presslab Posted September 25, 2011 Share Posted September 25, 2011 I have an 88 GL10 with the digidash. It works fine, except the temperature gauge has been acting up. The temp gauge works fine until I load down the electrical system with headlights, interior fan, etc., and then it shoots up into the red. When I turn off the load, it jumps back down to normal. This points to a grounding issue, but I've checked the engine grounds and even added another fat ground cable so I don't think the engine ground is the problem. Has anyone else tackled this problem? I suspect it's some ground in the dash. I have the 88 XT diagram, but the wiring is different. If someone could scan the FSM wiring diagram page for the instrument cluster wiring/grounds that would be great! Link to comment Share on other sites More sharing options...
nipper Posted September 25, 2011 Share Posted September 25, 2011 I have had this ( i miss the his gauge set). The way things are wired a weak alt can cause this, so check your alt output and battery. Low output can look the same as lower voltage flow (higher resisitance = higher temp) and give false readings. Link to comment Share on other sites More sharing options...
presslab Posted September 25, 2011 Author Share Posted September 25, 2011 I have had this ( i miss the his gauge set). The way things are wired a weak alt can cause this, so check your alt output and battery. Low output can look the same as lower voltage flow (higher resisitance = higher temp) and give false readings. Thanks nipper. Yeah I thought alternator too, and it had some AC ripple. Not a lot but some, voltage was ok. So I thought what the heck and I did GD's 90 amp Maxima alternator upgrade, and the digidash problem remained the same, but now I have a 90 amp alternator. Link to comment Share on other sites More sharing options...
nipper Posted September 25, 2011 Share Posted September 25, 2011 Well lets check one more thing, whats the output at 1800 rpm with everything on? Check all your grounds. How freely does your electric fan move? Is this change instant with a change in electrical load? Link to comment Share on other sites More sharing options...
presslab Posted September 26, 2011 Author Share Posted September 26, 2011 Well lets check one more thing, whats the output at 1800 rpm with everything on? Check all your grounds. How freely does your electric fan move? Is this change instant with a change in electrical load? The alternator at 1800 RPM is 14.12 V. The electric radiator fan is easy to spin by hand, and it does come on when it's hot out and idling with the AC on, like I would expect. I see this gauge issue even when the radiator fan is not on. The engine grounds seem pretty good, I checked/cleaned them before and added another for good measure. Where is the ground for the digidash located? The digidash display change is not "instant" but there is some delay in the digidash. But it doesn't slowly move down: The gauge will be in the red, I turn off the loads, and then after a couple seconds the gauge will jump from red to the middle. Link to comment Share on other sites More sharing options...
nipper Posted September 26, 2011 Share Posted September 26, 2011 EEk did not realize it was in the red. Your car is old enough that the radiator may be decrepid. Check all the cooling fins between behind the AC and see what condition they are in. How old is the radiator cap (or have we been through all this already ) Link to comment Share on other sites More sharing options...
presslab Posted September 26, 2011 Author Share Posted September 26, 2011 EEk did not realize it was in the red. Your car is old enough that the radiator may be decrepid. Check all the cooling fins between behind the AC and see what condition they are in. How old is the radiator cap (or have we been through all this already ) Well the gauge is in the red, but it's not really overheating. The IR thermometer on the top rad hose shows 180F, so that's fine. I don't see how the engine could really go from in the red overheating temperature back to normal in two seconds either, just sitting in my driveway idling... And the gauge reading is directly related to the electrical loads. The radiator and cap are about 5 years old. Link to comment Share on other sites More sharing options...
nipper Posted September 26, 2011 Share Posted September 26, 2011 that leaves the gauge set Link to comment Share on other sites More sharing options...
