1984 El Camino Conquista failing first smog check ever

MarcD

Not-quite-so-new-guy
Apr 15, 2023
9
15
3
Hi, All, and thank you for a great forum! I posting here because my 1984 El Camino Conquista (305 V8/ 4 bbl) is failing smog test...on its first ever test.

The El Camino was purchased new by my father in San Francisco; as he lived in a non-biennial inspection county in California, the car was never smogged during his ownership; beyond religiously 3500 mile oil changes, he had the car serviced sporadically at a local good ol' boy shop. When he passed at 94 in 2013, I inherited it with probably 100k miles (odometer broken), and in California that doesn't require a smog inspection for in-family transfer of ownership.

The car remained registered in the non-biennial county until this year, when we sold the house. I now have to register it in San Francisco county, so it must pass smog....which it doesn't. All the factory equipment appears to be in place and the check engine light was not coming on, so I took it to a test-only local inspection station known for experience with older cars.

It passed all the visual inspections, and failed only NOx, with the following readings:

15mph CO2 13.7 O2 2.6 HC 30 (93 max allowed) CO 0.01 (.62 max) NO 1002 (783 max allowed)
25mph CO2 13.6 O2 2.7 HC 25 CO 0.00 NO 1018

The smog technician noted that the EGR valve appeared to be non-functional; manually lifting the diaphragm at idle had no effect, and the valve wouldn't hold vacuum with a hand pump connected to the EGR hose port, suggesting a broken diaphragm. He suggested having the EGR replaced and ensuring all the vacuum lines and sensor wires were intact.

I took the car to a mechanic who replaced the EGR, and found the coolant temperature sensor was defective, and replaced it and its connector. He also discovered the thermostat was missing, so he flushed the cooling system, installed a 180 degree thermostat and refilled with fresh coolant/water mix.

Following these repairs, the mechanic suggested adding a can of Sea Foam to the fuel tank and driving it around while before re-testing; added 16oz Sea Foam to 16 gallons gasoline and drove for 30 miles.

On the re-test, results were basically the same. The Smog technician suggested "adjusting the carburetor for a richer mixture" because the high NO was likely due to a lean mixture condition, and also consider replacing the O2 sensor. The mechanic suggested just driving it around some more with the Sea Foam, and felt there was no point in replacing the O2 sensor.

I found this excellent forum, and located the resource videos regarding CCC carburetor smog systems. I was particularly overwhelmed by the "CCC drivability" video, with it's punches and chisels on the carb base (at around 7:00) to access the mixture screws! Given the car's service murky history (and the absence of a thermostat), I looked at the carb on the car and sure enough, the base had been "serviced' with the plugs covering the mixture screws missing. I'm not familiar with the fuel circuits of a Quadrajet...are these the main jets?


So, what to do now? I'm fortunate that the smog shop will re-test at no charge (the technician is the owner and really likes El Camino's), but I'm reluctant to just fool around with the mixture screws and hope for the best. The "CCC Drivability" video mentions (at 9:06) that the mixture screws setting can be anywhere from 1.5 to 6 turns...given the high NO and low HC/CO, it IS likely that the engine's running lean and with high combustion chamber temperatures, but I'm unclear about the ECM's role in affecting air/fuel mixture in a CCC Quadrajet. No wonder they invented fuel injection!

Any help is appreciated; This car's been in my family since new, and I'd hate to retire it or give it up for an LS motor swap.

Thanks,
Marc
 
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86LK

Royal Smart Person
Jul 23, 2018
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it may be time for a carb rebuild. if so, take a look at Mountain Man fuel systems based out of Arkansas. it certainly wouldn't hurt if someone has been diddling with the carb in the past. MM will ask you all about your setup and intended usage and your current situation. many folk can vouch for their reputation.
 
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PVDave

Apprentice
Oct 28, 2021
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18
Arvada, CO
The California emissions test checks emissions on a dynamometer with the vehicle under load, so the mixture screws at the base of the carburetor shouldn't have much effect on the readings.

Under load, the CCC system uses an oxygen sensor in the exhaust and a Mixture Control solenoid on the carburetor to keep the fuel mixture at stoichiometric (14.7 to 1). Given the CO2 reading is quite high and the CO reading is very low, the system appears to be controlling the mixture as designed- If the system was extremely rich the CO numbers would be at 2 to 6 percent.

