77 gauges to 82 eng sensor issue or ground issue

[Nditiz1]

Do I need to replace the temp and pressure senders in the 82 SC engine to allow the stock 77 gauges to work properly.

Currently the gauges peg to max when the key is on.
If I ground the pressure wire (removed from sender) the pressure gauge drops to 0
If I disconnect the 14 pin connector the temp gauge drops to 0, but the pressure still stays maxed.

Almost sounds like a bad ground. Wires aside, the main ground point for the engine is the trans strap correct or the engine mounts?

Maybe when I was in replacing the tach I jostled something loose on the temp/pressure gauge.

[Nditiz1]

The wonky pegging of the gauges might be the result of me forgetting to attach the big black wire to the starter. Standby...

[Flat6pac]

The 77 uses a 0 -10 atm pressure sender and gauge.
The SC uses a 0-5 atm sender and gauge
The temp sender went to a silver 911 sender in model year 77 replacing a 901 brass sender.
Go you have body ground off the transmission?
Bruce

[spuggy]

Originally Posted by Nditiz1

Do I need to replace the temp and pressure senders in the 82 SC engine to allow the stock 77 gauges to work properly.

Yes. Neither the pressure sender nor the temperature sensor in the SC are correct for the '77 numbered gauge.

'77 numbered oil pressure/temp gauge requires a 10 bar sender (SC and later, except 930, got a 5 bar) and the matched temperature sender (pre-74 cars, 930, 3.2 - but NOT SC). 74-76 oil temp gauge is 0-300 (0-340 was used on the '77) - and match the SC temp sender.

Originally Posted by Nditiz1

Currently the gauges peg to max when the key is on.
If I ground the pressure wire (removed from sender) the pressure gauge drops to 0
If I disconnect the 14 pin connector the temp gauge drops to 0, but the pressure still stays maxed.

You probably need to go through both wiring diagrams pin-by-pin and figure out which one(s) need to be moved.

And then check the diagram against reality - e.g. what you actually have connected/to where - in the harness. Fun, eh?

You may also want to double-check that things in the rear relay panel are connected where/how you expect; it supplies power to the CIS etc.

But the pressure gauge sounds like there's a wire not connected.

Originally Posted by Nditiz1

Almost sounds like a bad ground. Wires aside, the main ground point for the engine is the trans strap correct or the engine mounts?

Trans strap. They turn to green dust surprisingly quickly. The engine/trans mounts are electrically isolated I think..

Originally Posted by Nditiz1

Maybe when I was in replacing the tach I jostled something loose on the temp/pressure gauge.

Kinda sounds like it...

[spuggy]

Originally Posted by spuggy

You probably need to go through both wiring diagrams pin-by-pin and figure out which one(s) need to be moved.

And then check the diagram against reality - e.g. what you actually have connected/to where - in the harness. Fun, eh?

You may also want to double-check that things in the rear relay panel are connected where/how you expect; it supplies power to the CIS etc.

Oh, heh, nevermind - just saw your other thread.. Nice job on the diagrams!

[Walt Fricke]

From memory, only maybe three of the pins in the 14 pin connector need to be moved to do the 2.7 to 3.0 conversion. You can use the search function to find guys giving specifics, but you can also figure it out by having the wiring diagrams for both models easily enough.

If the oil pressure gauge or the oil tank level gauge pegs when you turn on the ignition to run, most likely there is a discontinuity in the gauge line between gauge and sender. Broken wire or connectors not together. Or the sensor itself is broken, though most likely a broken sensor will look OK to start, and then while the car is running will peg because of a break in the rheostatic winding in the sensor.

Good dope on matching gauge and sensor. I knew about the oil pressure deal, but not that there was a change (fairly small) in the oil temp sender (and then a switch back??? - maybe a supplier availability issue short term? VDO supplied all this stuff). The temp sender doesn't have moving parts, so tends not to fail the way the oil temp/level sensors eventually do.

[Nditiz1]

Thanks all. I ordered a matching temp sensor and found out that I had a leftover 0-10bar pressure sensor from the previous 914 engine. I also found out the wiring behind the cluster was mismatched. The green/white was going to the temp gauge, the green/red was going to the idiot light and the green/black was going to the pressure gauge. After getting all those wires sorted I turned it on and BAM! every gauge looking as it should. No more pegging.