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Another failed California smog candidate

D

Donski

NAXJA Forum User
Location
San Leandro, Ca
Hi
I'm new to the forum, and need some help. My Daughters XJ failed smog on high NOx on the low speed test, and I'm looking for some possibilities other than a factory Cat. The other emission reading look really good, and so it makes me curious as to the problem.
Vehicle is a 98 XJ, 4.0l Automatic trans. I did some mods to it about 6 months ago which included a Gibson header, and a newer intake manifold. New o2 sensor, injectors, plugs wires and dist cap. Not sure which plugs I put in it, but I think they're the OEM Champions.
Here are the results of the test. http://img.tapatalk.com/d/
14/01/11/e4yba4a3.jpg

I appreciate any help you can offer. My first thought is to run some techron and see if it cleans up any carbon buildup.

Thanks
Don
 
e4yba4a3.jpg
 
What tires/gearing? Everything looks good but that. Tall tires with stock gearing will have the engine running an lower RPM's and can effect the smog test.
 
you're not hugely above the max, I would suggest seafoaming it (put some seafoam in the tank) burn through that tank, and when you're low, go get half a tank of 91 octane and try it again, I bet it'll pass.
 
Thanks guys.
The gearing is stock, and the tires are 235/70-15, which are actually a little smaller diameter than the stock 225/75's.
I'll try the seafoam. I've also thought about seafoaming it through the intake, to see it that can burn off the tops of the pistons
 
Yep. I'd seafoam through the intake and through the gas tank as well.
If you feel like it, pull a spark plug and shine a flashlight in there, crank the motor by hand. See if you can get a look at the piston tops before and after.
My factory cat gave out somewhere around 120,000 miles. I put a Magnaflow cat in there and it passed Berkeley smog a couple times and Nevada County smog once so far, still going strong.
From the numbers, I don't think you'll need one - but if you do - give Magnaflow a call and see if they still have a CARB part number for the XJ.
But yeah, injectors & piston tops cleaned, drive it at least 20 minutes before pulling in to the smog station, you'll probably be fine.
 
Seeing as only NOx is high and all your other numbers are good, check your cooling system.

How is the state of your cooling system? NOx is created when combustion temps are too high. Have you ever run 100% water? If so it's possible that a thin layer of rust has formed on your cooling jackets, preventing proper cooling under load.

It's worth looking into because it failed under the higher load test. (The main difference between the two tests is that the first one is at 50% load on the engine and the second is at 25% load)

Also, there's a chance it could be carbon deposits, SeaFoam would help with that. But, I would say that's unlikely because your engine is running so clean.

Finally, running higher octane fuel reduces engine temps, so put some octane booster in there and I'd bet on lower NOx readings.

Good luck
 
Seeing as only NOx is high and all your other numbers are good, check your cooling system.

How is the state of your cooling system? NOx is created when combustion temps are too high. Have you ever run 100% water? If so it's possible that a thin layer of rust has formed on your cooling jackets, preventing proper cooling under load.

It's worth looking into because it failed under the higher load test. (The main difference between the two tests is that the first one is at 50% load on the engine and the second is at 25% load)

Also, there's a chance it could be carbon deposits, SeaFoam would help with that. But, I would say that's unlikely because your engine is running so clean.

Finally, running higher octane fuel reduces engine temps, so put some octane booster in there and I'd bet on lower NOx readings.

Good luck
 
BulletMaker said:
Usually the high NO is caused by a lean mixture as the result of: Slow O2 sensor response, Plugged injectors, or carbon buildup in the piston.
Click to expand...

This. I prefer BG44k to seafoam. Run a can of that through it. How many miles are on it and are the 02 sensors original?
 
BulletMaker said:
Usually the high NO is caused by a lean mixture as the result of: Slow O2 sensor response, Plugged injectors, or carbon buildup in the piston.
Click to expand...

Yes, this is true as well. But, a lean mixture can be ruled out in this case.

Lean mixture can be identified on the smog report as high percentage of O2 There is no O2 (0%) (Or if O2 and CO are more than 1% difference).

Like I said, Seafoam can't hurt, I do it a few times a year on my vehicles.

And boosting the octane will help the NOx numbers, I'm pretty sure.

But it doesn't hurt to cover all your bases. I've seen more than a few 4.0 motors with bad rust when owners ran just water.
 
Thanks everybody for the help. So to answer some questions, I believe the O2 sensors were both replaced when I did the major tune. It has 160K now. One thing that I couldn't chase down was a stumble at idle. It never idled very smooth, and It always sounded like it was running rich at idle. Could it be a sensor that's part of the problem? Maybe an IAT?

One of the things Ive considered is putting some smaller tires on it, just to smog it. If they were smaller diameter, it wouldn't load up so much during the low speed test. It's got 235/70-16's now. Is there anybody in the neighborhood that has a set of steelies with some maypops I could borrow? I'm going to check a couple of friends, one that has an XJ, and another that has a Liberty, to see if they are smaller.

And BTW, there's an Addco 516 for sale on Craigs list for $100 in SF now. My front bar is just over 1", so it doesn't make sense for me to upgrade.
 
The stumble at idle is good to know. It's possible that one or more of your injectors are slightly restricted. Which would cause a lean burn in that cylinder(s) which could be causing your NOx issue.

Speculation: the reason that the other numbers are good is that the O2 sensor probably saw a slightly lean condition and enriched the fuel trim and the cat is doing a good job burning up the excess HC and whatnot.

Have you tried anything to fix the stumble? Injector cleaner, ect?

Fix the stumble and you'll pass. Or...put the smaller tires on and risk failing again. The dyno calculates the load on the engine and smaller tires mean that the dyno will put relatively more load to get the 50% load on the 15mph test.
 
Thanks for the info about the smaller tires. Thats time I won't waste.
I'm going to run some fuel system cleaner through the tank, and see what happens. I'm also going to see if I have any exhaust system leaks as suggested by the previous poster. Since I just put a muffler and a header on it, I would't be surprised if one of the connections is leaking. That could also be the reason for the stumble, if fresh air is being introduced into the exhaust path.

I'm going to head out there now. I'll report back
 
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