oil pressure gauge

Tue 01 May 12 21:51

oil pressure gauge

The oil gauge is stuck on max all the time, with engine on or off.
Tried the first step off tapping glass on gauge but no success, its now past my expertise.
Hope someone can help Thanks Bob

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1978 silver anniversary edition.

Wed 02 May 12 16:58

Re: oil pressure gauge

If its reading off the scale with ignition on or off im guessing you have a stuck needle. If it happens only when the ignition is on the needle will peg out of you have no resistance i.e. earth the sensor lead (of the sensor to the block)

You will proberbly need to take the gauge out and check the needle hasnt stuck on the stop, quite a big job as you have to remove the whole cluster and deal with the flexi pcb (which may be the issue) getting the guage out the cluster is easy enough and while you are there you may as well give them all a clean up, but dont remove the gauge needle unless you know how to calibrate them, this can be time consuming and fiddling with lots of resistors to get the correct reading.

This is something i found a few yeas ago when i was re-calibrating mine:

Miscellaneous Information

1977 was the first year for the new center cluster and console that accepted a standard GM radio. The connections between the gauges and the wiring was through a flex circuit. It is prone to cracking and poor connections. New ones are available. The 77-80 had a very similar console. The gauges had white pointers after 77. 77 gauges are unique for this reason.
81-82 - Clock replaced with Oil Temperature Gauge. No change to flex circuit. New mounting plate. New bezel. Round opening for clock is now like the others. Bottom is flat. This console will not mount on a 77.
Calibration Resistors - Don't mix them up! They are color coded. The go in specific locations. They must be installed exactly as they were removed. Make sure you take pictures or notes if you remove the console to work on the gauges.
Resistors are year specific in some cases. For example, larger gas tank cars will have a different resistor on the fuel gauge.
Temperature Gauge

The sensor is a variable resistor. The outside case is grounded at the engine. The terminal goes to pin 20 on the PC board and on to the gauge. So you need to make a connection from the sensor case to the ground on the gauge for testing.

The Gauge has 4 posts but only 3 connect to the outside.

If you are looking at the face as it would be in installed in the dash, here are the connections:

12 o'clock - Should be Switched 12V - Flex circuit to Pink wire.

9 o'clock - Should be Ground - Flex circuit to Black wire on connector.

6 o'clock - Certain that it is the wire to sensor - Flex circuit to Dark Green wire on connector.

3 o'clock - is not connected to the flex circuit. It is used to calibrate the gauge. There's an external resistor that goes from this post to the post at 9 o'clock.

Calibration Resistors

All the gauges have a calibration resistor on the rear. It is below the flex circuit but can be seen though an opening. Your gauge should have come with one. It's a flat ceramic rectangle shape with some color. Orange, blue, green, etc. Changing the value of this resistor will move the gauge up and down it's range. Lower resistance moves it one way. Higher resistance moves it the other way.



Colors / Measured Values

Light Blue - 125 ohms
Green - 90 ohms
Dark Blue - 83 ohms
Red or Orange - 85 ohms
Yellow - ?
Pink - ?




Volt

The Light Blue (125 ohm) is used on the Volt gauge.
If you use something with less ohms, the voltage reads higher.
With a Green (90 ohm) resistor, the reading jumps to 18 volts from a normal 13.5V.

Water Temperature

Red (85 ohms) is used on the water temperature gauge.
Less ohms = lower reading
If you lower the resistor to about 40 ohms (testing) the reading will lower 25 - 40 degrees.
I have also seen Yellow on the temperature gauge in an original 1980 Vette. I don't know the value.

Oil Pressure

Dark Blue (83 ohms) is used on the oil gauge.
Oil - Less ohms = higher reading
If you lower the resistance to 40 ohms (test) the reading will jump from the normal 30 to 60
I have also seen Pink on the oil gauge in an original 1980 Vette. I don't know the values.

Gas Gauge

Green (90 ohms) is used on the 77 Gas Gauge.
Less ohms = lower reading
Green on a 77 with a 17 gallon tank causes the low fuel light to come on with slightly over 4 gallons in the tank and read full with a full tank.
If you put a Red (85 ohm) on this gauge, the low fuel light comes on at about 2 gallons but the gauge never reads completely full. Red might be the right one to use on the later C3's that
have the 24 gallon tank.



Water temp
Temp gauge was a little more tricky, i had to mackle up a few old resistors to make up the resistance to the required spec as follows,

220 degrees = 70 ohms
200 degrees = 90 ohms
160 degrees = 140 ohms
120 degrees = 250 ohms
100 degrees = 340 ohms

Last edited by wev on Wed 02 May 12 17:02; edited 1 time in total. [2 %]
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Corvette 1977 coupe
She LIVES
Now 383ci