06-23-2007, 02:59 PM
Join Date: Apr 2006
Location: Kirkland, WA
Total Cats: 0
O2 Signal error
Ever since I installed my megasquirt, my Zeitronix display has always read lower than the Megasquirt. Last night I decided to track the issue down.
At first, I was pulling power and ground from the O2 heater. With this, the reading was WAY off. So I moved the ground to the megasquirt's ground. This got it close, but when it went to the lean end of the range, it got farther and farther off. Then I looked at the wiring and realized there was a sensor ground on the Zeitronix that I hadn't hooked up, so I hooked it up to the megasquirt, and moved the main ground back to the heated O2 circuit. This made no difference. Next, I moved both power and ground and sensor ground to the wires going into the MS. Again, no difference.
Next I opened the Zeitronix sensor include file, and compared it against Zeitronix specs. Other than extending the curve below 9.7 and above 21, the values were all right on.
So I opened MTConfig and set my wideband to "Unknown" so the gauge would display volts. Sure enough, when the wideband outputs 2.5v for stoich during sensor warmup, the megasquirt was reading 2.55v. The error got worse as the sensor warmed up and voltage increased.
This morning, I hooked up my multi-meter across the WB Signal and ground wires, and it read 2.50v, when the megasquirt was reading 2.55v.
So, it looks like there's something internal in the megasquirt that's skewing the O2 signal. Any ideas what it could be?
(PS- This is unrelated to my issue in my other thread about AFRs getting leaner with higher intake temps)