Help me pass emissions
 

I am having a hell of a time passing Texas emissions. Will be exempt in 2 years but for now I am getting sniffered, which I wasn't aware would be required.

1993 W\VVT swap using a Reverant MS3.

Initially I had no CAT, things went poorly. I had purchased a CAT from rock auto during the rebuild, but it disengrated within 100 miles. With no CAT I failed everything but the "high speed" HC.

Test Requirements:
15 mph (~2000rpm)
HC: 166PPM
CO: .93%
NOx: 1304ppm

25mph(~2300rpm)
HC: 160ppm
CO: .90%
NOx: 1179ppm

Results will be in % of spec -

No CAT 15mph
HC:95%
CO:198%
NOx: 108%
O2: .3%

No CAT 25mph
HC: 101%
CO: 257%
NOx: 101%
O2: .2%

So no CAT,failures all over, no way to tune around it. I installed a magnaflow direct fit cat, did a small amount of driving and took it back.

W\CAT 15mph
HC: 96%
CO: 159%
NOx: 17%
O2: .1%

W\CAT 25mph
HC:96%
CO:197%
NOx: 25%
O2: 0%

So the CAT is working, it knocked down the NOx significantly, and made some difference on the CO, though almost none on the HC. Looking at the numbers, and noticing that there was next to no O2 left for the CAT to work with so I figured that it was running rich for some reason, not fully warmed up, EGO correction not enabled in the right area or out of range, etc. I drove the car for awhile trying to duplicate the RPM they were testing at, at a wide range of MAP pressures, using VE auto tune to correct the map. I also verified that the AFR table was targeting stoich, and I changed the WUE to cut off at 160ºF from 175ºF. The car generally runs between 175 and 180.

After these changes, retested and also convinced them to let me datalog the test.

15mph:
HC:82%
CO:165%
NOx:36%
O2:.1%

25mph:
HC: 84%
CO: 193%
NOx: 62%
O2: .1%

So the changed I made brought down HC, but CO was mostly unaffected. Increased NOx too, O2 still very low. All consistent with a car that is running leaner than before, but still rich. Then I looked at the datalog. My EGO correction is pulling almost 10% fuel, but wideband shows the car running very close to stoich.

So now what? Can the Innovate LC wideband be off in calibration enough to cause this? Just skew targets lean? Some other hardware issue? Send injectors out for cleaning? new spark plugs? I'm kinda stumped with the O2 still low I think the CAT would work better running leaner. Log of two speed test attached.

I think the best way to approach this would be to run ignition timing swings at different cam positions while targeting lambda 1 and measure the exhaust emissions.
Then set the ignition and cam to the best position and swing injection timing and see what that does to the emissions as you may be able to put some timing back in or set the cam phase for improved fuel economy with an improved injection timing.

Also fuel in the oil will increase your HC. If the oil is old take the car for a hard drive pre emissions test to boil off all the fuel in the oil, or just change it.

Did you look at the log you posted? Your AFRs are all over the place during the test. No wonder you failed. Probably EGO is setup wrong so it's making large adjustments overshooting/undershotting the target AFR by a lot. That's why you failed, you're not running Stoich during the test, you're running 14-16 variable and you won't pass doing that.

I'd also put the VVT fully retarded, that will reduce overlap/emissions.

What's timing at idle? Emissions likes stock, or 10 degrees. Turn on EGO control for 14.7-15afr. Should be operating 1-2 times per second. Any more and it'll just be all over the place. You'll know it's working of your afrs are rock steady at idle for 160-190 degrees. Then run it a lot, let it sit (heatsoak) and turn it back on. Should be rock steady again. If not something's wrong. Base fuel table, EGO settings, etc.

l2t.

Excellent point on the oil. I don't have access to tune on the dyno/sniffer though so I just have to take my best shot at it, then retest. Two tests costs me $30

I just assumed that the dithering back and forth across stoich was intended. I know that this is how a narrowband car operates, though I don't know the magnitude of the oscillation they use. During the measurement the average AFR is 14.7, Min is 14 and max is 15.5. When you said EGO is setup wrong you mean the control loop I assume?

