Hi guys
:Vader this is the first time I have needed help from you but I follow your posts and I think if anyone can help me its you. As they say in radio "long time listener.. first time caller":
any who
this just started the other day. I was driving to work and my temp gauge just spiked like up to 320deg. It went up fast too real fast like someone fliped a switch. It had just been at 160deg so I knew I wasnt really that hot. I tryed reving up the motor a bit and that seamed to make it drop about 10deg but thats all. I turned the motor off and took the key out(on the fly) after it started the gauge worked fine. Its done this for the last few days now. Today at work it did it agian and after I turned it off I turned the key back to run still the thing read 320deg when I got home today and once mor it was messed up, with the car runnig I got out and wiggeled the cuplure on the coolent temp sensor that didnt do anything but I did notice that neather of the fans were on. one last thing I replaced my Coolent temp sensor not 3 months ago its from NAPA and its there good one.
if you now whats up HELP I dont know where to start at i.e. Gauge,Wiring,Sensor,.....?
thanks jacob

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Ya sure it is just an RS

B4Cyaa

1991 RS B4C
Former Nebraska Highway Patrol Car 1 of 3
305 TPI
WC T-5
Four Wheel Disk Brakes
Only Options
Rear Defrost
Am-Fm Radio
Red-int White-exe
One BA Of A 350 In The Works
Mods
Dynomax Cat Back (to hold me over till I got the $$$ for the Borla)
best 1/4mile Run of 14.92@94.83
with 145,000 on her

[This message has been edited by 91B4C jacob (edited October 27, 2000).]

 

Jacob,

It sounds as if the system is working properly most of the time, so I would suspect a problem with the wiring instead of the instrument. Still, the sensor could be intermittently shorting.

Make sure the CTS connector is clean, tight, and not grounded. Trace the wiring back to the firewall and make sure you have no melted insulation and grounded wiring. The system operates such that a low resistance will cause a high temperature reading, so a direct short to ground will in effect peg the meter on the high end. The wiring is fairly close to the exhaust manifolds/headers, so a short to ground is not out of the question. It's also possible to have a ground somewhere in the passenger compartment, but since teh wiring there is not subjected to movement and high temperatures, I would look forward of the firewall first.

You could try unplugging the connector from the CTS and driving that way for a while. If the gauge still pegs, the sensor is probably still O.K.

Incidentally, which CTS sensor did you replace? The one used to signal the dash gauge is at the head opening on the left bank, and has a single green wire connected to it. The one used to signal the ECM is at the front of the intake manifold coolant crossover, and has both a yellow and black wire in the connector. If you have dual electric fans (not sure on the SEO vehicle) there is a third CTS in the right head for the secondary fan cut-in. I'm not sure if there is a single wire color for all years for this CTS.

The reason your fan(s) didn't start is because the CTS for the ECM is reading correctly, and the engine temperature is not above 223°F. The dash instrument is completely independent of the ECM. Normal failure mode for the temperature gauge is toward the low temperature end of the scale, so I doubt the gauge is failing.

Hope I covered it well enough.

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Later,
Vader
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"Make Me Bad"
Adobe Acrobat Reader 4.0

 

Once more Vader your "THE MAN" I didnt know that the ECM and the gauge ran on two different sensors. I replaced the the two wire one on the front bottom of the intake the one for the ECM. I have been haveing a little bit of a rough idle and yesterday when the board was down I remover the cupler on the ECM CTS and there was a ball of grease in one of the pin holes. I cleaned it out and the idle smoothed out and the power band feels much cleaner now (not just all up in the high revs)
yes I do have duel fans and they both work as they should reguardless of what the gauge reads.
I work at NAPA and when I look up a coolent temp sensor all it gives me is the listing for the ECM CTS not for the gauge sender(thats why I thought they all ran off the same sensor plus my chilltons only tells ya abiut the ECM one also) well I guess that I will have a look at the gauge sender and get back to ya
thanks man
jacob

------------------
Ya sure it is just an RS

B4Cyaa

1991 RS B4C
Former Nebraska Highway Patrol Car 1 of 3
305 TPI
WC T-5
Four Wheel Disk Brakes
Only Options
Rear Defrost
Am-Fm Radio
Red-int White-exe
One BA Of A 350 In The Works
Mods
Dynomax Cat Back (to hold me over till I got the $$$ for the Borla)
best 1/4mile Run of 14.92@94.83
with 145,000 on her

 

Jacob,

Your parts listing may have the sensor you need defined as "Temperature Gauge Sending Unit", not "Coolant Temperature Sensor". It should have a single brass terminal in the center instead of a two-wire weatherpack type connector.

