Analog temp signal to dash

[Jetjock]

We just got done replacing the starter, coil packs, injectors, spark plugs and two new temp sensors. Started the engine and the didgital temp gauge works but the analog temp gauge just sits there and doesn't move. For some reason, I seem to remember that the temp sensor for the gauges runs off the one sensor but having a hard time finding it in the service manual. Is this true about the sensor or is another one at fault because I can't find the location for another one?

[sammy]

the analog guage sensor is located on the drivers side inj housing. if you replace the sensor as i did with one from autozone be mindfull that the guage might read different as mine did . i thought i had a real problem until i hooked up my scan tool and found that 180 deg. was now in the middle of the guage . if nachos isnt working you might just have not got the connection back on all the way . i dont know if it would effect the digital guage . i would call corey henderson he would know .

[Jetjock]

Okay. Are we talking about the two temp sensors inside under the plenum? I know about those. What my question is is what drives the analog gauge in the insturment cluster? I know that the bottom sensor feeds the digital gauge and the top one feeds the ECM. Where is the sensor that feeds the analog gauge in the cluster? I think that the digital sensor also feeds the analog one but can't find the proof that I need in the service manual.

[-=Jeff=-]

Okay. Are we talking about the two temp sensors inside under the plenum? I know about those. What my question is is what drives the analog gauge in the insturment cluster? I know that the bottom sensor feeds the digital gauge and the top one feeds the ECM. Where is the sensor that feeds the analog gauge in the cluster? I think that the digital sensor also feeds the analog one but can't find the proof that I need in the service manual.

there are 2 sensors in the IH.. one for ECM one for analog gauge. the digital one gets the info from the CCM which gets it from the ECM

[sammy]

from what i understand each gauge is independant. the digital gauge is the one that goes to the ecm. and the analog just goes to the inst cluster. if they were interwired to each other then you wouldnt have the need for 2 sensors. the ecm deals with digital info. the analog or sweep gauges are a totally different deal dealing with resistance to get the reading

[sammy]

to clarify the analog sensor only feeds the gauge. the ccm and ecm cant convert analog readings info into usable info. they need digital info

[sammy]

it the same reason we have 2 oil pressure sensors . one on top is analog and the one thats a bitch to get to is the digital info for the computor

[Jetjock]

Believe it or not, I was told by a well respected Corvette ZR-1 type that the bottom sensor was the digital one for the dash. I knew that the other one was for the ECM but that does make sense since you would need a converter to change the information to read both. The service doesn't really clarify that point. I understood that the ECM is strictly digital but the info that I got from this guy was freaking out the understanding that I had about it.

[Paul Workman]

it the same reason we have 2 oil pressure sensors . one on top is analog and the one thats a bitch to get to is the digital info for the computor

Ummmmm..... Of the 65 electrical connections on the LT5, there are actually 3 oil-related sensors, if I'm not mistaken. They're on the oil filter housing: The top one is a 3-wire analog pressure sensor, the one in the middle toward the front is the oil temp sensor, and that one down underneath is (a single wire) low oil pressure switch (turns on the idiot light). As far as oil sensors go...that's about it.

BTW, ALL of the oil measurement sensors are analog, unless you want to call the low pressure switch "digital" in that it is a two-state device.:-D (None have A/D converters in them) The output of the pressure sensor runs the analog pressure gauge on the dash, but the feed is split off to an A/D converter before feeding the ECM.

P.

[-=Jeff=-]

Believe it or not, I was told by a well respected Corvette ZR-1 type that the bottom sensor was the digital one for the dash. I knew that the other one was for the ECM but that does make sense since you would need a converter to change the information to read both. The service doesn't really clarify that point. I understood that the ECM is strictly digital but the info that I got from this guy was freaking out the understanding that I had about it.

I will check tonight, but I am pretty sure the one sensor is the analog and the other is ECM & digital

[Jetjock]

I looked in the service manual and found a section that discusses the CCM sending out the signal to the digital gauge and actually has it in the CCM twice. Still can't find the info about the analog gauge other that there is an "air core" gauge for coolant temp. The description of the sensor indicates that it is a thermocouple device which can go either way depending on the need.

[-=Jeff=-]

did not get a chance to look tonight.. will check tomorrow.. sorry

[gbrtng]

I will check tonight, but I am pretty sure the one sensor is the analog and the other is ECM & digital

All the engine sensors are analog except for the on/off switches. Any analog to digital conversion is done in the ECM.

[Jetjock]

Hey Glenn, I figured that you would know. How you doing?

[-=Jeff=-]

All the engine sensors are analog except for the on/off switches. Any analog to digital conversion is done in the ECM.

