Problems with MTX-L Accuracy (Complicated)
 

I have a DIYPNP in 99 miata. THE MTX-L was calibrated two weeks ago and the analog out is connected to the power ground at the megasquirt. The ground run is maybe 2-3 feet. It is powered from the cig lighter. I was told by diyautotune not to wire it to the sensor ground(SG) because it does not support enough current.

Prior to installing the megasquirt, I was running the MTX-L with the stock ecu and everything looked in sync with the mtx-L gauge. When idling or crusing, afr would be 15ish (from memory), but WOT would go down into 11s. When lifting between shifts it would go very lean.

Had car dyno tuned last week and when I left the shop, the MTX-L GAUGE was reading very lean (like 15afr on a wot pull) and of course the dyno sheet had the afr at <13. They used a tail sniffer.

Since then I pretty much decided to work on my own tune, but the MTX-L has got some problems. Even wired as above, the AFR signal in TS jumps around alot (pic). Sometimes +/-.5 lamda. So I don't really know what the afr is.

To get TS to be in sync with what I see on the gauge, I have to use a custom value of .40v for 7.35. (Which is higher than usual .25-.28)

When I do a WOT pull, I watch the gauge and see it is around 12.8-13 (good). This appears to be in sync with what TS is showing on the dial, but when I bring it up in log viewer, the points logged in the logfile do not show what I saw on the gauge, during pull, they are .5 or more lower (In the pic, the gauge was reading 12.7-12.8 on wot pull, but log is showing lower on average.)

I talked to innovate and they said that the gauge reading is an averaging to make it readable, and what is important is the output...



So I have no idea what is accurate. Questions:


Does the MTX-L usually jump around this much?

Could the cars afr REALLY be jumping around this much (maybe bad injector) and it didnt show on the dyno because of smoothing?

Does a tail sniffer usually read richer than afr gauge?

When choosing the custom value to sync TS with MTX-L, do you "eyeball" it? Do you try to get the gauge to match the average of what you see in TS or the peaks?

Wait.


Why are you not grounding wideband to same place as ECU, again?

It is grounded at the same place.

https://www.miataturbo.net/attachmen...ine=1410401550

This is my MTX-L reading 13.8+/-.1, and what comes across in logs.

I tried powering the MTX-L through the DIYPNP 12V supply, using the same ground. My logs looked like yours, super noisy. Now mine is set up on a relay, power and ground directly from the battery.

The offset is really common, you need to use a custom wideband profile to sync the MTX-L and TS. I used LM programmer and set a fixed output across a few different values to average mine out.

Thanks. What are you using the relay for?

Edit: I suppose you are using it for switching? The MTx should be powered by 12v that is on when key, battery is always on. I got it... Only on when keyed signal is hot.

Removing possible misinformation

Most people just ground it at the main ECU ground at the ECU harness and never have issues... running a ground wire all the way out to the engine bay is silly.

IIRC the main grounds are blk/yellow and not at that point.

Blk/red and Blk/blue at the TB are the sensor ground points.

since the MTXL has the sensor and power grounds tied together, i suggest you use main grounds, not sensor grounds. and as close to the ECU as you can.

I first ran it to the engine bay throttle body and was having noise, so I tapped the power ground at the ecu and am still having noise.

Only thing I havenet tried is relay and direct batt connect. Wondering if gauge is bad?

+/- .5 AFR swings are normal. I'm leaning towards there's no actual issue.

tail sniffers are always lean by almost exactly 1 AFR, especially when after a cat; and they apply a lot of smoothing to the signal.

the LC/2/MTXL are very precise and very fast reporting. you can add lag factor to your AFR input and make it so the signal looks dead flat on logs.

Thanks. Now I understand why some did not like the MTX-L design.

Thanks again. I suppose the gauge is accurate so I should endeavor to get my logs the same as the gauge.

typically the .22-.25v = 7.35 and 5v = 22.4 calibration does the job.

Thanks. After smoothing I was able to get the gauge in sync with log.