Is your NSX failing smog? Read this.

johnnymo · 28 March 2012

After a complete engine rebuild at 225k miles, I was puzzled that my '92 car failed CA smog, running rich.

Turns out a lot of owners here in OC of pre '93 cars are having trouble right now according to the smog shop guys, and it's puzzling to Ramon and the guys at Niguel Motors, who sees NSXs all day.

Well, due to a lead from fellas on the board, I found the one sensor I hadn't replaced on the car was the culprit. Blowback from 20 years of intake valves had soiled the Air Intake Temperature sensor to look like this. Yes, that's oil dripping off it. Yes, that grey color at the very base is the original color. Yes, it's one of the cheapest parts on the car at $31 bucks and takes 10 minutes to replace. And yes, the car passed smog easily now.

On an OBDII '95 at the shop, we checked the output pre and post cleaning this same sensor right after my experience and the computer measured a full 10 degrees F lower air temp after cleaning, FWIW.

Hope this helps cars failing smog.

PHOEN$X · 28 March 2012

Good info, thanks for sharing.

SMYLDOC · 28 March 2012

Great tip thanks

Just out curiosity, what part of the smog test did you fail??

in my 92 3.8 NA rebuild by SOS I have had problems passing HC (hydrocarbons) at low speed (15 MPH)

did your fix help pass CO, CO2, O@ NOx or HC??

thanks

liftnot · 28 March 2012

johnnymo said:
Blowback from 20 years of intake valves had soiled the Air Intake Temperature sensor to look like this.

Where is the location of this sensor?

RYU · 28 March 2012

liftnot said:
Where is the location of this sensor?

Bottom of the intake manifold, on the front bank under where the throttle cable is roughly and to the right of the EGR. Will try to find a pic for you...

EDIT: It's #10
37880-PE2-013 SENSOR ASSY., AIR TEMPERATURE $48

liftnot · 28 March 2012

I've found it!...saz the Grasshopper.

Larry Bastanza · 28 March 2012

johnnymo said:
After a complete engine rebuild at 225k miles, I was puzzled that my '92 car failed CA smog.

Turns out a lot of owners here in OC of pre '93 cars are having trouble right now according to the smog shop guys, and it's puzzling to Ramon and the guys at Niguel Motors, who sees NSXs all day.

Well, due to a lead from fellas on the board, I found the one sensor I hadn't replaced on the car was the culprit. Blowback from 20 years of intake valves had soiled the Air Intake Temperature sensor to look like this. Yes, that's oil dripping off it. Yes, that grey color at the very base is the original color. Yes, it's one of the cheapest parts on the car at $31 bucks and takes 10 minutes to replace. And yes, the car passed smog easily now.

On an OBDII '95 at the shop, we checked the output pre and post cleaning this same sensor right after my experience and the computer measured a full 10 degrees F higher air temp after cleaning, FWIW.Hope this helps cars failing smog.

Are you suggesting that cleaning it would have accomplished the same result? Anyway, nice writeup and good find.

BTW, since this is a "PE3" part it was not an original NSX part, and if it is used on many cars it will be around for a while

......

Regards,
LarryB

Dhalsim · 28 March 2012

I just failed smog so I will check this although I think I will also have to replace the Prospeed cats with my OEM cats as well.

If you have a CTSC can the sensor still be easily found?

Other than allowing the car to pass smog how else will cleaning or replacing this sensor help out?

Hapa88 · 28 March 2012

Larry Bastanza said:
Are you suggesting that cleaning it would have accomplished the same result? Anyway, nice writeup and good find.

BTW, since this is a "PE3" part it was not an original NSX part, and if it is used on many cars it will be around for a while......

Regards,
LarryB

To the OP,
Yeah, I'm confused too.. Did you replace it? Or just simply clean it?

RYU · 29 March 2012

Dhalsim said:
I just failed smog so I will check this although I think I will also have to replace the Prospeed cats with my OEM cats as well.

I agree. You're likely culprit is probably the HF cats.

Dhalsim said:
If you have a CTSC can the sensor still be easily found?

The OEM IAT sensor is in the same general area on the CTSC intake manifold.

Dhalsim said:
Other than allowing the car to pass smog how else will cleaning or replacing this sensor help out?

Keep in mind, if the ECU is having problems tuning in closed loop the smog test will fail. The ECU relies on a bunch of different sensors, not just the IAT sensor. On a CTSC NSX if the IAT sensor senses it's too hot it will retard timing and run the mixture rich (that's everyone's best guess at the moment and sr5guy is close to telling us exactly how much timing is pulled and how much fuel is added). A bad sensor could potentially aggravate the situation. During a SMOG dyno test I wouldn't be surprised if your IATs are at around 140+ degs. If the ECU tells it to run rich then the OEM cats would be struggling let alone a set of HFs.

