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post #1 of (permalink) Old 06-13-2004, 11:07 AM Thread Starter
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Emissions failed - Update - PASSED!

First let me start by saying that I thoroughly searched on emissions and took almost every bit of advice ever given on the subject.

The setup: 84 CJ7, fresh 258(<15,000), MC2100, TR upgrade, nuttered.

The day before the test I changed the oil &amp; filter, new Autolite plugs (.045), new wires dist cap/rotor, new air filter, cleaned carb, poured in 2 quarts iso alcohol, set timing (I think).

Day of test I drove on the interstate for 30 minute prior to test (engine/cat very hot).

The results:

HC PPM 1422 @idle 95 @ 2500 RPM ---> Max 400 (FAIL)
CO% 0.11 @idle 0.15 @ 2500 RPM ---> Max 1.5 (PASS)
CO2% 7.4 @idle 12.9 @ 2500 RPM

All the visual stuff passed even though most is not active due to Nutter bypass (ie O2 sensor, Pulse Air, EGR, etc).

The problem is at idle HC way too high. If I can get this fixed I am golden for two more years.

Can anyone tell me what to do? I leaned the idle mix screws as much as possible as well.

I am stumped.

UPDATE - RRICH was right on the money. I had a vacuum leak at the base of the carb where it meets the adapter plate. Once I fixed this reset idle and timing it ran great and passed the idle HC test easily. Thanks RRICH I was skeptical when I first read your post as it seems counter intuitive to be lean when HCs are high. Hopefully this update will help anyone in the future with similar issues.

Thanks for you help.
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post #2 of (permalink) Old 06-13-2004, 11:53 AM
 
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Re: Emissions failed - tell me what the numbers say

In a nutshell, HC emissions from your Jeep are unburned fuel. High levels of HC are usually caused by incomplete fuel combustion - misfire, low engine compression, etc. ( Are you running too rich at idle?)
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post #3 of (permalink) Old 06-13-2004, 02:07 PM
 
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Re: Emissions failed - tell me what the numbers say

Get a vacume gauge,I swear by mine to pass emissions!Hook it up to the carb and set the timing and the fuel mixture.It might take awhile but when that needle is reading a steady vacume,your engine is running clean.It works for me in phoenix on a 73 cj and a 72 commando!

Good luck and make sure that needle holds a steady vacume!
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post #4 of (permalink) Old 06-13-2004, 09:18 PM
 
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Re: Emissions failed - tell me what the numbers say

can you tell me how to do this

i have a 78 chevy c-10 with a holley 4 barrel you can litterly smell gas around the engine while it is running
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post #5 of (permalink) Old 06-13-2004, 09:38 PM
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Re: Emissions failed - tell me what the numbers sa

Modern catalytic converters work much better than older ones, you may be able to pass by replacing the stock cat with a modern universal one, so the catalyst burns off more HC's...

You should be able to adjust the idle mixture on the MC2100, and lean it out a bit... this would probably help a bit.

If the nutter bypass disabled the controls for the pulse air / air injection at the catalyst, you might not have enough oxygen in the exhaust for the catalyst to convert unburned HCs... so you might try enabling the air injection by triggering the appropriate solenoid controlled vacuum valve...

-Howard
post #6 of (permalink) Old 06-13-2004, 09:38 PM
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Re: Emissions failed - tell me what the numbers say

Don't forget as you reply to this thread...

Loc: Colorado Springs, CO

That's about 5,000 feet above sea level making the O2 a little thin.

I was stationed at Ft. Carson years ago, found it hard for me to breath some days after leaving and coming back. Never had much luck at getting a carb to work well there either.

Just a thought

Dale
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post #7 of (permalink) Old 06-13-2004, 09:44 PM
 
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Re: Emissions failed - tell me what the numbers say

Well hook the gauge to a extra port on your carb,and just start adjusting!I am no master mechanic so it takes me a while to get it set.I just turn the distributer and the mixture screws until the needle holds a steady vacume.I repeat,it takes me a while

RRICH had a write up over on the commando board about how to inturpit the readings,but could not find it.Sorry I am not much more help,I just hook it up and go,kind of! [img]images/graemlins/AR15firing.gif[/img]
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post #8 of (permalink) Old 06-13-2004, 11:31 PM
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Re: Emissions failed - tell me what the numbers say

You are too lean!


You have:
HC PPM 1422 @idle Max 400 (FAIL) too high!
CO% 0.11 @idle 0.15 @ 2500 RPM ---> Max 1.5 (PASS) too low!

You don't fail because of too low, but the readings are interdependant.

Low CO is good normally, but when it's starved for fuel it misfires slightly. The missfire lets a little raw gas escape -- driving the HC reading up.

I'd first check for vacuum leaks - use a BURNABLE carb cleaner - Gumout's OK for this. Test to make sure it's burnable -- dribble a few small drops down the carb throat - if the R's INCREASE, it is. If it drops RPM, it's not burnable. Normally I'd say lean the mixture before doing this, but you are already there now.

Spray a little at a time - around the carb base, vacuum trees, hoses, -- anything that operates on vacuum. If you find a leak the R's will increase just like they did when you tested the "burnability."

Fix anything you find.
If you find no leaks, adjust the idle mixture screws slightly richer. HC should come down nicely.

HC is raw unburned gas, the stuff you pay $2.50 for - never even tried to burn.
CO is gas that partially burned but didn't completrely burn -- ran out of oxygen before it completed combustion. Since the internal copmbustion engine isn't 100% efficient, they all put out some of each.

Be aware - the nutter bypass - it disables the computer - illegal for emissions in most states. You cannot modify or disconnect emissions devices, the original carb and computer are emissions devices. Not just state law, Federal law too.






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post #9 of (permalink) Old 06-15-2004, 09:09 AM Thread Starter
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Re: Emissions failed - tell me what the numbers say

Thanks RRICH you were correct. See update above.
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post #10 of (permalink) Old 06-15-2004, 11:05 AM
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Re: Emissions failed - tell me what the numbers say

[img]images/graemlins/goodpost.gif[/img]
Exellent Post.
Thank you for giving us the update.
Congrads on passing
Happy Jeeping !
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