I am starting a new thread from another that I jumped into. OLD THREAD WAS : Emissions fail
(Meant to say Failing, not Dailing) How can I fix this?

Last I installed newly welded Exhaust Manifold since was cracked and leaking . It failed miserably NOx. Pulled everything off. While apart, changed out Drivers side Engine mount since it was toast. Mounted everything back and couldn't get the pipes and the manifold to meet up easily. The engine mount was so bad that there was literally no rubber inside. Think changed the exhaust pipe location. Bolt on one of the two (Exh Manifold) was stripped part of way. C Clamped them together best I could then snugged it down.
Just got back from smog and it still failed. When it cools down, I'll put low pressure thru the back end of the tailpipe and look for leaks. I think I have a problem with that donut gasket.
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HEY Moderator. Can you correct my fat finger typo heading? Should say Failing Not Dailing Thank you

 

Causes of High NOx emissions:
1. Lean Mixture
2. Defective/missing EGR
3. Defective Catalytic Converter
4. Worn/failing cooling system

 

Have a New Catalytic converter.
Mine is a 1994 Cherokee and it has No EGR. Checked that right away, first thing.
I see no cooling issues. Never overheats.
I suspect leaking exhaust at that 'donut gasket connection to the exhaust manifold. Or STILL the exhaust manifold itself. I went to a yard and took one out of another 4.0L Jeep (1996 Grand Cherokee). Checked for leaks. Welded up the front tube and reinforced the downtubes where they normally leak. Spent all weekend on it. So will tackle it again tomorrow. Do a check for leaks. I suspect the donut gasket connection because had such a hard time connection. Would that cause the lean condition? I suspect it would.

 

i would suggest a lean condition by a vacuum leak. or a faulty 02 sensor.

those would be the 2 i would be looking for the most..

but exhaust leak still needs a fixin too.

 

New O2 Sensor too. NTK(made by NGK)
I replaced a couple vacuum lines. Which one is most critical to worry about? Which one most likely to cause a lean mixture? And fail smog?
Did have an issue with a broken line from the valve cover to the intake manifold. I replaced with a vacuum hose and shoved it into the fitting on top the valve cover (Back by the firewall. ) What does this one do?

 

CCV system (similar to PCV- it ventilates the crankcase) The rear line sucks fumes out of the crankcase through a small metering orifice which is part of the plastic fitting on top of the valve cover. The front line pulls in fresh air from the air filter box.
Is that rear plastic fitting broken? If it is and that metering orifice is gone it could cause a vacuum leak.

So...what are you running for spark plugs? Have you checked your fuel pressure? What were the rest of your readings? CO? O2? HC?
Ever de-carboned the combustion chambers?

 

Yes . the fitting is broken. I shoved another vent hose into it so it's a snug, no leak fit. Didn't realize a that it's a metering device inside? A reduced orifice. Would that cause fail in Smog? I'll replace it . Is it rubber mounted to the valve cover? It does not pull off. Do I need to pull the valve cover to replace it? How much of a problem is that valve for smog failure?
But still need to check the exhaust at that donut gasket tonight.

All new plugs (NGK), wires, cap, rotor,
1st smog was high on everything. At the limit on HC. After plugs, wires HC,,O2,CO dropped dramatically to easy passing. Original plugs were bad. New catalytic converter. Only issue is NOx.

 

Just checked the system for leaks. Good news there is No leak at the donut gasket at end of Exhaust Manifold and the rest of the exhaust. That held tight. Bad news is that I found a crack in the newly welded Exhaust manifold. At a different spot. So the bad news is that I get to take it all apart again. But the really good news, I'm a veteran at this job so won't be so tough.
One question: There is virtually no run time on the manifold gasket. Only put on and run to smog. Should I still replace with a new one?

 

I decided to take my old one and weld it up. Realized why it failed so badly. Cracks everywhere. It is so welded up that its ugly. I'll install the old one this weekend. Old Manifold will fit better so no real exhaust pipe work will be needed.

 

if you're near san bernardino I have a buddy with a smog shop that will hook you right up...

 

Thanks. I have a smog shop here that does all the pretesting. Found my problem with the exhaust leak. Be finishing it up today. Smog tomorrow or tuesday. I'll post the results. Then I may 'discuss' what to do next to pass this beast, San Bernadino is close.

 

Still failed after brand new manifold put in. I gave up welding the old one. Everytime I welded it, Found a new crack. So it was really worn out. I installed new manifold . at the torque settings from the repair (Haynes) manual. The Torques were 17 in-lbs at the ends. Rest were 23 in-lbs. I didn't do a exhaust leak with pressure from the tailpipe. Thought was a done deal. When it cools a bit, I'll do that check. The only thing haven't changed is the MAT or MAP sensor on the firewall. Would that cause High NOx readings? Or should I be doing the engine clean with the B..44 stuff.? Will that help NOx.
Maybe need to run the Jeep longer on the road to teach and burn in the O2 sensor. ? Not many miles on it. ? Could I have wrecked the O2 sensor with the new manifold- oil etc from it?
. I'll post the latest readings shortly.
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SMOG NUMBERS

 

CO numbers low. HC midrange. NOx sky high.
HELP !

 

High NOX is caused by excessive combustion temps, I installed cooler heat range plugs and passed

 

Maybe should do that. I have NGK 7252 Plugs. I have to verify the number. I took the recommendation off this site. So far, everything has been good. What range should I be looking at? 2 steps lower? Maybe the easiest solution.