MSefi.com read only forum (Jan.15,2018)

Does anybody know what the voltage / lambda settings are if you use the default settings for the LC1 wideband controller in Tuner Studio? For some reason. The default set-up for the wideband output on the LC1 controller is 0 volts - lambda = 0.5 and 5 volts - lambda = 1.523. I am thinking that Tuner Studio is using 0 volts - lambda = 0.5 and 5 volts - lambda 1.5. Does anybody know for sure?

The reason I ask is that under steady state conditions, I notice a slight skew between the AFRs as they show up on my dash AFR meter versus the display in Tuner Studio. I have confirmed that the two analog outputs in the LC1 are programmed the same and even switched the outputs between the gauge and Megasquirt and the bias remains (Tuner Studio always reporting a slightly richer AFR). The bias is not huge, in the 0.2-0.3 range and is variable (larger for lean AFRs and smaller for rich AFRs. I am wondering whether the default slope in Tuner studio is out slightly. If not, it could be a problem with my analog gauge

First, check where the MS and the LC1 are grounded.

Absolutely everything is grounded at a common point on the engine intake manifold - so no offsets.

I fixed the problem. I used the custom wideband with linear curve in Tuner Studio with 0 volts - 7.35 AFR and 5 volts - 22.38 AFR. The dash gauge and the AFR display in Tuner Studio now read essentially the same value. Of course, now all my Ve values are a little bit off and I am running more EGO correction than before!

142 guy wrote:Absolutely everything is grounded at a common point on the engine intake manifold - so no offsets.

The common signal ground point should be the MS.

trakkies wrote:

142 guy wrote:Absolutely everything is grounded at a common point on the engine intake manifold - so no offsets.

The common signal ground point should be the MS.

What do you mean the MS is the grounding point? The megamanual is pretty clear that the various ground points on the MS 37 pin connector are brought out to an external common ground point. The common ground is where the LC1 is grounded.

The sensor grounds and the power grounds should all meet at the MS. Not the engine block. If you unplug MS, the sensors should no longer be grounded.

trakkies wrote:The sensor grounds and the power grounds should all meet at the MS. Not the engine block. If you unplug MS, the sensors should no longer be grounded.

Dave is correct of course! Here is a link to the schematic for the v3 board in the MegaManual. Note that all sensor grounds return to the board via pin 19.

Thus, Dave's point applies! That is: "If you unplug MS, the sensors should no longer be grounded."

My experience is that, proper grounding is essential for proper operation!

Not intending to be critical of course, but merely reinforcing the importance of proper grounding.

Ken

No criticism taken. B Sc in Electrical Engineering so I am well aware of the effect of offsets that can arise from ground loops.

The LC1 controller has two separate grounds, the heater and the system ground. Because of the large(r) DC currents and the potential for unnecessary DC offsets, the heater is not grounded through the MS 37 pin connector (as per the B&G diagram). The controller power supply and signal out share a common ground. That LC1 controller ground could be grounded through the 37 pin connector which would eliminate any offsets that might be occurring in the ground connection between the MS ground plane and the common ground on the block. The only problem is that for calibration purposes, Innovate wants the heater ground and the controller ground separated to eliminate offsets but brought to a common grounds point.

Since the LC1 is usually calibrated with the MS turned off, perhaps grounding the controller ground through one of the MS 37 pin connector might work out. As long as the MS is turned off and there are no currents flowing through any of the MS grounds (other than the LC1 controller), it should be possible to do a correct calibration of the LC1.

Grounding the LC1 controller through the 37 pin connector would address any offsets that might be occurring in the ground connection between MS and the common ground on the block; however, I will now also have to ground the dash AFR gauge through the 37 pin connector. Other wise any DC offset in the ground between the MS chassis and the engine block will now just end up in the dash AFR meter. As long as I don't create a problem with the sensor calibration, grounding the LC1 and the gauge through the 37 pin connector would represent a best practise.

Before I do that, I might just connect my scope between the MS internal ground plane and the external ground to see if I am getting enough of a DC offset to explain the different AFR values that I was getting.

THAT's what had me confused about the LC-1 - I thought they had one common ground, but it's two grounds wired to the same point. Call me crazy (so many do! ), but that seems to me to defeat the purpose of two ground wires.

My thought would be to wire it up in the tried and tested MS way - signal ground to the MS, power ground to the block or head. If the WBO2 is calibrated with everything else off, there are (should be) no extraneous current flows causing voltage offsets, giving the same effect as having it wired to the same point, but giving better performance once everything is powered up and running.

I decided to go and measure any potential offsets between the internal ground on the MS (pin 19) and the ground connection that I was using for my LC1. Connecting my scope between the two ground points and with the car idling, there is no measureable DC offset between the two points. The only thing that does show up is a recurring pulse of less than 0.04 volts magnitude associated with the opening current for the injectors. Clearly, any the consistent offset between what MS and my dash gauge are displaying for AFR based upon the signal they are getting from the LC1 is not due to a ground offset between the internal ground of the MS and the external ground point on the intake manifold.

I am running fuel only without an idle control valve. I plan to implement spark control; but, will either use integrated coils with their own drivers or mount the drivers externally from MS on an external heat sink. I see no up side to introducing the nasty coil primary currents into the environment of the MS box. I also plan to implement an idle control valve which may introduce some additional current into the MS ground path. At that point I might rewire the LC1 sensor ground into the MS internal ground as a best practise. For now, I will leave the LC1 sensor ground connected as per Innovate's instructions.

It occurs to me that the offset could be due to a calibration error in the analog dash gauge. Perhaps I will hook up my DVM to the signal line from the LC1 and see if the dash gauge display jives with the DC signal voltage from the LC1. If there is a calibration error, that would be a pain since I don't think the Innovate analog gauge provision for calibration.