Failed Emissions
Thread Starter
Instructor
Joined: Nov 2006
Posts: 207
Likes: 0
From: Duluth Georgia
Failed Emissions
Yep, I failed emissions. 
Here's the read out.
25/25 Test
TEST / READING / ALLOWABLE / RESULT
HC - ppm / 054 / 152 / PASS
CO - % / 0.64 / 0.97 / PASS
NO - ppm / 0010 / 1082 / PASS
rpm / 1432 / 1250-2500 / PASS
CO+CO2 % / 15.1 / 6.0 MIN. / PASS
50/15 Test
TEST / READING / ALLOWABLE / RESULT
HC - ppm / 050 / 157 / PASS
CO - % / 1.37 / 0.88 / FAIL
NO - ppm / 0014 / 1184 / PASS
rpm / 1855 / 1250-2500 / PASS
CO+CO2 % / 15.4 / 6.0 MIN. / PASS
This is the second time I tested the emissions, the first time arond I failed the 25/25 test in the CO category. My mistake is that I had only driven the car 3 miles before the test. So, the second time I ran the car down the expressway for 25 miles running at about 70mph and then headed to the emissions station and tested....you can see the results of this one above.
Does anyone have any ideas of what I can do to pass the emissions test? Any ideas what might be causing me to fail? Need anymore info to determine what it might be?
Thanks!
Here's the read out.25/25 Test
TEST / READING / ALLOWABLE / RESULT
HC - ppm / 054 / 152 / PASS
CO - % / 0.64 / 0.97 / PASS
NO - ppm / 0010 / 1082 / PASS
rpm / 1432 / 1250-2500 / PASS
CO+CO2 % / 15.1 / 6.0 MIN. / PASS
50/15 Test
TEST / READING / ALLOWABLE / RESULT
HC - ppm / 050 / 157 / PASS
CO - % / 1.37 / 0.88 / FAIL
NO - ppm / 0014 / 1184 / PASS
rpm / 1855 / 1250-2500 / PASS
CO+CO2 % / 15.4 / 6.0 MIN. / PASS
This is the second time I tested the emissions, the first time arond I failed the 25/25 test in the CO category. My mistake is that I had only driven the car 3 miles before the test. So, the second time I ran the car down the expressway for 25 miles running at about 70mph and then headed to the emissions station and tested....you can see the results of this one above.
Does anyone have any ideas of what I can do to pass the emissions test? Any ideas what might be causing me to fail? Need anymore info to determine what it might be?
Thanks!
Burning Brakes
Joined: Apr 2005
Posts: 1,109
Likes: 2
One thing that really helps is to drive for a while the car until it is at working temperature or even hotter, and go take the test but avoid turning off the engine so the engine will not cool off and the catalitic converters are still hot. This is really important.
Also have a new clean air filter.
If you can a couple of days before take the car for a road drive, the idea is to let the engine work for a while without stopping, that will help remove carbon deposits.
Also have a new clean air filter.
If you can a couple of days before take the car for a road drive, the idea is to let the engine work for a while without stopping, that will help remove carbon deposits.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
A 3 mile drive is plenty - my cars pass and the station is less than a mile away. The standard is Closed Loop, a/c off. A tech should be able to tell that it's at operating temp - if not find another station.
High CO means it's rich. A functioning system blows a barely neglible amount; ie, pretty much 0. Hook up a scanner and see what's going on with fuel delivery at the same RPM as the test. If it's dead on, it needs a new CAT. If not, post what the 02 is reporting to the ECM for further help.
High CO means it's rich. A functioning system blows a barely neglible amount; ie, pretty much 0. Hook up a scanner and see what's going on with fuel delivery at the same RPM as the test. If it's dead on, it needs a new CAT. If not, post what the 02 is reporting to the ECM for further help.
Drifting
Joined: Dec 2003
Posts: 1,344
Likes: 0
From: Conyers Ga
I failed mine also two weeks ago on the CO. I tried a can of Sea Foam in the tank and it helped a little bit but ultiumately my mechanic adjusted the timing to make the car run leaner. It passed by a wide margin on but it ran horrible until he could set it back. The car runs rich but now I have a year to figure out why.
And this may sound odd but ask the guy to test with the clamshell DOWN........It made a difference in my test last year.
And this may sound odd but ask the guy to test with the clamshell DOWN........It made a difference in my test last year.
Last edited by nyernga; Jan 3, 2007 at 10:00 PM.
Thread Starter
Instructor
Joined: Nov 2006
Posts: 207
Likes: 0
From: Duluth Georgia
I checked for codes and got these. I'll reset the computer later and see which codes stay and which go away.
