AEM wideband connected to Xcal2

[SHOgoFast]

I recently got my AEM wideband prepared to be connected to an Xcal2. I used the 9pin mini din connector and spliced it onto the output from the wideband. So far so good. I grouned the din cable to chassis, but have the wideband itself grouned with the same wires that ground my EL Glow gauges.

Now, with the key on, engine off, the wideband pegs lean, as it should. I measure the voltage coming off the Male end of the din cable and only get 2.35V, if I apply that to the suggested formula of (v*2)+10, I get 14.7.

My assumption is that the voltage with the gauge showing ultra lean should be more like 3.5V which would yield a 17.0 result after running through the formula.

What gives? Should I have the gauge itself grounded to chassis too? And do you really think it will make a dramatic difference? Or, is 2.35V in this situation normal.

 

[Ray]

Voltage drop, or reference voltage between the two grounding locations is CRITICAL for optimal operation of a guage.

Check out SCTs forums for WAY more info..

below is a grab from one thread on Ground offsets:

Ground offsets come from ground currents. If you use the battery negative terminal as the absolute ground, you will find that you can in many cases measure a voltage from other ground points to that absolute ground. Most notorious is the engine itself. As the alternator is grounded to the engine typically, the charge current from the alternator makes the engine block to be at a higher voltage than the battery negative. Most ECUs therefore are grounded at the engine block, not the battery or frame because most engine sensors are grounded also to the engine and therefore "see" the engine block as the reference ground.
Better dataloggers and ECUs use "differential" inputs. This means that each input has both a + and a - terminal. The datalogger measures sensor voltage not between its input and its ground, but between + and - terminal. This ways you can connect the - input to the sensor ground and the datalogger "sees" the same ground reference as the sensor. A datalogger/ECU with a single ended input (no - input per channel), does measure only the input voltage referenced to its internal ground, independent of what ground reference the measured sensor used. This causes ground offsets.
If your datalogger has only a single ended input, you want to ground the LC-1's System ground and Analog ground to the datalogger ground. This is to ensure that both use the same ground reference.
You can connect the heater ground still to the frame.

If your datalogger has a differential input, you can connect all the LC-1 grounds together to a frame ground. Connect the dataloggers - input (its ground reference input) also to that same ground point because it needs to read the ground the sensor "sees".

Regards,
Klaus

Just make sure your heater ground is seperate and your other grounds (analog, etc) are all together at the same point.

Here is a thread posing some of your same questions.
This is where I got that quote above.

 

[SHOgoFast]

Ray, Thanks for the input.

You are right there is a ton of info in their forums. However, it is almost solely related to innovate products...i even did a search for AEM and got zero results. My AEM unit does not have an individual ground for the heater. I have 4 wires to work with...

1. Red, power, connected to 12v source
2. Black, ground, currently sharing a ground with my EL glow gauges
3. White, analog 0-5v out, connected to 9 pin din cable for use with xcal2
4. Blue, serial output, Not used.

I also have the gound FROM the 9 pin din cable itself grounded to the chassis. My concern is with the grounds of the AEM unit and of the 9 pin cable...can they share a ground and if so, can they share with OTHER electronics or should they get their own somewhere. Also, would grounding somewhere beneath the dash be sufficient or should I run some wire all the way to the block.

Lastly, am I running into a grounding loop by grounding the 9 pin cable since the xcal is grounded itself when connected to the OBD terminal?