MTX-L gauge vs TS AFR
 

Fresh install of a rev built MS3 basic last night, it has a db37 wiring harness that has
BLACK/GREEN - Analogue sensor ground
BLACK/YELLOW - Ground / Heater Ground (LC-1 Wideband)

Well, when I hook the MTX-L gauge's ground up to the black/green it doesn't power up. when I hook the MTX-L gauge's ground to the BLACK/YELLOW it powers up, but then MS reads about .6ish AFR leaner than my gauge does.

I tried twisting the grounds together (black/yellow and black/green) and hooking the mtx-l ground to those twisted together is the same as hooking it to black/yellow.

Rev asked what WB i had and i assume he punched the numbers in, but just to be safe I got the voltages from the manual and punched them in to the calibrate AFR Table under Tools... exactly the same.

So, it seems like a grounding issue to me, but where the hell should I ground it if the ground built into the MS is giving me faulty readings? I suppose i *COULD* just calibrate around the problem... but that sounds like bandAIDS to me.

As an aside, i did not have this issue with the MS2E

EDITing so I don't spam: just found this post with both rev and brain weighing in, and it sounds like just adjusting the calibration is the way to go.

http://forum.miata.net/vb/showthread.php?t=435219

The simple fix is to figure out how far off it is and adjust your numbers in the cal table to make it match the gauge reading. I am using 6.4 for the low and 21.4 for the high. The other option is to have Reverent build you an input box and have the digital output from the gauge go to the box and then from the box to the MS3... then it will read exactly the same.

Keith

That's a bad fix because the offset changes with how much the heater needs to run to maintain temperature.

The correct fix is to ground the MTX-L at the other end of the MS3, at a power ground wire, close to the MS3 chassis. The error shrinks to about 0.1~0.2 AFR.

I helped my friend Ian troubleshoot this. I've emailed Reverant already. There are 2 causes of this:

1) Innovate combined the power and signal grounds into a single wire (stupid).

2) There is too much resistance from the DB37 power ground connection, to the point in the MS3 PCB where the signal ground and power ground meet. There is less resistance from the point I recommend connecting it. But there is still some, thus the 0.2 AFR error.

the voltage offset on our installs is almost always the exact same.

use the .22-.25v offset on your 7.35:1 calibration point.

Yeah, I ended up using 0.28 and it was 0.1 off from the gauge.

Was just weird, didn't happen with the other ms.

Thanks for your help (past and present) lol.

I have been struggle with this exact same issue for a while now (MTX-L and Reverant built MS3X). I also observe that the delta between the MTXL display and readings in TS from the MS3X varies. I have gotten it dialed in at times using the MTX-L settings or in TS by setting up a custom WBO calibration, only to find that the delta has drifted.

With issue #2, is the delta a constant 0.2 (AFR)? Or does it drift significantly?

My plan when I have the time is to utilize a Tiny I/O board to feed the digital signal to the MS3X over CANBUS. See TinyIOx v1.0 Board

Please us know what Reverant has to say.

It's hard to say, because i have to look back and forth between the gauge and the laptop, but it seems pretty constant at 0.2.

I also have it so that TunerStudio sees values slightly LEANER than the gauge does, that way when I VEAL I'll be adding 0.2afr worth of fuel, and not pulling it, so I'm erring on the side of being slightly rich instead of slightly lean.

I think that Reverents solution is the same as yours. He is making me an interface box to take the digital output from my MTX-L and feed it to the canbus of the MS3. It should be a direct "plug and play" solution :) Since I havn't done serious soldering since ETMS (advanced trouble shooting and repair school) in the NAVY 15 years ago I let him put my stuff together :D

Keith

Im using an mtxl and reverant ms3. Wideband is wired to the db37 connector and i have had to alter the wideband calibration numbers in TS to get them to match.

Where exactly are you running the ground for the mtxl to reduce the error? I know of a few grounds under the hood on my NA

Umm, read my 2nd sentence carefully.

Oh yeah gotcha, understand what your saying now. Im using a reverant ms3 that is pnp, no boomslang.

Which ground wire on the stock harness can i ground my mtxl on? Or does it need to be grounded inside the MS?

Power ground wire, close to the connector that plugs into the MS3.

So 2a or 2b? Here is a wiring diagram.

https://www.miataturbo.net/attachmen...chmentid=90579

And id be fine tapping into the stock wire on the stock connector that plugs into the ms3 correct?

Either one.
Yes, but within a few inches of the MS3.

Sounds like moving the ground is even more important on LC-2 as both the gauge and the MS3-Basic are using Analog signals. And, if I understand correctly, if I go to the digital conversion into the MS, then that is the reading I should trust, and correct the G5 gauge to match it. Still move the ground so the correction to the gauge is consistent.