Inconsistent guage readings in 1977 Cherokee

The regulator is stuck open... believe it or not, there's a bimetallic strip that opens/closes faster or slower, depending on the ambient temperature... the voltage looks like it's going crazy, but it's average is regulated over time. Either the contact is dirty, or something else is preventing it from shorting itself and cooling down, hence your lowered reference voltage to your instruments when the temp is high. __ Steve .

Steve,

Are you talking about the cluster voltage regulator (CVR) that fits down on two posts beside the temperature gauge? Doesn't it provide a constant 3.2 volts to the cluster gauges? If so, it is no longer available. The dealer (whom I know personally) can't get it anymore. NAPA no longer handles them for any make. Another local parts house does, but not for Jeep. The two or three they do carry looked like they might fit, if all gauges use the same voltage. A Jeep mechanic I know said I've lost the ground to the dash. Someone in another Jeep news group also thinks it's a ground problem. Anyway, my friend is going to be checking out a rear joint for me later this morning (I have no safe place to raise two wheels), and he can look at the gauge problem, too, if it doesn't get too hot for him. He has heart problems and a previous stroke.

That CVR would be a salvage yard item now, and I figure they would want to sell me the entire circuit board and cluster.

Dan

It's a good thing for you, it's not a Chrysler product of the same vintage. If you lost the ground to the dash on one of those, you would fry your fuel gauge. Ouch!

Before you do anything, try fixing the instrument panel ground. I have a policy with vehicles, of addressing the easiest to fix problem first. It is amazing how often this works.

If it turns out to be the regulator, and there is no replacement available, one is easily made with parts available from your local Radio Shack. Radio Shack has the books you will need, too. Before you get that far, perform a proper diagnosis using a voltmeter. It is essential to have the proper manual for your vehicle. Many public libraries have old Motors Manuals still on the shelves. These are the best, next to the factory service manual. Chilton's is not too bad. Haynes is economical.

Earle

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That's the one... and no, it's not constant, at least on the one's I've messed with... all the gauges it supplies are also based on the thermo-electric bimetallic, so they all are temperature-sensitive and should be supplied with a temperature-sensitive regulator.

Indeed a bummer... perhaps another could be made to fit, or you could repair the one you have by cleaning or replacing the contacts. The bimetallic strip shouldn't have failed, and the heater wire around the strip is probably OK too. If these parts are good, then try burnishing the contacts with a good tool... never use a matchbook striker for electrical contacts, it's emery and bad for them... likewise with an emery board. Look at GC-9337 and GC-9338 here:

I know. I do the same thing. One person thought it might be the ammeter starting to ground out, since the readings change when the motor is running (but they change if it sits in the hot sun all day, too).

I have the original AMC manual.

Dan

I'll check that page out. I've also been told I can get all the parts to make one at Radio Shack. I had already thought about that, but will have to check my service manual to determine the correct voltage output.

Dan

Dan,

The AMC manual should tell you the voltage at the terminals of the regulator, or the current draw, or both. It should, in fact, have a troubleshooting procedure. Then you take a multimeter to the terminals with the engine running, and see what's up. If the regulator is bad, you can try one of those aftermarket or other OEM regulators that was mentioned, and see if it is a better fit, electrically speaking.

As a last resort, you could buy or make a power supply to deliver the proper voltage and current. This seems like a lot of work, but with the original parts no longer available, it is better than non-working gauges, or a custom panel full of round aftermarket ones.

Earle

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Twice in the last three days, when I started my Jeep to leave work, the oil pressure gauge stayed on zero (not new-I have a bad connection on the 4-prong flat plug's orange wire that plugs into the circuit board ). However, both times the fuel and temperature gauges read accurately until the oil pressure gauge started working. Then, both of them dropped. Any possibility that the oil pressure gauge is loose, or something like that? I'm going to be working on this stuff tomorrow morning, and would like any other suggestions to check out. Of course, if it isn't something like that, I'm also going to check out the ammeter, too. Thanks.

Dan

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That's the rub... constant voltage won't do it, the bimetallic regulator compensates for temperature. Now if you use a circuit that varies the voltage with temperature, *that* might work... just plugging in a 7808 TO220 three-terminal regulator won't get you happiness, I'm betting... __ Steve .

On Tue, 30 Aug 2005 02:28:09 GMT, "Stephen Cowell" wrote:

Actually, the service manual (AMC) calls it a "Constant Voltage Regulator." Anyway, my career Jeep mechanic friend says they virtually never fail, that I have a ground problem. It stopped raining yesterday, so I pulled the panel out. I found a loose grounding lug and tightened it, and the oil pressure gauge was loose, so I tightened the nuts on it's mounting studs. I got proper readings when I started the Jeep, and also on the way to and from work today (but that's only six minutes each way). I especially got much better oil pressure readings. I know I'v had a bad sending unit for a couple of years. Every one I bought back then gave different, and erroneous, readings (both too high and too low) regardless of the source. The only one I've had that gave accurate readings was the one I got from the Jeep dealer (made in USA, not Mexico like all the others) and paid $70.00US for when I rebuilt the engine five years ago. It was damaged in the violently superhuman effort necessary to remove an oil filter improperly installed by the local Jiffy Lube. It was as though it had been installed using red loctite and an impact wrench. We finally removed it's remnants with a hammer and chisel, with the pump cover removed from the engine. The effort took over an hour. I've had to run a screwdriver through them before in order to turn them off, but nothing like that. Even with the can removed and the end cap bent upwards, it refused to come off. Any idea how they did it? Can a filter wrench get one THAT tight? Anyway, I'll probably buy another sending unit now, or try a couple I already have that I got from a salvage yard about a year ago.

Dan