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Unread 08-12-2009, 10:07 AM   #1
gregoryp
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Join Date: Aug 2009
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Coolant Temp Sensor Resistance Measurement

Just thought I'd share this. I recently ran into a no start condition, but had spark and fuel. Checked a bunch of stuff with no luck. Found that when I unplugged the coolant temp sensor (on T-stat housing) that the engine (1995 YJ 2.5L) ran fine. I didn't see a resistance range for the sensor on the forum, maybe I didn't search enough? I bought a Haynes manual and it doesn't give the range. I did a little test. At room temperature 73.4 (F) the resistance was 8.82 Kohms at 125.6 (F) (water from coffee pot at work) the resistance was 2.37 Kohms.

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Unread 08-12-2009, 10:28 AM   #2
Que89YJ
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1989 YJ Wrangler 
 
Join Date: Apr 2008
Location: Detroit, Michigan
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Temp sensor should never keep the rig from starting. If you narrow it down please keep the post up dated because it is definitely interesting. The resistance for the sensor can be found here:
http://books.google.com/books?id=ze_...stance&f=false
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Unread 08-12-2009, 10:34 AM   #3
dos0711
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Unread 08-12-2009, 04:27 PM   #4
gregoryp
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Thanks for the info. With the old sensor the thin would die when I plugged it in. I'm thinking it was dumping so much fuel from the bad signal that it was flooding it? With the new sensor it runs fine and at operating temperature I'm getting about 0.6 Kohms or 600 ohms measured at the back of the connector, which is consistent with the above chart. Now after about 10 minutes of driving (which must be the drive cycle for OBDI) I get a check engine light and its throwing codes 22 and 51. 22 is the temp sensor and 51 is the O2 sensor lean condition. Seeing how the temp sensor seem to be ok is the O2 sensor also dead from getting so much fuel dumped on it? I'll hook up the volt meter tonight and see if it is cycling between 0 and 1 volt.
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Unread 08-12-2009, 04:38 PM   #5
Neo1130
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2009 JK Wrangler 
 
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Yeah, you won't get a very clean signal from an o2 sensor... They usually go all over... But I would clear the computer first and see if the codes come back... Could be the comp was used to the old sensor and learned off that and now it has a new sensor with different values causing it to go wacky... Just a thought...
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Unread 08-12-2009, 05:20 PM   #6
gregoryp
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I've cleared it twice and it comes back after about 10 min. of driving. I'm just wondering if this particular O2 problem typically throws the temp sensor fault also. I hate to just throw parts at it. Typically the O2 should cycle between 0 and a number no greater that 1 volt. The upper end varies depending on how lean or rich the mixture is, can't remember which way it goes. Whey they die they typically don't cycle at all. Thanks again for all the advice it helps maintain sanity.
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Unread 08-12-2009, 06:28 PM   #7
Neo1130
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Quote:
Originally Posted by gregoryp View Post
I've cleared it twice and it comes back after about 10 min. of driving. I'm just wondering if this particular O2 problem typically throws the temp sensor fault also. I hate to just throw parts at it. Typically the O2 should cycle between 0 and a number no greater that 1 volt. The upper end varies depending on how lean or rich the mixture is, can't remember which way it goes. Whey they die they typically don't cycle at all. Thanks again for all the advice it helps maintain sanity.
LOL! I take it you have never owned a narrowband A/F gauge? They do cycle... Very much...
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Unread 02-21-2013, 11:41 AM   #8
iced98lx
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1995 YJ Wrangler 
 
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not to drudge this up from the dead but wanted to say thanks as my coolant temp sensor went out and an injector failed me at the same time. Using this I got 680 ohm resistor out and jumped the leads going to the temp sensor once the trunk was warm, so I could verify an additional problem. Got the injector fixed and can drive to town to get a coolant temp sensor without all the issues associated with a bad temp sensor!
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Unread 07-12-2013, 02:51 PM   #9
BabyHuey94
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Follow-Up

I'm dealing with the same issue. Have the new temperature sensor but do not know how to troubleshoot which injector is giving the bad signal - or what to do about it (engine runs fine). How do you diagnose which injector is the bad actor?

Thanks!
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Unread 07-12-2013, 03:10 PM   #10
pete1991YJ
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Quote:
Originally Posted by BabyHuey94 View Post
I'm dealing with the same issue. Have the new temperature sensor but do not know how to troubleshoot which injector is giving the bad signal - or what to do about it (engine runs fine). How do you diagnose which injector is the bad actor?

Thanks!
Welcome to JeepForum, you've just found one of the best jeep sites anywhere!

There are a few ways to test injectors. One of the simplest ways is to unplug them one at a time on a rough running engine. The one thas causes no change in the idle is likely bad.

Another way is to check the solenoid coil inside the injector with an ohm meter. I don't have any specific details on this method hewever.

A third and popular way is to use what is called "noid" lights - basically little lights that clip into the injectors and light up whenever one of them fires.

hope that helps!
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