Hello guys,

Here I am just trying to sort out my computer bugs, and I think I only have one left to go.

What does a IAT sensor on 1993 car suppose to read?

My scans show that on cold engine with ignition key on (engine off) it reads 155 degrees Farenheit. I cannot get it to run colder. Ambient thermomether says its 95 degress outside.

In a attempt to get it to read colder, I went to good ol' Radio shack and got me some resistors, 4.7k, 3.9k, and 3.3k. I tried the 4.7k and tempature went over 200 degreess Farenheit? What is the problem?

It should have read colder. Witt the 3.3k resisteor it read 181 degrees farenheit. I think my sensor is showing to much resistance, how is this possible? I already thried new sensors, and the problem persists. I checked the 5-volt reference, and it is good.

What else?

 

it reads the air temperature keep in mind if the elbow is heat soaked from the engine then it might read hotter

 

how much does it read with the car running?

 

It does not drop much, runs about 144 degrees Farenheit.

 

The elbow is not heat soaked,

Remember this is on a cold engine with ignitio key on (engine off), so everything is cool, yet it still reads 155 degress Farenheit.

I read it in the same manner but with the IAT sensor disconnected, and it read 332 degrees farenheit as opposed to

-35 degess Farenheit.

 

here is one for ya maybe because the engine is cold it is still in open loop and it is not reading the iat and it is just throwing some default reading out there

 

hmmm,

can anyone confirm this? I believe the IAT is used at all times on a Speed Density set-up.

 

Mine reads the IAT at start-up. Sounds like a bad IAT.

 

It is need not a bad IAT sensor, I proved it by measuring the resistance on the sensor itself. I then matched the results with Injuneer's resistance to temp conversion table.

The car does read it at all times, it is just that it is always far off.

 

Of course the ECM reads the IAT at all times... how else would a speed-density 93 measure the air flow. Doesn't matter whether its in open or closed loop... it needs the inlet air temp to calculate the "density" part of speed-density.

When you bought the resistors, how did you connect them? It sounds like you may have put them in parallel with the sensor while it was still connected to the harness. What you need to do (and may have done) is unplug the harness from the sensor, then stick the resistor wires into the contacts in the harness connector. When you do that, the PCM should give you the readings that correspond to the temp vs. resistance shown in my ScanMaster writeup.

If you correctly plugged the resistors into the harness plug, without the IAT connected, and you got the incorrect readings... and they appear to be higher than actual temp... that would indicate you have too little resistance, and there must be a short in the wires. What is the voltage accross the harness pins when the IAT is not connected?

 

Well, I know I indeed connect the resistors correctly, just like you stated.

I will check the voltage accross the two wires today, but what shoud it be, just for reference. How could it be shorted, do you mean that both wires are making contact along the lines, or do you think that somehow the leads inside the harness connector are touching?

I already re did all my wiring, (not redid, I visually checked and put the on new wire looms). The ground for these sensors is not derived from anywhere in the engine bay, all I know that is that they lead directly into the ECM. The same groundwire also is used by the MAP sensor, but I have already proved that one reads correctly. The other sensors are insignificant (they are for A/C, which I have none).

What you guys think.. Is there anything I can do to trich the ECM to read What I want it too.?

 

.....ttttt.......


Just getting around to it again, after installing new lifters on car.

To recap:

My IAT sensor reads 155 deg or higher with key on (engine off) and cold engine. Reads the same with engine on, and only moves along about 8 to 10 degrees in either direction. Texas ambient tempature is around 85 to 90 degress right now.

I also checked if the ECM is reading the default value of -35 to -45 degrees when the sensor is disconnected, but it reads more than 335 degrees.

I already replaced the IAT sensor, and registered no chane. I know that in my 93 T/A, this sensor is super critical in measuring air flow.

I also traced the wires, and I saw no breaks, could this be a ECM problem? What should the voltage across the two pins on the harness connector?

Thanks

 

sounds like a pcm problem to me. you can check ea. of the two wires by unplugging the pcm, and the IAT. make sure there is no continuity between these two wires at all. should read OL then read the continuity from ea. wire from the pcm side to the sensor end. should be around .3 ohms or less for ea. wire. if that checks out good, and the sensor is good, then there is nothing else left to be possible. the pcm would be bad for sure. good luck.

chris

 

Please educate me, I have a digital voltmeter with me. How do I check continuity. What is 0L?

 

Isolate the wiring by unplugging each end like IrocSS85 said. Connect your meter to each of the wires and read resistance. There should be none unless the wires are pinched together and slightly shorted (which might be your problem). OL= over limit.

If there is no short between the two wires measure the resistance of each wire by itself. Put the meter leads on each end of the wire.

With the computer connected, you should be able to read 5v across the terminals at the IAT plug (unplugged) with the key ON.