Timing at idle is 14º nominal, I do have Idle advance enabled and set to bump up if idle falls 50rpm below target. I am not emissions tested at idle though. So to get this straight, you are suggesting I set the EGO to only correct above 14.7 and below 15.0? Seems like I should use a larger range. The other change would be to significantly increase the number of ignition events per step. It was set to 16 by default, to have 1-2 seconds between changes this would need to be much much higher.

https://www.miataturbo.net/attachmen...1&d=1453000042

I think I may have found a big screw up though. I don't remember doing the "Calibrate AFR table" step previously. I just assumed that wideband=wideband as far as voltage vs AFR, so when I set it to "wideband" I thought I was done.

Don't use the table, just use a 10, 15, or 20% authority.

And set ignition events to 30 or 60. Right now it's correcting about 4 times a second. Seems a little fast, might produce some oscillation.

The OEM will be between 14.6X to 14.7X AFR, mostly at 14.7 but it will overshoot and undershoot that target about every 4 seconds. It stays VERY close to 14.70 AFR, not bouncing around like yours is. You gotta fix that, you'll never pass an emmissions test with your AFRs moving around like yours are.

For my EGO correction, I do every 8 events, PID, the P, I, D terms are 0, 200, 0. Try those, they're probably better than what you're running. My AFRs stay between 14.6 and 14.8 in cruise with those settings. Also, I run no smoothing on my AFR input.

Your PID settings are the problem, that's WAYYY too much Proportional vs Integral on your PID settings. Try the ones I posted. I tried a lot and 0-200-0 gave the best results with 8 events setting. Basically give up proportional gain but speed up the cycle to make up for it. Any less than 8 and my setup oscillates more than .1 AFR (.2-.3 with 4 events for example, way worse with any P in the settings).

This is what I get with my settings. 14.6-14.8 at idle, you can see EGO making tiny adjustments up/down in the log and AFR moving but overall a flat line.

Attachment 183816

I played a with the PID settings quite a bit, anything over ~0,75,0 causes oscillations and I found the best settings at 1,30,0 I tried 0,30,0 as well and found no change in oscillation but it was slower to respond to changes. Still seeing the oscillation in AFR no matter what settings I used. I am starting to think I really do have a HW issue somewhere that is causing the AFR readings to bounce around, or there is a electrical interference issue...

https://www.miataturbo.net/attachmen...1&d=1453063735

The large jumps in AFR remain no matter what I do, and they do not seem to be tied to changes in the EGO correction or PW. They are present even with EGO control turned off. Crappy spark or sticky fuel injector maybe?

Welp. 99% sure its an electrical issue. I am pretty sure I wired up the ground correctly per instructions, and have pictures to prove it, but when I logged the LC2 and the MS3 at the same time they showed a ~.5 delta in readings for the AFR. The MS3 was doing its dance around 14.7 and the LC2 was reporting 14.2 over the serial connection. I offset the AFR calibration table to correct the bias, which means the MS3 was logging ~.17 higher than the LC2 should be outputting.

For the Reverant ECU the OBD2 stuff was all on the DB37 connector. I recall wiring up the ground for the LC2 to pin 2, which was designated as the "ground/heater ground" for LC-1 Widebands" maybe I need to tie it to pin 3 instead which is the "analog sensor ground"?

As I see it these are the possibilities
LC2 analog output is noisy/biased
MS3 ground reference being used is biased/noisy
MS3 wideband input is supposed to have filtering capacitor or similar on the analog input that isn't present and the bias is the result of my shitty soldering

10 seconds of data from the LC2 vs from the MS3. They are not from the same 10 seconds, just typical of the logs. Note the Scale difference the AFR.

MS3:
https://www.miataturbo.net/attachmen...1&d=1453263235

LC2:
https://www.miataturbo.net/attachmen...1&d=1453263235

Pin 2 is the correct ground to use with either the LC-2/MTX-L or say, the AEM UEGO.

Obviously, the MS3 does have hardware filtering for the analog wideband input. You may want to decrease the lamda averaging lag factor though. I set it to 100 as this results in the fastest response and accuracy, but if your wideband is noisy, the above can happen.

Btw the log posted above over the analog input is not helping, as it autoscales to 14.2-15.4 AFRs and makes the issue appear much larger than it is.

