spiderw31 Posted April 19, 2009 Report Share Posted April 19, 2009 During my lengthy top end job after t-belt failure, I though it'd be nice to swap the dummy oil pressure sender for a real one so that I'd have a functional gauge. The problem is that now the needle barely gets above the red zone. If I get the motor over 3k, it just barely makes it to the next mark above the red. Warm idle definitely puts the needle in the red. Now based on how quiet and well the thing runs, there's no way its actually running that low; the gauge has to be lying. So my question is this: other than swapping the dummy sender for a real one, what do I need to do in order to have a usable gauge? Quote Link to comment Share on other sites More sharing options...
Crazy K Posted April 19, 2009 Report Share Posted April 19, 2009 wait.. you have the proper LONG sender in there now and it says you have "low pressure"? Quote Link to comment Share on other sites More sharing options...
spiderw31 Posted April 19, 2009 Author Report Share Posted April 19, 2009 wait.. you have the proper LONG sender in there now and it says you have "low pressure"? Yep. The gauge does at least, but no idiot light or anything (although I've never checked to see if there is such a light ). Quote Link to comment Share on other sites More sharing options...
spiderw31 Posted April 19, 2009 Author Report Share Posted April 19, 2009 Just thought of something though... The "dummy" sender is basically just an on/off switch, right? If so, the gauge only read about 2/3 of the way up with that sender, which would tell me that is the absolute maximum value that the gauge could read. If thats correct, then wouldn't all the "real" readings be skewed substantially low, just like I'm seeing? Quote Link to comment Share on other sites More sharing options...
Crazy K Posted April 19, 2009 Report Share Posted April 19, 2009 CORRECT!!!!!!!!!!!!!!!!!!!!!! now... supposedly there is a resistor in the engine wiring harness that you can remove and it will allow you to get the right reading. I have never seen it, but TAYLOR says he has. and he says it is a foot or so up the wire from the sensor. I'm not sure how much the accuracy of your gauge will improve, however. Quote Link to comment Share on other sites More sharing options...
White93z34 Posted April 19, 2009 Report Share Posted April 19, 2009 I thought that was only on the later Cutlass' ?? by all rights the switch should make his gauge read maximum PSI all the time. the sender should tell what it actually has bad sender maybe? Quote Link to comment Share on other sites More sharing options...
spiderw31 Posted April 19, 2009 Author Report Share Posted April 19, 2009 by all rights the switch should make his gauge read maximum PSI all the time. That exactly what I'd expect, but the gauge would only read a constant 2/3 of the way up with the switch. now... supposedly there is a resistor in the engine wiring harness that you can remove and it will allow you to get the right reading. I have never seen it, but TAYLOR says he has. and he says it is a foot or so up the wire from the sensor. I'll take a look for that resistor and see what I find. Also, I discovered that the oil leak that I thought was coming from the back of the motor is actually coming from the area around the oil filter, so I wonder if the sender is not fully tightened. It seemed as though it was when I installed it , but maybe not. If that is leaking oil, I'm guessing that would also skew the reading as well? Quote Link to comment Share on other sites More sharing options...
Crazy K Posted April 20, 2009 Report Share Posted April 20, 2009 did you coat the threads with liquid teflon or equivalent? Quote Link to comment Share on other sites More sharing options...
spiderw31 Posted April 20, 2009 Author Report Share Posted April 20, 2009 IIRC, it had thread sealant on it out of the box, so I didn't put anything on it. Quote Link to comment Share on other sites More sharing options...