presslab Posted September 26, 2011 Author Share Posted September 26, 2011 I still think it's a ground issue, or something related to electrical noise. The current from the headlamps doesn't flow through the insturment cluster so I don't see how it could be something inside it that's bad. I've even taken it apart and replaced the electrolytic caps, to no effect. I have the '88 XT diagram, and it looks like there is a different ground path for the temp sensor. Unfortunately the connectors are different than mine, so I don't know which ground wire is used. If anyone could scan the instrument panel wiring diagram for my '88 GL10 I would really appreciate it! Link to comment Share on other sites More sharing options...
naru Posted September 26, 2011 Share Posted September 26, 2011 If yours is similar to ea-81s(probably),dash,headlights and fan share a ground point under the dash.Common problem. Confirm poor grounding by putting a voltmeter between the dash ground and battery negative w/fan and lights on.Any significant voltage indicates a poor ground.Repair by cleaning the ground attachment or running a dedicated ground wire to the battery. Link to comment Share on other sites More sharing options...
presslab Posted September 27, 2011 Author Share Posted September 27, 2011 I measured from body ground to the large black wire going into the digidash, and it measured 0.07 V regardless of what was turned on. Hmm. Next I will test from the black wire to battery ground and the black wire to the thermostat housing, but I ran out of daylight tonight. I also need to find the actual ground screw for the digidash. No need for a wiring diagram, I found one. A curious difference between the '88 XT and my '88 GL-10: The XT has a dedicated ground for the temp sensor that connects to engine ground - a brown wire. My GL-10 does not have a dedicated ground wire, it uses the two black wires for everything. Hmm. Link to comment Share on other sites More sharing options...
nipper Posted September 27, 2011 Share Posted September 27, 2011 There is no such thing as haing too many grounds. ON a car that old I usually just add a ground as part of maint on an older car from the engine to the battery. Link to comment Share on other sites More sharing options...
presslab Posted September 28, 2011 Author Share Posted September 28, 2011 Well the two black ground wires going to the digidash aren't the same ground. One of them (the larger wire) has the constant 0.07 V regardless of loads, and the other smaller wire changes from 0.005 V to 0.1 V when I turn on the headlights. I checked the ground to body connections in the dash I could find and they were fine. So I decided to just add another fatty ground wire to the body on the smaller black wire. This seems to have solved the headlight related problem; on/off has no noticable effect on the gauge! The gauge still changes one notch when I turn on the interior fan, but it's not near as bad now. I might attach the other black wire to my new fatty ground wire to see if that fixes the slight fan problem. Link to comment Share on other sites More sharing options...
nipper Posted September 28, 2011 Share Posted September 28, 2011 Well the two black ground wires going to the digidash aren't the same ground. One of them (the larger wire) has the constant 0.07 V regardless of loads, and the other smaller wire changes from 0.005 V to 0.1 V when I turn on the headlights. I checked the ground to body connections in the dash I could find and they were fine. So I decided to just add another fatty ground wire to the body on the smaller black wire. This seems to have solved the headlight related problem; on/off has no noticable effect on the gauge! The gauge still changes one notch when I turn on the interior fan, but it's not near as bad now. I might attach the other black wire to my new fatty ground wire to see if that fixes the slight fan problem. Mine woulod change one notch too, but that is better then running in the red! Link to comment Share on other sites More sharing options...
Cougar Posted September 28, 2011 Share Posted September 28, 2011 My '88 GL-10 did the exact same thing with the temperature gauge as yours is doing. I hope you are cleaning the ground connections you are checking using a small wire brush along with some sort of cleaning solvent and not just looking at them. This would assure a good solid low resistance connection. Adding a #12 gauge wire from the dash to the negative battery terminal may help reduce the remaining voltage drop to ground you are seeing. Link to comment Share on other sites More sharing options...
presslab Posted September 30, 2011 Author Share Posted September 30, 2011 I hope you are cleaning the ground connections you are checking using a small wire brush along with some sort of cleaning solvent and not just looking at them. Oh yeah, I am cleaning the connections and putting some silicone grease down before I put it back together. Link to comment Share on other sites More sharing options...
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