However, I can see an issue over the serial port data you posted as well. The data shown does not reflect my experience with the LC-2 - it's output is heavily filtered and does not swing so much back and forth. So if that's the data from the serial port, I would expect the analog to look much worse.

One thought on that: Those heavy swings could be caused by EGO over-correcting, caused by the noisy input and could therefore be accurate.

would have to see the EGO log to find out.

just leave EGO on simple algorithm for now. that's all you need.

disable the authority table.

and just set it to be active above 1500rpm.



now work on autotuning fuel so you dont really need ego. it should take like 10 minutes of driving at 15mph and 25mph (or whatever your test is) to nail down a perfect 14.7:1 afr for sniff session.

This is my thinking. That "heavy" swing looks much more like my EGO correction, and note the scale. It's running from 14.5 to 14.8, those other jumps on the MS3 log are .5 AFR. I tried to figure out how to overlay both in MLV and couldn't figure it out, nor how to manually set the scale for the Y axis.

I'm going to pull the passenger kick plate this weekend and measure the resistance across the crimps for the three wires between the LC2 and the MS3. The bias between the two really points to there being a voltage reference issue with the ground being the mostly likely culprit since the MS3 is logging a higher voltage than the LC2 should be outputting. I can also scope the ground, 12v, and 0-5v signals.

Tonight I can rescale the LC2 output to report 0-5V over 10.7-18.7 AFR instead of 6.8-22.8. If the AFR jumps in the MS3 log drop by half in magnitude it will confirm that its entirely electrical.

I don't really want to increase the filtering, either in the HW or SW. Those jumps are .3 to .5 seconds to filter enough to kill them it would really impact the responsiveness of the control loop. Knowing there is an offset between the LC2 and MS3 I could probably fudge my way through the emissions test, but I would rather just get this fixed right first. The bias does make my emissions results make sense though.

I agree with this big time, once you verify you don't have a grounding issue spend some more time dialing in the fuel maps and you wont need EGO for your purposes.

The noise in this pic isn't caused by EGO, that's some electrical something causing your ground to shift, making it jump up/down sharply. EGO wouldn't make it jump THAT sharp, that fast, that consistently.

If I were you, I'd grab the manual for the wideband you are running and start from step one. Free air calibrate it if needed, rewire anything that is not wired exactly as outlined in the manual, setup your Outputs on teh controller how you want them, and put the same calibrations in TS so they match up. Just do it all once, do it right, and be done with all those problems.

I believe we were talking about the variations that Rev alluded to, which was in the "LC-2" graph, showing the serial data.

Well I fucked up....


While testing the grounds my probe slipped on pin 2 and connected pin2 and pin 1, shorting the 12v to ground and blowing the fuse. Good things its fused! Need to be more careful, just need to order a new fuse, could have been much worse.

I did find an odd oscillation on the ground for the wideband with the key on and the engine off, but it appears that the ground for the LC2 is good, it follows the oscillation great and there is a very small voltage bias on the ground, not enough to explain the observed in AFR, and the oscillation is much to fast to be what I was observing. It is interesting that the oscillation is not present on the "analog device ground" pin 3. The oscillation is ~.05V, which if not followed by the signal (which I cant test cause I blew the fuse) will result in an oscillation of .15AFR at my current scaling. The frequency is high, so a little bit of smoothing should take it right out.

https://www.miataturbo.net/attachmen...1&d=1453568129

https://www.miataturbo.net/attachmen...1&d=1453568129

Yep. With the car running I see a .2V bounce on the ground just like above, referenced to pin 3, which feeds right into the signal, which bounces along as well. Depending on the sampling frequency of the MS3 on the signal wire it will bounce as well, though the frequency will be corrupted. Time averaging would get rid of it, but .2V is an unacceptable amount of bounce.

Anywhere I can get a schematic of the mainboard? I would think that the input for the 02 sensor should be referenced to this ground, but I am betting it is not based on what I am seeing. I am also curious about what is going on behind pin 3 vs pin2, why I see the bounce on 2 but not 3... A simple differential circuit to clean the input would work, or finding a clean ground source, or correcting the bounce on pin 2...

need to do some research.

*edit* so pin 2 is apparently tied directly to chassis ground, pin 3 must be some sort of special filtered ground. Off to investigate why my chassis ground is bouncing.

