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Another Failed Ca SMOG thread - High HO & CO

G

Guerillastyle

NAXJA Forum User
Location
SF
Failed my most recent smog done on my jeep:

Jeep Cherokee Chief XJ
1988
Renix
4.0, Automatic

Before I went in for a smog I replaced wire harness, distributor cap, rotor, plugs, and did an oil change. Since the tune-up I noticed an increase in exhaust smell, noted by the technician as well.

Emission results:

Ibc6VrD.jpg


After the smog test I installed a new CAT, and changed both the MAP sensor and the O2 sensor. I went back to the smog station, but the tech told me it'd be a waste of money to retest because he could still smell the exhaust. I went through and checked for vacuum leaks with starter fluid. I am at the end of the list and am about to take the jeep into a mechanic. If anyone could have any further advice it'd be greatly appreciated.
 
high O2 % you may have an exhaust leak. really low no2 but high HC and CO seem like its running really rich. any intake leaks?
 
I would check every single vac line from the front of the valve cover to the airbox to the charcoal canister, and not with starter fluid (Ether is extremely flammable, explosive even), but look at each line from front to back and look for loose/bad connections, CCV fittings, breaks, holes, cracks and rubs. Then I would replace any compromised hoses, grommets, elbows etc. No tape, new stuff.

You might also replace or at least test the coolant temp sensor (the one in the lower block...under the manifold) that sends info to the ECU to adjust A/F ratio. It's a Renix
 
Definitely check your MAP sensor vacuum line. And check the fuel pressure regulator for a broken diaphragm, it could be leaking fuel into the vacuum line. Also check your O2 sensor and see if the voltage is fluctuating between 1-5 volts and not pegged on one side of the spectrum. Can't remember which side means rich.
 


A simplified vacuum diagram...and don't forget the lines to and from the EGR and EGR solenoid (not pictured)
 
Thanks for the help and advice guys. I am going to head out and inspect the vac lines further. I did already do a fuel pressure test, with the FPR connected and disconnected; both gave proper readings within appropriate standards. Is there any other way in which I can check the FPR?
EDIT:
Also forgot to initially mention my first approach of attack was doing a compression test; cylinders ranged from 120-145 all of which should check out.
 
Last edited:
Guerillastyle said:
Thanks for the help and advice guys. I am going to head out and inspect the vac lines further. I did already do a fuel pressure test, with the FPR connected and disconnected; both gave proper readings within appropriate standards. Is there any other way in which I can check the FPR?
EDIT:
Also forgot to initially mention my first approach of attack was doing a compression test; cylinders ranged from 120-145 all of which should check out.
Click to expand...

Ya im all between 120-145 as well.
 
I visually checked all the vacuum lines and did not seen any issues. I also took a look at the air filter, which was trashed with oil and road debris. Tomorrow I will build a diy blow-by filter, and install a new air filter. I was also able to run a resistance test on the coolant temperature sensor, the results I received showed the sensor is in need of replacing and had been reading inaccurately. Unfortunately the CTS was not in stock and I will have to wait until next weeks shipment.
 
A better way to check for vacuum leaks would be with brake cleaner. It dries up quickly but still does the job.
 
I like the brake cleaner vacuum test as well as the next guy but be careful. You really only need to cause *one* engine fire before you start looking for alternatives...
 
yossarian19 said:
I like the brake cleaner vacuum test as well as the next guy but be careful. You really only need to cause *one* engine fire before you start looking for alternatives...
Click to expand...

That is why I'm a fan of a propane torch, just the gas with no flame.

If your air box is oily your MAT is likely coated in a blob of gunk.

My intake/exhaust bolts tend to come loose over time, no matter what I do to keep them in place. One of my first stepa in finding a vacuum leak is to test the torque on a few random intake/exhaust bolts near the center.

An indicator of vacuum leak can be a hunting idle, the idle kind of rhythmically goes a little high, then a little low. Not always, it depends on how big the vacuum leak is, but often enough. Most of the vacuum connections are off center, as is a intake/exhaust gasket leak. Off center means some cylinders are running a little lean, while others may be running a little rich as the ECU tries to compensate. The right circumstances and the ECU can get really confused.
 
So I'm back and still looking for advice/help.
I relocated the intake air temperature sensor to the air box, and cleaned the EGR diaphragm; other than that I am stumped and there has been no change.

