Strange reaction of digital gauges on 1983 Monte Carlo

[rmorman]

Hello,
I have a 1983 Monte Carlo that I recently inherited. The previous owner had installed a set of digital gauges in a cluster where the ashtray would have been from the factory. There is an oil pressure, water temperature, and volt gauge. I recently noticed that when I turn on the blower fan, press the brake pedal, turn the radio on, or do ANYTHNG that causes the use of electricity, the water temp shows a jump of as much as 15 degrees immediately and stays there. As soon as I shut off the fan, or stop doing whatever I'm doing that spikes the gauge, it immediately returns to "normal." The oil pressure gauge will spike 4 lbs, but then returns to "Normal". I have isolated the Temp gauge 12 volt power away from the other two gauges, and even isolated the ground. I also cleaned both ends of the grounding cable from the battery to the alt bracket and even cleaned the positive battery cable. Any thoughts on what I can do to fix this? It does not matter if the engine is running or not, the reaction is the same.

Thanks,
Russ

 

[L92 OLDS]

Sounds like a power supply and or ground issue. Is your engine grounded to the chassis correctly? Where does the gauge power come from? Are the gauges a respected brand or china crap?

 

[rmorman]

Anubis,
I'm still betting on it being a grounding/electrical issue, but having trouble nailing it down. I was going through the paperwork I got with the car and found the paperwork for the gauges. They are Summit gauges. Part numbers SUM-G2984, SUM-G2983 & SUM-G2985. The power for the gauges comes from an ignition switched power in the fuse block. According to the installation instructions, that is how it is suppossed to be wired. I cleaned up the main gound cable between the battery and the alt bracket and I just cleaned the smaller strap that goes from the firewall to the back of the drivers side head. I didn't take that strap loose from the firewall as it still has the factory "coating" on it and didn't look like it was ever disturbed. I did take it loose from the head and cleaned the bolt, star washer and the cable. It still jumps the temp by 5 -7 deg when I turn the heater fan on and it jumps 5psi on the oil until I shut the fan off.

Thanks,
Russ

 

[rmorman]

Any other thoughts?

 

[rmorman]

I contacted Summit, and they suggested testing the battery and alternator. I had the ALternator/battery tested at O'Reilly's. The Alt tested fine, but they said the battery was toast. The battery is an Interstate, so I went to the Interstate store for a second opinion and to see about a replacement. They did a load test which indicated the battery weak. When the tech pulled some fluid, it showed that the battery just needed a charge. Which makes sense as the car has been sitting a lot the last 2 years. So, I trickle charged the battery for 16 hours. Results..... NO CHANGE. I'm really not liking these gauges.

Thoughts???

Russ