I'm a bit reluctant to post yet another thread regarding the install of an Innovate LC-1 wideband system, but it seems that a lot of people have experienced somewhat different results despite using similar/same methods so I am trying to get a more succinct idea of what should work best for my install. I came up with an idea that seemed brilliant at the time but which I fear might be foolish in reality.

So, here is my scenario: I have a completely stock naturally aspirated 1997 OBD2 1.8L engine. I would like to remove the stock narrowband sensor and install the wideband sensor in that bung, and use one of the analog outputs to feed an emulated narrowband signal to the OEM ECU.

My idea: I could use the pigtail from a dead stock heated O2 sensor and solder the appropriate leads to the corresponding LC-1 wires. This should provide me with an apprpriate clean +12V (LC1-RED), a direct signal feed to the OEM ECU (LC1-YLW), and a ground for the signal (LC1-WHT) and heater (LC1-BLU).

My Concerns: I'm sure I'm not the first one to think of this, and I have seen no indication that anyone is doing it this way, so it seems likely that there would be problems associated with this approach. The power supply should be adequate, because the LC-1 shouldn't draw significantly more power than the stock NB sensor, correct? The signal wire should be adequate because it goes directly to the ECU. However... The LC-1 instructions indicate that the WHT and BLU ground wires should be soldered to the same connection. If plugged into the factory harness, this could lead to potential ground offset issues because I think that the heater wire passes through the ECU before going to ground, and I'm not 100% sure that it even grounds in the same location as the signal ground. Looking at the wiring schematics for the 1997 Miata, I'm not 100% about the path that the grounds actually take. It looks like the O2 signal grounds attach at the right side of the intake plenum, but the ground distribution chart states that it grounds at the left rear wheel well? I may have to get out the multimeter and try to isolate some circuits to confirm exactly where things connect, but if someone knows for sure how these grounds are routed then I would appreciate a heads-up.

If the OEM grounds present an issue, then I should be able to just run a direct ground to the engine itself and only use the power & signal wires from the factory harness.

But then I also found this post [view single post] by Joe Perez regarding the OEM 4-wire heated O2 sensor, which makes me wonder if anyone else running OBD2 and MS in parallel have had CELs when unplugging the OEM O2 sensor? Or is everyone who tries to keep OBD2 compliance just running 3 O2 sensors (WB, NB pre-cat, and NB post-cat)? Is the current monitored via the heater ground (which is passed back to the ECU)? If so, and if I can't use the OEM grounds, then I assume that I could emulate the current draw with something like a small light bulb, right?

I apologize if this idea has been discussed before, but I don't recall seeing this specific idea addressed in the various LC-1 threads that I found. Thanks in advance for any thoughts, concerns, suggestions that you can contribute!

EDIT: OK, so as soon as I posted this I did find some relevant threads. It's amazing how seemingly relevant keywords won't turn up any meaningful hits but seemingly obtuse keywords yield a handful of worthwhile threads. :ulls hair out:: I would still appreciate your thoughts/concerns/suggestions though.

 

Good luck soldering to the O2 sensor wires. They're made from aluminum (or some similar material) and it's damn near impossible to make solder stick to them. They must be crimped.

Heater power (Black / Yellow on the harness side) comes directly from the 15A meter fuse and is thus entirely adequate current-wise. The problem is that this wire is hot during cranking, and some folks have observed that the LC-1 gets pissy if it is on during cranking, as system voltage drops to a point where the processor becomes unstable. It is most advisable to take power from a wire which is hot in RUN but cold in START. In my car, I have the LC-1 powered by a relay which sources contact power directly from the battery, and coil power from some random wire I found which is hot only in RUN (probably the radio.) I also have the LC-1 grounded directly to the ground wires which exit the Megasquirt.


They don't. You could connect both WHT and BLU to sensor ground, which is Black/Blue on the factory harness. This line is part of the "Sensor Ground" circuit, which does pass through the ECU but only for the purposes of common-point grounding. It's possible that in doing so, you may introduce some noise into the other analog sensors.


I don't have a copy of the detailed ground schematic for the '97, so I can't help you there.

