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That Guy
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Can anyone a good uninstalled oil pressure sender check something for me?
If you happen to have a known good oil pressure sender laying around, i would appreciate if someone can check the resistance between both posts and the threaded portion of the sender. Both posts should read very little resistance when grounded to the thread or engine block, less than 1 ohm i think.
I installed a new FAE aftermarket sender which i believe i may have narrowed down to it being my problem. I feel it reads higher than the actual oil pressure and need someone to verify something for me. If i measure the resistance for the gauge wire post to a ground point on the engine block i get around 18.8 ohms (this is with the car off). This is why i am getting 1 bar oil pressure with the engine off and key in. If i do the same with the low pressure warning light wire, i get something like 1 ohm. Which is correct, the light comes on when grounded. I have a feeling the sender i have is giving extra resistance for some reason when the engine is off, and when the car is on, and i do have oil pressure, does not drop below 4 bar. So basically its always giving more resistance than actual. I tested this theory with my bad sender which was pegging the gauge.. warning light shows very little resistance (around 1 ohm) between post and threaded portion, and shows infinite resistance between the gauge post and the threaded portion. Infinite resistance will peg the gauge. I have ruled out the gauge as if i ground the wire directly to the engine block i get 0 bar with the key in and engine off. It also tested out with the variable potentiometer. So before i have Lindsey send me a new sender, id just like to verify and make sure im right! This all stems back this problem i was having.. Oil pressure sender / gauge..collective wisdom needed
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Jon 1988 Granite Green 911 3.4L 2005 Arctic Silver 996 GT3 Past worth mentioning - 1987 924S, 1987 944, 1988 944T with 5.7L LS1 |
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01-15-2008, 12:31 PM
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Politically Incorrect
Join Date: Aug 2005
Location: Hoover, Alabama
Posts: 1,497
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Note: The sender is supposed to be installed without any pipe thread sealant or tape. The aluminum gasket makes the seal.
The VDO sender is supposed to be 10-180 ohms for a 0-5 BAR gauge. The gauge should read 1 bar at 29.6 ohms and zero bar at 10 ohms. If you truly have zero oil pressure and get 18.8 ohms, the sender is bad.
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Edek '87 924S '91 535i |
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01-15-2008, 04:47 PM
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Registered
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I'm not at home right now or I would check it for you. Do you have a known good sender on your other car or have access to another sender? If so, swap and see what happens. If you need to try another sender, I'll call home and have it sent to you.
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Tom 1990 944S2 Cabriolet 2002 Chevy Silverado 2500HD 2003 Maroon Ford F350 dually |
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01-15-2008, 06:25 PM
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That Guy
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Edek, good point about the ohm range. I grounded the lead directly to the frame and got exactly 0 bar on the gauge. With the lead connected to the post, it reads 1 bar. This is all being done with the ignition on, but engine not running. I tested the resistance from from the low warning light post to the block and got something like .03 ohms. Im assuming it should be the same for the actual pressure level post when the engine is off.
Tom, im down to just one 944 now  , so cannot test it on another car. The old sender i have is shot for good. I can test my theory at work saturday, but was hoping someone would have one handy to test for me now. The suspense is killing me i guess you can say as im really curious to know what the problem is.
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Jon 1988 Granite Green 911 3.4L 2005 Arctic Silver 996 GT3 Past worth mentioning - 1987 924S, 1987 944, 1988 944T with 5.7L LS1 |
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01-15-2008, 06:38 PM
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Registered
Join Date: Jun 2007
Location: San Angelo, Texas
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I for sure would like to be in on the final answer. I am having problems with mine and ordered a new one, should get it in the mail in the next few days. Hopefuly that is the main problem with it, not something else!
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I Love the Smell of Jet Fuel in the Morning! 86 Silver Porsche 944 N/A - Alpine CDA-9857 KYB Front, Weltmeister 250lb springs, MSD Master Blaster Coil, K&N Cone Filter, Blue LED Dash, Clock and Defrost Upgrade http://www.c28.com/?adid=st&iid=25349 |
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01-17-2008, 05:17 PM
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That Guy
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Going to test my friends known good sender tomorrow afternoon. Emailed Lindsey Racing about exchanging it for a new one, just need to hear back now. Not looking forward to changing it again. Its not really hard, just a pain in the neck on a 951. So i will post what are mostly conclusive results then.
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Jon 1988 Granite Green 911 3.4L 2005 Arctic Silver 996 GT3 Past worth mentioning - 1987 924S, 1987 944, 1988 944T with 5.7L LS1 Last edited by Techno Duck; 01-17-2008 at 08:56 PM.. |
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01-17-2008, 05:34 PM
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Sorry Jon...I feel bad because you have helped me so much but I wasn't able to get you that reading. Hopefully I'll be home next time and can help you out.
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Tom 1990 944S2 Cabriolet 2002 Chevy Silverado 2500HD 2003 Maroon Ford F350 dually |
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01-17-2008, 08:49 PM
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That Guy
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Dont sweat it Tom, its not a big deal. Its just been bothering the heck out of me (these small issues always do). I should have my definitive answer tomorrow in determining if the new sender is defective and hopefully a new (non defective) sender by next weekend.
On the bright side i am basically a master of all issues regarding the operation of the oil pressure gauge and sender now .
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Jon 1988 Granite Green 911 3.4L 2005 Arctic Silver 996 GT3 Past worth mentioning - 1987 924S, 1987 944, 1988 944T with 5.7L LS1 |
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01-17-2008, 08:59 PM
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LOL...but it's so much easier when you don't have to learn the hard way.
