92RS_Ttop

iTrader: (3)

First things first: 1-yes I searched and 2-this is probably going to be long and I appreciate any help you guys can give me.

I just swapped a carbed 350 into my 92 RS, replacing the V6 that was there. Everything was working great until I went to drive the car to get it inspected. On the way there, I noticed the temp gauge was barely moving. While driving, it didn't rise past 100. After 5 minutes sitting in construction, it went up like it normally would to 220. I turned the fan on(manual switch) and it stayed there till I pulled out and then went back down to the line between 100 and 220. On the way home and ever since, I have gotten NO readings from the temp gauge at all. It will not move off of 100.

I figured I cooked the sensor as the engine did get quite hot while breaking it in(260) because I had the timing WAY off. I checked the resistance of the sensor and I'm getting the proper ohm readings as near as I can tell. At an ambient temp of around 75-80* I get 1465ohms, and after a 20 minute test drive, I got 297 ohms which tells me the sensor should be working ok.

I should also mention I tried this with the original 6 sensor as well as one I pulled from an 87 formula at the junkyard. They both read roughly the same. The V8 one is in the head between #6 & #8 and the V6 one is in the intake manifold.

I bought a new fan switch at Advance and tested it in a pot of boiling water. Cold is 1865ohms, boiling was 98ohms. I know its a fan switch, not a CTS, but I was planning on using it to control the fan if my manual switch fails. When I connected the gauge to it and warmed up the engine, I still get no movement on the gauge.

I figured its the gauge, its a used V8 gauge cluster that I never tested previously. I swap my V6 cluster back in which was working fine when I parked the car for the swap last fall. I get nothing from that gauge either.

I thought maybe it was the DK GRN wire that connects to the sensor in the engine bay as I did shorten it after I swapped the engine. I cut it and soldered the ends together and shrink-wrapped it so I should have a good connection.

Here is the part that I don't get:

Both gauges will max out when grounded, and I am reading perfect continuity between the CTS connector in the engine bay and the appropriate gauge contact in the dash cluster connector. I am also getting the correct ohm reading at the cluster when the sensors are connected.

I tried removing the actual gauge from the V6 cluster, and connected it directly to the sensor, battery, and ground and I still get no reading from either sensor.

I'm about ready to just slap a mechanical gauge in it and be done with it, but I REALLY don't want to do that.

If you're still with me and have any ideas, I'd love to hear them.

John in RI

iTrader: (167)

After all you have done already this will sound stupid - but ge sure that the terminal end on teh Gark Green Wife is not corroded and is making good contact with teh sensor mounted in the drivers side head. It's possible that simple crud is not allowing a good connection.

If both gauges ( while tested in different clusters ) is operational when tested independantly than you need to figure out why the signal is getting lost between the sensor to the gauge.

92RS_Ttop

iTrader: (3)

I cleaned the connector on the sensor with 400 grit sandpaper and the one on the wire is in good shape. I've also tested the gauge by removing it from the cluster and connecting it directly to the sensor, power, and ground and I still get no reading on the gauge. Maybe the resistance in the gauges is too high? Any idea what the resistance of the gauge itself should be?

BigBadLou

iTrader: (3)

Good troubleshooting. I wish more users did a search like you and educate themselves on the matter before posting "help - my car don't work".

It does sound like the gauge is not right.
You can get a 100ohm resistor and put it between the green wire and the block. The gauge should read pretty hot (235F). You can put three 100ohm resistors in there (forming resistance of 300ohms) and the gauge should read around operating temp - 180F.

Also, when you tried grounding the gauges, did you have them outside of the dash, on a workbench etc? You could potentially have a ground issue between the gauges and the engine, effectively throwing off the gauge reading. I'd measure the voltage between the block and the cluster ground. With key on. You're looking for 0V.

Let us know what you find, I am curious now.
Lou

92RS_Ttop

iTrader: (3)

Thanks. I try to do as much on my own as I can, posting on here is a last resort.

I do plan to try the resistor(s), I just haven't been able to find the appropriate ones yet. When I removed the gauge, I removed it from the dash cluster and held it in my hand in the engine bay while connecting separate wires to power, ground, and the sensor. I would get a very slight movement of the needle, just like while it was in the dash. Its not even enough to move it off of the 100 mark. When I connect just the power and ground wires, the needle moves the whole way over to where 260 would be if the gauge were still in the dash.