When you state that your chassis ground is bouncing, what are you using as a reference to measure against? Usually I would think you measure against chassis ground...

I was referencing the analog sensor ground on pin 3, which I assume is a digital ground, and is what the A/D in the MS3 is referencing when it measures the EGO input.

So... I checked continuity to chassis and had good connectivity, but as i've learned elsewhere, you really gotta check grounding with a 4 wire meter, which I dont have at home. So in the absence of that I checked the voltage differential between the chassis ground at the ECU and the floor pan with the car running and and found it to be over 1V! I dont know where pins A&B on the ECU are terminating to, but wherever it is, sucks. Similar differential to the head and the grounding points in the engine bay. I noticed that the chassis ground was tied to the jackscrews for the DB-37 connectors when I was replacing the fuse earlier, so I hooked a wire under one of the jackscrews and put the other end in a hole in the floorpan. Voltage differential while running dropped to 200mv or so, and I could certainly improve the grounding. The bouncing is still there, but its much reduced, ~.050V while running now, rather than .2V

After thinking about it, I sent an e-mail out to innovate, the best solution would be to separate the heater and sensor grounds in the LC-2, similar to how the LC-1 was done. That way I can tie the sensor to the clean analog ground, and then the signal generator will be referenced to the same ground that the signal receiver uses. The grounding of the ECU to the chassis is certainly an issue, but there is a basic design issue here with the signal generator and the signal receiver operating from different ground planes.

Omg. Wire the lc2 to the ecu ground and move on with life.

First you post a useless l2t, then you post that I need to refine my VE table , ignoring the fact that the feedback for tuning the VE table is from the wideband, which currently is returning junk, then you post this, ignoring the fact that I already verified the ground connection between the LC2 and the ECU is good, unless you are proposing that I wire the heater ground for the wideband into the digital ground for the MS3, which is a terrible idea for what should be pretty obvious reasons.

Either you are not reading, you dont really know whats going on, or you are somehow offended by the content or by me and are purposely sabotaging. Whatever the case may be, I would reccomend unsubscribing.

Your lc2 logs are good. It's a clean signal. If there was a problem with the ground then that log would look as bad as the ms's.

The problem seems to lie with the input at the ms. The input circuit on your ms seems to be junking it up. That's where I'd be looking at least. You'll have to reach out to Dimitri for his help here as his ms unique and I couldn't suggest where to probe before and after the input circuit for the signal.

The voltage offset is 100% normal.

Thanks. The difference in the ground reference is the source of the problem I suspect. The lc2 logs are clean because it's self consistent. It's logging it directly off of wideband. If I was sending the data digitally over to the MS3 over serial/can bus I would be just fine.

My theory is the problem arises as the LC2 generates the analog output. It generates a voltage relative to the ground it sees. If the ground goes up, the output voltage goes up. The MS3 measures the EGO relative to the digital ground, which doesn't have the bounce the ground of the LC2 has, so the MS3 logs the bounce.

Solutions:
Get rid of the bounce on chassis ground

Feed the LC2 the digital ground of the MS3

Differential Op Amp with zero gain to clean up the EGO signal into the MS3

I'm a mechanical engineer, mostly because I hated electrical issues.

Pin 2 is the I/O ground, meaning all MS3 outputs sink current through this ground, hence why you see noise it.

It's rather obvious why I use a different ground for the I/O, and a different one for the digital/analog logic, right?

Do the following test with the engine off, ignition on: disconnect the idle valve and see if the issue goes away. It's the only current pulsing device operating while the engine is not running.

Very ovbious. Wouldn't want the injector drivers or similar hooked up to the digital ground.

I already disconnected the IAC valve with the key on and engine off and it made no difference. I also disconnected the VVT actuator for good measure and the bounce remained. I am really baffled by what could be causing it.

Sorry- I can't tell you what's wrong here. I can only give general troubleshooting advice. In situations like you're in right now, it helps me to draw a schematic of the problem. Aids with visualization. Also helps explaining the problem to others whenposted.