Yes, I should have clarified.. one analog sensor feeds the gauge

the other analog sensor feeds the ECM and CCM ( digital gauge)

[Paul Workman]

In short, power comes from the "HOT IN RUN" circuit, and goes to the gauge. The gauge is a three-pole bridge; one is the 12-volt power input, one is ground (G201), and the third goes to the temp sensor - a variable resistor - which is grounded in the IH housing.(1)

If I'm not mistaken, of the two sensors, the one that has the single wire with the slide-on connector is the sensor you're looking for.

With a VOM, and the switch on, you should get a voltage reading between the connector and ground. With the connector removed from the sensor, you will get a higher reading than with the connector attached to sensor. Sorry, I don't have data on what that reading should be - maybe someone has their plenum off and could check that out for us?

Anyway, No voltage at the connector when detached from the sensor (ignition switch in "ON" position) means a connection or the fuse (which would affect all the analog gauges, BTW) is bad. The voltage will drop when connected to the sensor, but it should not go to ZERO, unless the sensor is bad (shorted).

Hope this helps,

P.
_______________________

(1) FSM, Ch 8, pp 8A-80-0

[John Boothby]

Since you changed the sensor, it could be a bad one. Chances are though, the connection is bad. Common when working under the plenum and the secondary plumbing. Ask me how I know?

[Jetjock]

While this isn't the first time that I have changed the sensor, this is the first time that the analog gauge stopped working. The connector itself distegrated in my hands while I was trying to put it back on. It's entirely possible that the connector fell off the new sensor. The analog gauge doesn't show anything; it just sits at the middle of the gauge and doesn't move. I'm thinking that it could have shorted out to ground or something happened to the gauge. Don't know at this point but the other sensor has a much better connector to it. New sensors all round. We have to pull the plenum again which is no big deal to put in new spark plug wires. Didn't have them the first time.

[Paul Workman]

While this isn't the first time that I have changed the sensor, this is the first time that the analog gauge stopped working. The connector itself distegrated in my hands while I was trying to put it back on. It's entirely possible that the connector fell off the new sensor. The analog gauge doesn't show anything; it just sits at the middle of the gauge and doesn't move. I'm thinking that it could have shorted out to ground or something happened to the gauge. Don't know at this point but the other sensor has a much better connector to it. New sensors all round. We have to pull the plenum again which is no big deal to put in new spark plug wires. Didn't have them the first time.

OOOOOoooh! You are having too much fun! This thread makes me chuckle. NO, I'm not laughing at you, but memories are still so fresh! I see I'm not the only one that can open a can o' worms!

Good luck!

P.

[Jetjock]

The LT5 motor that I am working on isn't my car. It belongs to a guy that decided to buy it and doesn't know anything about the car. He did something that he shouldn't have and it stopped running. So I helped him out by replacing the starter, coil packs, spark plugs, injectors and coolant hoses. The motor had been worked on before and various things moved around so it got interesting. The engine started right up and we checked the coolant. Then a couple of things happened. The analog gauge did not work and the service engine soon light came on. The digital temp was only reading 203 degrees at the time. There could be one or two items for that but I checked the codes before and nothing came up. He wants to put new plug wires in which is okay by me but time consuming. The Z hasn't had a lot of attention in the past five years so these things keep cropping up. The car is a 92 and a dark red color of which only 17 were made. It has multiple issues with clutch, brakes, headlight motors, etc.

[Paul Workman]

The LT5 motor that I am working on isn't my car. It belongs to a guy that decided to buy it and doesn't know anything about the car. He did something that he shouldn't have and it stopped running. So I helped him out by replacing the starter, coil packs, spark plugs, injectors and coolant hoses. The motor had been worked on before and various things moved around so it got interesting. The engine started right up and we checked the coolant. Then a couple of things happened. The analog gauge did not work and the service engine soon light came on. The digital temp was only reading 203 degrees at the time. There could be one or two items for that but I checked the codes before and nothing came up. He wants to put new plug wires in which is okay by me but time consuming. The Z hasn't had a lot of attention in the past five years so these things keep cropping up. The car is a 92 and a dark red color of which only 17 were made. It has multiple issues with clutch, brakes, headlight motors, etc.

Well, Good you could be of assistance. The Brotherhood is the best source of assistance to keep these babies in top shape. Good luck!!

P.

[Jetjock]

Well, the analog gauge doesn't work and I suspect that it became disconnected somehow. The codes show a H44 in the ECM which is a left O2 sensor fault. Started up the car and no service engine soon light on and the fan came on at 227 degrees. Took it out for a spin and the brakes started getting real hot. When we brought it back to the house, Carlos said that it acted like the emergency brake on on. Both the calipers on both front brakes were smoking as well as the brake pads. Got a small amount of coolant laying under the injector housing. Fix the analog gauge, put in new plug wires and check the underside of the plenum and see if we can locate the leakage.