I've got a MTX-L to install, and I've done a bit of reading on the best way to do so. It only has one ground, and I guess ground loops can be a problem. I've decided to jumper the DB-15 on my DIYPNP straight over to 1B/4B, seems easy and clean, should keep it on through cranking. I don't really want to wire it straight to the battery off a relay like the manual calls for, seems excessive.

So, all the wires for my MTX-L are going to the DB-15. There's the dimmer wire, which apparently dims the display when supplied with 12V. 1U is "-12v when TNS relay is closed" or just headlamp switch.

Is 1U 12V when the lights are on, or is it grounded? I've got 1B "-12v key on" wired to 12V on the DIYPNP, so I'm leaning towards the former. Just like someone to check my work before I go burning things out!

Thanks!

Edit: Found a post by Joe, better explaining ECU grounds. Think I'll move my MTX-L ground to 2A instead of 1B.

 

1U is exactly what you'll use.

It supplies 12v when the headlights are switch on. When the MTXL sees the 12v, it'll dim the display.

This wire is reb/black and goes into the radio, so that's a better place to tap into it. Assuming you're putting the gauge somewhere around there.

 

Cool, thanks Scott!

I picked up a dual gauge A pillar from Moss, which I'm a bit disappointed with. Doesn't match very well. I'm hoping to keep all the wideband connections together at the DB-15 to keep it clean.

I've got the MTX-L jumped directly over to the same 12V that powers the diypnp, and 2B, which I think eventually goes to the block jc-03?

A post from Joe Perez, at some point, better described the grounds on the stock harness. I think using 2B is the best bet, we'll see!

"The official, according-to-Hoyle nomenclature for the ground wires on the 1.6 ECU is as follows:
2A: Injector ground (goes to ground common JC-03)
2B: Output ground (goes to ground common JC-03)
2C: CPU ground (goes to ground common JC-02)
2D: Input (sensor) ground (goes to ground common JC-02)

Eventually, JC-02 and JC-03 wind up getting commoned together, and terminate at the ring lugs on the back of the intake manifold.

They key point is that the sensitive stuff (sensor and CPU ground) is kept separate from the noisy stuff (injector and output drivers) for as long as possible, right up until they common at the end. "

 

a-b chassis grounds. (black)
c-d sensor grounds.(black/lt green)

they all connect anyways around the fuel rail if you look.


basically exactly what joe said.

red/black wire feeds into the dimmer switch fwiw.

 

I got her working, kinda! MTX-L was lighting up, briefly. Fed all the wiring behind the cluster down to the ECU, which sure was fun. Looks pretty decent now, besides the phone photo. Ran the sensor wiring through the throttle cable grommet, as well as the vac line for map/boost gauges.



I forgot the fuel pump fuse and blew up my DIYPNP. Feel like an idiot, knew exactly what it was when I turned the key. Think I may have got lucky, can't see any burned traces. Argh!

Oh well, gives me a chance to order a crimp style db-15 I guess. Looks like DIYauto might keep the exact transistor slightly secret though, I can't tell what it is, it went poof pretty decently.

Hacked a birds nest out of my miata tonight too, and finally killed the ground loop my radio was picking up. The PO did my favorite "home-made" t-taps splicing into the dimmer (and everything else) for this stupid alarm. Cut, and silence
My airbags go beepbeepbeep too, guess someone stuffed the airbag light. Don't know how I missed that one, but I guess it stays unplugged. If this was your old miata, I have some words to share with you



Edit : TIP125? And radio shack is just as useless as evar!!

 

okay, so move the fuel pump to 2O and jump the afm connector like a real man.

the high side driver method is a hack i dont like.

 

My Miata has no 2O though, only uses connectors 1 and 4. From doing some tracing, I think somewhere along the line 2A-2Z started being called 4A-4Z. Maybe the same time DIYPNP came out?

