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`98 SMOG Woes...

xcm

xcm

NAXJA Forum User
Location
Southern Oregon
So it appears im having trouble getting my 98 to pass smog... as I have failed 3 tests in a row due to NO emmissions.

First time around, I had a cracked exhaust manifold, and a clunking cat, so no surprise i failed on the high speed NO. Im still looking for the paperwork to post a pic, but cant find it. The high speed NO was slightly too high.

So i had a new cat installed, retested, and the NO went down slightly, but not enough. At this point I assume its the cracked manifold, so I pull it, and reweld the crack, do a quick seafoam treatment (Half in crankcase vacuum, half in gas tank), and new autolite spark plugs and retested.

Heres the fail slip from round 3:
smogwo.jpg


The low speed NO skyrocketed... great...
Anyone got anything to read into this?
 
Wrong heat range plug could cause the NOx to go up? Just a thought since thats what you changed last.
 
I got what the parts store gave me for a 98 xj with 4.0. Is it possible to get a plug with a colder heat range to lower them? I know its been recommended in other search-reading ive gone thru, I just dont know the part number system to get 1 step colder plugs.
 
Running too rich? Thats the only thing that seems to be sensible. New plugs, cat,fixed header shold be able to pass no problem.
 
xcm after my wifes failed, I replaced the header and gasket. Her numbers went to almost zero with that and her new cat on.These are her failing numbers.I can't find her passing numbers, sorry.But like i said almost zero
wifesjeep_zpsdf9321f7.jpg


She was leaking i guess like the man said, thats why i changed them.I couldn't hear it myself.
 
I just replaced the spark plugs again, back to champion 412's. I also pulled the manifolds to make sure it got seated correctly, which it did. I also replaced both o2 sensors.

I hooked up a fuel pressure, and vacuum gauge, and both gave me worrying results. For the fuel pressure, the second i killed the motor, it started falling, and when running, it reads in a range of about 5 psi, constantly twitching back and forth, quicker than the eye can see.

As for the vacuum, I have a steady ~17psi at cold idle, and it dips about 5psi when i blip the throttle, eventually rising into the 20+ green range on my gauge. I tried the brake cleaner spray trick to try and find any leaks, but cannot find any. There was an open 90 degree vacuum fitting in front of the battery box... do 98's have a vacuum bottle? Because i dont see one...

Thanks for your suggestions.
 
xcm said:
There was an open 90 degree vacuum fitting in front of the battery box... do 98's have a vacuum bottle? Because i dont see one...
Click to expand...

That was probably what your vacuum canister was connected to. On the late models it's located on the passenger side where the OEM lower fascia is usually located.

I plugged mine with a bolt.
 
Ok so late models do have a canister? I was looking around on all data, but couldnt find that info.

This 98 had a passenger front tire blow out doing 85, which took out the flare and bumperette, plowed in the rear bottom of the fender, and even dented my slider's capped end. So it wouldnt surprise me if it is missing.

Im new to late models, but what confuses me is how it passed smog visual without it...
 
xcm said:
I just replaced the spark plugs again, back to champion 412's. I also pulled the manifolds to make sure it got seated correctly, which it did. I also replaced both o2 sensors.

I hooked up a fuel pressure, and vacuum gauge, and both gave me worrying results. For the fuel pressure, the second i killed the motor, it started falling, and when running, it reads in a range of about 5 psi, constantly twitching back and forth, quicker than the eye can see.

As for the vacuum, I have a steady ~17psi at cold idle, and it dips about 5psi when i blip the throttle, eventually rising into the 20+ green range on my gauge. I tried the brake cleaner spray trick to try and find any leaks, but cannot find any. There was an open 90 degree vacuum fitting in front of the battery box... do 98's have a vacuum bottle? Because i dont see one...

Thanks for your suggestions.
Click to expand...

Fuel pressure definitely needs to be higher...Either a bad pump or a bad hose in the tank I would guess. Either way, low pressure will make it go lean and cause high NOx. Could be a plugged filter, but doubtful.

17psi at idle? Is it supercharged? JK Dropping to 5 inches when you blipped it is normal, when floored it should be close to zero inches.
 
The canister on 98s is that square box under the jeep right near the frame bracket for the rear brake softline.
 
kastein said:
The canister on 98s is that square box under the jeep right near the frame bracket for the rear brake softline.
Click to expand...

Sounds like you're talking about the evap canister?

Vacuum reservoir on my 97 was a 4-5 inch diameter round black sphere located behind the right side of the front bumper.
 
:doh:

Correct. I was talking about the wrong canister :dunce:

Yeah, the vac reservoir is the same black softball or football located right where you just said it is.
 
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