Failed Emissions Test Today...
Thread Starter
Instructor
Joined: Apr 2008
Posts: 153
Likes: 7
From: Painesville Ohio
Failed Emissions Test Today...
Went for the test with a warm engine and failed the NO portion of the test.
#'s are:
HC 56.4 Limit of 117.0
CO 0.28 Limit of 0.65
NO 1195.1 Limit of 821.0
CO2 14%
My gas cap also failed but is an easy fix (new one).
The engine was hot and the temp here is about 85F.
No check engine lights on. Only issue is sometimes idle isn't steady (fluctuates between 600 and 1000) I plan on cleaning the throttle body and IAC valve this weekend to try to fix the idle problem.
Anyone know where to start?
#'s are:
HC 56.4 Limit of 117.0
CO 0.28 Limit of 0.65
NO 1195.1 Limit of 821.0
CO2 14%
My gas cap also failed but is an easy fix (new one).
The engine was hot and the temp here is about 85F.
No check engine lights on. Only issue is sometimes idle isn't steady (fluctuates between 600 and 1000) I plan on cleaning the throttle body and IAC valve this weekend to try to fix the idle problem.
Anyone know where to start?
Melting Slicks
Joined: Dec 2004
Posts: 3,284
Likes: 51
From: Jacksonville, FL
St. Jude Donor '08 thru '26
Just a couple of thoughts......isn't NO the thing that the cat is supposed to clean up?
How are the O2 sensors, really old?
Did you check for vacuum leaks?
The fluctuation in the idle speed happens in closed loop or open loop or both?
Wish I could be more specific but I'm not really up to speed on these here computer cars...
Tom
How are the O2 sensors, really old?
Did you check for vacuum leaks?
The fluctuation in the idle speed happens in closed loop or open loop or both?
Wish I could be more specific but I'm not really up to speed on these here computer cars...
Tom
Drifting
Joined: Nov 2005
Posts: 1,324
Likes: 5
From: Charlotte NC
O2 Sensors are relatively cheap, but that still wouldn't explain the fluctuating idle. I'd look at spark there. My LT was fluctuating then moved on to missing. Turned out I had 2 wires that were arching to the engine block. For you that would mean unburnt fuel.
Arching can be best checked in a dark garage. Just my 2 cents.
Arching can be best checked in a dark garage. Just my 2 cents.
Thread Starter
Instructor
Joined: Apr 2008
Posts: 153
Likes: 7
From: Painesville Ohio
Car was at operating temp 210F and a/c was off, by the time the test was done the operating temp was 230+, not enough air from their fan on the dyno!
Thread Starter
Instructor
Joined: Apr 2008
Posts: 153
Likes: 7
From: Painesville Ohio
O2 Sensors are relatively cheap, but that still wouldn't explain the fluctuating idle. I'd look at spark there. My LT was fluctuating then moved on to missing. Turned out I had 2 wires that were arching to the engine block. For you that would mean unburnt fuel.
Arching can be best checked in a dark garage. Just my 2 cents.
Arching can be best checked in a dark garage. Just my 2 cents.
Racer
Joined: May 2006
Posts: 426
Likes: 16
From: Concord CA
Any Details on your vette, year, mileage, has maintance service been done. Get your engine scanned ODBI or ODBII scanner and not a code reader.
Things I always do before smog test:
Change the oil and filter.
PCV
Air Filter
Check and repair any vacuum leaks.
Tune up (plugs, cap, rotor, if needed).
Clean the MAF with MAF Cleaner spray.
Run a few tanks of good cleaning gas (Chevron or there bottle additives Techron is good).
Make sure the EGR and AIR system are working correctly.
Check and clean all of the electrical connections to the related equipement (MAF and its relays were key for me).
For the idle, I would suggest checking the IAC and TPS (get it on a scanner to diag the whole system) using FSM procedures.
Check and change any sensor, O2 is the most likely one to change after 80k or more. IAT can cause bad idle. (had some of these problems and swapped out many of the old sensors when I picked up my 88' this year, had many code, I got them al cleared).
Things I always do before smog test:
Change the oil and filter.
PCV
Air Filter
Check and repair any vacuum leaks.
Tune up (plugs, cap, rotor, if needed).
Clean the MAF with MAF Cleaner spray.
Run a few tanks of good cleaning gas (Chevron or there bottle additives Techron is good).