Is 20 the same as 4O on the DIYPNP breakout board? It's gotta be



I can still jump the fuel pump manually through the diagnostic port, right? I ordered a new transistor (well, a lot of them, but they are cheap.) I wouldn't mind jumping it for a week while I set timing and try and idle, probably won't even drive anywhere. Nothing wrong with the high side driver if you remove the fuse right, besides the whole backfeeding thing?

 

Running the MTX-L through the ECU harness has put the biggest ground loop I've ever heard into my miata, it's bad enough to distort the door buzzer while it's heating up

I'm thinking my negative battery terminal might be shot, because "jumping" the negative terminal to the block ground point with jumper cables seems to knock the whine out. I don't really understand ground loops, but they are annoying as hell. Plan to start at the source and work my way up, Wouldn't be surprised to find half the factory grounds missing after dealing with the mess under the dash!

A loop that bad probably does bad things to the fine tuned signals my DIYPNP is trying to manage right? I've made killing the loop my priority, just in case..

 

2O - AFM. its on your stupid chart. Which is 4O in the DIYPNP. Jump that to ground in the AFM connector itself.

 

Made me lol for some reason

 

the chart made me lol.

 

My miata has ghost fuel pump, or the high side driver transistor still works after you violently decap it lol

It runs, really well actually. Drove her home on the DIYPNP

I ran my wideband directly to the battery like the manual suggested, made a new ground lead for the battery too. Harvested a relay and socket from the car alarm mess I cut out the other day for the MTX-L. Still whines, but not as much. PITA....

Found this cool chart though, plus a lot more. Going ground hunting tomorrow lol

 

that chart is better in color.

you should ask us for better charts...instead of fishing for BS.


where did you install the ground for your MTXL, lets start there.

 

Haha, I've been using charts like this one I found in a PDF somewhere. Just stole that one as a reference for no reason, and didn't want to upload my own

My MTX-L is grounded out straight to the battery, now, instead of sharing the ECU harness ground. I've got it wired exactly like the manual asks for, with a "hot thru crank" ignition source driving a relay. 12V straight from the battery too, 5A fused feed. I ran 14ga ground, which was quite a bit larger than the factory MTX-L ground wire.

I think I need to look at the dimmer circuit, because dimming the dash lights causes the most noise now. Leaving them at full brightness isn't all bad. The harness to the dimmer was pretty hacked up. I can still hear what sounds like PWM switching when the "htr" display is up on the MTX-L, any other time and it's not that bad.

I've got a slight discrepancy in TS and MTX-L AFR readings, but it seems that might be normal. I've got a general idea of how to measure the offset, I'm just trying to get LM Programmer to find my MTX-L now, not wanting to work at all...

Here's a quick run across town, and my current tune. It seems to run beautifully, albeit slightly rich (esp because I'm reading about .3-4 richer than shown in TS. Startup is terrible, but I'll figure that out. Seems to be really lean...

Somehow I got her to idle at ~800/35kpa without stalling, my overrun is set pretty damn good for a SWAG, too. If I get past cranking and after start conditions, it's a blast

 

Don't know why but the forum won't take my .msl file

http://www.filedropper.com/2014-08-24

 

.23v = 7.35 AFR
5v = 23.4 AFR

that'll fix the offset.

I've installed plenty of LC1/MTXL/LC2s; running power/ground directly off the ECU harness has never leads to any ground loop noise. With 12v off the battery, I assume you wired in a relay too so it's not always on?

Sounds like your car has gremlins--I think I'd look at replacing the dimmer itself.

I dont understand the PWM switch noise commet whatsoever.

 

Thanks for the numbers, they're a lot better than what I had. Idling closer to 13.8 (batch, still) now that TS reads right.

I scavenged a relay and socket from the car alarm I ripped out of my dash for the MTX-L, since it was there and free...

I think there's a 91 in the crush row at the scrappers, might go see if it has a dimmer

 

Do I need to wire both the brown and yellow wires from my MTX-L to my DIYPNP?

 

No, that is entirely pointless.

 

i just want to say i reread this entire post and just loled at my posts.