Very rough signal from the wideband controller
 

Hello!

Once again I need your input on this. I've tracked down all the bugs from my ECU, my car is now almost perfectly tuned and running smoothly except for a small detail or two... I have to thank a lot of you guys (especially Braineack) for your input as you've been very helpful in tracking down all the problems I've had.

The Megasquirt sure has a steep learning curve initially, but it all makes perfect sense now ;)

However there is still a detail I haven't been able to figure out a solution to, and for that matter, I don't even know if this is normal.

I have an Innovate MTX-L wideband controller, and I've set it up nicely on the MS. The controller has worked fine for a long while and the measurements on the controller gauge are correct and accurate. However, the same doesn't happen on the Megasquirt. The input from the WB controller, despite being "correct" as an average signal, is not stable at all. In fact the signal constantly oscillates with a deviation of about +/- 1 AFR at a rate of about 5-6Hz maybe?

While this was not a problem for base tuning the car, it does become a problem now that I want to enable EGO corrections and log the AFR data for further fine-tuning.

Is this even an expected behaviour?

I've added a screenshot from MegaLogViewer that shows this problem (notice how the AFR keeps oscilating). Sadly I can't upload the whole log, it's several megabytes too big! :giggle:

looks normal.

So it should actually oscillate that much? It's sad I can't upload a video from the computer screen, but the AFR dial on TS is all over the place while running! Does seem a bit dramatic and errr... erratic?

If I'm tuning for a specific AFR of 14.7 for example, it doesn't help me much that the dial is just randomly pointing somewhere between 13.8 and 15.6... Can't I somehow minimize this effect?

MIght be some ground related noise.

MTX-L has a single ground wire. This should be connected to the ECU power ground pin.

I have, in fact I've even taken the work of welding that wire to one of the MS harness grounds.

Power ground and not signal ground?

What do you mean? There's only one ground in the wideband controller...

Or you mean the ECU grounds? I have no idea which is which to be honest.

Yes, the wiring harness should have a separate ground for the sensors that is only grounded through the ECU. Seeing that you have a '91 Miata, that probably is not the case:

http://www.boostedmiata.com/MS/harness_MS_pinouts.jpg

The second wires from the right, black with green stripes, should be the signal ground. However, in early miatas (at least in mine, which is a '91) the black/green wires were grounded to engine block from several spots. I ended up joining those wires with the black grounds and running new wires to the sensors to make a separate signal ground. This seemed to work pretty well in clearing the noise altough mine was never as bad as yours.

I must check that. Since I soldered the wb wire to the harness adapter, both ground wires were completely black.

So you're saying you've had a better signal than mine all along? That makes me pretty sure this isn't normal. I must re-check my wiring!

Thanks for your tips! :)

Yeah, my AFR signal actually never had such an oscillation, just checked from some old log files. It's worth a try though..

I'm really sorry to be a dumbass and resurrect this thread, but I need to fix this problem properly rather than continue to fudge my AFR target table.

I have:

1994 1.8
MSPNP Gen 2
Innovate MTX-L

When I first installed the MTX-L I followed what was common practice and ran the single ground wire to the ground location found underneath the throttle body.

Ever since I installled the MTX-L I've always had problems with the AFR figures not matching up to what I see in Tuner Studio and I'd like to fix it.

Now looking at this pin out diagram, what wire should I splice the MTX-L ground wire into?

2A
2B
2C
2D?

https://www.miataturbo.net/attachmen...ine=1346104034

I'd be seriously grateful if someone could give me a concrete answer and solve my AFR mismatch issues. BTW - massive thanks to whoever runs that Boostedmiata website. It's a great resource. :bowdown:

Bump. I'm sure someone must know the answer to the above question.

*

I would try and wire it to 2A. Ideally it must share the same chassis ground as the ECU!

2C or 2D since sensor ground is ground for the sensors, right?

this. And thanks, I made that diagram and run that site.

the LC-1 handled the grounds a bit better with the seperate heater and sensor grounds...but now that they tie together, I'd opt to put the Black wire of the MTX-L on 2A/2B.

The sensor grounds actually ground the sensors to the ECU, so there should be no voltage offset, if you tie things into that which need a chasis ground, it'll screw up all the sensor readings as it introduces an offset. Or something to that matter.

Or run it directly out on its own wire to the TB grounding screw.

Another option here is, what is your output set to on the controller to the megasquirt? In the advanced tab on the lc1 connect you should have a speed choice. It should be set 1/12 (or the 1/6th if you still have the jumping with 1/12) and not instant.

I don't think we have that for the MTX-L... Could check though!

And sorry its not lc1 connect its LM Programmer, and I just checked the manual for the mtx-l and you do have this.

Thanks for the feedback. I'll wire it into 2A and see what happens.

Just to let you guys know something. I had my wideband previously wired to the ground wire on my MS1 adapter cable. It still had a fair bit of noise, although much better than before. However the MTX-L resetting and failing to sync with the probe became a lot more frequent!

I unwired everything, but since I'm dyno testing my car tomorrow, I figured I'd wire the MTX-L back again temporarily. I wired it back like it was (+12V on IGN from radio and output 1 to the MS input)...

However, because I didn't want to take the protection plate from the footwell, I wired the ground to one of the plate retaining nuts. I figured I'd test it afterwards, and what do you know, the signal oscilations reduced even further!

So if wiring to 2A didn't solve it for you, I'd at least suggest you try this. It's effortless!


Attached are screenshots from the small log I took. You can see it only oscilates between 13.2 and 13.6 roughly, while standing still. The gauge was steady on 13.2 though.

https://www.miataturbo.net/attachmen...ine=1346425495

it needs to ground back to the engine, not the chasis.

Widebands with a single ground wire should have it connected to the ECU's power ground pin, not to the engine block.

Widebands with a separate sensor ground wire should have the latter connected to the ECU sensor ground pin, then the power ground wire to the engine block.

the ECU grounds back to the engine block does it not? sorry im not a noise cancellation black arts wizard expert like you :)

The ECU has two different grounds, power and sensor end up at different spots. Dont quite remembe which goes where.

the sensors pretty much ground back at the ecu, that's the point of a sensor ground, although the miata is not perfect, as they take a few detours and acutally connect to the fuel rail and chasis (under booster) along the way. All the Black/Green wires for sensors connect together and back to the ECU at pins 2C and 2D, but also ground at the fuel rail.

Pins 2A and 2B run from the ECU directly to the....fuel rail.


see page 2: http://www.miataforumz.com/1990-200-...ing/92diag.pdf

Thats odd. I expect all the sensor ground wires to go directly back to the ECU and then the ECU has two grounds with the sensor ground and the power ground divorced from each other.

That's what you'd expect...

Yes but the voltage isn't the same at the end of the wire at the engine end as it is at the ecu end. Picking a ground point has to do with realizing that wires are not perfect conductors.

gotcha.