Smog Issues
07-06-2016, 08:03 PM
#1
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Smog Issues
Alright, another smog post. Yes I've searched. No I can't move out of California. Looking for outside opinions. 
91 3vze/3.0 at 12*, has Doug Thorley headers and upgraded injectors. O2 sensor and Cat are about 18 months old. No exhaust leaks. Follow along below for timeline of events...
First smog test results:
(Numbers read MAX/AVE/MEAS)
15MPH- 1735RPM 2nd gear
CO2
14.0
O2
0.4
HC
89/30/ 90
CO
.55/.06/.26
NO
721/218/1035
25 MPH-2682 RPM 2nd gear
CO2
14.1
O2
0.4
HC
75/25/17
CO
.69/.07/.05
NO
891/188/1484
What I did: Installed "new" used EGR from the local pick a part. Ensured there were no vac leaks, all passages are clear, and egr is functioning.
2nd smog test results:
(Numbers read MAX/AVE/MEAS)
15MPH- 1741RPM 2nd gear
CO2
13.3
O2
0.9
HC
89/30/ 163
CO
.55/.06/.92
NO
721/218/1680
25 MPH-2703 RPM 2nd gear
CO2
14.1
O2
0.4
HC
75/25/50
CO
.69/.07/.13
NO
891/188/534
What I did: Checked for vac leaks again. Ensured all hoses are routed correctly. Cleaned out vacuum modulator. Ensured VSV was functioning as it should. I then unplugged the VSV to ensure the EGR was open for the entirety of the 3rd test.
3rd smog test results:
(Numbers read MAX/AVE/MEAS)
15MPH- 1747 RPM 2nd gear
CO2
13.8
O2
0.6
HC
89/30/ 122
CO
.55/.06/.49
NO
721/218/1771
25 MPH-2692 RPM 2nd gear
CO2
14.1
O2
0.3
HC
75/25/39
CO
.69/.07/.08
NO
891/188/542
As you can see, I'm struggling with the 15mph. My thought is this: The newish EGR is functioning as it should, but clearly something is up. I'm going to retard the timing back to 10*, but aside from that, I'm pretty much stumped. Any input in appreciated.
EDIT- It's a Fed truck, not the Cali edition with the EGR temp sensor nonsense.
91 3vze/3.0 at 12*, has Doug Thorley headers and upgraded injectors. O2 sensor and Cat are about 18 months old. No exhaust leaks. Follow along below for timeline of events...
First smog test results:
(Numbers read MAX/AVE/MEAS)
15MPH- 1735RPM 2nd gear
CO2
14.0
O2
0.4
HC
89/30/ 90
CO
.55/.06/.26
NO
721/218/1035
25 MPH-2682 RPM 2nd gear
CO2
14.1
O2
0.4
HC
75/25/17
CO
.69/.07/.05
NO
891/188/1484
What I did: Installed "new" used EGR from the local pick a part. Ensured there were no vac leaks, all passages are clear, and egr is functioning.
2nd smog test results:
(Numbers read MAX/AVE/MEAS)
15MPH- 1741RPM 2nd gear
CO2
13.3
O2
0.9
HC
89/30/ 163
CO
.55/.06/.92
NO
721/218/1680
25 MPH-2703 RPM 2nd gear
CO2
14.1
O2
0.4
HC
75/25/50
CO
.69/.07/.13
NO
891/188/534
What I did: Checked for vac leaks again. Ensured all hoses are routed correctly. Cleaned out vacuum modulator. Ensured VSV was functioning as it should. I then unplugged the VSV to ensure the EGR was open for the entirety of the 3rd test.
3rd smog test results:
(Numbers read MAX/AVE/MEAS)
15MPH- 1747 RPM 2nd gear
CO2
13.8
O2
0.6
HC
89/30/ 122
CO
.55/.06/.49
NO
721/218/1771
25 MPH-2692 RPM 2nd gear
CO2
14.1
O2
0.3
HC
75/25/39
CO
.69/.07/.08
NO
891/188/542
As you can see, I'm struggling with the 15mph. My thought is this: The newish EGR is functioning as it should, but clearly something is up. I'm going to retard the timing back to 10*, but aside from that, I'm pretty much stumped. Any input in appreciated.
