Passing Emissions with Turbo Power - Page 2 - Lexus IS Forum
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post #16 of 21 (permalink) Old 05-15-2019, 08:10 AM
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Wow, it's starting to sound like cracking the OEM ECU might be an easier task.
Engineering software to reprogram/tune the stock ecu is not easy lol. Thats why everyone tries to fake the signals
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post #17 of 21 (permalink) Old 05-15-2019, 08:21 AM Thread Starter
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"register" it in Maricopa (like I do) or payson where there isnt any emissions
This is your best bet
Except that I would like to avoid having to do that.

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Engineering software to reprogram/tune the stock ecu is not easy lol. Thats why everyone tries to fake the signals
/s That was the joke. Again, I've been hearing some back and forth across the forums about the O2 sims. Some say they work, and others complain that they don't completely work especially with the trick lean and rich conditions the computer will run to test the downstream O2s.
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post #18 of 21 (permalink) Old 05-15-2019, 08:54 AM
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I've been hearing some back and forth across the forums about the O2 sims. Some say they work, and others complain that they don't completely work especially with the trick lean and rich conditions the computer will run to test the downstream O2s.
The ecu doesnt care about the rich/lean on the downstream. Only the upstream. You can leave the OE O2s for the with the car in the exhaust system upstream (and add additional O2s for your standalone). But then when you tune, your stock ecu is going to freak out about the variation from the stock parameters.

You only want an O2 sim is only after the cat. Entire idea of the O2 sim is to make the ecu think theres a cat there still. You dont want a cat because cat on a turbo car is like exhaling through a straw.
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post #19 of 21 (permalink) Old 05-15-2019, 11:37 AM
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The ecu doesnt care about the rich/lean on the downstream. Only the upstream. You can leave the OE O2s for the with the car in the exhaust system upstream (and add additional O2s for your standalone). But then when you tune, your stock ecu is going to freak out about the variation from the stock parameters.

You only want an O2 sim is only after the cat. Entire idea of the O2 sim is to make the ecu think theres a cat there still. You dont want a cat because cat on a turbo car is like exhaling through a straw.
Basically, the upstreams need to switch from rich to lean, and do it fast. If they don't switch, they're bad. If they don't switch fast enough, they're bad:

This diagram gives idea of good and no good regarding whether or not they're switching:


This diagram describes if it's switching fast enough. The slope of the O2 sensor signal is calculated by the ecu, and the slope must be steep - or else it is too slow:



Regarding downstreams:


You've gotta understand the purpose of the O2 sensors... We know from above that a properly controlled engine will have it's fuel mixture purposefully dithered between rich and lean - quickly. This is because catalysts work best when run that way. However, if the catalyst itself (or themselves) are working correctly, the fuel mixture should be fully oxidized and normalized. Thus, the downstream O2 sensors are there to diagnose the operation/efficiency of the catalyst...

So basically:

1. If the DSO2 switches kinda like the upstreams, it means the catalyst isn't having any effect on the exhaust, so therefore the catalyst is most definitely bad.
2. The DSO2 should read full-tilt lean for seconds at a time, else the catalyst's "oxygen storage capacity" is in question.
3. During decel fuel cut, the DSO2 needs to immediately recognize the change in fueling. This is part of the diagnostic of the sensor itself, not the catalyst.

Are the "O2 sims" smart enough to massage the signals all the time to satisfy the ecu?
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post #20 of 21 (permalink) Old 05-15-2019, 05:01 PM Thread Starter
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The ecu doesnt care about the rich/lean on the downstream. Only the upstream. You can leave the OE O2s for the with the car in the exhaust system upstream (and add additional O2s for your standalone). But then when you tune, your stock ecu is going to freak out about the variation from the stock parameters.

You only want an O2 sim is only after the cat. Entire idea of the O2 sim is to make the ecu think theres a cat there still. You dont want a cat because cat on a turbo car is like exhaling through a straw.
So basically:

1. If the DSO2 switches kinda like the upstreams, it means the catalyst isn't having any effect on the exhaust, so therefore the catalyst is most definitely bad.
2. The DSO2 should read full-tilt lean for seconds at a time, else the catalyst's "oxygen storage capacity" is in question.
3. During decel fuel cut, the DSO2 needs to immediately recognize the change in fueling. This is part of the diagnostic of the sensor itself, not the catalyst.

Are the "O2 sims" smart enough to massage the signals all the time to satisfy the ecu?
My question exactly. The computers in cars have gotten incredibly sophisticated and in some ways the Lexus ECUs were ahead of the curve from what I understand. And it seems many on the forums have the same sentiments. Like I said, some people seem to have zero issues with a sim, and others can't go 5 miles without a MIL. If there is a sim that can accurately and consistently fool the ECU, then I'd be more than happy to take a look at it. But it seems most are a crap shoot at best.
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post #21 of 21 (permalink) Old 05-15-2019, 05:29 PM
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My question exactly. The computers in cars have gotten incredibly sophisticated and in some ways the Lexus ECUs were ahead of the curve from what I understand. And it seems many on the forums have the same sentiments. Like I said, some people seem to have zero issues with a sim, and others can't go 5 miles without a MIL. If there is a sim that can accurately and consistently fool the ECU, then I'd be more than happy to take a look at it. But it seems most are a crap shoot at best.
As I kinda mentioned before, referencing the dude on clublexus trying to get his diagnostic monitors to work...

I don't see why the OEM ecu can't be satisfied, provided the catalysts and O2 sensors are in place and functioning.

I think the key to it may be getting the medium load fueling correct. No monitors run during WOT, so no worries about the fat mixture during heavy acceleration. However, during light and medium load, the mixture MUST switch lean/rich/lean. If you calibrate the engine to run dead steady from a linear-output wideband, the OEM narrowband sensors are going to "stick rich", "stick lean", or have "slow response" (because the slope of the lean/rich switch isn't steep enough and they're not constantly passing thru the .55V stoich point), which will not satisfy the upstream O2 monitor (reference my last post) or the operational needs of the catalyst, which will in turn not satisfy the downstream O2 sensor monitors.

I wonder if anybody has tried this with a good programmable ecu with NARROWBAND closed loop feedback?

The ecu might additionally need calibrateable gain on the PID algorithm driving the closed loop (to get amplitude and frequency of the waveform right). Hell, now that I think about it, calibrateable PID of wideband closed loop oughta be able to achieve this, but the non-linear characteristic of a narrowband might achieve it naturally.

Also, part of the DSO2 monitor strategy relies on proper response to a DCFC... So getting the fuel cut calibrated correctly would also be a requirement.
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Last edited by Hodgdon Extreme; 05-16-2019 at 03:47 PM.
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