Yesterday, I took the dash back apart to install the mechanical gauges so I can drive the car while I work on this. While I had it apart, I checked the temp signal connection again, and I'm getting almost the same ohm reading at the cluster connector as I am at the sensor when I heat it up with a lighter. I used the original v6 sensor for the test so it wasn't in the block at the time. I tested it with the gauge connected then and still got no reading. I thought, "Ok, maybe its a bad connection between the cluster and the connector in the dash," so I removed the connector and tried bending the pins out for better contact. They were not corroded or had any other signs of anything that would give a bad connection. I put the cluster back in and still no reading.

I'll check for voltage on the cluster ground tonight after work, I didn't think of that.

John in RI

iTrader: (167)

Not knowing how the gauge was tested - I'm guessing it's the Printed circuit.

Here is what the 91 Shop manual shows as steps for diagnosing,..........





The temp sensor pin on the back of the clusters pinted circuit is on plug C1 Pin #4 ( bottom middle, Dark Green wire ) The gauge should read 100F@1365 OHMS & 260F@55 OHMS



I'm curious as to hear the resolution too !

92RS_Ttop

iTrader: (3)

Yep, thats basically the same procedure outlined in my 92 shop manual. I checked continuity on the printed board(that's being generous to call that sheet of plastic a "board" but anyhow) and everything checks out like it should. Power, ground, and signal are good on the board. Ground and signal seem to be good on the connector in the dash. I just realized I haven't checked power on that connector yet. I assumed it was good because the other gauges are working fine, but maybe I'm not getting good voltage on it. I'll have to check that tonight as well.

BigBadLou

iTrader: (3)

Since you tested the gauge out of the cluster, with "fresh" ground, power and signal, I would really start suspecting the gauge now.
However, you said you tried two separate gauges with the same result.
If you had a way of borrowing/getting another gauge that you know works, that would tell you for sure.

Lou

92RS_Ttop

iTrader: (3)

Yeah, I was thinking of doing that too. Having tried 2 gauges and 2 senders with the same result is what is getting to me too. I will mention that the V8 gauge is an unknown quantity. I purchased a 92 V8 cluster from a member here mostly for the tach for my engine swap, and just put the whole cluster in instead of messing with swapping the tach over. He said that all the gauges worked fine and I have no reason not to believe him, but as I haven't seen it work flawlessly for myself, I can't say with 100% certainty that it is good. The other gauge I used is the original V6 gauge that was in the car and worked fine for the year I Owned the car before the engine swap.

IIRC, the V6 gauge is the one I removed from the cluster and tested in the engine bay. I can't remember for sure if I did that with the V8 gauge as well or not.

As for getting another gauge, there is a U-Pull near me that has an 84 Camaro in it that still had the dash intact the last time I was there, but I'm not sure when I'll be able to get there again. It's a different gauge of course, but I would assume it works on the same basic principles.

92RS_Ttop

iTrader: (3)

I got a chance to test some of the suggestions tonight, here is what I found:

Voltage to cluster is good, within .05 of battery voltage.

No voltage between cluster ground and the block.

I used some resistors I had laying around to test the gauge. I had to solder a couple different value ones together to get close to the proper values.

44 Ohm - gauge reads 260
100 Ohm - gauge reads a little over 220
1300 Ohm - no reading(needle stays below 100)
744 Ohm - no reading(needle stays below 100)

IIRC, according to the shop manual, 100 degrees is at 1365 Ohms, 220 degrees is at 697 Ohm, and 260 is at 55 Ohms.

Resistors were connected to the sensor wire in the engine bay and held to a good ground. The gauge does peg out when the wire is grounded. These tests were done with the V8 gauge installed in the dash. I was gonna try the same tests with the V6 gauge, but I must have messed it up when removed it from the cluster as it doesn't read anything now, even when the sensor wire is grounded or during the self test when the key is turned to "Start".

BigBadLou

iTrader: (3)

At 744 ohms, it should have been reading around 140.
It is probably safe to conclude that the gauge is imprecise in the lower range. They do wear out eventually.
Sorry to hear that your other gauge is completely dead.

Let us know if a new gauge solves your problem!
Lou

92RS_Ttop

iTrader: (3)

Yeah, when the 744 gave me nothing, I figured the gauge was toast. It sux, but it happens. I did put a mechanical gauge in so I can drive the car for now. Next time I hit the JY I'll pull a gauge and hook it up to test it but won't be able to leave it in unless I get lucky and find a 90-92 Camaro. Most of the JY's around here have Camaros from the earlier 80's. I do want to make sure thats the problem though. I eventually want to switch over to an all digital setup like Dakota Digital or Nordskog offers and I'll make sure I get the right sensors to match.

I'll probably be a little while till I find a gauge to test it with, but I'll make sure I post up my results when I do.

Thanks for the help!