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Hi All, I just purchased a 1985 Supra with the 5M-GE motor. The motor has been rebuilt with new pistons, rings, bearings, valves, valve springs, retainers etc. The rebuild has been to stock spec.

The car has a catalytic converter and also has the stickers for emissions controls (attached). Do these cars that are mainly stock, have problems passing CA smog? The seller said he was pretty confident based on all the emissions equipment still being on the car that it will not be a problem.

At 35 years, it may need a new cat, and I am ok with doing that. Any thoughts are welcome!

Thanks

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It's pretty hard unless it runs very good. The passing numbers were quite low last I snogged mine. The EGR is commonly plugged up. The converter needs to be stock or have an eo #
 

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I just got my car to pass. Was marginal, but passed. If everything in your engine is pretty fresh, and all the smog gear is correctly hooked up and working, you should pass without much trouble.

I failed first few times due to high NOX. Fixed the EGR by replacing the vacuum modulator and that did the trick.
 

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Discussion Starter · #5 ·
I just got my car to pass. Was marginal, but passed. If everything in your engine is pretty fresh, and all the smog gear is correctly hooked up and working, you should pass without much trouble.

I failed first few times due to high NOX. Fixed the EGR by replacing the vacuum modulator and that did the trick.
Thanks! Are you in SoCal? Did your car have a newer Cat, or the original?
 

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CA's rules are rigged to fail older cars, they really want them off the road to be replaced with Teslas! Some things you can do to prepare:

1. test EGR system beforehand to make sure it's working! Test vsv, modulator and EGR valve itself according to manual. Make sure final test of manually applying vacuum to EGR valve causes engine to shudder and stall. This confirms EGR passages from head to intake is clear. Wouldn't hurt to disassemble and clean out all carbon deposits.

2. verify O2-sensor is operational. Best test is with oscilloscope showing full swings between 0.15-0.85v




For test itself:

3. pour in 1:5 ratio of denatured alcohol (1-gal in 5-gal of petrol). Or 1:4 ratio of E85. This cools down combustion and lowers NOx. Also on-board oxygen supply of alcohol will reduce HC

4. run car HARD before arriving at smog-station. Like 3rd-gear WOT with brakes ON for 2-3 blocks leading up to smog-station so cat is nice and HOT. DO NOT turn off car, idle in their driveway. Best to make appointment so you can pull right up on rollers as you pull in so it spends as little time idling as possible

5. do pre-test if available. This used to not be reported to State and you can inspect test-results and update car if necessary. Now I think it's still logged to State, but doesn't count against you if it fails.

6. depending upon results, you can adjust ignition-timing to change criss-cross ratio of HC vs. NOx. You're allowed +/- 3 degrees ignition-timing either way. High HC can be lowered by advancing ignition-timing (raises NOx). Conversely if you have high NOx with low HC to spare, you can reduce ignition-timing to lower NOx and increase HC.

 

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Impressive tips!
(I'm so happy I don't have to do smog tests..)
 

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As Dannoxyz stated 100%...

I would also recommend an oil change as well...dirty oil carries a lot of unburned hydrocarbons in it!!

The seller is required under CA DMV to provide a recent smog test (less than 90 days I believe) to sell the vehicle.

ALSO you can check the vehicles smog history here...

Enter VIN # or License plate...

 

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Now, there's possibility cat is no longer 100% efficient. This will show as high HC and NOx even with working EGR system. Not sure when transition was to ceramic substrate cats was, but those do not melt and clog up matrix when overheated. Most common cause of cat inefficiencies are contaminants coating surface of catalytic mesh. This prevents catalysts from touching and reacting exhaust gasses into more inert H2O and CO2.

Forget about videos and old-wive's tales about "washing" your cat clean with solvents. Deposits are sulphur/phosphorus and organo-metallics from fuels and oils. No kind of polar or non-polar solvents of any kind will remove them. You need to use series of acid treatments to remove the deposits and cat will be good as new. This process has become more attractive due to outrageous CA extortion on "approved" cats (exact same part as 49-state cats with EO# stamped on them).

Check out this paper: ResearchGate - Reactivation of an Aged Commercial Three-Way Catalyst by Oxalic and Citric Acid Washing.

Full article - Academia

Google for "Reactivation of an Aged Commercial Three-Way Catalyst by Oxalic and Citric Acid Washing, Environ. Sci. Technol. 2006, 40, 2030-2036" to find the original study.

With some real-world experience from 18-yr ASE master-mechanic:

Actual before and after smog-test numbers here:
 

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Danny that's some high level haz mat decon sheesh my friend!!

Beyond Impressed with your breadth of knowledge on this topic and in general!!
 
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Pretty sure the cat on this particular car isn't working so hot considering there isn't one.... 🤔

I think we scared the buyer off since he's trying to back out on BAT and hasn't been back in 3 days.

