Failed Emission test - 1988 Cherokee Pioneer

[perkyb]

I went to register my jeep today and I failed the emission test. It passed the equipment inspection and the Oxides of Nitrogren (NOX) test. It failed the Hydrocarbons and Carbon Monoxide tests however. The results are as follows:

HC: my truck = 3.16 standard = 3.00
CO: my truck = 65.98 standard = 25.00

Obviously the Carbon Monoxide is my biggest problem. Anyone know what the quickest and cheapest fix to this is?

Any help is greatly appreciated!

 

[MudderChuck]

I went to register my jeep today and I failed the emission test. It passed the equipment inspection and the Oxides of Nitrogren (NOX) test. It failed the Hydrocarbons and Carbon Monoxide tests however. The results are as follows:

HC: my truck = 3.16 standard = 3.00
CO: my truck = 65.98 standard = 25.00

Obviously the Carbon Monoxide is my biggest problem. Anyone know what the quickest and cheapest fix to this is?

Any help is greatly appreciated!

I'm by no means an expert at this, but have had reasonable success. High CO is often a lean burn condition, combustion temperatures too high. The normal culprit is the O2 sensor, though there can be other causes. I usually do an injector (in the gas tank treatment) before a test and check my vacuum lines very closely. Many of the vacuum taps into the intake manifold are off center, meaning a leak can affect some cylinders more than others, that is bound to give some contradictory readings. The vacuum cannister and the vacuum line under the battery to the canister are likely trouble spots, though any of the vacuum lines are very old plastic or rubber that deteriorates over time or gets brittle with age. Higher idle isn't always an indicator of a vacuum leak, if the leak is small the IAC is going to correct. Checking the intake/exhaust bolts for tightness is often a good idea, use a torque wrench and be extremely careful of the studs at the ends of the manifold. Snapping one off can be the beginning of a very bad day.
I always take my XJ for a banzai run up the interstate before a test. My hydrocarbon numbers are a lot lower that way.
But like I said, I'm by no means an expert and may have just been lucky with my assumptions.

 

[Bounty__Hunter]

There's a bottle of product at most parts stores that, when added to your fuel, is guaranteed to get a pass on emissions test. May help for a little insurance once you fix the mechanical problems.

 

[ka041a]

the only way you could get the carbon monoxide levels that high is with way too much fuel. the excess fuel burns up all the oxygen so that there isn't enough to form carbon DIOXIDE so only carbon MONOXIDE can form. if this is a 4.0 engine with sequential fuel injection, i would suspect a leaking injector. a lean misfire or ignition problems would push the hc through the roof, not co. hope this helps, john

 

[perkyb]

Thanks for all the tips. I couldn't find any vacuum leaks and I ended up taking out and cleaning the IAC motor, which instantly fixed my erratic idling problem. Ultimately I ended up adding about 750ml of 92% isopropel alcohol from the grocery store once I got down to 1/4 tank. It worked like a charm and my jeep passed with flying colors!

 

[TennesseeCJ]

I've got an 86 CJ7 with an inline 6 that failed emissions with a high CO2 level. I waited until I had 1/4 tank of fuel left, went to Home Depot and bought a gallon of denatured alcohol, poured it in and took a fast trip down the interstate. After about 10 minutes of this, I went straight over to the emissions testing and passed with no problem at all! If you do this, be sure to fill your tank up directly after the testing to dilute the alcohol since it's a bit hard on the engine.