Air Temperature Sensor?

[argniest]

I have been told that the Air temperature sensor in my current (older looking) Air Flow meter is bad. Is there any way I can test it myself to find out if it really is functioning correctly or not?

I bought a new refurb AFM, and when I put it on the car, it made it run just horrible. My local Z mechanic was mad at me for putting the new AFM on there, but I really wanted to see how the car ran. Someone else (a relative of mind told me I should try a new AFM and see how that helped the car run). However, now that I have found these forums, I think it was way too premature to get a new AFM.

So now I have a new AFM and an old one, and the car definately runs a lot better with the old one. Of course I realize there is an adjustment screw on the AFM. But I dont know how to properly adjust that. my local Z mechanic had a air fuel meter on the tailpipe, and was showing me how the AFR numbers looked with the old one and the new one. He put the old one back on the car before wintertime.

I would really like to be 100% if possible if the old one has a bad air temp sensor.

thanks

[cozye]

The air temp sensor testing instructions are listed in the factory service manual under the EFI section. It's a simple multimeter test from two pins on the 35pin ECU connector. The air temp sensor is basically a switch. It only comes on below a certain temp which I cant remember off the top of my head, and will allow the ecu to richen the fuel mixture by a small amount to make up for the denser air.

[FastWoman]

Eric, the air temp sensor is actually a thermister. The spec resistance values are shown on EF-31 of the FSM. At 68F, it should read 2.25 - 2.75 kOhm. Resistance should go up as temp decreases (e.g. 7.6 - 10.8 kOhm at 15F) and down as temp increases.

[cozye]

Eric, the air temp sensor is actually a thermister. The spec resistance values are shown on EF-31 of the FSM. At 68F, it should read 2.25 - 2.75 kOhm. Resistance should go up as temp decreases (e.g. 7.6 - 10.8 kOhm at 15F) and down as temp increases.

Yeah, I knew the values went up and down, I was confusing the 68 degree cut off. at 68 degrees it stops enrichment all together. I missed the part about it variably increasing enrichment as the temp got lower (on EF10)

Thanks for the correction

[argniest]

Hey that sounds faily easy to test, for even a dummy like me.

I will look it up in the FSM, and give it a try. I will test it several times at different temperatures, and see what I come up with. I have a multimeter, just never needed it for too many things. But now that I have the car ;-) its a different story. I am sure I will be needing it for several things to help troubleshoot

SO also, that sounds like in the summer its not even using that, or anytime the outside air temp is above 68 degrees, right?

Thanks again!

Edited January 15, 2011 by argniest

[cozye]

SO also, that sounds like in the summer its not even using that, or anytime the outside air temp is above 68 degrees, right?

Thanks again!

Unless the air temp sensor gave a false ohm reading to indicate that it was below 68F

[argniest]

Unless the air temp sensor gave a false ohm reading to indicate that it was below 68F

Yes, that is true. And I think that is what my relative the mechanic was telling me. That it was reading 20 or 30 degrees colder than it should be. Which is why I reaaaaaaaaaaaaaaaly want to understand how to do this myself and see what its doing right now. The problem is that its cold out, and I dont understand how it would even NOT be enriching the fuel mixture...because its going to be cold for three more months before we even think about hitting the 60's again.

So help me understand this if you dont mind. When its cold out, its always going to be below 68 degrees. So wouldnt it always be telling car/computer to enrich the air/fuel ratio?

Edited January 16, 2011 by argniest

[cozye]

Yes, that is true. And I think that is what my relative the mechanic was telling me. That it was reading 20 or 30 degrees colder than it should be. Which is why I reaaaaaaaaaaaaaaaly want to understand how to do this myself and see what its doing right now. The problem is that its cold out, and I dont understand how it would even NOT be enriching the fuel mixture...because its going to be cold for three more months before we even think about hitting the 60's again.

So help me understand this if you dont mind. When its cold out, its always going to be below 68 degrees. So wouldnt it always be telling car/computer to enrich the air/fuel ratio?

see post 4 for explanation. also the fsm ef section gives good detail on how it operates

[argniest]

see post 4 for explanation. also the fsm ef section gives good detail on how it operates

hmmmm I read that over, and its very interesting. But I am not sure I yet comprehend what it is really telling me. Not in laymans terms.

[FastWoman]

Eric is saying that the temp sensor tells the ECU the temp of the intake air, and the ECU richens the mix accordingly. At 68F and above, the ECU doesn't richen the mix. At 67F, the ECU starts to richen the mix. As temperature drops, it richens it even more -- the lower the temp, the richer the mix.

[cozye]

hmmmm I read that over, and its very interesting. But I am not sure I yet comprehend what it is really telling me. Not in laymans terms.

What fast woman said, but if you look on page EF-10 of the factory service manual, there is a very clear description and a picture graph of what is going on, a picture is worth a 1000 words

[argniest]

Eric is saying that the temp sensor tells the ECU the temp of the intake air, and the ECU richens the mix accordingly. At 68F and above, the ECU doesn't richen the mix. At 67F, the ECU starts to richen the mix. As temperature drops, it richens it even more -- the lower the temp, the richer the mix.

Ok now that does make sense to me, thanks! So that means if my temp sensor in the AFM is giving a colder reading than it should be all the time, its never going to stop enriching the system? right?

I mean its wintertime here and generally below freezing for months and months. So that makes me think it will always be making the mix richer??? How or when does it know to stop making it richer? I am not clear on that. But it seems like it should have some other logic to tell it, once the car engine warms up, to stop doing that? sigh....

That picture/diagram is crazy looking on EF 11. Its cool but confusing a little bit.

Edited January 17, 2011 by argniest