Make sure the EGR and AIR system are working correctly.
Check and clean all of the electrical connections to the related equipement (MAF and its relays were key for me).
For the idle, I would suggest checking the IAC and TPS (get it on a scanner to diag the whole system) using FSM procedures.
Check and change any sensor, O2 is the most likely one to change after 80k or more. IAT can cause bad idle. (had some of these problems and swapped out many of the old sensors when I picked up my 88' this year, had many code, I got them al cleared).
Thread Starter
Instructor
Joined: Apr 2008
Posts: 153
Likes: 7
From: Painesville Ohio
Any Details on your vette, year, mileage, has maintance service been done. Get your engine scanned ODBI or ODBII scanner and not a code reader.
Things I always do before smog test:
Change the oil and filter.
PCV
Air Filter
Check and repair any vacuum leaks.
Tune up (plugs, cap, rotor, if needed).
Clean the MAF with MAF Cleaner spray.
Run a few tanks of good cleaning gas (Chevron or there bottle additives Techron is good).
Make sure the EGR and AIR system are working correctly.
Check and clean all of the electrical connections to the related equipement (MAF and its relays were key for me).
For the idle, I would suggest checking the IAC and TPS (get it on a scanner to diag the whole system) using FSM procedures.
Check and change any sensor, O2 is the most likely one to change after 80k or more. IAT can cause bad idle. (had some of these problems and swapped out many of the old sensors when I picked up my 88' this year, had many code, I got them al cleared).
Things I always do before smog test:
Change the oil and filter.
PCV
Air Filter
Check and repair any vacuum leaks.
Tune up (plugs, cap, rotor, if needed).
Clean the MAF with MAF Cleaner spray.
Run a few tanks of good cleaning gas (Chevron or there bottle additives Techron is good).
Make sure the EGR and AIR system are working correctly.
Check and clean all of the electrical connections to the related equipement (MAF and its relays were key for me).
For the idle, I would suggest checking the IAC and TPS (get it on a scanner to diag the whole system) using FSM procedures.
Check and change any sensor, O2 is the most likely one to change after 80k or more. IAT can cause bad idle. (had some of these problems and swapped out many of the old sensors when I picked up my 88' this year, had many code, I got them al cleared).
I will also have it scanned and look into picking up a scanner for my OBDI system.
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Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
A/c is exempt from emissions certification (the EPA would like to include it) and if it wasn't, none of our cars would pass, so it should be off.
Fluctuating, surging idle, points to a vacuum, intake or exhaust leak which can make it lean and the ECM responds with too much fuel - only your fueling (HC's and CO) looks good. I'd confirm with a scan, but that high NOX, assuming fueling is ok, is either an EGR problem (if used) or a bad CAT. Scan it and see.
Fluctuating, surging idle, points to a vacuum, intake or exhaust leak which can make it lean and the ECM responds with too much fuel - only your fueling (HC's and CO) looks good. I'd confirm with a scan, but that high NOX, assuming fueling is ok, is either an EGR problem (if used) or a bad CAT. Scan it and see.
Thread Starter
Instructor
Joined: Apr 2008
Posts: 153
Likes: 7
From: Painesville Ohio
A/c is exempt from emissions certification (the EPA would like to include it) and if it wasn't, none of our cars would pass, so it should be off.
Fluctuating, surging idle, points to a vacuum, intake or exhaust leak which can make it lean and the ECM responds with too much fuel - only your fueling (HC's and CO) looks good. I'd confirm with a scan, but that high NOX, assuming fueling is ok, is either an EGR problem (if used) or a bad CAT. Scan it and see.
Fluctuating, surging idle, points to a vacuum, intake or exhaust leak which can make it lean and the ECM responds with too much fuel - only your fueling (HC's and CO) looks good. I'd confirm with a scan, but that high NOX, assuming fueling is ok, is either an EGR problem (if used) or a bad CAT. Scan it and see.
Racer
Joined: Mar 2005
Posts: 379
Likes: 95
From: Ingersoll Ontario
I understand your situation as I just went through the exact same issue. I thought the excessive engine temp caused excessive combustion temps which in turn caused the high NOx reading. However I was informed that the high engine (coolant) temp has nothing to do with high combustion temps (high combustion temps are related to high NOx). Ltx engines run most efficient at higher temps and thus will pass e-test easier at those higher temps. I would be more inclined to think you have a vac leak or ignition wire/spark plug issue. If the car is not throwing any codes, a scan is the best way to diagnose the problem. Does it smell rich at the tail pipes?