White93z34 Posted April 20, 2009 Report Share Posted April 20, 2009 I think there is some misinformation here.... IIRC the only cars that had the dummy gauge were certain year cutlass supremes a 92' GP with the Sport cluster should have the 1.5 inch or so long oil pressure sending unit. the switch is a tiny little thing that is just that. IF a switch were to be used on a car with the gauge, the gauge should read max PSI all the time. Also I believe if the sender is unplugged it will read max all the time Quote Link to comment Share on other sites More sharing options...
spiderw31 Posted April 20, 2009 Author Report Share Posted April 20, 2009 Well, I've got the full gauge cluster with all six gauges (mind you the oil pressure gauge is not marked numerically, but just "H" and "L"), and I definitely pulled a short "dummy" switch style sender unit off the car, and I've still got it. And as I mentioned, the gauge always read 2/3 with that old sender in. The new sender is twice as long, and now gives very low (but not constantly the same) readings. Quote Link to comment Share on other sites More sharing options...
tdvs Posted April 21, 2009 Report Share Posted April 21, 2009 I hope this gets resolved. I want to install an electric oil pressure gauge with numerical markings in my '95 Cutlass with the 3.4 which only has an idiot light now. I've asked a similar sender question, but I guess I'm dense cause I'm still not sure what to order when I go to GM. Then all I will have to do is figure out how to wire it Quote Link to comment Share on other sites More sharing options...
Crazy K Posted April 21, 2009 Report Share Posted April 21, 2009 I think there is some misinformation here.... IIRC the only cars that had the dummy gauge were certain year cutlass supremes a 92' GP with the Sport cluster should have the 1.5 inch or so long oil pressure sending unit. the switch is a tiny little thing that is just that. IF a switch were to be used on a car with the gauge, the gauge should read max PSI all the time. Also I believe if the sender is unplugged it will read max all the time I disagree. mid 92 is when the cars went from real to dummy gauges. early model 92 CSs even had values, but they were reduced to H and L mid-year, though the 3.4 cars didn't lose their "valued" clusters until much later [in the model year] than the 3.1 cars. on the Lumina, they completely discarded any use of an oil gauge sometime during the 92 model year and had voltmeters instead.... and just like with the CS... 3.1 cars lost it first, later followed by the 3.4 cars during the model year. Quote Link to comment Share on other sites More sharing options...
spiderw31 Posted April 21, 2009 Author Report Share Posted April 21, 2009 Well that would certainly explain it, as mine is a late '92. It was raining today. I'll probably have time to get out there on wednesday and reseal the sender threads and look for a resistor. I'll report back on what I find out. Quote Link to comment Share on other sites More sharing options...
Crazy K Posted April 21, 2009 Report Share Posted April 21, 2009 on my 92 vert... it has a "fake" oil gauge, but when I swapped the engine, I also swapped the wiring harness with it and the donor had a real guage. once hooked up, everything worked. So the sender and something in the underhood wiring harness is different... the "resistor" is NOT in the cluster. Quote Link to comment Share on other sites More sharing options...
White93z34 Posted April 21, 2009 Report Share Posted April 21, 2009 Fair enough. I did not know that. I believe my old euro has a real gauge (that was broken) I think my new z has a real gauge too, both 1992s. Quote Link to comment Share on other sites More sharing options...
spiderw31 Posted April 23, 2009 Author Report Share Posted April 23, 2009 *UPDATE* I found the resistor. It's less than a foot up the harness from the sensor, right after the spot where the the harness splits between the A/C compressor and the oil pressure sensor. The resistor is a couple inches long, encased in heat shrink tubing. It appears that it shunts from the sensor lead to ground, thereby lowering the voltage the gauge sees. Based on this hypothesis, I snipped one lead on the resistor, thus disconnecting it. I started the car and voila! Proper oil pressure gauge . So if you want to make your gauge functional, swap the switch for the real sender, and cut the resistor. On another note, my oil leak was DEFINITELY at the sender. I got some light under the car, and you could see the oil running out. Disassembled the ludicrous amount of parts required to get at the sender, and pulled it out. Not only was there no sealant on the threads, the sender was barely tight at all! Put sealant on the threads and made sure it was good and tight, and I'll put everything else back together later. Quote Link to comment Share on other sites More sharing options...
Crazy K Posted April 23, 2009 Report Share Posted April 23, 2009 good to know! Quote Link to comment Share on other sites More sharing options...
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