I have this unusual electical problem with my dash gauges. ('85) If I move my heater selector to any position except off (a/c, heat, vent or defrost), the oil pressure gauge reads real low, the engine temp reads about 15 degrees or so higher and the voltage reduces by at least one volt. Sometimes my average fuel mileage will cycle from 99 to 49 to 12.5 then back to normal. Moving the heater control back to off fixes it.

I disconnetced the connector to the a/c compressor and the problem still happened. Any other suggestions?

Thanks!

 

I had the EXACT same thing with my 85. Anytime the climate control was moved from "off" to any other position, the oil pressure dropped about 20 psi, the water temperature raised about 20 degrees and I lost about 1/4 tank of gas. As soon as the control was moved back to "off", the readings returned to normal. I never could find the problem, so I decided to live with it. Then one day about a month ago, I turned the air conditioning on and the dash, odometer, climate control fan, and windshield wipers all died. It wasn't the fuses, so I took it to the local GM dealer. After working on it for a day and a half, they found that ground G140 was bad. Not only was it bad where it connected, the wire had also chafed inside the wiring harness, causing it to be bad in two places! They replaced the wire and ALL of the problems were solved (but don't ask what it cost :eek: ). Since your symptoms are the same, this is where I would have them look first. It's a bad ground that will get worse. One thing that it didn't fix (I'm curious to see if this is happening to you, too) is that the heater won't warm up if the temperature control is moved from "cold" to "hot" while the car is running. Mine won't. But if you move the control from "cold" to "hot" while the car is off, it heats up just fine! These cars definitely have their quirks! Good luck! I hope this helps! :seeya

 

Thanks a bunch. I'll let you know what I find.

 

I forgot to address your heat issue... I had a similar problem and changed the heater valve piece under the hood in front of the a/c, just behind the right wheel well. It's a double metal tube. Not cheap either...

 

I'll have a look at the heater valve. If you changed it yourself, was it hard to do? I'm afraid I've got five thumbs on each hand! :)

 

I did change it myself and it was no biggie. Four hose clamps and a mounting bolt... (or two...) :smash:

I see that G140 is the ground behind the LH engine head. I had that off a year or so ago to clean it up and had a hard time tightening the bolt up afterwards. I hope I just didn't tighten it enough and can avoid pulling the dash!