weird temp sensor problem

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Nov 10, 2007 | 07:52 PM

12SEC SS

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From: Brooklyn, NY

weird temp sensor problem

I have a weird temperature sensor. I ordered the 3-wire sensor from a '98 F body, and got the STANDARD brand. All wired in, now when im idling for like 10-15 mins, temperature reading starts rapidly going up, highest i've seen so far is 254 and holding. With my laser temp gun, sensor body and the head are at 200deg, is this just a bad sensor? car doesnt boil over or overheat, both fans kick on since computer thinks its that hot...

Nov 11, 2007 | 03:56 PM

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From: Brooklyn, NY

anyone?

Nov 11, 2007 | 04:02 PM

RE AND CHERYL

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From: Dover DE

Is it wired right? Does the gauge and the PCM read the same. I assume you got the 254 deg temp reading from scanning the PCM.

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Nov 11, 2007 | 04:07 PM

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I think its wired right, from searching the forum I got that top left is ground. Top right is pcm, middle is dash, this is looking at the sensor side of te plug. Both dash and pcm are reading same, dash pegs into overheat...

Nov 11, 2007 | 04:11 PM

lt4malibu

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how do you have it wired up and what type of gauge are you running?? the Dark Green wire (ckt 135) should go to the gauge, the brown wire (ground) goes to PIN#25 in the blue PCM connector and the yellow goes to PIN#49 in the blue PCM connector.

Nov 11, 2007 | 06:48 PM

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Quote:

Originally Posted by lt4malibu

I dont have the original pigtail, the replacement one from GM has all 3 white wires. The ground I grounded to the instrument cluster ground, not to the Pin#25 on the blue connector...does this make a difference?

btw, I just looked at the pcm pinouts, and its pin#74 for yellow wire, and #80 for brown ground wire?

Last edited by 12SEC SS; Nov 11, 2007 at 07:04 PM.

Nov 11, 2007 | 07:06 PM

lt4malibu

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what year is the engine out of?

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Nov 11, 2007 | 07:15 PM

Jrp1978

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hmmmmm

did this happen after u changed to a new one? or did i miss that part?

Nov 11, 2007 | 07:17 PM

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Quote:

Originally Posted by Jrp1978

did this happen after u changed to a new one? or did i miss that part?

You mean after I changed to the new sensor? I never ran it with the old factory sensor, so I dont know what that read...The only thing I can think of is ordering an ACDelco sensor...My steam pipe goes into the upper radiator hose, I installed a Moroso filler neck in the upper hose, and tapped it for a fitting for the steam pipe.

Nov 11, 2007 | 08:42 PM

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RE AND CHERYL

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From: Dover DE

This is the only thing I can think of. Get the engine up to temp and measure the resistance between the ground wire and the wire going to the PCM. Then get the temp with your laser gauge. The last partis the hard part. You need to get someone with a Helms manual to check and see what the resistance should be for the given temp. This will tell you if the sensor is bad. I'd use mine but I just sold them on Ebay.

You could also get a mechanical gauge and run the sensor head into the upper radiator hose and clamp the hose around the metal sensor lead. It's a crude way to get a temp reading.

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Nov 11, 2007 | 08:57 PM

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lt4malibu

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Temperature vs Resistance Values (Approximate)

302 °F
47 ohms

284 °F
60 ohms

266 °F
77 ohms

248 °F
100 ohms

230 °F
132 ohms

212 °F
177 ohms

194 °F
241 ohms

176 °F
332 ohms

158 °F
467 ohms

140 °F
667 ohms

122 °F
973 ohms

113 °F
1188 ohms

104 °F
1459 ohms

95 °F
1802 ohms

86 °F
2238 ohms

77 °F
2796 ohms

68 °F
3520 ohms

59 °F
4450 ohms

50 °F
5670 ohms

41 °F
7280 ohms

32 °F
9420 ohms

23 °F
12300 ohms

14 °F
16180 ohms

5 °F
21450 ohms

-4 °F
28680 ohms

-22 °F
52700 ohms

-40 °F
100700 ohms