Failed Smog Again - JeepForum.com
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post #1 of 20 Old 09-20-2017, 07:32 PM Thread Starter
TVojtko
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Failed Smog Again

I am, once again, living a smog failure nightmare for high NOx!

Pre-test, I ran Techron through a tank of gas then I changed the oil and air filter. I didn't change the plugs, wires, cap and rotor since I replaced them about 18 months ago in order to pass smog and I actually changed the plugs again less than a year ago after I was having a misfire. I also aired the tires (33's) up to 38psi to reduce the surface area on the dyno.

Test 1 results:
15mph - CO2=14.8; O2=0.16; HC-MAX=86, MEAS=32; CO-MAX=0.51, MEAS=0.06, NO-MAX=711, MEAS=1043 (FAIL)
25mph - CO2=14.9; O2=0.10; HC-MAX=72, MEAS=16; CO-MAX=0.65, MEAS=0.02, NO-MAX=613, MEAS=912 (FAIL)

After that I de-carbonized a few times with both seafoam and water and added a bottle of 'guaranteed to pass'. Before going to the smog shop, I drove the **** out of it on the freeway for about an hour and a half really getting the RPM's up to try and blow any crap out of there.

Took it back to the smog shop and they ran it on the dyno in test mode....no change in the NOx readings.

Had the Cat replaced and took it to the smog shop....he ran an official test thinking that it would fly through the test with the new cat.

Test results:
15mph - CO2=15.0; O2=0.07; HC-MAX=86, MEAS=22; CO-MAX=0.51, MEAS=0.01, NO-MAX=711, MEAS=1284 (FAIL)
25mph - CO2=14.9; O2=0.05; HC-MAX=72, MEAS=7; CO-MAX=0.65, MEAS=0.01, NO-MAX=613, MEAS=1130 (FAIL)

The smog tech was concerned about how lean I was running and pulled the vacuum hose off the fuel rail and there was no noticeable change in pressure or RPM's, so I went to the local auto parts store and rented a fuel pressure gauge - the pressure sat at 35psi at start and idle. Pulled the hose of the fuel rail and there was no change in pressure.

I replaced the fuel pressure regulator and threw a new MAP sensor on since I had one laying around. Tested the fuel pressure again an it was still at 35psi, with no change after pulling the vac hose.

Took it to the smog shop anyway just to check it in test mode and there was no change in the NOx readings.

My primary concern is that the fuel pressure and RPM's don't change when pulling the vac hose off the fuel rail, but I took the Jeep to my regular mechanic this morning thinking it was possibly the fuel pump, but he didn't think that was it....the jeep is running great.

I'm at a loss at this point and have an appointment with an official state smog repair shop to do a full diagnostic on Friday.

However, I just wanted to see if anyone here had any ideas, since you've never let me down before.

One last thing, both the smog tech and my regular mechanic think it may be the 33in tires, but it has a passed previously with those tires on and I don't have access to stock tires.

Thanks a lot in advance!!

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post #2 of 20 Old 09-20-2017, 11:40 PM
lclark2074
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Have you tried to pull codes off the computer? exhaust leaks before the o2 censer will drive your numbers up. and vac leaks will confuse censers.

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post #3 of 20 Old 09-21-2017, 08:23 AM Thread Starter
TVojtko
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Quote:
Originally Posted by lclark2074 View Post
Have you tried to pull codes off the computer? exhaust leaks before the o2 censer will drive your numbers up. and vac leaks will confuse censers.
Yes, I pulled the codes and there are none. I also sprayed carb cleaner all around the engine bay around the vacuum lines and didn't detect any leaks.

The smog tech also crawled under the jeep to check the welds on the new cat and he said that they looked great.
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post #4 of 20 Old 09-21-2017, 08:39 AM
Mr.B
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I've had my Jeep for almost 12 years. It stared out with a new cat on the first smog check for high NOx. It barely passed 2 years later. The next time, fail. So I decided to take it to a shop. They put it on their machine and recommended a new O2 sensor, and a new timing chain. The timing chain they said was because the firing was variable and could be causing early and late detonation. I thought that was a stretch at the time(pun intended). But I went ahead and let them do it. Plus replace the water pump since it was out. But the thing still had high NOx. So they had to replace the cat again anyway. Fast forward the dreaded 4 years later. I was so worried that I borrowed 4 stock XJ tires to do the test, which looked really funny.


wheels.jpg



I think I passed NOx with a 2 at 15mph. So this year,(year 6) I got bold and went in with the 35's still on. I passed NOx with a 5 at 15mph, and 17 at 25mph.


I don't know which repair fixed it or both. But I'd try the O2 sensor first, if I were to do it over again.

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post #5 of 20 Old 09-21-2017, 09:08 AM Thread Starter
TVojtko
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Quote:
Originally Posted by Mr.B View Post
I've had my Jeep for almost 12 years. It stared out with a new cat on the first smog check for high NOx. It barely passed 2 years later. The next time, fail. So I decided to take it to a shop. They put it on their machine and recommended a new O2 sensor, and a new timing chain. The timing chain they said was because the firing was variable and could be causing early and late detonation. I thought that was a stretch at the time(pun intended). But I went ahead and let them do it. Plus replace the water pump since it was out. But the thing still had high NOx. So they had to replace the cat again anyway. Fast forward the dreaded 4 years later. I was so worried that I borrowed 4 stock XJ tires to do the test, which looked really funny.


