Failed smog

[94xjstud]

I went to get my jeep smog and it failed. The guy say that it failed becuase the engine appeared to be being over worked. He was not sure of the problem but said it could be a clogged cat, bad O2 sensor, intake leak or something else. Not sure what that means but here is what I have.

94 xj, straight six, intake routed through the cowl, magna flow 40 series exhaust (about 3 years old), 5" lift, D30 - 4.56 gears and aussie locker, D44 4.56 gears and aussie locker and 33" tires.

Before the smog, I recently did an oil change, transmission fluid flush, new oil pressure switch and changed the valve cover gasket. Since I did the value cover gasket and oil change, my oil pressure gauge was been consistantly at about 60.

Any ideas? I want to do as much as possible on my own because I am on the unemployment budget

 

[94xjstud]

It looks like I failed this:
NO (PPM)
15 mph - MAX(517) AVE(203) MEASURED(852)
25 mph - MAX(539) AVE(233) MEASURED(674)

 

[blondejoncherokee]

personally i would start with
plugs (10$)
plug wires(20$)
cap and rotor(24$)
o2 sensor (50$)
sea foam(10$) the intake and gas tank

about 120$ right there and youve knocked out alot of variables

test tps, cps, (free if you have a DMM)
check for exhaust leaks
test fuel pressure(why not?)
check all vacuum lines(free)
maybe repalce the exhuast/intake manifold gasket (20$)
check the cat (free)

another 20$ and some time and youve really gone through

 

[old_man]

It looks like I failed this:
NO (PPM)
15 mph - MAX(517) AVE(203) MEASURED(852)
25 mph - MAX(539) AVE(233) MEASURED(674)

NO is normally related to high combustion temps. In effect, running lean. My bet would be on the O2 sensor or a vacuum leak of fairly large proportion. Adjust the throttle position sensor if it is adjustable. You didn't state the year model but I suspect it is a 94. In that case, there is no EGR valve to check/replace.

 

[94xjstud]

Could you please explain "vacuum leak" a little more? Does it have to do with air leaking into the air intake tube that did not go through a filter, or air leaking from the manifold?

Engine stuff is still new to me.

 

[Bryan C.]

NO is normally related to high combustion temps. In effect, running lean. My bet would be on the O2 sensor or a vacuum leak of fairly large proportion. Adjust the throttle position sensor if it is adjustable. You didn't state the year model but I suspect it is a 94. In that case, there is no EGR valve to check/replace.

Sounds like a bunch of rabbit chasing if you ask me.



Try this. Go to this site and use the Lambda calculator for a difinitve answer as to whether you are running rich or lean. Input the numbers exactly as they are shown on your smog check results. Once you do that report back with the findings and we can help you more.
http://www.smogsite.com/calculators.html

 

[XJensen]

I would have thought the cowl intake would fail the visual inspection. Don't you need a stock box or CA legal intake to pass?

I know the filter may be CA approved but how do you inspect it in the cowl?

Josh

 

[94xjstud]

As long as I tied the to tubes that were originally connected to the air box to the intake tube it was fine because that made it a "sealed" intake.

 

[94xjstud]

At 15 mph - Lambda=1, perfect for emission and CAT operation and Air/Fuel ratio=14.7

At 25 mph - Lambda=0.9999, perfect for emission and CAT operation and Air/Fuel ratio=14.7

I am getting good readings from this and double checked my numbers so they are right.

 

[MONSTERxbla]

after you change all that stuff and if it still didn't pass, I would start thinking about the catalytic converter. my experience with combustion (water tube boilers...not little water heaters, but 150,000lbs/per hour steam) is that when you start making a little bit of CO or NOx it can turn into a lot quickly. we are now using a catalyst which reduces our NOx levels after combustion(from 50ppm to 5ppm). this is basically what your xj is doing. but eventually the catalyst is no longer effective in reducing the NOx and needs to be repalced. just an idea.

 

[Bryan C.]

At 15 mph - Lambda=1, perfect for emission and CAT operation and Air/Fuel ratio=14.7

At 25 mph - Lambda=0.9999, perfect for emission and CAT operation and Air/Fuel ratio=14.7

I am getting good readings from this and double checked my numbers so they are right.

OK, so it sounds like your cat is most likely the cuplrit based on the fact that your numbers look good. Be sure to check for any exhaust leaks between the cylinder head and the cat converter first. Even small ones will have an effect on emissions.

 

[94xjstud]

Is there a good/ practical way to do this or just inspect the exhaust manifold to the cat looking for cracks?

 

[94xjstud]

I was looking around for leaks and spotted a good sized (1-3") crack in my exhaust manifold where the two pipes connect. IIRC that is very common on stock 4.0L manifolds.

I would like to fix this asap and cheap, would JB Weld work or do I need to take it completely off to get it welded.

 

[XJensen]

As long as I tied the to tubes that were originally connected to the air box to the intake tube it was fine because that made it a "sealed" intake.

Good to know I figured they would freak out about this setup out here.

Josh

 

[Bryan C.]

I was looking around for leaks and spotted a good sized (1-3") crack in my exhaust manifold where the two pipes connect. IIRC that is very common on stock 4.0L manifolds.

I would like to fix this asap and cheap, would JB Weld work or do I need to take it completely off to get it welded.

Go to ebay, buy one of the $99 exhaust manifolds that comes with a gasket set. Not the best quality, but my last one lasted over 5 years. On my second one now.

 

[the_weirdo]

Good to know I figured they would freak out about this setup out here.

Josh

In San Jose, the guy wouldn't even look at my 98XJ unless it had the stock airbox. Had to remove my cone filter and put the box back in.

 

[NorCalChris]

i have a muffler/cat combo for sale. Cat works good. make an offer

 

[94xjstud]

In San Jose, the guy wouldn't even look at my 98XJ unless it had the stock airbox. Had to remove my cone filter and put the box back in.

That's where I got mine done. The guy was super cool about it.

 

[Bryan C.]

In San Jose, the guy wouldn't even look at my 98XJ unless it had the stock airbox. Had to remove my cone filter and put the box back in.

There is a law on the books that states if your vehicle is 95 or older then you can install a modified air intake as long as all the factory hoses can still attach to in a similar fashion to stock. 96 and newer OBDII vehicles need to have a CA approved part with the accompanying EOD sticker stating it is an approved part for your vehicle.

Seems a bit complex for just a stupid air intake, but it seems to work well.

 

[ParadiseXJ]

In San Jose, the guy wouldn't even look at my 98XJ unless it had the stock airbox. Had to remove my cone filter and put the box back in.

There is a law on the books that states if your vehicle is 95 or older then you can install a modified air intake as long as all the factory hoses can still attach to in a similar fashion to stock. 96 and newer OBDII vehicles need to have a CA approved part with the accompanying EOD sticker stating it is an approved part for your vehicle.

Seems a bit complex for just a stupid air intake, but it seems to work well.

I have a "50 State Legal" on the XJ (90 4.0 AW4) and it's got a CA approved sticker. I've had it in since 03 and passed smog/inspection everytime.

This thing is just a straight pipe between intake hose and filter with two vac nipples and a K/N cone. The 2 large vac lines to it are the fresh air up front and the cannister purge line.

I deleted the line to the front of the old airbox and plugged the loom end.