90' xj 4.0i with 80k. the jeep passed everything except the 15mph CO% reading was 1.55, limit is 1.38! the 25mph reading was 1.22 and passed. What would cause it to fail at 15mph but pass at 25mph?

I made the mistake of driving the jeep down the road 2miles to the station for testing without warming it up, could this simply be the cause?

so far i have replaced, spark plugs,wires,cap,rotor,water pump,belt,hoses,thermostat,oil,oil filter,air filter,pcv vaccum line, seafoam (1/3oil, 1/3 booster,1/3 gas).

I plan to retest next week. Is there anything else I could replace/inspect?

Thanks.

 

you need to warm your jeep to operating temp before an e-test.

otherwise your jeep thinks its still cold and it is dumping tons of fuel to try and warm it up quicker.

not certain this is the cause of your fail, but very well could be.

 

Do you still have a mixture of junk in the gas tank???

Some of those additives contain stuff that will throw off the test numbers.

 

So glad we don't have emissions test where I live.....Sounds like a huge pain. How does that work if its your DD and you fail? Is it like inspection where they just dont pass you and you are not suppose to even drive it or do they give you time to get it fixed? Sounds like a huge pain

 

here in colorado you have 10 days to retest for free. after that you have to pay another $25 to get it done again, then you have 10......so on and so fourth.

it is a huge pain. they will only run up to 33 inch tires on the dyno when they test. i have 37's on my jeep and drive to the emissions with stock size tires on the back.

 

note to self : don't move to a state with emissions tests

 

oh yeah....there is more stuff that is a PITA with emmisions. i dont have the energy to type them all out.

 

try seafoam, that stuff does wonders. and i do believe you it will clean up the injectors and clean up the carbon build up which would be making those high numbers.

 

Yeah, dont, Ill probably get sick reading them.

 

if you read his first post, he says he put in seafoam

 

In Ontario we would 2 stage that. All Grand Cherokees just get a 2 stage Emissions test since they cant be run on a dyno. In other words theres just an at idle test basically.

 

Yeah colorado sucks badly for emisions testing and my number is up to go get retested in a couple months. I failed horribly my first time then past after I put a new cat and new o2 sensor in. Hopefully I will be moving before I have to re do it. If I move 15 miles east they dont have the e tests there.

 

x1000

 

I just failed yesterday on hydrocarbons and co2 what a drag My 1990 cherokee is getting an overhaul in las vegas they have high standards i bought a new catalytic converter and muffler and running a vacumm test new o2 sensor and gonna try that seafoam!

 

a bad pre-cat o2 sensor can cause a bad fual/air mixture also, dont overlook that if it fails again. Dont think the 90's had those... but good info for anyone who reads this that has a similar problem