C1500 - V8 - 5.7L - 2WD - Gas Engine 95' GMC Burb'.. My volt gauge has been increasingly dropping to red. I removed the alterntor and it tested good, but replaced it. All fuses were good, but replaced. The battery is only 7 months old and tested good. There are no wires loose, burnt, disconnected, etc. The same thing happend to my Jeep a couple of years ago, so I rn it into a boulder on purpose. I really don,t want to damage ''MEAN GREEN'' , but I have eliminated all the obvious posbilities that I could see or do. PLEASE HELP!!! -- Katie
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Re: 1995 GMC Suburban Volt Gauge Dropped
Put a temporary voltmeter @ the battery....see what IT reads...If your charging system reads between 12.8 and 14.2 volts, with all of your acc's. on (headlites,wipers etc.) you don't need to drive into a boulder. Just get a new voltage gauge!!!!!!!
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The rough running is the cause of the voltage gauge movement.. As the engine speed increases and decreases the voltage output of the alternator goes up and down. So the gauge is a symptom not a problem.
All your gauges are working. The gas gauge Is also working. When you fill it, you will fill over the limit the fuel level switch will go by a couple of gallons. So the gauge will not drop for a few miles. until you use up the excess fuel
Buick dealers have a diagnostic box that checks gauge sweep and range, an 0-100 Ohm variable potentiometer with key on can check this gauge however you must tap into the wire going for the sending unit at the tank. With a voltage meter check the four wire connection (only one)connector going to the top of the tank, find a good ground and check for voltage one will be 12 volts with KEY ON ENGINE OFF look for a 12 volt reading for 5 seconds and then it will stop this is for priming fuel rail and is to fuel pump, you want the ground side of the gauge the other two will be grounds, fuel pump and gauge. The grounds may be near the wiring harness going to the frame. In either case they will be grounds you are looking for the one that is not either ground or power, most likely it will be either a flashing light or very low voltage. Attach the pot to the gauge wire and have someone watch the fuel gauge if it is erratic the gauge is the problem. If the gauge sweeps slow and steady the problem is in the sending until in the tank. AND HAS TO BE DROPPED! Run the tank down on fuel as low as you dare and drop tank. Be carefull working with fuel can be very DANGEROUS if you are not experienced working around fuel DON'T Attempt!
Volt gauge in Instrument Panel Cluster sounds bad, just off a little bit. Would have to replace IPC, through dealer. That can be a little expensive, if reads ok at
alternator, would not worry about it. May want to have checked with a alternator tester at a dealer to be sure. hope this helps.
Per your description, it sounds like you are missing an injector pulse from the ECM.
Check the under-hood fuse box and verify the "ECM1" fuse is good (12 volt supply to injectors).
With the key in the run position, verify you have 12 volts at an injector.
Barrow or purchase a "noid" light to verify you have an injector ground pulse from the ECM.
Let me know what you find and we can proceed from there.
This could be as simple as the needle is stuck on your gauge or the gauge may need to be replaced. Thousands of these in salvadge yards and not extremely expensive. First make sure you are getting a good connection between the gauge and rpm sending unit this is easily checked. I suggest getting a chilton or haynes manual for aroung $20 It will be well worth it if you have any other problems later. Also much cheaper than the $90 an hour for labor for a mech. Who it will ony take about 15 minutes to test this.
Sounds to me like you need to clean the battery post and the cables. Take off the batter cables and either take some sandpaper or a wire brush and clean the post and then do the same to the inside of the battery cables that comes in contact with the batter post.