Emissions Failure -- HC at idle (1 Viewer)

[Cascade Cruiser]

I've just failed the dreaded emissions test (twice) here in WA state. HC is too high at idle (800, limit is 400). HC passed at cruise (50, limit is 400). CO passed at both idle and cruise.

Here's the details:
- Between failures I replaced the air filter, spark plugs (NGK), and changed the oil....HC emissions remain high.
- The old spark plugs looked pretty clean, tannish-white, properly gapped, no obvious fouling, carbon, erosion, etc.
- Air injection system has broken VSV's, but I had air pumping into the exhaust manifold ports for the test.
- EGR system is disabled (I have passed the test in previous years with system disabled).

And the kicker...
- the cam shaft has an RV grind (250S grind from Delta Cam). This is the first emissions test I've taken with the new cam profile.
- Timing is advanced well beyond the stock setting to allow a smooth idle w/ this cam.

I have not touched the carb.

Any sage advice is greatly appreciated to help get the HC numbers down! Thanks

 

[35inchoverdrive]

You should try the ethanol trick that others have described. A quick search should pull it up, but it seems like the most effortless way to pass a smog check. I would try it myself if we had any inspections in SC.

 

[lehiguy]

Where is your static advance? The high HCs are from either too lean a mixture, (poor state of tune or vacuum leak) or too much timing advance or both. Your EGR would reduce them as it introduces deoxygenated air to reduce the combustion temperatures (and power).

 

[Toadhopper]

Maybe put a vacuum gauge on it and see how much vacuum you're pulling.
Also make sure the valves are adjusted.
The new cam seems suspect as well.
Bryn

 

[lehiguy]

Maybe put a vacuum gauge on it and see how much vacuum you're pulling.
Also make sure the valves are adjusted.
The new cam seems suspect as well.
Bryn

The cam would be suspect as it was recently done, but it is still a very mild cam. Valve overlap would create high CO, not high HC.

 

[Cascade Cruiser]

Where is your static advance? The high HCs are from either too lean a mixture, (poor state of tune or vacuum leak) or too much timing advance or both. Your EGR would reduce them as it introduces deoxygenated air to reduce the combustion temperatures (and power).

Thanks, I really appreciate the feedback. If I were running lean would I have seen evidence on the plugs I replaced? They were tan and looked fine.

My thought on the EGR is that it is normally de-activated at idle so it shouldn't be a factor in my emissions failure.

The timing is well advanced past the stock 7 deg BTDC. I'm not sure what degree it's at, but I advanced it until it idled smoothly at about 800 rpm. The engine will barely idle if I set the timing at 7 deg (I assume because of the cam). My approach with the timing was to get it as smooth as possible...would it be a benefit to retard the timing even if it means rough idle? I'm thinking that I want to avoid any misfire,

 

[rchalmers3]

I've just failed the dreaded emissions test (twice) here in WA state. HC is too high at idle (800, limit is 400). HC passed at cruise (50, limit is 400). CO passed at both idle and cruise.

Here's the details:
- Between failures I replaced the air filter, spark plugs (NGK), and changed the oil....HC emissions remain high.
- The old spark plugs looked pretty clean, tannish-white, properly gapped, no obvious fouling, carbon, erosion, etc.
- Air injection system has broken VSV's, but I had air pumping into the exhaust manifold ports for the test.
- EGR system is disabled (I have passed the test in previous years with system disabled).

And the kicker...
- the cam shaft has an RV grind (250S grind from Delta Cam). This is the first emissions test I've taken with the new cam profile.
- Timing is advanced well beyond the stock setting to allow a smooth idle w/ this cam.

CC,

Can you please state the entire gas readings you received? We should have all the parameters to review. This will aid providing a proper diagnosis.

Excessive HC's at idle are symptomatic of incomplete combustion. The CO readings (along with O2 and CO2) can indicate if the HC's are from a lean fuel mixture or something else.

The timing adjustment you indicated should have also caused a test failure. I recommend you put it where it belongs and suffer the lumpy idle. I recommend instead you raise the idle speed to just under the allowable testing limit instead.

If after repairing the If your cam is too wild (excessive overlap) you may be performing a song and dance to get it passed. I presume the cam is not emissions compliant, is that correct?

lehiguy is incorrect in stating the EGR controls idle emissions. EGR is for loaded mode operations. However, a stuck open EGR valve will affect idle quality and emmissions to a degree.

lehiguy is also incorrect about valve overlap creating excessive CO. Excessive HC's are created by overlap. The incoming air/fuel charge is laden with HC's (Hydrocarbons) some of which exit the cylinder through the exhaust valve due to the cam lobe overlap. It is this unburnt fuel being measured that is creating the failed emissions.

Please post those numbers and we will continue the discussion.

Rick

 

[Cascade Cruiser]

CC,

Can you please state the entire gas readings you received? We should have all the parameters to review. This will aid providing a proper diagnosis.

Excessive HC's at idle are symptomatic of incomplete combustion. The CO readings (along with O2 and CO2) can indicate if the HC's are from a lean fuel mixture or something else.

