Failed Emissions.

TheSaint

Not-quite-so-new-guy
May 26, 2021
30
8
Hi everyone! I’ve failed emissions on my car again, have been trying to find the problem with no luck. Does anyone have any suggestions? Any help would be appreciated! 1984 Chevy Monte Carlo V6 229 3.8L
 

scoti

G-Body Guru
Supporting Member
Sep 5, 2019
814
93
Texas
Can you share the testing info/readings? What was out of range or was it a visual/equipment failure?
 
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TheSaint

Not-quite-so-new-guy
Thread starter
May 26, 2021
30
8
image.jpg
 

scoti

G-Body Guru
Supporting Member
Sep 5, 2019
814
93
Texas
You need to get the codes pulled so you know what the computer indicates. Most cars 'auto-fail' if the check engine light is on.

What's the drivetrain & maintenance history for the vehicle?
When was the last tune-up?
When was the last oil change?
How old is the catalytic converter?
 

ck80

Comic Book Super Hero
Feb 18, 2014
2,811
113
With the age of these cars it's pretty common to pull the cat converter only to learn it's hollow straight through, the catalyst having melted down years ago from a car that ran rich and generated excessive heat inside.

HC and CO that high lend themselves toward running rich and the catalytic not keeping up with the unburnt residuals.

Step 1: put a paperclip into the dash port and pull the code(s) by counting the dash blinks.

Step 2: unhook the battery for a couple minutes, test drive the car, and see which if any codes re populate after you clear the ecm.

Without knowing what code is in the engine, being an 84 you may have an o2 sensor that could be fouled if that much fuel is coming out the back.

A healthy tuned up ignition plugs/wires/cap/etc wouldn't hurt things, but, my guess is there's other issues.
 
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TheSaint

Not-quite-so-new-guy
Thread starter
May 26, 2021
30
8
You need to get the codes pulled so you know what the computer indicates. Most cars 'auto-fail' if the check engine light is on.

What's the drivetrain & maintenance history for the vehicle?
When was the last tune-up?
When was the last oil change?
How old is the catalytic converter?
The OBD1 I got read 4 codes at one point. I took it for emissions last year really high HC and CO. I changed plugs, 02 sensor had an oil change. I rebuild the carb, changed throttle position sensor, sent it off to be live tested it came back and I was told it was running great. I just ordered a new cat and installed it last Friday before the second emissions test. I had the radiator rebuilt recently. The codes reading are

12-Diagnostic mode; no distributor signal to Electronic Control Module; System PASS

21-Throttle position sensor (TPS) - signal voltage to high

35-Idle air control (IAC) system problems - can not set desired RPM or idle speed actuator (ISA) carbureted system problems

45-Rich exhaust indicated (Left side on dual oxygen models)
 

TheSaint

Not-quite-so-new-guy
Thread starter
May 26, 2021
30
8
With the age of these cars it's pretty common to pull the cat converter only to learn it's hollow straight through, the catalyst having melted down years ago from a car that ran rich and generated excessive heat inside.

HC and CO that high lend themselves toward running rich and the catalytic not keeping up with the unburnt residuals.

Step 1: put a paperclip into the dash port and pull the code(s) by counting the dash blinks.

Step 2: unhook the battery for a couple minutes, test drive the car, and see which if any codes re populate after you clear the ecm.

Without knowing what code is in the engine, being an 84 you may have an o2 sensor that could be fouled if that much fuel is coming out the back.

A healthy tuned up ignition plugs/wires/cap/etc wouldn't hurt things, but, my guess is there's other issues.
The OBD1 I got read 4 codes at one point. I took it for emissions last year really high HC and CO. I changed plugs, 02 sensor had an oil change. I rebuild the carb, changed throttle position sensor, sent it off to be live tested it came back and I was told it was running great. I just ordered a new cat and installed it last Friday before the second emissions test. I had the radiator rebuilt recently. The codes reading are

12-Diagnostic mode; no distributor signal to Electronic Control Module; System PASS

21-Throttle position sensor (TPS) - signal voltage to high

35-Idle air control (IAC) system problems - can not set desired RPM or idle speed actuator (ISA) carbureted system problems

45-Rich exhaust indicated (Left side on dual oxygen models)
 
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