Good idea. Looking at it, I have not checked to see if I see the bounce on the 12V line, maybe the voltage regulator is causing the 12V to bounce, and thus the ground to bounce along with it. Seeing as without the strap I am really floating away from the chassis it could explain the problem. I am off to do my real job for a few hours.


https://www.miataturbo.net/attachmen...ine=1453646425

I think you have started down the right path of looking for ground currents. I would consider the possibility that the WB heater current is the culprit. As drawn up there ^ all of your heater current is flowing through the reference plane of the MS. A few suggestions:

- Decouple the sensor return to the chassis with a low ESR capacitor
- Add a common mode wrap on the lines running to the WB
- Decouple both the 12V and the signal out of the WB to their local return with capacitors
- Provide a local (to the WB) low impedance DC path from the sensor directly to the chassis return. Run a second low current return reference back to the aquisition system. You could force the heater currents through the low Z path with a common mode choke on the power lines and then another on the signal/reference lines (assumes high z input on the DAQ)

WRT the emissions...

The CAT needs O2 to convert CO into CO2. Lean/retard results in best no-CAT content. Stoich/retard with CAT. If too rich, you wont have enough O2 to convert the HC and CO. You can get more O2 by increasing NOx

Heat is needed for the reaction. -> retard

NOx is a function of combustion temperature/pressure, when 02 goes up so does NOx, but it's correlation, not causation. Leaner burns (up to a point) increase combustion temperature, and also result in leftover O2. My retest results showed that the car was running rich, but the MS3 log showed it bouncing around stoich. My initial assumption that what the MS3 was logging was biased was true.

Honestly I could probably get a low mileage waver at this point, and maybe with the bias corrected it would pass even while bouncing, but it's now a tuning issue. Thread title should probably be "LC2 grounding scheme sucks, LC1 was better and here is why" since the LC1 has separate ground wires for the heater and the signal.

The graph I posted in post 9 is my LC-2 with zero smoothing. It works just fine.

Could be wrong here... But I believe oxides of Nitrogen are broken down to produce Oxygen in the CAT which can then be used to comvert CO and HC.

Just out if curiosity, what alternator are you using?

I'm not saying the LC2 can't work, but from a signal integrity standpoint it's a poor design. Not to say there isnt something else wrong with my car, but using the chassis ground for a signal ground is pretty poor form. I've done a fair amount of EMI testing in my day job and shit like this always causes issues. I bet you could take your clean signal and drive somewhere with alot of EMI, like the top of Mt Wilson in CA, and you would pickup the noise in your signal.

I've always seen them described as separate reactions. But I suppose it's possible that the NOx breakdown would provide some O2 for the CO and HC converters.

I'm running a Chevrolet 220A alternator, 1 wire internally regulated. LC-2 wired as the instructions said to do.

have you actually looked at the signal voltage yet? both before the MS input circuit, and then just before the CPU, using either ground as a reference?

Have you determined that the LC2 isnt itself outputting junk on the yellow analog one output? or that the MS itself is doing something to the signal after it's own input circuit?



i was finally able to log at your log, it looks like a lot going "oddly". This was during the emissions run?

what's your setup like? can you post your actual msq?

The log was from the two speed emissions test

I'll post the MSQ when I get home. I am sure there are a thousand things wrong with it, I just got started messing with it from the base tune Reverant gave me I've only made some changes to the knock threshold, adjusted the idle control loop and the EGO loop.

Its a 2004 VVT motor in a '93 chassis with the 5speed and the 4.3 viscous diff. Intake is an AEM thing from 949. Exhaust is a racing beat header with a magnaflow direct fit cat and a junkyard special kind of catback. Injectors are the OEM 2004s, as are the ignition coils. I put new NGK Sparkplugs in gapped at .044 thinking that the bounce in AFR was crap combustion (before I checked the serial output of the LC-2). Intake manifold is the 2004 VTCS, with the VTCS system removed and sealed (though not between the runners). No EGR system hooked up. I posted wiring diagrams in the build thread here: https://www.miataturbo.net/meet-gree...9/#post1224622 On the DB37 connector I have the knock, VVT and wideband +12v, Ground & signal wired up (5 total connections)

I've not scoped anything inside the MS3, what things I have checked are in measured relative the digital ground of the ECU, when you measure the signal relative to the chassis ground you get a pretty clean output. MY initial assumption was that I had a bad connection so I checked the ground, signal and 12v on the LC2 CCA and on the DB37 and found them to be nearly identical, Both in voltage and in the noise. The MS3 logs look exactly like the noise, except the frequency is off because the noise has a higher frequency than the MS3 is sampling at.

