Oil Pressure Gauge....

[Jimmy914]

The previous owner of my 912E replaced the original gauge set, so I have a combination Temp./oil pressure gauge; however, unlike other Porsche VDO gauges that I've seen, the temp. and oil pressure gauges are split top and bottom, rather than side by side. I can NOT get this oil pressure gauge to work. Apparently the OP warning light and gauge both receive power from a single wire coming from the sender. The warning light works, but as soon as the gauge gets power, it just slams to the max, whether or not the motor is even running. A local Porsche expert has looked at this and determined there is something wrong with the OP gauge, and advised me to be looking for a used similar gauge, to at least put the guts in with my "white face" gauges. I can not find ANY trace of info on a VDO gauge of this type. Anybody know the origins of this gauge? Also, is there any reason the sender would just be incompatible with this gauge for some reason? My Porsche guy tried 2 or 3 types of senders, and couldn't get the gauge to function properly.

Jimmy,

These white faces are just after market ones, put on the original VDO instruments. They look to be a nice quality product. Basically, if one of the gauges from an instruments should be replaced, you simply replace the black face from the new gauge with the white one and put it in your available white faced housing.

But before replacing the gauges, I just want you to do some more tests. If the needle slams to the maximum, it tells me that the wire connecting to the sensor is grounded. If you are able to measure resistance (Ohm) with a multimeter, check the resistance, with the meter in a low range, from the wire connector at the instrument side to ground - disconnect it from the gauge. Basically you should read the resistance of the sensor, but I guess it will be something between 0 and 1 Ohm.

If your multimeter reads that low value, indicating a short, disconnect the wire from the OP sensor and repeat the measurement. Is the reading from the multimeter still at that nearly zero Ohm, the there is a short to grond in the wire. Is the reading a high value, also in the higher ranges, there is an open circuit and the wiring is correct. The sensor is shorted to ground.

If this test setup is to difficult, just use a separate wire to connect the gauge to the sensor. Of course disconnect the factory wire from the sensor to the gauge at bothe sides.

Could it be that you changed wires from the OP sensor?

Otto

[WFBowen]

Jimmy:
Here are a few points to consider with your situation. 1.) The OP warning light is activated by what is basically an on/off switch. When the pressure gets to a certain low level, it goes on; above and it goes off. Flickering at idle, etc., is merely this switch rapidly going on and off, as the pressure level is right at the switch's activation point.
The OP gauge you have appears to be for a 911/914-6 engine, which came with oil pressure gauges. The sender for these motors (and, most likely, your gauge) sends an ever-increasing signal, based on electrical resistance at the sender. Therefore, since they're basically two very different things (a switch vs. a progressive signal sending unit) I don't see how they could share a wire to a gauge(s.) It's basically like a home light switch vs. a progressive dimmer switch.

What you'll need to do is "Tee" off of the sender hole in the case, with two senders- 1 for the OP warning light and 1 for the progressive gauge. These hardware pieces are readily available thanks to the hot VW motor crowd.

Now. to add to the confusion, there are several sensors available for the Porsches - each calibrated to a specific VDO gauge insert unit. Finding the correct one might involve some numbers/markings on the back of your gauge module.

[Jimmy914]

Well, now I am definitely confused, but perhaps I can add even more to the confusion.... I haven't actually examined the back of this gauge, and I'm just going by what the Porsche shop told me, when they recently had the dash torn apart. The sender has connections for two separate wires, however there is only one wire going to the gauge; I have switched between the two connections on the sender and it makes no difference. Here's what I noticed when driving the car this afternoon: I turned on the ignition (without starting the car), OP warning light came on as it was supposed to, gauge did NOT move from zero (usually it goes to max as soon as the ignition comes on); started the car, warning light goes off, gauge goes to absolute max. I shut off the car, but leave the ignition on; gauge is still stuck at max, OP warning light is OFF. After thumping the gauge a bit, needle releases and goes to zero, warning light comes ON. So apparently, among other things, the gauge is sticking at far right, and as long as it is stuck there, the warning light will not come on, even if the motor is not running. So, this is telling me that the gauge and the warning light are somehow working off the same circuit.... am I correct? Like you said, WFBowen, I expected them to be connected separately. I did aircooled VW's for years, and anticipated a sender with two connections to be for separate warning light and OP gauge. However, from talking to the mechanic who worked on it, who is supposed to be a Porsche guru with decades of experience, he seemed to think the single wire was correct. Does any of this make any sense?

[Jimmy914]

Another question directed at Otto, with regard to these aftermarket white faces: After reading your post, am I correct in assuming that what I essentially have here is a 911 temp/OP gauge, but with an aftermarket face that rotates the gauge 90 degrees? That did not even occur to me. I found the receipt in the previous owner's records, and he apparently purchased these as a complete VDO gauge set, rather than just replacement faces. Can't remember what the date was on the receipt, but it was a while back, and they were quite expensive.

[WFBowen]

Jimmy:
Double check your wiring on the back of the gauge & if there's a 3-spade connector fitting, make sure they all are in the right place. Also, make sure that no one has jumped the warning light wire so it can go to the warning light and the gauge element at the same time.
Bill

Jimmy,

In general these white faces are after market parts, but if you have the receipt of the purchase of a complete set, I must be wrong in assuming that ALL white faces are after market products. With original VDO gauges it will be certain that the faces are fixed to the instrument by two little screws.

It's definitely not a 914/6 instrument The 914/6 had three warning lights in the combo-instrument. If I remember well, the parking brake light was the third one. Remember that the 914 only had a 3-instrument dash. The 914/4 has no oil temp gauge.

As WFBrown wrote - and I already suggested in my previous post - could it be that you changed wires at the sensor?

Do you have amultimeter available? Simply checking the resistance between each terminal seperately and ground will give you the answer if the sensor is faulty or not. With engine not running and cold, the terminal for the light should read very low resistance, theoretically zero. The terminal for the gauge should read a value in the hundreds range. Rund the engine and repeat the measurement. The terminal for the light should give a high/infinite value, an opened contact. The terminal for the instrument should give a lower value than during the measurement with a cold not running engine.

The sensor type depends on the instrument you use, not on the car. If you ahve the instrument type data available (receipt?) VDO could help you to determine what sensor you will need. I once had a gauge from the 70's and VDO - here in the Netherlands/Europe - could help me to find the correct sensor for it. Great service!

Otto

[Jimmy914]

OK, thanks for the help! I do have access to a multimeter, so I will get out there in the garage when I have a chance and see what I can find. I will also try to dig up that gauge receipt again and see if that tells me anything. Thanks!

[Jaems]

Otto is right the 914/6 had only three gauges The left was the Combo with the oil temp at the top and the fuel at the bottom, with four idiot lights. First one was the oil pressure , next the Alternator, oil temp light for the sportomatic if installed, and the last was the brake warning light.

The gauge looks like a converted 67 912 oil temp gauge. The other one to the left is the same gas gauge for a 67 912.

Thanks Jaems, I didn't remember the exact configuration ...

Otto