jpandes

Have any of you guys seen this? I occasionally see negative intake temps on my PFC commander. Sometimes, I see a dashed line across instead of a temp number.

I'm thinking that I may have a bad intake temp sensor. Although, it should've been changed with the recent motor swap.

Any ideas or is this common?

93 R1

That just means your intercooler is working really, really good

twokrx7

iTrader: (1)

Check out your connections, make sure the sensor is securely plugged into the harness and verify the harness is in good condition. If you unplug the sensor, I believe you'll see the dashes instead of a temperature on the commander.

jpandes

Hmmm. interesteing. That means that I have pull the UIM, huh?

I'm a lazy bastard.

SanJoRX7

I've seen this too, occasionally. I can't yet correlate it with any driving behaviour, or wierd weather (I generally don't drive the FD in the rain). I'll be interested to see what you find.

DCrosby

Something's reversing the polarity or grounding out the sensor... either way, look to see if the harness / wires have cracks, and or make sure if you're only seeing dashes, or negative values, that the connector is plugged in the right way

jeff48

I have also seen this intermittmently for the past few weeks. It is probably caused by either the sensor or wiring going "short" (there is an inverse relationship between +volts and reported temperature). I have yet to be able to get a datatlog during a failure. I will replace both while the engine is out, but while out, I am moving the sensor to the IC outlet piping.

Alpha-7

iTrader: (1)

I've noticed the same thing!!!

jpandes

I need to check my wires/harness still.

Michael Filippello

I too just had the same problem. I replaced the IAT sensor and all is fine now. If you change the sensor, now is a good time to move it to the outlet of the intercooler. You'll get better response. I think alot of cars are seeing around 100k+ now and they are starting to fail.

mike

SanJoRX7

What's IAT stand for? Intake air temp? Got a part #?

jeff48

Yes IAT=Intake Air Temp Sensor. Call Mazda and tell them you want the air temp sensor that plugs into the underside of the upper intake manifold.

jpandes

OK, I reached behind the UIM and jiggled the cable/connector to make sure that they were firmly connected. So far, no more negative temps(3 days now)

SanJoRX7

You did that w/o removing anything? I had planned a half day to remove everything and pull that bad boy out to clean it off. I have suspicions that my temp oddities may be due to what appears to be a prodigous amount of oil in my intake track, presumably due to leaky turbos. Since I've got the car apart right now anyway, will probably continue with this, but let's hear how you did this

jpandes

Yeah, I just reached behind the UIM and grabbed the connector/harness.

I'd like to relocate the air intake temp sensor soon to the IC pipe(outflow) to get more accurate AI readings. The UIM heat sinks the crap out of the sensor and doesn't allow the temp to change fast enough.

I just need to find a good write up.

SanJoRX7

There is a good writeup on this one...but for the life of me I can't remember where it is or who did it. The person took the IAT out of the UIM and moved it to their greddy elbow, to avoid that heat sinking phenomenon that you're talking about. Definitely a good plan, just for more accurate temps.

SanJoRX7

Ok, this isn't it, but it's decent enough, considering this isn't a difficult thing to do:

https://www.rx7club.com/showthread.p...p+sensor+elbow

jpandes

Thanks SanJoRX7,

That was a pretty good write up. I just need to get off my lazy butt to do the mod. The first and only time I removed the UIM it was a pain in the butt.

John

cavellm

It's the same with mine. Every once in a while it'll do it, and since it's reading negative numbers, dropping shitloads of fuel in the car and it idles horribly. Just wiggling the connector back and forth fixes it.

Being non sequential or single turbo helps this immensely. Not a bunch of **** to get in your way under the UIM.

SanJoRX7

Man, this is such weak problem...tho, i didn't realize that the temps being wierd would actually change the way the PFC does it's fuel allotments, etc. I guess this will definitely get done while the car's in pieces

Hopefully tomorrow I'l have some time to look into this.

neit_jnf

iTrader: (17)

my car showed negatives ait's yesterday for a little while, i shut it off and restarted it and everything went to normal.

is the sensor at fault? should I get a new one?

dradon03

iTrader: (2)

FWIW The Power FC only adjusts timing on really high IATS which you can configure in the FC Edit.

cewrx7r1

iTrader: (2)

It can be the sensor or it's connector or the wiring from it to the PFC.
When either fails, the engine will run very rich as a safeguard.