The heater is only on when first turning the car on I thought?

When it comes to fixing this electrically I think I will either separate the heater and signal grounds on the LC2 (studying the PWB it looks like this should be easy, but I want confirmation from innovate) or I will add a zero gain differential op amp referencing the 0-5V output of the LC2 to the chassis ground and feed its output into the MS3. Based on what I've seen with my scope this should result in a clean signal into the MS3 and its how we deal with common mode noise at work, where we deal with dirty aircraft power and grounds, and need EMI hardening.

I assume you mean a gain of 1 ;)

The diff amp is effective for impedance transformations to be sure. If you believe the noise source is due to victim coupling then it certainly could improve things for you.

Based on your results described above (from my couch that is) it sounds to me like you have enough ground current to react with the impedance between the sensor return and chassis. If you can separate the high current return from signal and route it directly to the chassis, I say thumbs up brother!

Lol, based on your emi work, you could have meant a gain of 0dB

Terminology is fun. Looking up parts its also called a "Unity Gain Differential Amplifier."

Attached is the .msq for the curious. Pretty confident the problem isn't in here but who knows.

You should/could have clamp on donuts ... You could scope up the currents

You may also be able to save some $s by building a 3 amp differential amplifier out of a cheap quad.

All this buisness about adding something to filter the noise, why can't I just modify the RC circuit on the MS3 to kill it? The noise is right around 500hz. By the MS3 schematics the RC circuit for the EGO input has a cutoff frequency of ~700hz (R=1k, C=.22uF)

What if I just changed it to match the MAT input filter, with a cutoff frequency of 70hz? (R=2.2K, C=1uF) Per the calculator the transient response would go from .0015s to .015s but the LC2 only runs at 12hz so the transient only makes up 18% of the time between updates and would give me 15db or so of supression at 500hz. That would turn my .2V noise into .036v noise, combined with the improvement of grounding on the chassis would make the noise .009V, which should be acceptable. I do lose some transient response, but I should be able to tune in the EGO delay somewhere right?

im still going with the grounds are fine and you need to look at the wb's 0-5v signal output.

but if you wanna build crazy circuits you absolutely dont need and wont fix the problem.... thats on you :P


LC1s, LC2s, MTX-Ls are all very common among members here. So are MS Labs MS3-Basics; no one else here is jump through hoops like this. The problem lies within the ECU or WBo2.

I did look at the 0-5v output, when measured relative the the analog ground of the MS3 it has a .2V 500hz square wave on it. That's the whole reason for messing with it.

How does it look measured relative to the single ground on the LC2? If that has the same 0.2V square wave your LC-2 is toast. If not you need to redo your wiring.

I talked to innovate today, the PCB for the LC-2 has a common ground plane that the processor sits on, without any jumper resistors or similar to be able to modify it. I would have to lift a pin on the chip and then solder a jumper onto it to separate the grounds. They suggested that they have seen lots of issues when installed into NA Miata, and the the best solution is to run a wire directly back to the battery up to the ECU/LC2 to ground to.

So I got some 10 gauge wire and ran it up to the passenger compartment. I added a wire to pin 21 of the DB37 which is another chassis ground, and attached it to the 10 gauge wire. The wire off of the DB37 is much smaller 24 gauge though so its not an ideal final solution. The ground\signal bounce was much much improved, though still present. I could measure the ground bounce at the ECU, but not at the exposed end of the 10 gauge wire, so I suspect with more copper grounding the ECU I could drive the issue to ground.

With that in mind I looked at the stock connectors on the other side, plan would be to strip and wrap solder 20 gauge wire to each of the 4 ground wires, then tie all 4 leads to the 10 gauge wire to the battery. Investigating this I noticed that 3 of the 4 ground pins on the ECU are not connected to the chassis ground pins on the DB37 connector. The other 4 ground pins are connected to the analog ground. This seems incorrect, considering the power put into the chassis ground by injectors/WB heater, etc.. I would expect the chassis ground to have 3 pins, and the analog ground to have 1. Can someone else with a MSlabs MS3 basic check this out?

