Failed smog today

[justjeep94]

its a 1994. I just dropped in a new engine less then 500 miles ago. my NO level is really high. ill post my numbers below. Do you know what it could be?


15mph-rpm=1710 C02=14.5 02=0.8 HC=76 CO=0.12 NO= 626

25mph-rpm=1647 C02=14.7 02=0.5 HC=30 CO=0.06 NO= 603

The bold is what i failed.

 

[Bryan C.]

Go to www.smogsite.com and punch those numbers into the Lambda calculator and tell us what the results are.

 

[justjeep94]

15 mph= Lambda=1.031 Air / Fuel Ratio=15.16

25mph= Lambda=1.021 Air/ Fuel Ratio=15.01

 

[Bryan C.]

Looks like you are running a tad lean. Since you just put the engine in, check for any intake manifold vacuum leaks. Also check for any exhaust leaks as well. Once the lean running problem is fixed, then you may need a cat.

 

[justjeep94]

so i most likely need to get a new cat. just checked all vacuum lines no leaks. Would the numbers be that high with a small exhaust leak?

 

[Bryan C.]

so i most likely need to get a new cat. just checked all vacuum lines no leaks. Would the numbers be that high with a small exhaust leak?

No vacuum leaks does not equal fixing the lean condition.

Yes.

 

[cracker]

so i most likely need to get a new cat. just checked all vacuum lines no leaks. Would the numbers be that high with a small exhaust leak?

A cat will help reduce your HC numbers but will not reduce your NO numbers.

 

[l1kenother]

My smog guy says that many cars will fail smog if they take it in cold. He says they should be running for a while before taking it in. He always runs mine for at least 10-15 minutes before and says many other places will not. Took my GFs s-10 into him because it failed at another place and he smogged it warm and it passed easy.

 

[Bryan C.]

A cat will help reduce your HC numbers but will not reduce your NO numbers.

Maybe. A good cat can clean up a poorly running engine's exhaust gas readings. Of course the new cat probably won't last very long if you don't fix why the original cat failed to begin with.

 

[yossarian19]

NO numbers are almost always a worn out cat, this from my boss / head mechanic.
How old is your current cat?

 

[Bryan C.]

NO numbers are almost always a worn out cat, this from my boss / head mechanic.
How old is your current cat?

:shhh:

 

[cracker]

A cat will help reduce your HC numbers but will not reduce your NO numbers.

As I do more research online I beleive this statement to be wrong. :dunce:

I did fail with NOx on my '94 HO once with a brand new cat. My HC numbers were better than new yet my NOx was stupid high. I never fixed it and it became a buggy after that. :wierd:

 

[MoparMatt77]

What temp T.stat are you running? Running other then 195 temp T.stat can cause ECM to run to rich or lean. Jeeps love 195-210f for better emmisions.
Is fuel pressure on rail to low, or Injector partly clogged, Cracked fuel line? Is there a leak or crack in Vacuum bottle on front bumper or Evap system? Was the new motor used with carbon buildup on valves or bored over / built on stock injectors? All these could cause lean condition.

When I have a Jeep suspected of failing smog I'll use a decarb like Mopar comb chamber cleaner, Seafoam, ... etc. to clean top end of motor, and clean injectors. Then change oil and plugs, preffer cheap standard copper core champion brand plugs. I have yet to have problem failing Jeep yet.

From a Master Tech / Foreman I know.
High HC could be rich fuel, hotter temp. Rich fuel and burned oil Kills cat converters.
High Nox could be lean fuel, cool temp, Exh - Vac leak, or EGR. 91-06Jeep have no EGR.
High Co could be missfire and is a bit tricky to figure out sometimes.

 

[ArmyDad]

NOx is a byproduct of combustion temperature. Lean running conditions (in gas/gaso engines) or combustion ignition (in diesel). I had my cat tested with the LPG enrichment test before having it replaced.

As you replaced the engine recently, did you go up on displacement? Fuel injectors that are computer controlled will only add so much fuel.