Differential swap, TCM Tunes and Smog Inspections

Caprice and GM-related general tech topics. Questions & topics on vehicle tuning, HP Tuners use, etc.....
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Gboy
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Joined: Mon Aug 14, 2023 3:50 pm

Differential swap, TCM Tunes and Smog Inspections

Post by Gboy »

Looking to do a differential swap(Camaro SS 3.27 LSD) and everything I read it needs shift points changed in the TCM. With the current California smog inspections looking for changes to the ECM, are changes to the TCM tune(shift points) checked and could they cause a failed smog inspection?
I did a quick search and really didn't come up with anything. If there's a sticky or a previous post addressing this please point me in that direction. Thanks.
smwalker
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Re: Differential swap, TCM Tunes and Smog Inspections

Post by smwalker »

We have been discussing it a bit here:
https://www.newcaprice.com/forum/viewto ... 255#p35255

Summary, Only the Engine Diagnostic file seems to be polled. So TCM should be safe for changes. And since they seem to be ignoring any cars with AFM for tunes you are safe there as well. For now.
Steve Walker
Azusa, CA
'11 PPV 9C3 Huron White
Gboy
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Re: Differential swap, TCM Tunes and Smog Inspections

Post by Gboy »

I saw that thread, but didn't see anything that was related to the TCM. Some interesting info. Thanks.

Just being nosy (and not knowing a lot about tuning an ecu/ecm), how much adjusting can be done? Not deleting cats or anything Just optimizing fuel/timing etc. Will that be picked up by State during a test? Not just talking our vehicles, but any others? Sorry if this too much a noob question.
smwalker
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Re: Differential swap, TCM Tunes and Smog Inspections

Post by smwalker »

That's the unknown. We know no monitors can be turned off or bypassed. So any adjustments that could trigger a cel or prevent a monitor from completing will be a problem. So I think anything you do with in those parameters is fine for the AFM engines.
Steve Walker
Azusa, CA
'11 PPV 9C3 Huron White
JoeR
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Re: Differential swap, TCM Tunes and Smog Inspections

Post by JoeR »

California SMOG Checks will run CVN numbers that are stored in the PCM. They're generated using a complex algorithm and can't be spoofed. If you make any engine related changes, even something as harmless as changing fan cycling temps, it changes the CVN. If you don't have OEM CVNs in the vehicle, you can't pass SMOG. Transmission changes are OK. Engine changes are not.
Joe
smwalker
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Re: Differential swap, TCM Tunes and Smog Inspections

Post by smwalker »

JoeR wrote: Wed Jul 03, 2024 9:57 pm California SMOG Checks will run CVN numbers that are stored in the PCM. They're generated using a complex algorithm and can't be spoofed. If you make any engine related changes, even something as harmless as changing fan cycling temps, it changes the CVN. If you don't have OEM CVNs in the vehicle, you can't pass SMOG. Transmission changes are OK. Engine changes are not.
Joe
Except for GM AFM engines. They are letting them through because so many people have had to tune out CEL after a DOD delete.

BUt yu are correct any other non AFM enging any change is a fail. Although may of the european vehicle tuners have seemed to find away around it.
Steve Walker
Azusa, CA
'11 PPV 9C3 Huron White
JoeR
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Location: Central, NC

Re: Differential swap, TCM Tunes and Smog Inspections

Post by JoeR »

smwalker wrote: Wed Jul 03, 2024 10:00 pm
Except for GM AFM engines. They are letting them through because so many people have had to tune out CEL after a DOD delete.

BUt yu are correct any other non AFM enging any change is a fail. Although may of the european vehicle tuners have seemed to find away around it.
That's actually pretty cool of them to give them an exception, even though DOD cars can be just as clean after a delete.
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