The repairs you've done were focused on reducing the NOx numbers, and since the fixes have not impacted those numbers, I'd suspect a worn out catalyst. NOx is the hardest pollutant to break down, so older cats tend to do a good job on CO and HC, while failing to break down NOx. You don't mention mileage, but if the car has the original cats and mileage is around 100k, it may require a new cat to pass.
 
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Ribbedroof

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Supporting Member
Jan 4, 2009
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Wellston, OK
I am far from an emissions technician but it was my understanding that one of the reasons they went to a 195° thermostat on emissions cars was to increase the operating temperature to reduce emissions. The 180 thermostat may or may not be hindering you from achieving your goals
 
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ck80

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Feb 18, 2014
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It used to be CA had two things that might help you, but, it was years ago.

1) if you wanted to register it with antique plates, there was a subsection that as long as it was 25 years old, (not the 1975 exemption) and used 'primarily for' exhibition and club events, again, it didn't say exclusively for, you could get the special plates and be exempt from smog testing although visual tests for the components and mufflers were still required.

2) if you failed an emissions test related to re-registration, and, NOT related to taking ownership, if you paid the first $100 in repairs, the state would reimburse via grant on repairs above that amount made by a licensed emissions repair servicer - ie not buying parts and installing yourself.

Not sure if either is applicable anymore, but, it's an option.
 
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Texas82GP

Just-a-worm
Apr 3, 2015
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Spring, Texas
Based on prior experience with a GM CCC car of this era, I agree that she will pass with a new catalytic converter.
 
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Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
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Galaxy far far away
First check for vacuum leaks as they will lean out fuel mixtures. The main jets in the carburetor are computer controlled. The only jets you can adjust are the idle mixture jets along with the idle air bleed valve.

Ideally you should be checking the air/fuel mixture dwell with a analog dwell meter. If the car is running lean the dwell meter will quickly tell you. A 180 t-stant is too cold, the computer is designed for a 195 t-stant, warmer engines burn cleaner.

The cat convertors in these cars requires the smog pump to inject air into them to operate correctly.
 
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maxi426

Apprentice
Sep 20, 2018
86
82
18
Has anyone actually confirmed the operation of the EGR system? When the EGR valve is manually opened at idle, the engine should stall, or at least run roughly. You stated originally that there was no effect on the idle when the valve was opened manually. This would indicate that the passages in the intake manifold may be plugged.
 
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MarcD

Not-quite-so-new-guy
Apr 15, 2023
9
15
3
Hi, All, and thank you for a great forum! I posting here because my 1984 El Camino Conquista (305 V8/ 4 bbl) is failing smog test...on its first ever test.

The El Camino was purchased new by my father in San Francisco; as he lived in a non-biennial inspection county in California, the car was never smogged during his ownership; beyond religiously 3500 mile oil changes, he had the car serviced sporadically at a local good ol' boy shop. When he passed at 94 in 2013, I inherited it with probably 100k miles (odometer broken), and in California that doesn't require a smog inspection for in-family transfer of ownership.

The car remained registered in the non-biennial county until this year, when we sold the house. I now have to register it in San Francisco county, so it must pass smog....which it doesn't. All the factory equipment appears to be in place and the check engine light was not coming on, so I took it to a test-only local inspection station known for experience with older cars.

It passed all the visual inspections, and failed only NOx, with the following readings:

15mph CO2 13.7 O2 2.6 HC 30 (93 max allowed) CO 0.01 (.62 max) NO 1002 (783 max allowed)
25mph CO2 13.6 O2 2.7 HC 25 CO 0.00 NO 1018

The smog technician noted that the EGR valve appeared to be non-functional; manually lifting the diaphragm at idle had no effect, and the valve wouldn't hold vacuum with a hand pump connected to the EGR hose port, suggesting a broken diaphragm. He suggested having the EGR replaced and ensuring all the vacuum lines and sensor wires were intact.

I took the car to a mechanic who replaced the EGR, and found the coolant temperature sensor was defective, and replaced it and its connector. He also discovered the thermostat was missing, so he flushed the cooling system, installed a 180 degree thermostat and refilled with fresh coolant/water mix.

