor between power and ground on the meter made the ringing very, very quiet. Until I turned the head unit on. This is with the speakers and amp disconnected, so the sound is not coming through the speakers. With the cap between power and ground, and the meter off or the head unit off, there is silence. With both on, I have the ringing.

I am absolutely baffled and really, really do not want to have to uninstall and return the AEM UEGO. Any ideas?
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Old 05-29-2016, 10:34 PM   #2
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Where is it powered from?

Last case scenario power it with a relay straight from the battery, that's what I do.
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Old 05-29-2016, 10:52 PM   #3
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I powered it with it's own wire run strait from the battery and the grounded it with it's own wire back to the battery. Same exact behavior as if I grounded it and powered it off the radio harness. Where I am getting my power and ground from doesn't seem to matter.

Also, I broke out the spectrum analyzer and boy was I off. It's fundamental is right about 5khz, but it has a harmonic at 8.5ish and 14.2ish.

Also, without a filter between the positive and ground, it rings all by itself, even with nothing else on.
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Old 05-29-2016, 11:11 PM   #4
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More investigation. The AEM is dumping so much **** out it's ground that it is causing the headunit to physically ring, even when the head unit is off. With it on, it is louder. About 15dD above noise floor with the head unit off, about 25dB with the head unit on.

The AEM gauge itself also rings, but it is only a few dB above the noise floor with the mic right up against it.
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Old 05-29-2016, 11:53 PM   #5
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That has to be the heater PWM. Add a cap to the heater circuit?
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Old 05-30-2016, 12:15 AM   #6
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Id say its bad. Mine doesnt do that, nor have I ever heard of this.
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Old 05-30-2016, 12:19 AM   #7
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Quote:
Originally Posted by stefanst View Post
That has to be the heater PWM. Add a cap to the heater circuit?
That is exactly my thoughts. Man is it making a mess everywhere. What part of the heater circuit should I add a cap too? Just cut the heater line and run a cap to ground?

I have found a "solution". Though it really isn't, but gets the noise low enough I can deal with it for now. It doesn't solve it though. If I run a new B+ for the head unit and I run a biiiiiig freaking filter (1000uF!) between the power and ground for the meter it gets it to a tolerable level. Need to find some lower voltage caps. I stole these from a big old power supply, so they are rated at 250v 500uF each. Nice big Sprauges though!

I guess tomorrow I am implementing that and making a super nice ground for the wideband by scraping paint off and drilling a hole behind the kick panel. Thankfully, the previous owner decided to use a run of 2x16awg or 2x18awg speaker wire for the remote turn on lead. So I can just snag one of those wires to become my new B+ without having to run anything.

Why running a separate power line for the wide band doesn't work, I don't know. And why putting a filter between radio B+ and ground doesn't work I don't know either. I may add a big *** inductor as well to the filter and see if that gets it down any more.
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Old 05-30-2016, 12:21 AM   #8
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Originally Posted by hi_im_sean View Post
Id say its bad. Mine doesnt do that, nor have I ever heard of this.
I will be emailing AEM after the holiday. If you search for "AEM UEGO noise" you find a lot of people having issues with noise in the stereo after installing one.

It seems with enough filtering and a new B+ for the radio I can get the noise to tolerable levels.
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Old 05-30-2016, 12:30 AM   #9
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Mine does it, as does everyone else's. If you can't hear it, use ear plugs more often.
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Old 05-30-2016, 12:55 AM   #10
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Mine does it, as does everyone else's. If you can't hear it, use ear plugs more often.
Glad to hear it isn't just me then. But wow, you think they could come up with something to make it dump less crap on the ground. I can't believe there is a high enough modulation that three turns inside a ferrite choke make the choke sing like an old transformer. I will try and take a video before I put everything together tomorrow.

And a ~5khz, if you can't hear it, look into hearing aids...
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Old 05-30-2016, 01:07 AM   #11
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Hes old, his hearing was gone ages ago.

Fwiw, never had an issue with my LC-2
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Old 05-30-2016, 01:49 AM   #12
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My friend has an LC-2 and it works well... That said, I already have the AEM and it was a gift so...
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Old 05-30-2016, 02:37 AM   #13
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Yeah every single AEM rings a little due to the PWM heater. I don't think I can hear it in a running car, but I can definitely hear it on the test bench.
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Old 05-30-2016, 08:54 AM   #14
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I've never heard it with the 3 aem wideband I have, it could be because I'm always driving with the top down and flat out.
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Old 05-30-2016, 10:17 AM   #15
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Return it and get a new one. If mine is ringing, its so quiet, id have to have my ear on it, or use a stethoscope. Even with car off, over the last 3 years, its never made a noise.