EDIT- It's a Fed truck, not the Cali edition with the EGR temp sensor nonsense.
Last edited by KBAM; 07-06-2016 at 08:08 PM.
07-09-2016, 12:31 PM
#3
Registered User
I'll try to help you if I can. No smog tests at all where I am so I don't have any of my smog gear still hooked up. That being said, I really don't feel like the egr and reed valves are really doing much to reduce your HC and NOX. I say that because the odor and appearance of my exhaust did not change at all when I removed mine. I do know that they help to bring them down some but not to the extent that yours are too high. Your NOX is 8 times the average and more than twice the limit.
Starting with the HC or hydrocarbon reading. You are getting this because you aren't burning all of the fuel that is being injected into your cylinders. This could be due to the upgrade injectors. Your injectors fire based on signals sent from the air system and a few other sensors. If the MAF says that you have X volume of air coming in then your ecm sends a signal to the injectors to open long enough to deliver enough fuel for X volume of air. If your new injectors deliver more fuel per pulse than the system is calibrated for then you will overfuel. Down the line, the 02 sensor decides whether or not the combustion was successful or not and then will add it's input to the equation and the system will make the necessary adjustments based on the amount of O2 in the exhaust.
While you are passing your O2 test, if that is actually something they judge you on, you will see that your O2 reading is double at low RPM. This is just a guess as I don't know the algorithms that go into the fuel mix adjustments based on the input from the O2 sensor, but is it possible that your O2 readings aren't getting back to your ECM so it can make adjustments or it's readings are not accurate? High smog for a period of 18 months is more than enough to get your O2 sensor filthy. I would pull it out and clean it before your next test for sure.
Here are a few other suggestions. Let me know if you would like me to elaborate on any of them. I don't want to post a book if you already know what I'm talking about.
Maybe try some hotter or cooler plugs. Your plugs may not be a good match for your upgraded injectors.
Check your reed valve circuit. It dilutes the exhaust before it heads down to the Cat and O2.
Check your air filter. Poor air flow will affect your fuel burn especially at low RPM.
Test your throttle position sensor. It also gives input to the fuel equation.
Check ignition timing. Nox is a symptom of high combustion temperature which can occur when timing is too far advanced.
Man it could be lots of things and I've never had to worry about any of this before so I'm no expert but I can tell you this before. You have unburnt fuel in your exhaust at lower rpm. Find the cause of that and you will solve your problem.
Starting with the HC or hydrocarbon reading. You are getting this because you aren't burning all of the fuel that is being injected into your cylinders. This could be due to the upgrade injectors. Your injectors fire based on signals sent from the air system and a few other sensors. If the MAF says that you have X volume of air coming in then your ecm sends a signal to the injectors to open long enough to deliver enough fuel for X volume of air. If your new injectors deliver more fuel per pulse than the system is calibrated for then you will overfuel. Down the line, the 02 sensor decides whether or not the combustion was successful or not and then will add it's input to the equation and the system will make the necessary adjustments based on the amount of O2 in the exhaust.
While you are passing your O2 test, if that is actually something they judge you on, you will see that your O2 reading is double at low RPM. This is just a guess as I don't know the algorithms that go into the fuel mix adjustments based on the input from the O2 sensor, but is it possible that your O2 readings aren't getting back to your ECM so it can make adjustments or it's readings are not accurate? High smog for a period of 18 months is more than enough to get your O2 sensor filthy. I would pull it out and clean it before your next test for sure.
Here are a few other suggestions. Let me know if you would like me to elaborate on any of them. I don't want to post a book if you already know what I'm talking about.
Maybe try some hotter or cooler plugs. Your plugs may not be a good match for your upgraded injectors.
Check your reed valve circuit. It dilutes the exhaust before it heads down to the Cat and O2.
Check your air filter. Poor air flow will affect your fuel burn especially at low RPM.
Test your throttle position sensor. It also gives input to the fuel equation.
Check ignition timing. Nox is a symptom of high combustion temperature which can occur when timing is too far advanced.
Man it could be lots of things and I've never had to worry about any of this before so I'm no expert but I can tell you this before. You have unburnt fuel in your exhaust at lower rpm. Find the cause of that and you will solve your problem.
