ICVR Diagnostic
 

Hello Fellow Enthusiasts.

Like many others, my dash board gauges are misbehaving. I've got plenty of time on my hand so I hooked up a voltmeter to the back of my instrument cluster to see what's happening.

Wiring diagrams seems simple enough. Voltage comes in one way, flows throught the gauges, gets resisted by the sending unit and finally reaches the ground on the other side.

When I checked out the voltage at the fuel gauge terminal , I figured I would get a steady 5 or 6 volts. But I didn't. I got a regular heartbeat. However the voltage on each beat was fluctuating, anywhere from 6V to 10V. I got the same reading at the oil pressure gauge.

Could someone confirm that this is either normal or abnormal?

Thanks.

-Pauli

The IVR should maintain an average pulsating voltage of 5.0 volts at the gauge terminals.
The Fuel Sender will have a 10 ohms reading for a full tank and a 70 ohms empty.

The above is from the Ford shop manual.

If they are all reading high or low, then it usually is the IVR. It is a fairly primitive way of doing things, but the gauges are so slow, they average out the voltage. It works somewhat like a turnsignal flasher, and the heating element inside does a pretty good job in compensating for the voltage fluctuations in the elec system.

The heating element also does a good job compensating for the ambient temperature also. It takes a scope to read the output of the IPVR. It averages ~5 volts tho. The most common problem with the regulator is it looses it's ground connection intermittently and all the gages peg when it does. Usually all that is required is cleaning the contact surface under the tab, smearing on a little silicone dielectric grease and screwing the tab back down. I usually put an internal tooth lockwasher under the screw but due to plastic creep it will come loose in another 10-20 years anyway.:)

Thanks Fellas.

Both the gauges and sending units check out perfect. A new voltage regulator it is!

-Pauli