If its high enough in amplitude to cause physical vibrations in ferritic materials, then something obviously isnt right.
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Old 05-30-2016, 10:30 AM   #16
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Quote:
Originally Posted by x_25 View Post
That is exactly my thoughts. Man is it making a mess everywhere. What part of the heater circuit should I add a cap too? Just cut the heater line and run a cap to ground? [...]
Good question. As far as I know, the O2 heater circuits usually switch ground, not +12V. I'd put a cap in the output- the lines going to the heater between the +12V and the switched GND. Adding a small resistor before the cap in the switched GND line may also help. I'm talking maybe 0.1Ohms or so.
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Old 05-30-2016, 11:49 AM   #17
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Quote:
Originally Posted by Reverant View Post
Yeah every single AEM rings a little due to the PWM heater. I don't think I can hear it in a running car, but I can definitely hear it on the test bench.
Yeah, the gauge rings very, very quietly, not so much of an issue as what it was doing to the head unit.

Quote:
Originally Posted by hi_im_sean View Post
Return it and get a new one. If mine is ringing, its so quiet, id have to have my ear on it, or use a stethoscope. Even with car off, over the last 3 years, its never made a noise.

If its high enough in amplitude to cause physical vibrations in ferritic materials, then something obviously isnt right.
Actually, if you think about it, it's not that unreasonable. Figure the thing is fused for what, 5 amps? so if the heater does even just 1 amp at 12 volts, that's 12 watts. Then I coiled it and stuck a ferritic piece of metal on it and made a speaker. 12 watts into even a super low sensitivity speaker will make audible sound.

Quote:
Originally Posted by stefanst View Post
Good question. As far as I know, the O2 heater circuits usually switch ground, not +12V. I'd put a cap in the output- the lines going to the heater between the +12V and the switched GND. Adding a small resistor before the cap in the switched GND line may also help. I'm talking maybe 0.1Ohms or so.
Yeah, I was considering sticking an RC or LC circuit on the ground for the meter. Although just a cap seems to do enough to make the sound bearable with the head unit playing. I will have to do some sluthing to figure out what wires are what for the O2 sensor, since that is not in the documentation (haven't searched yet and have a working solution, so I will be looking for a better one later, once I get the car running).
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Old 05-30-2016, 12:01 PM   #18
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Quote:
Originally Posted by x_25 View Post
Yeah, the gauge rings very, very quietly, not so much of an issue as what it was doing to the head unit.



Actually, if you think about it, it's not that unreasonable. Figure the thing is fused for what, 5 amps? so if the heater does even just 1 amp at 12 volts, that's 12 watts. Then I coiled it and stuck a ferritic piece of metal on it and made a speaker. 12 watts into even a super low sensitivity speaker will make audible sound.



Yeah, I was considering sticking an RC or LC circuit on the ground for the meter. Although just a cap seems to do enough to make the sound bearable with the head unit playing. I will have to do some sluthing to figure out what wires are what for the O2 sensor, since that is not in the documentation (haven't searched yet and have a working solution, so I will be looking for a better one later, once I get the car running).

I must have read wrong, I thought you said it rang loud on its own. Feedback through stereo is obviously different, carry on....

Do you have a x-over coil or something with a lowish DCR to put in line with the AEM to test?

edit-if i get a second today, Ill put a scope on mine as im now curious. I removed the stereo the day I installed mine.
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Old 05-30-2016, 12:08 PM   #19
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Quote:
Originally Posted by hi_im_sean View Post
I must have read wrong, I thought you said it rang loud on its own. Feedback through stereo is obviously different, carry on....

Do you have a x-over coil or something with a lowish DCR to put in line with the AEM to test?
The AEM gauge rings quietly. Anoying, but quiet enough that with the car running it would be fine. The problem was it was causing the head unit to ring. The actual unit, with all the RCAs, speakers and amps disconnected/off, the head unit itself was actually ringing. I thought it was the gauge at first since high frequency tones are near impossible to locate. I used my phone and a spectrum analyzer to trace it down what was actually ringing after I made the post.

I do have some air coil inductors around. I tried putting it inline with the ground on the AEM, power on the AEM, and ground on the head unit. None of those spots made a difference. I am going to try making an LC filter on the ground of the AEM and see if that does anything.

Just looked it up, they are 0.33mH 18awg.
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Old 05-30-2016, 12:10 PM   #20
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Have you measured current draw yet?

Im a little rusty on filter design, but shouldn't you get input impedance first? based from current draw... or have you?
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