AEM AFR gauge and Oxygen Sensor

Newb question here. I just picked up a CTSC 94 NSX

It came pre installed with an AEM AFR gauge which I thought was useful. However driving it around the past two days and studying the trend, I feel like its not accurate. Do the sensor on the gauge go bad after a while? I believe this gauge must of been installed 10+ years ago.

Any help would be appreciated.

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What is doing?. Typically they swing up and down

chudson1549 said:

What is doing?. Typically they swing up and down

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Here is the best way I can explain the characteristics
- During Idle after it warmed up, it bounces around 15.5 to 16.
- When I let my foot off the gas and I am just cruising/rolling while still in gear, it may go to 18 during that time.
- When I step on the peddle a little harder to accelerate (not WOT), it may go to 14 ish
- When I step on it really hard, it goes to 11ish

I guess I don't know if its my AFR guage (or O2 sensor) that is bad since it is prob 10+ years old. Or I have something else to worry about.

Any thoughts would be really appreciated.

Sounds perfectly normal. If it stayed at a steady ratio during the three actions you mentioned I would think the o2 sensors was bad.

chudson1549 said:

Sounds perfectly normal. If it stayed at a steady ratio during the three actions you mentioned I would think the o2 sensors was bad.

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Thanks! You have been super helpful!

What do you think about the numbers in those ranges?
thanks I am a newb :smile:

I have the air-fuel gauge and boost gauges. Those are pretty close a/f ratios to mine and other sc nsx.

chudson1549 said:

I have the air-fuel gauge and boost gauges. Those are pretty close a/f ratios to mine and other sc nsx.

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That is exactly what mine does in fact if I accelerate a little and then take my foot completely of the gas the gauge goes blank as it doesn't read that lean. You are right on the money.

BobK said:

That is exactly what mine does in fact if I accelerate a little and then take my foot completely of the gas the gauge goes blank as it doesn't read that lean. You are right on the money.

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haha cool. I feel totally better. I was actually afraid that it was a problem when it registered that lean when I took my foot off the gas. Also I originally thought my idle numbers were also a bit lean at 15.5-16ish.

Thanks again

the only problem I have ever had with AEM wideband sensors is when the owner installs the sensor too close to the turbo (or head in your case). The sensor needs to be located about 3' away from the turbine in a cooler location that many OEM oxygen sensors operate. For instance on the nissan sr20det there is an O2 bung right after the OEM turbine on the OEM exhaust system. Many will see this as a logical place to install their wideband sensors, without realizing that it will get too hot, and malfunction in that location.

And when they malfunction, they read rich. So this was a very bad experience for me, seeing the sensor reading rich 11.8:1 in a high boost application, not knowing the A/F ratio was in fact about 15.5:1 and the engine was roasting it's piston rings. Which of course failed, and the engine started burping up oil due to blow-by. I had to break that motor down and re-install new rings, and basically do a complete rebuild. I got it all on video too D:

So take it from someone who has made that mistake, it wasn't AEM's fault though, I am pretty sure the manual says to install it a fair ways away from the turbine (out of the high EGT areas).

$0.02