Failed Emissions.

[ck80]

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)

Top of my head:

Code 12 - just means the diagnostics are being read from the ecm. No action necessary.

Code 21 - has the trans acted funny at all? Often this would be a poor electrical connection, damaged wire inside the insulation, something of that sort. I'd check the plug and wiring. Aside from a visual fail for a light,, I don't see that being an issue with the emissions.

Code 35, is that recent or before doing the carb? With things being unplugged for rebuild the IAC resets/relearns by being driven around a bit.

If your idle speed is high due to a vacuum leak it will trigger the code 35.

When replacing the carb, did you replace the old rubber lines, or just slip back on the old ones? Could have a vacuum leak somewhere.

Vacuum leak could cause the computer to call for a/f mixture to be off leading to some issues.

Code 45 would be your o2 sensor reading too little oxygen as I was guessing initially.

Old timer trick: spray around the base of the carb, and at various junctions with either carb cleaner or wd40 with the engine idling. If you hear the rpm race momentarily, that's because the vacuum leak pulled in some spray and let the engine race a little meaning you're in the neighborhood of the leak. Works on intake manifold, carb gasket, etc.

 

[TheSaint]

I haven’t messed with most of the vacuum system tubing. There is a part right before the O2 and Cat that I was concerned about (I can attach pic). I didn’t seem to move much and looks to be a sort of valve that I assume introduces more oxygen into the exhaust but I’m not for sure.

 

[Clone TIE Pilot]

That is the heat riser valve. It cuts off exhaust flow at cold startup to warm the engine faster. its supposed to open once the engine is warm, I would check it for faults like a leaking diaphragm or frozen valve, etc.

Torquing the carb is a bit tricky, it require an inch/lb torque wench. Torque it to 144 in/lbs at first then run the engine. After a few heat cycles measure the torque of the carb mounting bolts. If they are at least still 60 in/lb, no retorque is required, if less than 60 in/lb, then retorque to 96 in/lb. The old thick discontinued GM carb gaskets are the best, the thick Fel-Pro gaskets are not as good.

 

[TheSaint]

That is the heat riser valve. It cuts off exhaust flow at cold startup to warm the engine faster. its supposed to open once the engine is warm, I would check it for faults like a leaking diaphragm or frozen valve, etc.

Torquing the carb is a bit tricky, it require an inch/lb torque wench. Torque it to 144 in/lbs at first then run the engine. After a few heat cycles measure the torque of the carb mounting bolts. If they are at least still 60 in/lb, no retorque is required, if less than 60 in/lb, then retorque to 96 in/lb. The old thick discontinued GM carb gaskets are the best, the thick Fel-Pro gaskets are not as good.

Thanks I can try this out as well. I’d really like to go through all of it piece by piece and just fix everything that needs fixing as I go I just don’t have a clue as to where to start. I appreciate all the feed back and tips!

 

[JimmyCamino]

A cold engine will put out higher HC and CO, so that's where the heat riser helps. Also, if you have a thermostat stuck open it can prevent the engine from getting hot enough for more complete combustion.

 

[TheSaint]

A cold engine will put out higher HC and CO, so that's where the heat riser helps. Also, if you have a thermostat stuck open it can prevent the engine from getting hot enough for more complete combustion.

I recently had the radiator rebuilt, I didn’t change the thermostat. I didn’t even check it.