IAT resistance spec? MAP voltage? O2 ohms?

[scott in NH]

Does anyone have this number vs. temperature? I'm still troubleshooting a fast idle. I took the sensor out warm and put a ohm meter on it. It seemd to be working because I could see the resistance going up if I shook it in the cold NH air or stay put if I wrapped my hand around it. The idle does drop some if I disconnect it.
I'm not against putting a new one in, but this Jeep has been eating me alive for new parts all year, so I'm not into random replacement at this time
Same deal with the Map sensor, I can see the voltage change with vacuum, and it does hold vacuum, but are the values right?
I did replace the O2 sensor maybe 50k ago, I recently put a ohm meter on it and it did hold, what is the spec, 4-6 ohm? It did jump around a lot, but I couldn't tell if it was because of a poor connection to my meter or the sensor?
thanks,
Scott

 

[Smokey]

Got a manual ?? That would have the specs.
I'm at work now, so if no one else provides them today, I'll get them for you tonight.

 

[8Mud]

I usually check the temp. sensor in the block and the temp senor in the intake manifold, agaisnt one another with an ohm meter (digital). They have the same values at the same temp. or they are supposed to. An electronic themrometer is really handy for this. And a high impedance ohm meter.
Deg.F ohms
212 185
160 450
100 1,600
70 3,400
40 7,500
20 13,500

O2 sensor is 5-7 ohms between pins A and B.

Just for the heck of it, you might want to try what I´m gonna try as soon as it warms up a bit. Adjust the TPS (if you have an auto) at the three pin connector for 0.8 volts between A and B, ignition on throttle closed. Then check to see if you have close to 4.0 (3.9 or so) volts between between B and D at the four pole connector, shifts the tranny. The two halves of my TPS have different imput voltages, so I imagine adjustment is a compromise. Between the CPU half of the TPS and the TCU half of the TPS.
Adjust the TPS with the connectors connected through the back of the connectors or do what I do and make a littel cut in the wires and run the TPS cables over the top of the rubber TB intake. Record your readings before you make a change, be carefull of the Torx screws, they snap off.
Put a drop of oil behind the IAC piston (through the crack don´t pull), there is grease behind the piston (on the actuator rod) that gets old and thick, acts up and sticks when it´s cold.
A little light oil on the pivots of the throttle linkage probably won´t hurt anything, on the cable I always stick with a dry lubricant, teflon or graphit.
When it gets down in the teens and below and things start sticking.

 

[nate]

So the antifreeze temp and IAC temp are supposed to be the same? Last time I ran the scanner, my engine temp was 210*, and the IAC was like 80*. I assumed it measured the air temp coming in, so 80* made sense to me. Does that sound like a bad sensor? No MIL light.

 

[8Mud]

No they are not supposed to be the same temp, but have the same resistance values at the same temperatures. If they are both stone cold (engine has sit overnight), and the outside air temp. is say 40F (and has been for awhile), they should both read around 7,500 ohms.
These numbers are for the Renix.

 

[5-90]

8Mud -
Just to let you know, the values for those sensors are the same for the 1994 FSM, so they are probably the same to at least 1995 (through the OBD-I years. I don't know about 1996-up.)

Just thought you'd all like to know...

5-90

 

[goodburbon]

anyone have those numbers for the obd2 models?

 

[8Mud]

So the antifreeze temp and IAC temp are supposed to be the same? Last time I ran the scanner, my engine temp was 210*, and the IAC was like 80*. I assumed it measured the air temp coming in, so 80* made sense to me. Does that sound like a bad sensor? No MIL light.

I was guessing when you said the IAC (idle air control) you were menaing the MAT (manifold air temp).

 

[nate]

Yeah... brain fart. I meant IAT... IAT/MAT same thing.

 

[8Mud]

Yeah... brain fart. I meant IAT... IAT/MAT same thing.

Acronyms make me nuts also, they differ from FJ, YJ, XJ, from the Chiltons manual, Alldata and the FSM and manufacturer to manufacturer, throw in a few typos and/or eye strain, things get really crazy.

 

[scott in NH]

Thanks guys! How steady should the O2 reading be? Is there a spec for the MAP? I have a manual but it lacks these test procedures....

 

[8Mud]

I´ve always concidered the A pin B pin 5-7 ohms test, on the O2 sensor, to be just a continuity test on the heater circuit for the O2 sensor, not an indication of wether the sensor was within specs or not, just that the heater circuit was within specs. Can also test the engine harness side if the O2 plug at pins at A and B for volts, should be battery voltage with the ignition on, these wires come from the O2 heater relay.
Maybe you know this maybe not, so I´ll share anyway. Take your ohm meter and put it somehwere above the 1 M scale, hold the leads (at the tip) one between the thumb and forefinger of your left hand and one in your right hand. Notice how the resistance in your body changes, with the amount of pressure applied. Wet your finger tips and try it again, notice the readings show much less resistance. Rub your forefingers and thumb on the side of your nose and take another ohm reading, notice how it rises, oil increase resistance. You can´t accuratly measure ohms, while holding the metal part of the probe ends. Clean the probe ends and pins with a contact cleaner and take another reading. Can also move the wires around some, if the values change there s a good chance of a frayed wire or an iffy contact.
Seeing as how my typing sucks and I´m handicapped with a German keyboard (the darned letters are in different places), I´m gonna be lazy and let someone else, give you the MAP test, it is kind of involved and lengthy.

 

[PaulJ]

You shouldn't be looking at ohms on the O2 sensor. You want to look at millivolts with the engine hot and running. It should fluctuate all the time if it's working right and there isn't something else driving you extremely rich or lean. The FSM or otherwise should tell you how to check it. The ohms check is just for the heater that is used to get the sensor up to operating temp sooner so that you can run closed loop sooner.