91cherokeedev

Hi jeepers. I am new to this site am needing help.I bought this cherokee about a year ago. I have personally replaced new longblock cat all sensors( map o2 iac ect tps. It passed smog with flying colors but one year later the nox is too high. Its at the 25 mph that it won't pass. It runs about 210 at all times. The electric fan works. The plugs seemto be burning fine. Could it be the cat is out again? The smog shop said I need to replace it with a chrysler cat because of how hot the engine gets. I don't want to get rid of it . I have big plans for this cherokee.

Radi

Anything that might be making the engine run lean? What brand/type Cat did you install?
How about the O2 sensor? Intake bolts all tight?

91cherokeedev

I have checked and rechecked the intake bolts. The o2 sensor is one year old. -t does have a very slight miss at idle and I have checked all vacuum lines. The plugs are a slight brownish to almost white color. The last time I checked them they where black like carbon build up. The jeep has over 200000. Could the injectors be bad or regulator?

91cherokeedev

Oh ya the cat is a magnaflow from o rielly auto.

Radi

It's tough to troubleshoot this stuff from a recliner, lol. But if it were mine, since you had carbon on the plugs at one point, I'd clean the combustion chambers. Some folks like seafoam through a vacuum line, or you could dribble a small bit of water into the throttle body..rev it up to 1500 or so and dribble until the engine *almost* chokes.

Second thing I'd do is check the fuel pressure, particularly looking for numbers that are too low.

A tank or two of Techron or BGK44 injector cleaner might clean up the injectors if you think they may be dirty. I'd do it regardless, just because.

Verify that your TPS voltage and MAP sensor are operating in spec. I believe there is a write-up for both. I know you just replaced them, but aftermarket electronics just aren't what they used to be. Some fail in a remarkably short period of time.

If you have a Bosch O2 sensor, change it for an NTK. I know, I know....some folks swear by Bosch. But occasionally their aftermarket sensors get sluggish.

If that all fails you might consider an OEM cat. I hesitate to suggest that because they're expensive and only the problem about half the time...check the cheap stuff first.

91cherokeedev

Thank you for your help I really appreciate it. I'm going to smog place tommorowto get it rechecked. Acording to the smog guy the engine runs too hot which makes the nox level get very high and then the egr valve sucks or vacuums all of that back through the intake. I'm guessing it just recircs it back through the intake. So I got the motor to run about 10 to 15 degrees cooler and just plugged the vacuum from the egr. Again I really appreciate your help. I will let you know how it turns out.

Radi

I keep forgetting your year has an EGR valve. Later models' don't. At any rate, unplugging the EGR may make NOx worse.....the EGR actually cools the combustion event somewhat, lowering NOx. You might verify yours is working.

91cherokeedev

Ok so now it passed the emissions but the visual failed and I didn't change anything visual. Only in ca I guess. They said the hose going from pcv valve is too loose.