It's fairly well known about our cars that the voltage readings seen on OBD2 gauges like the Aeroforce Interceptor are not accurate and can also be erratic. Here's a pic of my car running, showing a 0.7v difference between the Interceptor and the multimeter hooked to the battery.
Here's a short video showing how much it bounces around. It gets even worse once I'm driving and everything is hot, making the gauge nearly useless.
Here's a datalog of a WOT pull. The graph shows voltage dipping all the way down to 12.9v even though I know for a fact battery voltage never went below 14.4v.
I'm really curious to know where the ECU is reading this voltage from and if there's anything that can be done to fix it.
My solution was to connect one of the analog inputs on the Interceptor gauge directly to the battery. The only problem is, the analog inputs only read 0-5 volts, not 12. After measuring the internal resistance of the gauge, doing some math and trial and error, I found that a 100 KΩ resistor between the battery and gauge would make the gauge see 5v at around 17 volts from the battery which was perfect. Then a little more math and trial and error to program the slope and intercept into the gauge so it can display the proper values for voltage. It ended up being intercept: 0 and slope: 3.17 to match perfectly what my Fluke meter was reading.
Here's a shot with the engine off showing the Interceptor matching the Fluke at 13.2v. It's also accurate at 14.6 as seen in the above pics.
I drove the car for 2 hours today in some hot weather and the lowest voltage I saw was 14.4v and the numbers no longer bounce around like before.
Here's a WOT pull, the voltage barely moves.
I'm happy with the result.
Here's a short video showing how much it bounces around. It gets even worse once I'm driving and everything is hot, making the gauge nearly useless.
Here's a datalog of a WOT pull. The graph shows voltage dipping all the way down to 12.9v even though I know for a fact battery voltage never went below 14.4v.
I'm really curious to know where the ECU is reading this voltage from and if there's anything that can be done to fix it.
My solution was to connect one of the analog inputs on the Interceptor gauge directly to the battery. The only problem is, the analog inputs only read 0-5 volts, not 12. After measuring the internal resistance of the gauge, doing some math and trial and error, I found that a 100 KΩ resistor between the battery and gauge would make the gauge see 5v at around 17 volts from the battery which was perfect. Then a little more math and trial and error to program the slope and intercept into the gauge so it can display the proper values for voltage. It ended up being intercept: 0 and slope: 3.17 to match perfectly what my Fluke meter was reading.
Here's a shot with the engine off showing the Interceptor matching the Fluke at 13.2v. It's also accurate at 14.6 as seen in the above pics.
I drove the car for 2 hours today in some hot weather and the lowest voltage I saw was 14.4v and the numbers no longer bounce around like before.
Here's a WOT pull, the voltage barely moves.
I'm happy with the result.
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