Hi!!

I recently installed an AEM 30-300 AFR gauge.

When I connect the white wire (out put ) to my old MS 1 PnP there is an off-set in the readings between Tuner Studio ad the gauge display mounted on the dash.

My MS doesn't have much in the way of calibration so I'm left with trying to minimize the ground off -set.

I have all the grounds going to the same ring terminal at the rear of the head.

Is there anything to be gained by running a ground wire from the black/green wire at the ECU connector harness to the metal of the ECU cover on the floor board ?

What about running the gauge ground directly to the above ECU ground wire ?

Thanks

 

These two are mutually exclusive.

Are all your MegaSquirt grounds at the ring terminal at the back of the head? If so, that's where your AEM needs to be grounded. If it has a "sensor ground" wire, that wire definitely needs to go to that ring terminal. If it only has one ground wire, that wire definitely needs to go to that ring terminal. Don't splice into existing ground wires. Go directly to the ring terminal, or a new ring terminal held by the same bolt.

 

Got it That's what I have.

 

Some widebands have two grounds, a heater and a signal ground. The heater ground should go to the ring on the head. The sensor ground should ground only at the megasquirt, from there megasquirt should ground to the head. You need more current capacity in the ground that returns to the head, more wires or bigger gauge.

If it's junk like innovate products then it will not have an isolated low/high current ground. Nothing you can do about it, it'll be randomly offset depending on what the heater is doing. If that's the case and MS1 can't run a custom wideband comp then I would just fudge the AFR targets to compensate.

If you run any sensor ground to the block you are going to have a bad time.

 

Thank you very much for your input. Very much appreciated.

OK. I have The brown wire grounded as per AEM instructions together with the black wire to a ring terminal bolted to the ground at the rear passenger corner of the head.

Sounds like I should bring the black wire to the ECU (?)

 

https://www.aemelectronics.com/files...ns/30-0300.pdf

Please do what it pictures in the manual......

 

We're talking about a MegaSquirt here, which does not separate its sensor and power or logic grounds.

You're wise in that all your MegaSquirt grounds go to one place. Job done with that.

Now on to your AEM gauge. There is no need to connect your gauge to the MegaSquirt. Why? Because guess where it's grounded? At that terminal on the back of the head.

Ground your gauge there. Now guess what the potential is between your sensor ground and your MegaSquirt ground? 0 volts.

 

In deference to deezums though, do check the wires coming out of your MegaSquirt and make sure they're of decent size and not all fouled up. Good crimps, no wonky splices, all that. If you've got one 30ga wire as your ground for the ECU, you're going to have a bad time. You want solid, unspliced runs of wire from the MegaSquirt to the ground terminal.

I'm not sure why you referenced the ECU cover in your first post, that should be a non-factor. If you think maybe there's some ground that's connected to the MegaSquirt shell, that's a problem. Put the MegaSquirt on an insulator and see if that changes any offset you might see. If it does, you've got problems.

 

My MS1 is a PnP So it plugs right into the stock harness. The ground wire that I extended to reach the ground at the back of the head is 14g.

No wires are connected to the shell of th MS. I was referring to the ECU ground in the factory Mazda connector. I think is a black/green wire at JC02 and 3

Thanks

 

You are right, the ground are not isolated inside the megasquirt. That is hardly the point, though, and not at all relevant. Seeing as how there's plenty on google about proper megasquirt sensor grounding I ain't going over it all again. Running a sensor ground/return to the head is a good way to introduce offsets depending on the total current running through the ground wire between the head and megasquirt. Considering that's all VVT/IAC/INJ and more it's pretty significant.

https://www.miataturbo.net/build-thr...7/#post1354392

Or you can ignore what all of the manuals say and ground the gauge at the head...

 

This is what AEM sent e via email. Now, aside for that my firmware has nothing close to the AEM 30-300 None of the AEM gauges supported give logical readings in TS. I down loaded newer firm ware but haven't figured out where to put it.

Brown wire needs to ground to the same ground that all 5v sensors are grounded to, typically labeled “sensor ground” on ECU pinout diagrams. A normal ground will work but you may see some offset of AFR values on the gauge and in your ECU since this ground is “zero” for the gauges voltage output.



Best regards,

Sam Chaysavang

AEM Technical Sales

Phone: (310) 484-2322

 

There should be a way to change the calibration, probably buried in a file somewhere. I think there was a change to tunerstudio that does the ini mod for you? I think that's what this thread is on about, might follow that.

https://www.miataturbo.net/mspnp-55/...bration-78512/

 

Thank you very much. I followed the instructions but the custom gauge option does not stay as an option. Maybe its something I'm doing wrong...

 

Not that one, you are looking to change the configuration inside tunerstudio which should give you a "calibrate AFR" menu that all the other megasquirts use. Then you don't need to use a custom gauge, it will know the right AFR.

 

Thank you much. I'll try again. Where should that option be on the drop downs ? A whole new drop down tab or part of another ?

 

If the ECU was grounded only at the head, my advice would have been fine. It isn't. So go ahead and listen to deezums.

 

Oh, and while you're at it. Check the connection from the engine to the chassis.

 

No. Even if the ECU is grounded only at the head, it would still be better to wire the WB “sensor ground” to the MS “sensor ground.” Nonzero current flowing through the wires from the ECU to the head causes nonzero IR drop — a.k.a. ground offset. What @deezums is saying is correct regardless of where the ECU is grounded.

 

Pretty sure the post linked says exactly where it is, but it's under "tools" on the menu bar -> calibrate AFR or something similar.

 

Yes !!! Thank you. I followed the instructions - switched to 029Y firmware and found the "custom linear wideband" and found the "calibrate wideband" under tools.

I'm having a problem when I connected to the ECU because the firmware were different . When I click update ECU configuration it opens up a windows screen but I don't know what to do from there.

I think I'm going to have the Megasquirt updated to an MS2