I think I passed NOx with a 2 at 15mph. So this year,(year 6) I got bold and went in with the 35's still on. I passed NOx with a 5 at 15mph, and 17 at 25mph.

I don't know which repair fixed it or both. But I'd try the O2 sensor first, if I were to do it over again.
I had high NOx issues on the smog check two years ago and the first thing I did was change the O2 sensor, so I don't think that's it (I put an OEM sensor in). I also put in a new TPS at that time.

The O2 sensor didn't fix the problem two years ago, so one shop put on a new cat which also didn't fix the issue, so they took it off and put the old one back on and told me to take it to a State licensed smog repair shop for a full diagnostic, which I did and they diagnosed a small crack in the exhaust manifold.

The new exhaust manifold didn't totally fix the issue, but a full tune-up with wires cap and rotor brought the numbers down enough that it passed smog with only a quick spin on the dyno.

Now here I am with everything replaced less that two years ago (closer to 18 months) with NOx through the roof again.

My water pump died three months ago, so that along with the thermostat, all the radiator hoses and radiator cap are also new.
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post #6 of 20 Old 09-21-2017, 09:13 AM
DirtKar
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Like Mr.B I was failing nox and used the small tires aired very high to squeak by. I mean by two points squeak by... Now that I've moved North from the Bay the rollers are not used and I have no issues passing smog,

Just saw your reply, are you sure you haven't developed a crack in your replacement exhaust manifold? If everything is present it sounds like you're on your way to a visit with the referee.

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post #7 of 20 Old 09-21-2017, 09:57 AM Thread Starter
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Quote:
Originally Posted by DirtKar View Post
Like Mr.B I was failing nox and used the small tires aired very high to squeak by. I mean by two points squeak by... Now that I've moved North from the Bay the rollers are not used and I have no issues passing smog,

Just saw your reply, are you sure you haven't developed a crack in your replacement exhaust manifold? If everything is present it sounds like you're on your way to a visit with the referee.
No cracks in the manifold that I can see.
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post #8 of 20 Old 09-22-2017, 10:41 AM
mike134
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Well, first things first.

There might be a separate issue that will magic bullet your NOx issue. But we KNOW that there is a fuel pressure issue. 35 is too high at idle. The creation of this fuel rich issue might be causing the computer to lean you out.

Can you buy/borrow a vacuum gauge from the autozone? Lets see where your vacuum sits.
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post #9 of 20 Old 09-22-2017, 01:37 PM
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Check for clear flow through the return line.
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post #10 of 20 Old 09-22-2017, 02:16 PM
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I can not prove anything I'm about to type, but I believe it in my heart and have some circumstantial proof to supply.

1. A friend of a friend had a 1995 Jeep XJ - 1 owner pristine vehicle. Ran fine, looked great, no issues. It failed smog for Hi NoX. (sound familiar Larry?)
2. The owner ran Seafoam through the heads thinking it was "crudded up" and causing the issues.
3. According to him, 7 months of two additional Seafoam treatments and other "fixes" (oil change, headers, tune up, etc. It still would not pass CA SMOG.
4. He and his wife got frustrated and sold it to me for $750.00
5. I towed it home, drove it through a tank of gas or two, maybe 400 miles (yes untagged and illegally) ran a bottle of Guaranteed to pass through the tank then refilled with fresh fuel.
7. took it to my SMOG Nazi (he's a stickler) hoping to see some improvement, and it passed with flying colors.

In my opinion as a guy who has build and smogged about 16 Jeep 4.0 or 2.5s in the last 30 months, Seafoam will make you fail. It coats something or the residu causes the Hi Nox condition. My advice is to drive the jeep for another 400 miles to get that crap out of there. Run the last 200 miles with GTP in the tank, then fill up with regular old 87 octane. THEN go pas smog.

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post #11 of 20 Old 09-22-2017, 04:53 PM Thread Starter
TVojtko
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Thanks for the suggestions, guys.

I had an appointment to drop it of at the state licensed smog repair shop this morning and it turned out to be the O2 sensor....that was the last thing I was considering since I just put a new OEM O2 sensor in less than two years ago.

I'll re-check the fuel pressure to see if there is any change.
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post #12 of 20 Old 09-22-2017, 10:05 PM
jcourt667
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Dump some GTP in and run the crap out it.

I failed NOx miserably on the first test, dumped some GTP and ran the Jeep for three days on a 120 mile round trip commute to work. Filled up with 94 octane on the last day drove straight the test station and passed with flying colors. I did have a new exhaust header, gaskets and cat.


FWIW: I've still have the original oxygen sensor in it and 258k miles.

94 Sahara YJ 4.0L HO. 255k miles! Been down for 8 years, time to get this out of the barn!
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post #13 of 20 Old 09-23-2017, 10:47 AM
mike134
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Quote:
Originally Posted by jcourt667 View Post
FWIW: I've still have the original oxygen sensor in it and 258k miles.
Woah. This is definitely supposed to be a wear item.
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post #14 of 20 Old 09-23-2017, 09:31 PM
timatoe
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There's a fuel additive called Blue Sky that's supposed to help with smog testing, no idea if it works or not.

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post #15 of 20 Old 09-24-2017, 06:13 PM
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Quote:
Originally Posted by mike134 View Post
Woah. This is definitely supposed to be a wear item.
I bought the Jeep with 44k miles on it, never replaced the sensor. Maybe the O2 sensor is BS and don't need it? Jeep passes emissions and runs great so why replace?

94 Sahara YJ 4.0L HO. 255k miles! Been down for 8 years, time to get this out of the barn!
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