Testing Map And Cts

[Dando]

I am trying to determine why my MJ is running like rich $#!&. I found this diagram and did the testing. I am unsure of how these two correspond. Both sensors test to the exact same number with ignition on and engine not running, after it was warmed up. Any explanation of how to read this or are my sensor good or bad?

 

 

[tugalo]

pull the sensors and heat them with a heat gun or in the oven with a thermometer and then read the resistance.  if it checks our fairly close to the given values, then the sensor is good and the problem is in the wiring.  map resistance value changes with vacuum so put a vacuum on it and see that its resistance goes up and down with vacuum changes.....

[MJCARENA]

You need to unplug the sensor and then read the resistance of the sensor. You should never read resistance with a voltage applied to it

[HOrnbrod]

Both answers above are correct, sort of. The table is basically useless since most of us do not have access to the specialized equipment necessary check resistance changes of coolant / ambient air temps throughout the sensor's range. The best way to check if the thermistors (temp-sensitive resistors) are operating is to remove them from the engine and check them at both ends of their range. For the coolant sensor, check resistance cold across the sensor tip and output terminal, then stick it in boiling water for a minute, then check again at the opposite extreme. The resistance should change roughly according to the table. For the air temp based MAT sensor, do the same thing except use a heat gun. Same same regarding the table vs. the resistance change.

 

Highly inaccurate; basically these tests determine if the thermistor sensors are functioning or not. If no resistance changes from one extreme to the other, it's junk. If the resistance increases or decreases according to the table, the sensor is probably okay and the problem is in the wiring continuity.

 

Make sense?

[cruiser54]

You do know that all 3 of those sensors share the same ground, right? 

 

IAT can be removed and cleaned.

 

Try this test.

 

Cruiser’s Renix Sensor Ground Test

 

 

This sensor ground circuit affects the CTS, TPS, IAT, MAP, ECU and diagnostic connector grounds. It’s very important and not something to overlook in diagnosing your Renix Jeep as it is common for the harnesses to have poor crimps causing poor grounds. If any or all of the sensors do not have a good ground, the signal the ECU receives from these sensors is inaccurate. 

 

 Set your meter to measure Ohms. Be sure the key is in the OFF position.  Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector of the TPS . The letters are embossed on the connector itself.

Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it runs parallel to the valve cover and also near the MAP sensor mounted on the firewall. If you have an 87 or 88 with the C101 connector mounted on the firewall above the brake booster, wiggle it, too.

 

You want to see as close to 0 ohms of resistance as possible. And when wiggling the harnesses/connectors the resistance value should stay low. If there is a variance in the values when wiggling the wires, you have a poor crimp/connection in the wiring harness or a poor ground at the engine dipstick tube stud. On 87 and 88 models, you could have a poor connection at the C101 connector as well. 

 

Revised 06/12/2012

[tugalo]

sorry,

 

i read MAP instead of MAT, hornbrod got it right.....