Yeah, the test was with the hood closed.
DTC #34: Manifold Absolute Pressure Sensor Circuit Low. MAP sensor signal voltage was too low (high vacuum) when engine speed was under 600 RPM or the engine speed was over 600 RPM with a throttle position angle above 6%.
DTC #36: Distributor Ignition System High Pulse. MAF sensor burn-off voltage was missing. Check MAF sensor burn-off relay and terminal "D" on MAF.
DTC #42: Ignition Control Circuit Shorted. The EST signal did not change when the ECM applied bypass voltage to the ignition module.
DTC #36: Distributor Ignition System High Pulse. MAF sensor burn-off voltage was missing. Check MAF sensor burn-off relay and terminal "D" on MAF.
DTC #42: Ignition Control Circuit Shorted. The EST signal did not change when the ECM applied bypass voltage to the ignition module.
Originally Posted by nyernga1
And this may sound odd but ask the guy to test with the clamshell DOWN........It made a difference in my test last year.
Last edited by Cadder; Jan 3, 2007 at 10:34 PM.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Your Year doesn't have a MAP. Unless your Vette has a burned out Check Engine Light, none of the Codes are current - current problems illuminate the light and keep it lit until it goes away or gets fixed.
If the timing was checked as a part of the Emissions Test, that set the 42. The Check Engine Light goes off when the Timing Connector is plugged back in and it stays in History for 100 ignition cycles or until you clear it.
If you're pulling codes with a Scanner, get some BLM history so we can see what's going on. Also check the Coolant Temp Signal.
If the timing was checked as a part of the Emissions Test, that set the 42. The Check Engine Light goes off when the Timing Connector is plugged back in and it stays in History for 100 ignition cycles or until you clear it.
If you're pulling codes with a Scanner, get some BLM history so we can see what's going on. Also check the Coolant Temp Signal.
Thread Starter
Instructor
Joined: Nov 2006
Posts: 207
Likes: 0
From: Duluth Georgia
Originally Posted by SunCr
Your Year doesn't have a MAP. Unless your Vette has a burned out Check Engine Light, none of the Codes are current - current problems illuminate the light and keep it lit until it goes away or gets fixed.
You're right, there is no MAP on mine.
Originally Posted by SunCr
If the timing was checked as a part of the Emissions Test, that set the 42. The Check Engine Light goes off when the Timing Connector is plugged back in and it stays in History for 100 ignition cycles or until you clear it.
Originally Posted by SunCr
If you're pulling codes with a Scanner, get some BLM history so we can see what's going on. Also check the Coolant Temp Signal.
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Racer
Joined: Dec 2006
Posts: 325
Likes: 2
From: Chattanooga TN
I failed mine also two weeks ago on the CO. I tried a can of Sea Foam in the tank and it helped a little bit but ultiumately my mechanic adjusted the timing to make the car run leaner. It passed by a wide margin on but it ran horrible until he could set it back. The car runs rich but now I have a year to figure out why.
And this may sound odd but ask the guy to test with the clamshell DOWN........It made a difference in my test last year.
And this may sound odd but ask the guy to test with the clamshell DOWN........It made a difference in my test last year.
i also dont see what effect having the hood open, or closed, would have on exhaust pipe emissions....
Drifting
Joined: Dec 2003
Posts: 1,344
Likes: 0
From: Conyers Ga
All I can tell you is that last year, I failed the first time.(hood open) My mechanic brought it back less then 30 minutes later,(without doing a thing to the car) instructed the operator to keep the hood closed and it passed.
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
Alot of guys have posted they retarded their timing by a couple degrees to help pass emmisions. Hows your MPG been, if it has declineing I'd be throwing in a new 02 sensor. My pre-emission testing procedures has always been 1/2 a can of SeaFoam through the brake vac. line, the other 1/2 in the tank...none in the oil, oil change,make sure the air filter is clean and no leaks in the duct work from the air cleaner to TB. IF you do the SeaFoam, and it states on the can "Helps to Pass emissions" YOU may throw a code, sometimes the SeaFoam puts a mist on the 02 sensor, don't worry, it burns off, just pull the neg. bat. cable for a few minutes to clear the code, then drive it for awhile. I've only failed one in many years and that was in my diesel...first thing they told me was to change the oil...damned thing past after that.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Without a scan, it's more of a guess, but if I had to make one, I'd say that the 34 (air flow too low for rpms or TPS signal) is intermittent (has to be if the Light is going on and off) and caused by a vacuum leak (as opposed to a bum MAF). That leak is probably in the air pump circuit, which is washing out airflow to the CAT at the rpms your car failed Emissions, so the CAT cools off and the CO and HC's go up. It also may be causing the O2 to sense a lean condition, so it's adding too much fuel. I'd check the vacuum hoses and fittings closely, particularly to the air pump solenoids. Make sure the MAF coupler is secure and not leaking or torn.