Dhalsim · 29 March 2012

^^ Thanks

scorp965 · 29 March 2012

I swapped mine out a few weeks ago, the one which came out looks exactly like the OP's.

The sensor is highly visible on top of the intake manifold, it has a grey connector, and is mounted on the top.

At first glance, it appears you can remove just the sensor without disassembly of any surrounding parts, however that is a mistake, you will need to remove the magnesium intake manifold cover, as well as the plastic fuel rail cover, in order to get a perfect angle on the sensor. The sensor itself is held in by two (very tight) phillips-head screws, which come out with limited effort once you have a secure attachment to them.

nikey22 · 6 April 2012

thank you scorp... good summary on how to get to it!

BTL3.0 · 7 April 2012

if the ait are similar to the b and h series u can get one here for cheap: $17+sh
http://www.inlinefour.com/oeminairtese.html

to me it look exactly like the one on my gsr motor and my gf's 01 prelude. I think they are interchangeable. only a 2 wire sensor.. should bolt up fine.

jaffaz32 · 7 April 2012

Interesting post!!

So these are on both OBD1 and OBD2 nsx?

Anyone have a picture of the exact location? I don't want to pull the wrong one

And would simply cleaning it do the job?

Thanks.

nikey22 · 8 April 2012

you can't miss this thing, if you take off the rear fuel guard rail plastic cover, you'll see it, but you should also take off the center manifold cover to access the other screw.

johnnymo · 12 April 2012

Sorry guys was away from the board for a while.

In response to LarryB and others, I replaced the sensor because mine was very stained/discolored even after cleaning. Since it was OBDI, I was unable to measure what dif the ECU saw, BUT we did take a 95 at the shop and just wipe down its sensor well and got a 10 degree change in air temp in its OBDII ECU.

My car was running rich according to the smog report (don't have it with me right now) with high everything, but then passed easily after the sensor was changed. And yes, Larry's right, it's the same air temp sensor found in lots of Honda cars.

Darkcyd · 28 April 2012

Very interesting find! I'm curious to try this at my next smog. Where did you pick up the part from (link)?

johnnymo · 12 May 2012

Darkcyd said:
Very interesting find! I'm curious to try this at my next smog. Where did you pick up the part from (link)?

Try this:

http://www.acuraoemparts.com/delray/jsp/prddisplay.jsp?inputstate=5&catcgry1=NSX&catcgry2=1992&catcgry3=2DR+NSX&catcgry4=KA5MT&catcgry5=INTAKE%2BMANIFOLD&ListAll=All&vinsrch=no

It's number 10 on the parts diagram shown for a '92.
Part number is 37880-PE2-013.

Now that a bunch of us in OC have changed out or cleaned this sensor, I can report we have noticed between 0.5-1.0 mpg improvement as well as more cars passing smog.

John

OLDMNSX · 15 May 2012

nikey22 said:
you can't miss this thing, if you take off the rear fuel guard rail plastic cover, you'll see it, but you should also take off the center manifold cover to access the other screw.

It looks like the FRONT fuel guard rail cover needs to be removed, not the rear.

Brad

UPDATE: I removed mine. It was dirty also. Cleaned it with brake parts cleaner and reinstalled. Took all of about 20 min.

Brad

rjwong · 17 May 2012

After reading this i decided to take mine out and see the condition. it was dirty but not as bad as the first post, cleaned it and reinstalled, hope this helps...

Btw i was able to take off the sensor without taking off the fuel rail cover or the manifold cover. i guess it helps to have smaller hands

Dhalsim · 30 May 2012

well I finally got around to doing this. Those screws must have been put in by the Hulk himself. It was crazy how tight they were.

My sensor wasn't as bad as the OP but there was some oil and I cleaned it off real good with brake cleaner and put it back in.

Here are a few pics for people like me who like to see pics.

rjwong · 30 May 2012

I took a drive to the vacaville outlets over the weekend. Before cleaning this sensor i would get about 17 mpg mostly city. This was all freeway but round trip i hit an average of 23 mpg!

About the screws being on there tight, what i did was take a screw driver and hammer the screw just a little before trying to take it off, as if you were taking off the screws on a brake rotor. mine came right off

Dhalsim · 30 May 2012

I put a little blaster on them inserted the screwdriver and gave a few good taps and was finally able to get them to turn even though I stripped them pretty good.

OLDMNSX · 30 May 2012

Dhalsim said:
I put a little blaster on them inserted the screwdriver and gave a few good taps and was finally able to get them to turn even though I stripped them pretty good.

Something else that works good for screws like this is to dip your screwdriver tip in VALVE GRINDING COMPOUND. It gives that extra bite on the screw head.
Brad

Is your NSX failing smog? Read this.

johnnymo

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