If you are still running the stock ECU, and you remove the stock NB sensor, then the ECU will most likely throw a code for P1135, Bank 1 Sensor 1 Heater circuit low or P1136, Bank 1 Sensor 1 Heater circuit high. This will not affect performance, but it'll probably fail you at an inspection.

 

aluminum's easy to solder...

 

Joe, thanks for the detailed feedback!

So it sounds like I would do best to simply run a ground directly to the engine at the same location where I will ground the MegaSquirt. I could still theoretically use the stock O2 sensor harness for power supply and signal delivery, though I may find that voltage drop during cranking causes problems..

Do you think that wiring a small light bulb (say 12-watts?) in to the O2 heater circuit would be effective at fooling the OBD2 computer into thinking that the HO2S is installed and functioning properly? You mentioned in the other thread that the current profile was similar to that of an incandescent bulb and that it stabilized somewhere around 13-watts (@ 12v).

 

Aluminum, stainless, whale *****... I knew it was some non-copper material.


Honestly, I'd advise that you not bother with the factory wiring at all. It's so simple to run the cable up through a slit in the upper rubber shifter boot, and you don't risk becoming yet another person who whines about how unreliable the LC-1 is, despite the fact that you've knowingly given it a worst-case-scenario power supply.


The underlying theory is similar. The profile is much different. An incandescent bulb reaches peak resistance (and thus minimum current) within a few milliseconds of being powered on. The NB sensor heater takes 10-20 seconds.

Now, I have no idea whether the stock ECU actually looks at the ramp time or merely the steady-state current, but either way you'd likely get just as good a result (and much better reliability) with a 12 ohm wirewound resistor. Or you could just go old-school and hang an actual NB sensor on the line.

 

Sounds like I've got some solid advice now for wiring the LC-1, and also some ideas to ponder (and possibly test) regarding the O2 heater circuit for the OBD2 computer. Thanks, Joe!

 

Thought I'd go ahead and update this.

I got the LC-1 w/ XD-16 installed and running to the OEM computer without any issues. I wired it up with power coming from the wiper fuse (if I remember correctly) which only has power in RUN and two separate ground wires soldered to a single ring terminal and run directly to the ground junction by the throttle body.

The OEM computer was satisfied by running the NB emulation analog signal to the 3C pin on the computer and by connecting a ~13-ohm (actually, I have successfully used a 14-ohm and a 15-ohm resistor and both values worked without issue) wire-wound resistor across the O2 heater circuit. I think that I calculated the minimum wattage for the resistor at around 15-watts, but I was able to get my hands on some inexpensive 50-watt resistors which provide plenty of peace-of-mind.

 

Why did the LC1 designers provide a separate heater grnd, and system gnd, and then *require* that they be connected at the same point? That's just dumb. They make it easy for their circuit, and then hard for the user.

The right way to design it is to provide separate grounds, a high current heater return and a low current system and output ground, and design it so it can tolerate up to a volt of offset between them. The way to do this, is to simply connect only the heater switch MOSFET Source pin to the high current ground wire. And then use a polyswitch aka auto-reset fuse aka a PTC thermistor, inside the controller between the two grounds, so that if one ground is left unconnected by the user, the unit won't be damaged. And a UVLO lockout circuit on the supply voltage so it doesn't balk during cranking.

Maybe it is designed the right way, but the instructions are wrong about it.

Sheesh, I just finished hacking the internal grounds of a friend's AEM ECU, because it was done wrong in the interface board section, and produces a significant offset in the sensor ground. And on his AEM WBO2, which has a *single* ground wire, resulting in a 60 mV or 0.3 AFR error. <shaking head>

<rant>Why do these companies make such newbie-analog-electronics-engineer mistakes?</rant>

 

Meth is a hell of a drug.

 

From the manual

That's dumb. Ideally to make it easy on the user, the heater ground goes to engine or chassis ground, and the system/output ground, goes to ECU sensor ground. The LC1 would have to be designed to not be affected by an offset between those 2 points.

 

I really don't understand what the fuss is about. You have two ground wires. Neither is carrying a hell of a lot of current, nor anything particularly noisy. Splice 'em both into the ECU ground, make sure that ground is solid, and profit.