Ground Bounce with key on, engine off

https://www.miataturbo.net/attachmen...ine=1453869282

Ground Bounce with engine running

https://www.miataturbo.net/attachmen...ine=1453869282

12V car running

https://www.miataturbo.net/attachmen...ine=1453869282

Signal Bounce relative to pin 3 (analog ground)with ground to battery

https://www.miataturbo.net/attachmen...ine=1453869282

Signal Bounce relative to end of 10 gauge wire (should be noted there was no bounce measured at the 10 gauge wire referenced to pin 3 analog ground)

https://www.miataturbo.net/attachmen...ine=1453869282

So the scales arent the same in your plots, but it looks like you have a significant DC offset between the analog ground and the chassis ground.

This could be the smoking gun bud.

Pin 3A on the front connector is used as the I/O ground (injectors, valves, etc). Pins 3B-C-D are used for the digital/analog logic and as a ground for the analog sensors (TPS, CLT, IAT).

On the DB-37, pins 2 and 21 are connected to pin 3A only, while pin 3 is connected to 3B.

So in the OEM harness, pins 3A and 3B are black and ground out somewhere, not sure where that is but they ground to the same location. Pins 3C and 3D are green/black and I have them grounded on the passenger side of the engine bay, near the washer fluid tank.

Since the problem I am seeing is exclusively related to the ground on pin 3A, I could just add a ground connection to the battery to that wire, or I could do all 4 pins. I can't see there being an issue with tying them all together on the harness side of the ecu. But you havent tied them together on the mainboard so I want to confirm. I really don't want to tie pin 21 to the ground like I have it, as that potentially puts the ECU between the starter motor and the battery.

what happens when you simply ground the LC2 to the battery (or directly to 3B) and remove it from the extra ECU input/output pigtail -- leaving everything else the same?


if anything you want to remove these grounds from the chassis so they actually ground at the ECU like a real sensor ground should.

Those are the grounds for the ECU, you can't remove them. It looks like there are 4 wires there, two of them are green/black, two of them are black, so I think that's all of the ground pins from the ECU.

Reviewed a ton of information on miata ground schemes and came to the conclusion that the ground wires from the ecu (connecting to pins 3A-3D) should be tied to the head, not the chasis. The megasquirt guys want the ecu tied to the motor, the NB cars have their ecu ground on the motor, and the FM ecu install instructions have you cut the wires from 3C and 3D and run a new ground wire to the head. So I cleaned the junctions with sandpaper and bolted them down to the head. I also did the same with the 5 wire junction block under the brake booster. I also added a new ground strap from the head to the chassis by the dipstick for now it's ghetto wire wraps under bolts, I'll add crimp terminals if it helps. I also cleaned a bunch of corrosion off of the positive terminal on the alternator. I'm going to verify that the ecu terminals only ground to the wires I just attached to the head tomorrow. I really don't want the ECU in the path between the starter and battery.

...

smh.


if you don't know the difference between the solid black and the black/green wires, then you shouldn't be making conclusions like above.

oh good idea. Let's rule out the ECU being the source of the problem and not the rest of the car's oe wiring that was perfectly fine before the MS install and 100% of all other MS installs.

I agree, rewire the car is the next logical step. For sure.

I know the difference. On the OEM harness the terminal rings they go to have two wires into each, one is green/black and the other is just black. The "good" oem setup treats them both the same, though I can't remember where they were grounded before, but I'm 100% sure that they were tied together, I didn't alter that part of the harness. The oem setup was an AFM with a narrow band with a large swing so it would be much more tolerant of noise on the signals anyway. If I were wiring it up brand new I would run the 3 signal ground pins to the head, and the chassis ground either to a local chassis point or a direct battery return.

Not that the difference even matters once I slap the MS3 on it. On the OEM ecu the green black wires are sensor grounds, the black are power grounds. With the MS Labs unit, 3 of them are sensor grounds, and only one is a power ground.

I fully intend to bypass the ecu and ground the LC2 directly to the battery. Just have not gotten there yet, and without fixing the ECU grounding, it will end up with over a volt of bias between the ECU and the LC2