Failed emissions (help the FNG please)

[JustinLN]

Hello all.

First, thank you for the awesome forum, been lurking for some time before buying my first Jeep 2 months ago.

I was finally been able to get an emissions test done on my 1999 Sport. It failed miserably.

HC and Nox are well within range, but CO was double the allowable amount through the whole test. Jeep was up to temp and had fresh tune-up.

By the excessive exhaust noise in the engine bay, I think I have the common 4.0 cracked manifold, though I can't see any obvious carbon tracking. My scan tool shows short and long term fuel trims at about + 4% each, but I'm new to jeeps and am not sure if this is normal for the elevation I live at, about 5500'. Spark plugs have about 500 miles and are still nice and white. It does have an off idle stumble though, not sure if its a rich condition or the aftermarket throttle body spacer.

My only other thought is it could be the catalytic converter, but I'm thinking I should maybe start with the manifold and O2 sensor?

Any other ideas?

 

[dbbd1]

TB spacer is easy, remove it. You'll need shorter TB bolts though. It probably does nothing but it cannot hurt to remove it. Also easy are the O2 sensors. How many times can you try the inspection before it starts to cost more?

 

[JustinLN]

Cool, shorter bolts are easy to come by. Will swap O2 as well.
I get one free retest if I get it done in the next 10 days, then $25 per test.

 

[dbbd1]

I have "heard" that running your car at high RPM's for about 15-mins just before an inspection will help get the cat nice and hot. It might help if it's marginal.

 

[Cross-Threaded-06TJ]

Pour the old bottle of "guaranteed to pass" in the tank and hit that test again. I mean the bottle says it will pass.

 

[JustinLN]

I have "heard" that running your car at high RPM's for about 15-mins just before an inspection will help get the cat nice and hot. It might help if it's marginal.

It has worked for me on other vehicles, but kinda hard to do these days. Station has been closed for 2 months and now the wait times to get in are stupid long... Will see what I can do though.

Pour the old bottle of "guaranteed to pass" in the tank and hit that test again. I mean the bottle says it will pass.

Well shiiit, if that's what it says...

 

[JustinLN]

Just an update, hope this may help someone with the same problem.

I swapped out the exhaust manifold and upstream O2 sensor. The Jeep passed with flying colors, CO readings down to 6.0 GPM from 30 GPM+.

Thanks again guys!

 

[Cross-Threaded-06TJ]

Just an update, hope this may help someone with the same problem.

I swapped out the exhaust manifold and upstream O2 sensor. The Jeep passed with flying colors, CO readings down to 6.0 GPM from 30 GPM+.

Thanks again guys!

Thanks for helping save the planet!

Just messing, pull the cat and go speed through a school zone!

 

[CharlesHS]

Just an update, hope this may help someone with the same problem.

I swapped out the exhaust manifold and upstream O2 sensor. The Jeep passed with flying colors, CO readings down to 6.0 GPM from 30 GPM+.

Thanks again guys!

The crack in the exhaust header was causing the O2 sensor to see a somewhat lean condition so the PCM adjusted the fuel mixture just enough to raise the CO. Since the NOx was within specs... the catalytic converter was doing its job. Since you replaced the cracked header there is no lean condition sensed and the replacement of the O2 sensor just provides the PCM with a more sensitive accurate reading.