Just purchased an exceptionally clean 1984 C4 with 42,000+ original miles. Well kept car. My 6th vette.

My issue is this. I was happily cruising home at 65 mph, turned on the a/c and shortly thereafter the oil pressure idiot light came on and the pressure was reading 8. (I just change the oil Sunday and knew I was topped off. Smog tested last week and the car came in way below average across the board.)

I reduced speed and the pressure went to 15, accelerated and it went back to 8. Shut off the a/c to reduce the load and pressure went to 35. Turned the a/c back on and down to 8 again. A/c back off pressure back to 35.

Now I know the a/c is in no way responsible mechanically for an oil pressure drop, so it must be a digital dash issue since the reading only drops with the a/c on.

Anyone with a clue to point me in the right direction?

Also according to the fuel mileage average readout I'm getting 21.9mpg, but the range readout is way off showing 80 miles left with half a tank of gas left.

I've read through the forum and am very impressed with your knowledge and courtesy.

Thanks

 

That sounds very odd. I'd check the oil pressure with a mechanical gauge just to be safe.

 

Check,
Battery age and condition?
Alternator output voltage?

 

Will do.

 

Battery ok, Alternator puts out 13.6

 

Condition of grounds?
I'm not worried about oil pressure. Of course a mechanical gauge is the only real confirmation.

 

While checking alternator output I discovered the oil pressure reading drops when the heater a/c control lever is in any position other than off and vent.

Thanks. I will follow-up after work today on grounds.

 

 

Glad to know that it's not more serious engine issues.

 

I discovered the same identical problem discussed on another vette site.
Thought it would be a wiring issue as several of you suggested.

http://www.corvetteactioncenter.com/...es-unique.html

Thanks again for your input and courtesy.