Instructor
Joined: Sep 2005
Posts: 113
Likes: 0
From: Albuquerque NM
I may be full of it, but the guy at the test station asked if my 91 was a single or dual exhaust. I said the exhaust runs through a single catalytic converter so it's a single exhaust. Why. He said the readings are doubled in a dual exhaust readout. No matter, I passed the test.
Thread Starter
Instructor
Joined: Nov 2006
Posts: 207
Likes: 0
From: Duluth Georgia
Hows your MPG been, if it has declining I'd be throwing in a new 02 sensor.
make sure the air filter is clean and no leaks in the duct work from the air cleaner to TB
That leak is probably in the air pump circuit, which is washing out airflow to the CAT at the rpms your car failed Emissions, so the CAT cools off and the CO and HC's go up. It also may be causing the O2 to sense a lean condition, so it's adding too much fuel. I'd check the vacuum hoses and fittings closely, particularly to the air pump solenoids. Make sure the MAF coupler is secure and not leaking or torn.
Just a thought....is the guy, the one doing the testing, supposed to place a small squirrel-cage blower in front of the car to direct cold air over the radiator and under the car? I noticed that while he was doing the testing that the coolant temp hovered around 160F the entire time. Even at highway speeds I've never seen the coolant temp get that low, maybe 185F at the lowest, but not 160F. Could that be causing any problems with my ability to pass the test? Granted, I haven't had to have an emissions test in about 8 years, due to living in an area that doesn't require them. So, I don't really know what's the normal procedure for an emissions test.
Thread Starter
Instructor
Joined: Nov 2006
Posts: 207
Likes: 0
From: Duluth Georgia
I may be full of it, but the guy at the test station asked if my 91 was a single or dual exhaust. I said the exhaust runs through a single catalytic converter so it's a single exhaust. Why. He said the readings are doubled in a dual exhaust readout. No matter, I passed the test.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
My experience with placing a big fan in front of a Vette is that it does nothing. The tech must have had something that could feed it from the bottom, but I've never had any success in maintaining a desired temp with anything other than the stock fan.
What thermostat do you have in it?
At 160, it can cool off enough to go open loop and nothing will pass if the O2 isn't controlling fuel delivery. It should be maintaining the thermostat (195) at cruise. If you've put a lower temp thermostat in it, get it back to stock.
What thermostat do you have in it?
At 160, it can cool off enough to go open loop and nothing will pass if the O2 isn't controlling fuel delivery. It should be maintaining the thermostat (195) at cruise. If you've put a lower temp thermostat in it, get it back to stock.
Thread Starter
Instructor
Joined: Nov 2006
Posts: 207
Likes: 0
From: Duluth Georgia
At 160, it can cool off enough to go open loop and nothing will pass if the O2 isn't controlling fuel delivery. It should be maintaining the thermostat (195) at cruise. If you've put a lower temp thermostat in it, get it back to stock.
I'm also thinking of going to a different emissions testing center because the guy that did the testing, at the one I went to, would have to do the test over and over, before he got it right, because he couldn't keep the RPMs or speed in range on the computer.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Sounds like a plan. I would still check the vacuum hoses - especially with the 34 popping up - and since it cooled to 160, make sure the main fan isn't running (it shouldn't come on until 226 with the a/c off).
Thread Starter
Instructor
Joined: Nov 2006
Posts: 207
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From: Duluth Georgia
Yeah, I just got finished looking over part of the engine bay and already found some rotted vacuum lines. It started raining so I had to call it quits, for the time being, and pull the car back into the garage. Unfortunately, I just don't have the room to wiggle around the car in my tiny garage.
Yep, the main fan is working just fine. Like I said, the only reason it got down to 160 is because the guy, that did the emissions testing, placed a squirrel-cage blower in front of the car that directed the air directly under the car, angled slightly upwards toward the radiator.
Thanks for the help so far guys! This has really helped me out with the troubleshooting.
and since it cooled to 160, make sure the main fan isn't running (it shouldn't come on until 226 with the a/c off)
Thanks for the help so far guys! This has really helped me out with the troubleshooting.
Racer
Joined: May 2006
Posts: 293
Likes: 0
Yep, the main fan is working just fine. Like I said, the only reason it got down to 160 is because the guy, that did the emissions testing, placed a squirrel-cage blower in front of the car that directed the air directly under the car, angled slightly upwards toward the radiator.