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voltage gauge inaccurate

ehall

ehall

NAXJA Member
NAXJA Member
Location
Southern Maryland
my voltage gauge is off by about half a volt, just enough to make it look bad when it it isn't

inaccurate voltage gauge is a long established, well known problem with these vehicles so I'm wondering if anybody has figured out a way to correct this
 
sure would be nice to know what wiring harness your jeep has. usually you can figure that out by what year it was made.
 
My '93 auto/4.0 has the same problem. have not addressed it yet... too much other stuff on the list to do first.
 
I don't see a problem with a half volt error. All the gauge is good for anyway is to tell you if something changes. If you know what it reads when things are working right, you don't need the number on the dial to be exact. If you're just a stickler for proper numbers, I think you'll have to get another gauge, and wire it directly to the battery terminals. Even if you find a way to reroute the source for the built-in gauge, there's no guarantee it will be correct. It's a cheap meter, calibrated with a glued-on weight.

e.t.a. By the way, you can recalibrate the voltmeter if you really care to, at least on the 95 I did. When I got a replacement cluster for my 95, the voltmeter was pinned to max, and when I opened it up I found the weight had fallen off. Take it out and apart, and you'll find that there's a little weight/magnetic mass glued to the needle mechanism. The position of the weight relative to the fulcrum determines the accuracy. If you have an accurate power supply, preferably set at 14 volts, you can reposition it. I think I used Shoe Goo on mine, to give a little fine tuning option before it set. I wouldn't bother with this ordinarily if the gauge is functional, but if you feel like tweaking, there it is....
 
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You could disconnect it from the spot where it's linked into the harness (right at the back of the IP iirc) and run a wire direct to the battery. I note a 1 volt drop when I turn on my vent blower and another 1 volt with the headlights on, mostly due to harness voltage drops. This shouldn't be an issue anymore on 97-up vehicles because the voltage is measured internal to the ECU and the value sent to the IP via CCD bus messages.
 
Sorry for forgetting, it's a 91. The gauge is off by half a volt at cold idle but drops more when the system is loaded up so that is what I'm concerned about (both electric fans, headlights, etc., and it is down at the 11.5 volt hash mark.

I like the idea of running direct wire. Maybe when I run wires for the switches I'll tap into that. I should try reading voltage at other places first I guess.
 
Matthew Currie said:
I don't see a problem with a half volt error. All the gauge is good for anyway is to tell you if something changes. If you know what it reads when things are working right, you don't need the number on the dial to be exact. If you're just a stickler for proper numbers, I think you'll have to get another gauge, and wire it directly to the battery terminals. Even if you find a way to reroute the source for the built-in gauge, there's no guarantee it will be correct. It's a cheap meter, calibrated with a glued-on weight.

e.t.a. By the way, you can recalibrate the voltmeter if you really care to, at least on the 95 I did. When I got a replacement cluster for my 95, the voltmeter was pinned to max, and when I opened it up I found the weight had fallen off. Take it out and apart, and you'll find that there's a little weight/magnetic mass glued to the needle mechanism. The position of the weight relative to the fulcrum determines the accuracy. If you have an accurate power supply, preferably set at 14 volts, you can reposition it. I think I used Shoe Goo on mine, to give a little fine tuning option before it set. I wouldn't bother with this ordinarily if the gauge is functional, but if you feel like tweaking, there it is....
Click to expand...

This is what I was looking for. I'm going to take the dash apart again for a bunch of queued up electrical items and will tackle this then.

Thanks
 
I was having MUCH greater variances in mine (reading 9v and charging at 13.9v) a while ago and looked into running the signal wire from the starter relay (Renix era) B+ battery lug. I found another jeeper who had done it and asked how well it had worked. Upon hearing his views on the repair/upgrade, I decided an aftermarket gauge driven by the cigar lighter circuit was a better option.

I'll copy-n-paste his response for clarity:

Hey Shorty,

You caught me at an idle moment, so I'll give you a quick reply.

First of all, I bagged the idea long ago (I still need to edit out the modification from my site) because after testing several factory gauges I discovered that no two gave the same reading. Very disappointing, ESPECIALLY because the markings on gauge are vague and nebulous to begin with. Its only slightly more useful than an Idiot light! So I deemed that it wasn't worth the effort and stopped promoting the idea.