The timing adjustment you indicated should have also caused a test failure. I recommend you put it where it belongs and suffer the lumpy idle. I recommend instead you raise the idle speed to just under the allowable testing limit instead.

If after repairing the If your cam is too wild (excessive overlap) you may be performing a song and dance to get it passed. I presume the cam is not emissions compliant, is that correct?

lehiguy is incorrect in stating the EGR controls idle emissions. EGR is for loaded mode operations. However, a stuck open EGR valve will affect idle quality and emmissions to a degree.

lehiguy is also incorrect about valve overlap creating excessive CO. Excessive HC's are created by overlap. The incoming air/fuel charge is laden with HC's (Hydrocarbons) some of which exit the cylinder through the exhaust valve due to the cam lobe overlap. It is this unburnt fuel being measured that is creating the failed emissions.

Please post those numbers and we will continue the discussion.

Rick

Thanks for helping out Rick, I'll try to answer your questions.

Complete test results:

>>Idle Results<<
Rpm = 870
HC = 806 ppm (fail, limit = 400 ppm)
CO = .72% (pass, limit = 3%)
CO+CO2 = 10.52% (not required to pass for this vehicle, but exceeded 6% limit)
O2 = 6.77%

>>Cruise Results<<
rpm = 2410 (unloaded, no dyno)
HC = 56 ppm (pass, limit = 400 ppm)
CO = .34% (pass, limit = 3%)
CO+CO2 = 11.94% (not required to pass for this vehicle, but exceeded 6% limit)
O2 = 4.44%

This isn't a wild cam, but it may not be emissions compliant since it's not stock:
Performance 250S grind by Delta Cam
Dur Intake = 250, Dur exhaust = 254
Intake opens 17, closes 53
Exhaust opens 60, closes 14
Rise = .255, L/C = 108 deg
Valve lash = .014 both intake and exhaust


Would a lean idle mix show up on my plugs?

 

[rchalmers3]

Complete test results:

>>Idle Results<<
Rpm = 870
HC = 806 ppm (fail, limit = 400 ppm)
CO = .72% (pass, limit = 3%)
CO+CO2 = 10.52% (not required to pass for this vehicle, but exceeded 6% limit)
O2 = 6.77%

>>Cruise Results<<
rpm = 2410 (unloaded, no dyno)
HC = 56 ppm (pass, limit = 400 ppm)
CO = .34% (pass, limit = 3%)
CO+CO2 = 11.94% (not required to pass for this vehicle, but exceeded 6% limit)
O2 = 4.44%

CO readings are measurable, meaning you are not experiencing a lean condition at idle or high rpm. So your carb's doing it's job. In fact, your Catalytic converter possibly could be dead or wasn't lit off for the test. You will need to have that thing well heated for future testing.

The gas mix and elevated O2 readings indicate incomplete combustion, with fuel mixture ruled out. You could perform a few more diagnostic tests to see how the gases change with the addition and elimination of fuel, and how the fuel is distributed to each cylinder, but I think you already have suspect #1 in the line-up.

This isn't a wild cam, but it may not be emissions compliant since it's not stock:
Performance 250S grind by Delta Cam
Dur Intake = 250, Dur exhaust = 254
Intake opens 17, closes 53
Exhaust opens 60, closes 14
Rise = .255, L/C = 108 deg
Valve lash = .014 both intake and exhaust

I'm pretty certain you have too much overlap for the converter to clean up. I recommend the following:

a) set the timing correctly
b) raise the idle speed to the upper limit
c) recheck emissions using a gas analyzer in diagnostic mode
d) recheck for proper spark on all cylinders and verify no vacuum leaks affecting mixture to isolated cylinders (power balance)
e) replace Catalytic converter if it does not fire off correctly
f) replace cam if the above don't improve emissions

Would a lean idle mix show up on my plugs?

Maybe, if that's the only way the engine ran. It's not lean anyway, so unless you are worried there's a vacuum leak affecting 1 or 2 cylinders, I'd expect they all look pretty good. I only trust plug reading for comparison to other cylinders or for oil consumption.

Let us know your findings!

Rick

 

[haryv]

The cat should light off at about 1,000-1,200 degrees with a 100-200 degree difference at the inlet and outlet of the cat. If you run up against a wall failing to find the issue with the other diagnostics, buy a cheap thermal hand reader to read the temp at the inlet. If you get to this test, do a road run up to full operating temperatures before taking the reading. If the cat is not getting up to full light off it could mean its plugged, melted from a previously poor running engine or mechanical damage of the monolith platinum structure from a rock hit on the cats shield. Your air pump if it is equipped is designed to provide the oxygen needed to make it light off.

Also, the EGR kicks in when the thermal temp switch if, its mounted on the intake opens up at a given full warm up temperature. The vacuum will then open up the egr at a predetermined vacuum to reduce cylinder temperatures under 3,500 degrees to prevent cylinder over temp and increased Nox.