Ok, my coolant temp guage always read low, so I replaced the sender unit. It still doesn't work. I have tested the wires and I have continuity through it, but I don't have power on them. I do have some funky resistance on one of them though. Well, I traced the schematic in the shop manual and it looks like the wires aren't even hooked up to the right connectors on the ECM??? :confused: I am also getting an error 21 Throttle Position Sensor High and 23 Intake Air Temperature Low. I traced them as well and they seem to be hooked into the same circuits as the coolant temp sender. Any ideas what is with this? I have been having this problem ever since I got the car.

This last week when I was driving the car the coolant temp guage skyrocketed up to 160 C (320 F) within about 5 seconds. It would bounce around from 140C to 160C and would eventually drop back down to low as fast as it came up. I know it wasn't actually out of spec since the oil temp and pressure were normal and the coolant wasn't boiling. It did this a couple of times and hasn't bothered since. Any idea what might have caused this?

This weekend I am going to look at it some more and document what exactly is going where, but I would appreciate any ideas that you guys might have so I can check it out when I have stuff apart. I am going to also try checking the temp sender and make sure it is ok as well. I am probably going to have to take the car to someone who knows this kind of car since I am not sure how exactly stuff is supposed to be. I am not sure if the car is wrong, or the manual is wrong. It wouldn't be the first thing I have found that is wrong in that shop manual.

EDIT: Oh yeah, it is an 85 :)


[Modified by DF, 10:58 PM 9/4/2002]

 

This is just an idea, but I do know that some of the sensors have common grounding points. Often, when a bunch of crazy things and codes occur, it is worth checking. I think they ground to the bell housing. Unfortunately, I'm not sure that the information in my '96 service manual is applicable to your car. Hope this helps a little...
Ted
96 CE LT4 Z51

 

Right now I am guessing it is something like that.

 

DF.........

I don't know how the Vette temp sensor is wired, but commonly, a temperature sensor isn't hooked up to DC power. They work by generating a small voltage when the temperature increases. The gauge then senses this voltage and displays it. If the readout is digital, such as the Corvette, a circuit senses the voltage then converts it to a digital sigal for the readout.

Rich

 

Well, from memory I think it is supposed to have +5v going to it, I don't have the manual here with me but I think that is what it is supposed to get.

 

Ok- first of all, which sensor are we talking about?

There's a coolant temperature sensor for the ECM which is in the front of the intake manifold. It has no voltage, only resistance:
185 Ohms @ 210F, 3400 Ohms @ 68F, 7,500 Ohms @ 39 F

The temperature gauge in the dash works off a seperate sensor in the R cylinder head. Same specs as the other one:
185 Ohms @ 210F, 3400 Ohms @ 68F, 7,500 Ohms @ 39 F

The difference is the gauge sensor is a single wire and is grounded to the engine block; while the ECM sensor is a two wire with it's own ground. Since your having other weird readings, I agree with the above posts that it's probably this ground that's bad.

 

I had assumed that the dash read off the one on the side of the engine between cylinders 6 and 8.

I guess I will go check the other one as well and make sure it is hooked up properly.

 

DF, The 85 has 3 sensors for coolant. The ones mentioned at the front of the manifold, between 6-8 and between 1-3. On the 85 (and it may just be one year only) I believe the 1-3 sensor was for the digital display. The 6-8 was a safety for the cooling fan in case it hadn't come on by the computer control.

 

Yes, I forgot these locations may be different between alum / iron heads. But the third one for the fan is just a switch- should read open (infinite) or closed (0 ohms) on your meter.

 

Ok, I will check that out when I go home today. Thanks!