Ok, so it's a weird implementation that seems a bit overly complex to us EE types. Doesn't mean it can't be made to work reliably.

 

The heater does flow a peak of 4 amps during startup, if that's of any concern.

 

my D1 gauge and TS do not output same AFR :(

 

Compared to the two O2 heaters, the four fuel injectors, and all of the various solenoids which are directly grounded through the stock ECU in the OEM design, no, I'm not really concerned about a single heater with a 4A turn-on draw and a nice, linear taper to its current profile.

 

The heater current is pretty high and worse, it's switched and it changes. The voltage drop across the ground wire is 0.2-.3V on the AEM and with the LC1, with edges on it (theh drop steps between 0 and 0.2V). This produces a significant offset on the reading that the ECU takes from the wideband. On the AEM WB, the error is as much as 0.7 AFR.

The heater in the sensor has to be switched; if you modulated its current linearly, the controller would either dissipate a lot of power, or would need to include a high frequency switching current regulator (the way I would do it, but the LC1 doesn't do it this way).

Worse, the new Innovate MTX-L, does the same thing as the AEM - a single POS ground wire.


The issue isn't the magnitude of the heater current. It's the fact that the design can't tolerate much ground offset between the two ground wires. The problems are:

1) it places a constraint on the wiring
2) more importantly, said constraint could possibly inject noise into your other sensor circuits

If I designed the LC1, I would design it so that it could tolerate 1-2V between the heater ground and the output (ECU sensor) ground. This way the heater ground can be either chassis or engine, and the output ground connects to the ECU sensor ground. This would ease the wiring constraints, and reduce the possibility of the LC1 wiring inadvertently injecting noise into the other sensor circuits.

The way to do this is to have the heater ground wire connect only to the return of the high current heater pulldown MOSFET, and internally connect the 2 grounds via a 10 ohm PTC (auto-reset-fuse), in case the user fails to connect the high current ground. The software could detect this condition and flash a warning on the LED. If the high current ground is disconnected the PTC would normally provide a return path for the MOSFET gate drive current, and if the wiring in to the car is such that a large external current is forced up and down the 2 ground wires, the PTC would act as a fuse and protect the circuitry.

In the OP scenario, the removal of the constraint that the blue and white wires need to be connected together would mean the LC1 heater ground could be connected to the chassis or engine, and the output ground could be connected to the factory wiring's O2 sensor ground. (The factory "heater ground" is actually an ECU pulldown output).

 

It's because these are small companies in a niche market. They make newbie-analog-electronics-engineer mistakes because they:

1. Either have newbie-analog-eletronics-engineers that they don't pay squat; or
2. Have older engineers that aren't worth a darn and to whom they don't pay squat.

I'm pretty fed up with my LC-1 right now. I've researched and I'm pretty confident I can get my issues working well enough to tune (no thanks to Innovate tech support -- 100% thanks to MT). But, dangit, I installed 100% in accordance with the directions. I shouldn't have to spend time rewiring grounds and reverting firmware. Sigh.

 

Ditto. That would not be an LC-1 problem though. That offset is happening on the MS board. I need to compensate for this too with some custom LC-1 curves. Grrrrr.

Oh, yeah, my spark plugs have rich-fouled because of this issue. Needed new plugs anyway . . . .

 

IIRC I just bumped my calibration in TS from 0-5v 7.35-22.39 to 0.2-5v 7.35-22.39. mathces perfectly now.

 

So that leads to the question: what happens if I just have the LC1? Can I hook it up serially to a computer and get an AFR readout to compare with the MegaSquirt, then tweak the MS to match values?

 

I tested an LC1 on the bench. I applied a variable DC offset (-0.5V to 0.5V) between the heater and system ground wires (blue and white).

I'm happy to report the analog outputs remain stable, wrt the system ground wire (white).

So the right way to wire it is to return the white wire to the ECU sensor ground pin, and the blue wire to the engine block. The current out the white wire was 60 mA.

I'm guessing the Innovate guys are doing a CYA by saying to return the blue and white wires to the same point from users blowing them by inadvertently leaving the white wire disconnected.