 
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Danny that's some high level haz mat decon sheesh my friend!!

Beyond Impressed with your breadth of knowledge on this topic and in general!!
Why thank you AJ! Having many old cars and bikes that I prefer over newer models have always placed me at odds with State for decades. Feels like some sort of arms-race where they come out with new regulations to defeat me and I have to devise ways around it! Lots of research and trial & error over the years.

And I like to mod my cars to extreme. Big-bore, bigger and bigger turbos for more boost. Gets real hard to pass visual-inspection. Had one track car where I would have to remove engine and re-install factory engine every time I wanted to get smog-tested! :mad:
 

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@PVsupra1985 no need to get discouraged. You just have to install new cat. There are many simple options:

1. Go to State CA's ARB catalytic database and look up your year & model: Aftermarket Catalytic Converter Database

2. search for various vendor's part# listed for that model. This automatically selects CA-approved catalytic.

3a. get ready-to-go direct-fit catalytic and that's it!!! Won't have any problems passing smog
RockAuto - Walker 81171
Summit Racing - Walker 81171
Amazon - Walker 81171
Oreilly - Magnaflow 332888

3b. or use CA-approved universal cat and have muffler-shoppe weld on 2 flanges and bolt it in, shouldn't be more than $75-125.
ECS Tuning - Magnaflow 332041
RockAuto - Walker 81126 (note EO# is same as direct-fit, it goes by application)
Amazon - Walker 81126

3c. or DIY CA-approved universal cat. This is what I did on '88 Porsche 951 I got from Chico, CA area about 7-yrs ago. Not realizing I went from rural area without NOx-testing to enhanced smog-test area with NOx, it failed horribly with 3x NOx allowable and was flagged as gross-polluter. This car does everything in software and doesn't need PCV or EGR to pass smog. Due to extreme amount of NOx, I assumed cat was just hollow shell. So I ordered Magnaflow 334009 CA-approved cat.

I didn't like how PO used smaller cat than exhaust-pipe and narrowed down flow. So I bought 3" version (same EO# as 2") and made some cones to adapt it to exhaust. Sure enough, when I cut off old cat, it was empty!


Then welded on new one and re-installed. Made sure to angle cat slightly so smog-tech can easily read CARB EO# on cat. Took all of 3-hrs, slightly longer than normal because this car has 2nd exhaust pipe for wastegate-dump that joins main pipe after catalytic


Went back to smog-station for free re-test and it passed easily with NOx at only 3% of what it was before with no cat! :) Previously NOx in +2100 range.

 

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Also note that this particular Porsche doesn't require "Thermostatic Air Cleaner", a sealed-airbox. So I can actually run massive K&N filters and it's technically legal. But some smog-techs grumble about it during visual-inspection. I make them pull out book and look up that it's not required.



This is what's needed for 800-CFM flow! It would actually suck in and collapse previous 4" K&N filter.



 

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I just got my car to pass. Was marginal, but passed. If everything in your engine is pretty fresh, and all the smog gear is correctly hooked up and working, you should pass without much trouble.

I failed first few times due to high NOX. Fixed the EGR by replacing the vacuum modulator and that did the trick.
Where can you buy a vacuum modulator or EGR valve. My Toyoto dealer never seems to have parts for my 1985 5M-GE.
 

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First step should be completely disassemble EGR system and clean out all passages. Lots of carbon build-up over years. Especially in that Z-shaped pipe connected to EGR valve. On one car, it was so plugged up, I had to use tiny wire-wheel on snake attached to drill to ream it out! :eek:

If you've tested modulator according to manual and confirmed it's not working, there's some other Toyota models that may work. I'll have to look up modulator test-procedures and find another with same process and results. Meanwhile, you can look for these interchanges at parts-countres:

Toyota 25870-43030
Airtex 2F1064
Carquest 73-9735
Wells EVM47
SMP - Standard Motor Products VS183

You can also try slightly different part. Adapt to fit with different hose, or factory hose may actually fit on bottom. Amazon's good about returns, can send it back if it doesn't work.

But again, test and confirm part is bad before replacing it. Otherwise, swapping perfectly-working parts with brand-new perfectly-working parts will change nothing and symptoms will persist. Because root-cause is elsewhere.
 

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Where can you buy a vacuum modulator or EGR valve. My Toyoto dealer never seems to have parts for my 1985 5M-GE.
There's also remote chance EGR valve itself is bad. Test by:

1. disconnect hose between modulator and EGR valve
2. attach vacuum-pump to EGR valve
3. start up car and idle
4. apply vacuum to EGR valve
5. engine should stall and die

If engine doesn't die, it could be bad EGR valve, extremely rare. Most likely EGR passages clogged. That's why you want to clean out EGR passages 1st. Otherwise tests for defective parts won't work properly.
 
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