------------------
Later,
Vader
------------------
"Make Me Bad"
Adobe Acrobat Reader 4.0

 

Vader
I have saturday off form work and I am gona pin down the temp gauge problem. But one last thing...
Am I looking for a bad conection (like from oxidation) or a short to ground. Basicly I am asking what makes the temp gauge go up, more or less resistance.
thanks again.

------------------
Ya sure it is just an RS

B4Cyaa

1991 RS B4C
Former Nebraska Highway Patrol Car 1 of 3
305 TPI
WC T-5
Four Wheel Disk Brakes
Only Options
Rear Defrost
Am-Fm Radio
Red-int White-exe
One BA Of A 350 In The Works
Mods
Dynomax Cat Back (to hold me over till I got the $$$ for the Borla)
best 1/4mile Run of 14.92@94.83
with 145,000 on her

[This message has been edited by 91B4C jacob (edited November 03, 2000).]

 

Jacob,

A decrease in resistance will cause the dash instrument to increase its indication. If you short the lead to ground (zero resistance) the gauge should read at maximum (280° I think). An open circuit (infinite resistance) will cause the lowest indication on the gauge.

The numbers should be about like the following table:


------------------
Later,
Vader
------------------
"Make Me Bad"
Adobe Acrobat Reader 4.0

 

Thanks for the quick reply vader I will let you know if I find it in the morning.

------------------
Ya sure it is just an RS

B4Cyaa

1991 RS B4C
Former Nebraska Highway Patrol Car 1 of 3
305 TPI
WC T-5
Four Wheel Disk Brakes
Only Options
Rear Defrost
Am-Fm Radio
Red-int White-exe
One BA Of A 350 In The Works
Mods
Dynomax Cat Back (to hold me over till I got the $$$ for the Borla)
best 1/4mile Run of 14.92@94.83
with 145,000 on her

 

Got it Vader turns out you were right it was grounding out on the exhaust pipe right bellow the manifold both my sender wire AND my O2 sensor wire were melted donw to the copper on the pipe The way that GM ran the wires there is just asking for problems. the stupid little plastic clips(they look like this <-O ) that hold the wire loom to the block broke and let the loom lay on the pipe. I spliced in new wire and made it slightly longer so I could run it up behind the brake boster and down along the shock tower Its no where near any heat so this won't happen again. But I do have one last question for ya. Both wires now have about a foot more wire on them Since both use such a small amounts of resistance to tell there systems whats up, will this extra wire make the computer "read" the O2 sensor wrong and make the gauge off? I did make the new wire one size larger then the line that they run to
thanks Vader you know your $hit

------------------
Ya sure it is just an RS

B4Cyaa

1991 RS B4C
Former Nebraska Highway Patrol Car 1 of 3
305 TPI
WC T-5
Four Wheel Disk Brakes
Only Options
Rear Defrost
Am-Fm Radio
Red-int White-exe
One BA Of A 350 In The Works
Mods
Dynomax Cat Back (to hold me over till I got the $$$ for the Borla)
best 1/4mile Run of 14.92@94.83
with 145,000 on her

 

Jacob,

The extra wire in the dash gauge circuit won't make a difference since the signal level is at 12 VDC, but the very low level of the oxygen sensor (0.3-1.0VDC) may be affected by the extra resistance of the longer wire. Even though the sensor gets a bias voltage from the ECM which raises the signal level to ground, the DIFFERENCE of the signal is the important part, and is very small over the full operating range of the sensor. More important is the kind of connections you made. Simple crimp-on connectors will eventually corrode and cause signal loss, whereas soldered connections will minimize that problem. Even with good connections, the extra wire length may cause a small signal loss from the O2. It probably will not make a substantial difference, but the eventual solution should be to replace the sensor and route it through a heat shield tubing if necessary to protect it. Mine has plenty of length to route directly away from the crossover, so it isn't an issue. Your's may have been routed differently.

It isn't the end of the world, either, since it's a good idea to replace the sensor about every 30,000 miles anyway.

------------------
Later,
Vader
------------------
"Make Me Bad"
Adobe Acrobat Reader 4.0