Tomorrow I am going to go out and test all the sensors:
TPS
IAC
MAP
O2

Let me know if I left any out. Is there any way I can test the fuel injectors?
 
blondejoncherokee said:
high O2 % you may have an exhaust leak. really low no2 but high HC and CO seem like its running really rich. any intake leaks?
Click to expand...
My brother had a cracked exhaust manifold on his YJ 4.0L, it did exactly what you describe.

The exhaust pulses in the exhaust manifold, because of valve overlap, you can get some vacuum as well. So a crack in an exhaust manifold or the exhaust close to the exhaust manifold, it will suck in air through the crack. The extra O2 in the air will be sensed by the O2 sensor.

The PCM will think the engine is running lean, and incorrectly richen the A/F ratio. It will run very rich, but the PCM will think its running the correct A/F ratio, because of the bogus info from the O2 sensor, created by the extra O2 getting in from the exhaust leak.

Running rich will cause less NOx emissions, but higher HC and CO emissions.

So check over the exhaust for cracks/leaks, that includes gaskets and seals, make sure manifold bolts are tight and not loosened up, if you've got one anywhere in the exhaust manifold to the O2 sensor up to a good foot after the O2 sensor, I'd say that is your most likely cause of the problem, but its NOT the only cause, like mentioned:
-A bad O2 sensor
-A bad MAP or vacuum leak to the MAP sensor
-A bad vacuum leak anywhere can throw off emissions
 
Rick Anderson said:
My brother had a cracked exhaust manifold on his YJ 4.0L, it did exactly what you describe.

The exhaust pulses in the exhaust manifold, because of valve overlap, you can get some vacuum as well. So a crack in an exhaust manifold or the exhaust close to the exhaust manifold, it will suck in air through the crack. The extra O2 in the air will be sensed by the O2 sensor.

The PCM will think the engine is running lean, and incorrectly richen the A/F ratio. It will run very rich, but the PCM will think its running the correct A/F ratio, because of the bogus info from the O2 sensor, created by the extra O2 getting in from the exhaust leak.

Running rich will cause less NOx emissions, but higher HC and CO emissions.

So check over the exhaust for cracks/leaks, that includes gaskets and seals, make sure manifold bolts are tight and not loosened up, if you've got one anywhere in the exhaust manifold to the O2 sensor up to a good foot after the O2 sensor, I'd say that is your most likely cause of the problem, but its NOT the only cause, like mentioned:
-A bad O2 sensor
-A bad MAP or vacuum leak to the MAP sensor
-A bad vacuum leak anywhere can throw off emissions
Click to expand...


Were your bro's emissions as high as mine?
I looked up a nifty way of inspecting for exhaust leaks and went outside and gave it a shot.
After I hooked up a shop vac to the tailpipe I sprayed bubbly water along parts of my exhaust & exhaust manifold, and found that there are indeed some areas where there are leaks. Could the found leaks be causing my issue even if there are many but small?

I also forgot to mention the spark plugs are covered in either oil or gas, or maybe even a mixture of both.
 
So as I got further into removing the intake and exhaust manifolds I found more and more larger cracks along the exhaust manifold above the o2 sensor. Would it be OK to weld the cracks and be good to go?
 
New manifolds with gaskets are like under 100$ shipped on eBay, but you can weld it for now- if you can reach it.

I bet fixing the manifold leaks and a new 02 sensor will do it.

Make sure the fuel pressure regulator is not going out and maybe consider cleaning the injectors.


Fix all of your exhaust leaks!
 
#S194 said:
If you already have the manifolds off, you might as well just order up a new exhaust manifold. No reason to take it all apart twice.
Click to expand...

Yep.

they are really cheap now- and a lot of them come with gaskets...
 
As well, welding exhaust manifolds are usually only a temporary fix. The thermal stress in exhaust manifolds is just too great, the weld usually just cracks again in a short time.

Especially cast iron exhaust manifolds, cause welding cast iron "properly" is very difficult and most people don't do it properly. I think a lot of 4.0L had metal tube exhaust manifolds, my brothers YJ did and we replaced it with an ebay manifold, worked great.

Cracks or leaks a foot downstream of the O2 sensor probably won't effect it, anything within a foot or upstream of it, will effect it. Of course if you have leaks before the Catalytic Converter, that might effect the cat and the pollution test, but NOT nearly as much as extra air getting in where the O2 sensor can sense it. Regular air has many, many times the amount of O2 in it than the exhaust.
 
Plus, if we're right, and even if we're wrong you need to fix those exhaust leaks, NOT only will you pass emissions, you probably get a little more power and gas mileage out of your motor. Cracked exhaust manifolds throw EFI systems for a loop.
 
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