XJ-WolF

I have a 1995 xj sport that wont pass smog, it passed when i first bought it 2 years ago but now i have these pretty high HC measures and high NO at 15mph.

After it failed the first time i did the normal tune up ordeal, plugs, wires, cap and rotor along with new pcv valves and some vacuum lines. The only thing i didnt change witch i probably should have is the O2 sensor

I been readng up on all the other smog related posts but not that many have the high HC like i do. Most of the post say that the O2 sensor is most likely the problem followed by the catalytic converter. I have never had any problems with over heating.

I just need more info on what is causing these high HC and what else could be done to fix it and if just replacing the O2 sensor will solve it

thanks

XJ-WolF

after reading some more on the smog threads here i have a direction to go

Jesse Hallum

You did not mention the "EGR Visual" failure on your inspection sheet. You'll never, ever pass CA smog unless all emissions controls are all fully operational. If your O2 sensors were to blame for the astronomically high HC count, your CEL would be lit up.

Bustedback

There is no EGR valve on a 91-01 4.0l Cherokee.

salad

Woah, that must be one stinky Jeep. If your O2 sensors are original, now's the time to replace at least the upstream unit. 18 years is a long time and they generally have an 80-100k mile life expectancy. Grab an NTK unit, these are the OEM for 91-01 XJs.

Does your XJ run cold or really hot or something? That super high NO is quite alarming. Did you warm the Jeep up before taking it to be tested? Or was it cold when they got to it?

mdnov

I agree with Salad. I would start with the O2 sensor. How many miles are on it?

XJ-WolF

It has 237,800 miles on it i bought it at 204,000 2 years ago and it passed ok. It runs cold it hardly ever reaches 210 on the temp gauge i have only gone over 210 (during summer in hemet) once and then the aux. fan kicked in and brought it back below quickly.

The visual fail was for a cracked vacuum line on the fuel pressure reg.

I brought it there hot but didnt do i any freeway driving and i left it running before they checked it and i forgot that the half tank of fuel i had in it was 91 with a few ounces lucas fuel stabil

It runs and idles perfect, pretty much no blow-by, only thing it was a slight shake while in the idle before warmed up

im hoping its just the O2 senor

salad

Ohhh I keep forgetting the older models with their FPRs on the fuel rail. That would DEFINITELY cause problems from too lean/too rich, which is the same problem an O2 can cause.

XJ-WolF

i was going to check the fuel pressure but i dont think a normal air pressure gauge will work for fuel pressure, and the the pressure reg. is expensive

Jesse Hallum

This will sound odd, but what brand of fuel was in the tank?

We had problems a while back passing CA smog when we used off-brand fuels. Never had a problem when using Chevron for some reason, but cheap out and buy something really cheap like Arco or USA, and the readings went through the roof.

I doubt this is the root of your problem, but I'm curious if it could be a contributor.

XJ-WolF

makes sense i had issues with fuel on my 87 toyota truck.

But that day it was half shell 91 and half arco 91

mdnov

Well with the milage, I would certainly change the O2 sensor. You might also wind up replacing the cat.

Jesse Hallum

Very interesting. Ours always blew nearly clean with zeros on both HC and NO using Chevron fuel. We once foolishly switched to El Cheapo Gas for a few months before smogging, and the numbers skyrocketed, even though nothing else changed on the engine.

I spent weeks trying to determine the problem; not an EGR issue, recent tune up, LT and ST fuel trims below 3%, o2 sensor voltages well within spec, cats working fine and IR'd, no intake leaks, etc. I even IR'd the exhaust ports to see how close to 2500-deg. it came, and it wasn't even close. I ran it across an old ASE guy I know, and he confirmed that fuels that contain really cheap fractions and questionable detergent packages were probably responsible. Food for thought.

XJ-WolF

definently something to think about, after i burn up the remaining fuel and put the O2 senor in i will stick to better fuel for the test, and possibly try some deuterated alcohol with the fuel

salad

I had no idea you could perform a hysterectomy on alcohol.