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DIACOM Shenanigans - Oil Pressure


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Something odd I noticed while running the new engine hooked up to the laptop:  My oil pressure on DIACOM registers exactly 20 PSI lower than what the dash/helm gauge shows.  Example at idle it may say 17 psi on DIACOM but the dash gauge says 37.  Can anyone think of a reason why this would be.  The sensor and gauge is obviously working but for it to always show exactly 20 PSI lower on DIACOM as it fluctuates with RPMs, seems odd.

I also noticed that the manifold temp always registers at -40 degrees in DIACOM.  However, I recently saw a post where someone uploaded a pic of their DIACOM stats and his read -40 as well.  Assuming that is a default and an irrelevant statistic. 

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@hawaiianstyln - I am not shocked that the readings do not match, I have noticed newer electronic gauge readouts tend not to have the accuracy I would expect (from speed to engine parameters), and Malibu's not having the best tolerance.  If it were mine, I would install a (temporary) mechanical gauge as a calibration tool, and simply using an air tank you can test your mechanical gauge for accuracy, kind of like using boiling water to check a temp gauge.  Typical for an iron SBC, idle oil pressure is closer to 20 than 40 psi (unless cold) and running tends to be 50 +/- a few.  Rule of thumb is to have 10 psi / 1000 RPM.   You an T it in where the current oil pressure sensor is located (probably near the distributor or by the oil filter).

Edited by Woodski
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On a side note, an oil pressure sensor is an analog sensor.  It’s output could be a number of different types and values.  The gauge then converts that signal to a pressure reading.  If you are going to read it with 2 different devices, you should also confirm they are both calibrated for the same reading or using the same conversion factor.

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@Footer613 @hawaiianstyln - Yep, my trusty ski partner / driver ordered the 'other' oil pressure sensor when I needed to replace one and guess what, its about 20 psi off.  Moral of the story, as you noted, different voltage to pressure signal sensors are floating around besides the electronic dash on a Malibu can be very inaccurate.  My buddy's RLX is off and with the current reliance on speed control and warning lights/codes, the importance of accurate gauges seems a lost art on the manufacturers.  

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