Thread Starter
Instructor
Joined: Apr 2008
Posts: 153
Likes: 7
From: Painesville Ohio
I understand your situation as I just went through the exact same issue. I thought the excessive engine temp caused excessive combustion temps which in turn caused the high NOx reading. However I was informed that the high engine (coolant) temp has nothing to do with high combustion temps (high combustion temps are related to high NOx). Ltx engines run most efficient at higher temps and thus will pass e-test easier at those higher temps. I would be more inclined to think you have a vac leak or ignition wire/spark plug issue. If the car is not throwing any codes, a scan is the best way to diagnose the problem. Does it smell rich at the tail pipes?
Drifting
Joined: Jun 2002
Posts: 1,945
Likes: 41
From: Corinth TX
Granted your temps were up but did that come from driving the car down the road for about 30 minutes of warm up time? The reason I am saying this is that you need to get the cats hot. The wife thought she was doing me a favor one time by taking the car to get it inspected while I was at work. Well, she drove it straight over and sure enough the thing failed. I then drove it for about 30 minutes to get it the cats hot and sure enough it passed. If the O2 sensors have never been replaced then I would definite change them out. You will see an improvement in your fuel mileage as well as a side benefit.
Thread Starter
Instructor
Joined: Apr 2008
Posts: 153
Likes: 7
From: Painesville Ohio
Granted your temps were up but did that come from driving the car down the road for about 30 minutes of warm up time? The reason I am saying this is that you need to get the cats hot. The wife thought she was doing me a favor one time by taking the car to get it inspected while I was at work. Well, she drove it straight over and sure enough the thing failed. I then drove it for about 30 minutes to get it the cats hot and sure enough it passed. If the O2 sensors have never been replaced then I would definite change them out. You will see an improvement in your fuel mileage as well as a side benefit.
Thread Starter
Instructor
Joined: Apr 2008
Posts: 153
Likes: 7
From: Painesville Ohio
Intermediate
Joined: May 2008
Posts: 36
Likes: 0
From: Katy TX
High NOx is the product of high combustion pressure/temperature. I would check the initial ignition timing and the EGR valve. If both are OK then I would suspect the converter(s), especially after a 100k miles. A
sticking EGR valve can also affect the idle.
sticking EGR valve can also affect the idle.
Racer
Joined: May 2006
Posts: 426
Likes: 16
From: Concord CA
The paper clip would only activate into the Diag mode in the computer and would flast the stored codes. You need to get a scanner to monitor the reading of the sensors that the ECM is getting input from. You can use a Digital Volt.Ohm meter by you would have to measure each sensor output one at a time.
I would change out the O2 and maybe the IAT. clean the Throttle body, IAC and MAF at a min...
I would change out the O2 and maybe the IAT. clean the Throttle body, IAC and MAF at a min...
Advanced
Joined: Oct 2007
Posts: 50
Likes: 0
Hey Mics, before you spend a lot of time and money...let me share my story.
I have had my 1990 C4 for about 8 months. At first, I failed emission in CT, in a similar manner to you. I ended up taking it to two other test centers to try and get it to pass. For the first two tests, I went in with a "hot" engine at normal operating temperature, after driving it for a while. I failed with high N.O.
For the third test, however, I went to an inspection station around the corner from my home, and only ran the car for a total of like 2 minutes before letting the guys run the test. The engine was still relatively "cold." I passed!!! You may want to try a retest with a "colder" engine.
*** I know that you may still have another problem to fix somewhere in the engine, BUT, this MAY get you through emissions while you try to fix it. Hope this helps. Good luck!
I have had my 1990 C4 for about 8 months. At first, I failed emission in CT, in a similar manner to you. I ended up taking it to two other test centers to try and get it to pass. For the first two tests, I went in with a "hot" engine at normal operating temperature, after driving it for a while. I failed with high N.O.
For the third test, however, I went to an inspection station around the corner from my home, and only ran the car for a total of like 2 minutes before letting the guys run the test. The engine was still relatively "cold." I passed!!!
You may want to try a retest with a "colder" engine.*** I know that you may still have another problem to fix somewhere in the engine, BUT, this MAY get you through emissions while you try to fix it. Hope this helps. Good luck!