Following these repairs, the mechanic suggested adding a can of Sea Foam to the fuel tank and driving it around while before re-testing; added 16oz Sea Foam to 16 gallons gasoline and drove for 30 miles.

On the re-test, results were basically the same. The Smog technician suggested "adjusting the carburetor for a richer mixture" because the high NO was likely due to a lean mixture condition, and also consider replacing the O2 sensor. The mechanic suggested just driving it around some more with the Sea Foam, and felt there was no point in replacing the O2 sensor.

I found this excellent forum, and located the resource videos regarding CCC carburetor smog systems. I was particularly overwhelmed by the "CCC drivability" video, with it's punches and chisels on the carb base (at around 7:00) to access the mixture screws! Given the car's service murky history (and the absence of a thermostat), I looked at the carb on the car and sure enough, the base had been "serviced' with the plugs covering the mixture screws missing. I'm not familiar with the fuel circuits of a Quadrajet...are these the main jets?


So, what to do now? I'm fortunate that the smog shop will re-test at no charge (the technician is the owner and really likes El Camino's), but I'm reluctant to just fool around with the mixture screws and hope for the best. The "CCC Drivability" video mentions (at 9:06) that the mixture screws setting can be anywhere from 1.5 to 6 turns...given the high NO and low HC/CO, it IS likely that the engine's running lean and with high combustion chamber temperatures, but I'm unclear about the ECM's role in affecting air/fuel mixture in a CCC Quadrajet. No wonder they invented fuel injection!

Any help is appreciated; This car's been in my family since new, and I'd hate to retire it or give it up for an LS motor swap.

Thanks,
Marc
Thanks for the info!

As mentioned, the car has around 100k (broken odometer, but I know the car’s history since new).

How is a high CO2 determined? The inspection printout has no parameters for that gas, and I could only find references to CO2 emissions in kg/mi, not in concentration percentage.

I thought a very low HC and CO, along with a high NOx indicates a lean condition and high combustion chamber temperature which would generate excessive NOx and prevent the catalytic converter from reducing it, since the cat requires a correct mixture to operate correctly.

I really appreciate your describing the O2 sensor’s function in telling the ECM to adjust the A/F mixture via the carb’s solenoid. I located the solenoid’s connectors on the carb and was able to verify it is working by applying 12V to the pins and hearing the “click” as it operates.

I’m thinking that the O2 sensor may not be sending the correct signal to the ECM, causing the solenoid to not operate and causing a lean mixture.

I connected a meter set at mV to ground and a wire inserted into the connector from the purple wire and the O2 sensor. I got readings the seemed to cycle from 680mV to zero in a rapid sequence. Does this make any sense?

The “check engine” light does come on with the ignition turned to “on”, the goes out with engine started. Disconnecting the O2 sensor does not illuminate the light…this seems odd, and I’m wondering if the ECM is malfunctioning.

I’m in California, and a CARB approved catalytic converter is over $700 installed; would like to rule out other causes before replacing it.

I’ve read discussion about checking/adjusting “A/F dwell” as a method to correct lean mixture. Anyone know the procedure for that?

Thanks again for the contributions!
 
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MarcD

Not-quite-so-new-guy
Apr 15, 2023
9
15
3
First check for vacuum leaks as they will lean out fuel mixtures. The main jets in the carburetor are computer controlled. The only jets you can adjust are the idle mixture jets along with the idle air bleed valve.

Ideally you should be checking the air/fuel mixture dwell with a analog dwell meter. If the car is running lean the dwell meter will quickly tell you. A 180 t-stant is too cold, the computer is designed for a 195 t-stant, warmer engines burn cleaner.

The cat convertors in these cars requires the smog pump to inject air into them to operate correctly.
Vacuum leaks have been traced snd corrected. The air pump is in place and operational.

Do you have a link for the Air/fuel mixture dwell checking/adjustment procedure? What exactly is being measured? I do have an analog dwell meter.

I’d always thought a thermostat’s temperature value controlled only the point at which coolant was allowed to flow through the radiator; in other words, it diverts flow to the block until warmup occurs, the thermostat opens and the system equilibrates to it’s optimal operating temperature. The thermostat wouldn’t close again until the engine is shut down and the coolant temperature falls to the thermostat’s set spec.

Thsnks agdd as in to all for the input!
 

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