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Back in the saddle again
Join Date: Oct 2001
Location: Central TX west of Houston
Posts: 56,267
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goofy Voltage question for you EE's and engine management specialists
This seems silly to me, until I started to think about it at which point I wasn't sure and now I have to ask.
Would too much voltage (ie Voltage Reg went out and was seeing 17 Volts) cause a DME car to run different. I just replaced my VR and now the car hums along at 13.5-14 volts. I know it seems silly, but it feels like it runs better. My first thought was the butt dyno was being fooled by the emotional dyno, but as I thought about it I surmised that it could make a difference since the dme is designed to run at a certain voltage, and since several sensors are designed to return a referernce voltage. My assumption is that if the cyl head temp, O2, etc... sensors are basically variable resistors then a higher input voltage will result in a higher output voltage which will result in an engine that is being fed and ignited as if it was operating under different conditions. OK, so you EE types and amatuer engineers let me know if my theory is sound or plausible. (I still think me feeling a difference is bunk, and I am thinking there's a difference because I am happy  that she's running right again.)
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Steve '08 Boxster RS60 Spyder #0099/1960 - never named a car before, but this is Charlotte. '88 targa  SOLD 2004 - gone but not forgotten
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02-04-2003, 08:38 PM
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PRO Motorsports
Join Date: Nov 2001
Location: Burbank, CA
Posts: 4,580
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Yep, it can definitely make a difference, for all the reasons you stated.
Also, if the alternator is charging at 17 volts, it is causing significantly more drag on the engine. Many people have reported that their car ran better after replacing the battery. I suspect this is because the alternator was working hard trying to charge a weak battery, so that caused a parasitic power loss from driving the straining alternator.
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'69 911E coupe' RSR clone-in-progress (retired 911-Spec racer) '72 911T Targa MFI 2.4E spec(Formerly "Scruffy") 2004 GT3 |
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02-04-2003, 10:10 PM
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Back in the saddle again
Join Date: Oct 2001
Location: Central TX west of Houston
Posts: 56,267
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cool, thx
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Steve '08 Boxster RS60 Spyder #0099/1960 - never named a car before, but this is Charlotte. '88 targa SOLD 2004 - gone but not forgotten
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02-05-2003, 06:03 AM
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Registered
Join Date: Aug 2002
Location: Dana Point, CA
Posts: 855
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To be honest, I'm not sure about the DME in our cars, but having some past experience with Engine Control Modules, I don't think the high voltage would effect the sensor readings.
The sensors are typically supplied a 5 volt reference voltage from the DME, not from the ignition voltage. As long as the ignition voltage supplied to the DME is within range then the 5 volt reference will not be affected. If the sensor is referenced from the ignition voltage, the DME will compensate for the voltage shift based on it's reading of the voltage.
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John 86 Coupe - Sold Macan GTS Ducati Multistrada |
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02-05-2003, 06:50 AM
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