However it is a good idea even though I DO say so myself! There was also another problem for me as the author, there are quite a few variations in instrument cluster layout and circuitry thorough the models and years, so it was difficult for me to be sure I was giving the right information for the proper Jeep.

So it's pretty much up to you if you want to bother with the mod, I'll explain the basic principal and you should be able to tackle it if you have a sense of printed circuit board (PCB) layout and can follow traces, AND if you still feel up to it after hearing my thoughts and seeing for yourself what's involved.

Study the front and back of the instrument cluster. Notice that for each of the smaller gauges there are two studs with nuts that pass though the PCB, that serve as the securing point, and the circuit connection for the gauge. Now locate the Voltmeter and study where the traces go. You will notice that the Voltmeter and the nearest instrument lights, all share one the the Voltmeter's connection points. This trace is ground, you will leave it intact. Now study the other connection, Notice that it is shared by the Oil pressure gauge. It will be the 12vdc trace, you will want to isolate the voltmeter from this trace, without disconnecting the Oil pressure gauge. Here is where you either cut the trace and delicately remove the coating from the source side and the Oil pressure gauge side and solder a jumper to them, OR, (I haven't tried this) enlarge the hole in the PCB and fabricate an insulator (plastic or rubber) to isolate the Voltmeter stud from the PCB. Now you'll have to fugure out how to route a new wire from the isolated Voltmeter connection to the new source, through a relay to disconnect it when the ignition is off. You can add a manual switch to bypass the relay if you are interested in monitoring the battery when the engine is off. This is a handy feature and it isn't likely to run you battery down if you forget it turn it off, unless you leave it on when the Jeep isn't in use for an extended time.

Personally, I recommend installing an aftermarket solution if you are really interested in accuracy. I just have a Radio Shack indoor/outdoor thermometer with a digital voltmeter function that I have set up to monitor different points of my electrical system with a selector switch. This setup is also wire with a manual switch. I have enclosed a photo of it to give an idea of placement. In this shot it happens to be monitoring my accessory output which was loaded down by an inverter. I didn't really take the photo to show the voltmeter, I took it show the odometer! A picture is worth 300,000 words! Need I say more?

Well Shorty, there you have it. Let me know if you decide to pull it off and how it goes. For that meter, let me know no mater what you decide. You have the (dubious?) honor of being the one who finally got me to put this down in text sp I can now take the description portion of this email and put it on my site (whenever I manage get around to that!) for those who aren't willing to velcro a Radio Shack thermometer/voltmeter to their instrument cluster.

Good luck and best regards,

Craig
 
P.S. aftermarket gauge installed into the panel where the lighter was installed reads 13V-14V all day long and I still have the dash voltmeter screaming 9V-10V half the time and 12V-13V the other times.
 
THe gauge inaccuracy in the renix models is usually because of the voltage drop as you start adding more current to the crappy factory grounds. If you add some grounds in the cab and then tie those back into a better ground to the battery the gauge will sort itself out. It all has to do with the voltage potential across the entire circuit, and the fact that AMC couldn't wire a vehicle for crap..
 
87manche said:
THe gauge inaccuracy in the renix models is usually because of the voltage drop as you start adding more current to the crappy factory grounds. If you add some grounds in the cab and then tie those back into a better ground to the battery the gauge will sort itself out. It all has to do with the voltage potential across the entire circuit, and the fact that AMC couldn't wire a vehicle for crap..
Click to expand...

absolutely is the case!! It just turned out that I've not had any problems with any of the other accessories since the change. I'm all for adding ancillary (auxiliary-- not sure which) grounds to correct operation, but once I heard the gauges were closer to an "idiot light with a pointer" I decided to wait for the next reason to add grounds:clap:

P.S. this is all after adding two 2ga ground straps between the battery and the chassis and another between the engine and the firewall. I know I would benefit from cleaning and tieing all the dash/body grounds together in a common location that has a straight path to the battery, but I dont' have any problems with other electrical circuits.
 
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Joe that is one great write-up. I bookmarked that page. I'm always frustrated on the Jeep electrical system. Last night with my boat in tow running the A/C and sitting at a stop light the lights would dim and voltage would drop. Looks like my 96 needs some wiring.
 
Yeah, they really over-engineered the electrical--headlights, HVAC, blower motor, ignition switch, all of those circuits are problematic.

Good luck.
 
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