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Tom 1990 944S2 Cabriolet 2002 Chevy Silverado 2500HD 2003 Maroon Ford F350 dually |
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01-17-2008, 09:00 PM
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Registered
Join Date: Jul 2007
Location: new york
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Jon, if you want i can bring my car to you and we can test it from mine.
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 1986 PORSCHE 951 3.0 project has begun!1989 IROC-Z(Show Car) 1961 Willys Jeep w/ 283 chevy(straight open headers) 1995 Dodge Ram 2500 HD 1981 Corvette 4spd |
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01-18-2008, 07:36 AM
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Join Date: Nov 2005
Location: CA
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Hi Techno Duck,
I am not good as measuring ohm so I can only tell my brand new one, have not installed, measured to be more than 10 ohms. Now I have a question, since I am about to do this replacement, could I ask if you can be able to replace it without droping yoru engine? Thanks.
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Fat butt 911, 1987 |
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05-11-2008, 08:34 PM
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Politically Incorrect
Join Date: Aug 2005
Location: Hoover, Alabama
Posts: 1,497
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Quote:
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Edek '87 924S '91 535i |
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05-12-2008, 04:59 AM
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Jon, did you ever get the resistance readings on a known good new oil pressure sender? I have doubts on my current sender because it is reading a lower oil pressure. If you have resistance readings, could you post it here. Thanks.
After checking the electrical schematics, found out the sender has two terminals. One terminal with a blue/white wire goes to the oil pressure gauge. The second terminal goes to the oil pressure indicator light. When you get resistance readings, put the meter probe on blue/white terminal and the other probe to ground or casing. My resistance reading at zero oil pressure is 60 ohms. I will pressurize the sender to 75 psi and get the resistance reading when i find the time today. edit: Pressurized the sender this morning with 75psi compressed air and got 70 ohms. Did you get the same readings?
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1993 964 C2 still makes me smile Retired and work as needed as a pain in the **s. Last edited by bazar01; 05-20-2008 at 04:41 AM.. |
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05-20-2008, 03:12 AM
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Politically Incorrect
Join Date: Aug 2005
Location: Hoover, Alabama
Posts: 1,497
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The VDO sender is supposed to be 10-180 ohms for a 0-5 BAR gauge. The gauge should read 29.6 ohms at 1 bar and 10 ohms at zero bar. These numbers are out of the FSM.
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Edek '87 924S '91 535i |
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05-20-2008, 12:10 PM
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Thanks Edek.
Tested the sender with the ignition ON and using compressed air. Here are voltage readings at blue/white wire to ground. air pressure/DC volts / instrument gauge reading 0 bar / 0.8 volts / 0 bar 2.5 bars / 2.5 volts / 2.0 bars 5.0 bars / 4.8 volts / 4.0 bars I ordered a new sender and will see how it compares to the old one.
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1993 964 C2 still makes me smile Retired and work as needed as a pain in the **s. Last edited by bazar01; 05-20-2008 at 12:46 PM.. |
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05-20-2008, 12:41 PM
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Politically Incorrect
Join Date: Aug 2005
Location: Hoover, Alabama
Posts: 1,497
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If there is a way you could bench test it to get resistance readings, that would be better. If the resistance readings resemble what the FSM shows, your sender is probably OK and you can now move to fining and fixing a wiring issue (i.e. dirty/corroded connection somewhere between the gauge and sender OR between the gauge and +12VDC power source).
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Edek '87 924S '91 535i |
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05-20-2008, 01:29 PM
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Bench tested the oil pressure sensor.
air pressure / resistance ohms 0 bar / 20.2 creeps up to 45 ohms 1 bar / 41.2 ohms 2 bars / 72.5 ohms 3 bars / 102.8 ohms 4 bars / 126.5 ohms 5 bars / 157.48 ohms 6 bars / 170.7 ohms If the FSM states 10-180 ohms for 0-5 bars oil pressure, it looks like my sensor has low resistance at 5 bars, and could be reason why the gauge is only showing 4.3 bars when started cold. A new sensor is on the way and will compare resistance readings.
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1993 964 C2 still makes me smile Retired and work as needed as a pain in the **s. |
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05-21-2008, 04:22 PM
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Registered
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New oil pressure sensor arrived!
Bench tested and here is the result.. air pressure / resistance ohms 0 bar / 9.4 1 bar / 64.0 ohms 2 bars / 85.3 ohms 3 bars / 112.2 ohms 4 bars / 139.4 ohms 5 bars / 168.9 ohms 6 bars / 178.3 ohms New sensor definitely giving higher resistance readings. I will install and post back if oil pressure readings go up to 5 bars cold. Set up of the calibration. 
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1993 964 C2 still makes me smile Retired and work as needed as a pain in the **s. |
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05-29-2008, 03:05 AM
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Registered
Join Date: Feb 2005
Location: Portland, OR
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This has been a really interesting thread to read! I just finished doing a oil cooler reseal on my 85.5 944 NA and i'm having trouble with the new sender unit.
When I finished the project and started the car the first two days, the oil pressure gauge rose nicely after engine start to 5 bars. As the car warmed up, the pressure settled at 4 bars (idle in my driveway). All is good. Today, I took the car out for the first drive after all the work and the gauge pegged above 5 bars. In fact, when i turned the key off, the needle stayed pegged until i tapped at the instrument cluster face and the needle dropped back down. All I can think is that the new Pelican-sourced FAE pressure sensor has somehow failed. I looked at the sender and both wires are attached just as they were when i finished the project. Any ideas? The last sender lasted all these years. Could I have got a dud? |
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05-31-2008, 03:58 PM
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The Kraut Burner
The Bratwurst Burner
Das Boost
911
