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Unread 05-21-2010, 07:21 AM   #1
twmart
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Failed Emissions (High NOx)

We just purchased a 1994 Grand Cherokee with the 5.2 engine 160K. Went to get the emissions test done and it failed for high Nox. I found the old test from 2008 in the car the car only has 2,000 more miles now, so it looks like it sat for a while.
I did a vaccum test to see if it was good after the failed test we had 16 inches of vaccum it was steady no jumping around.

Old readings 2008 (passed)
HC .9684 limit 2.00
CO 8.8775 limit 20.00
CO2 602.2
NOx 2.6876 limit 4.0

My readings are
HC 1.2983 limit 2.00
CO 18.5306 limit 20
CO2 660.53
NOx 4.1738 limit is 4.00

We have not yet done anything to the Jeep since we bought it. I was looking at giving it an oil change this weekend and a tuneup (plugs, cap and rotor) I will also be checking the EGR to make sure it is working correctly.

Thanks

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Unread 05-21-2010, 07:59 AM   #2
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also look down the throttle body and see if you can see oil in there you may have a plenum gasket leaking and burning up oil. if it has bean sitting for a long time it may also be the old gas in the tank
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Unread 05-21-2010, 08:56 AM   #3
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Quote:
Originally Posted by ujoint View Post
also look down the throttle body and see if you can see oil in there you may have a plenum gasket leaking and burning up oil. if it has bean sitting for a long time it may also be the old gas in the tank
I will check down the throttle body tomorrow.. The tank was empty when we got it so it has full tank of fresh gas. I am going to add some injector cleaner tonight and get out on the HWY some....

Thanks
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Unread 05-21-2010, 02:44 PM   #4
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Question; if the plenum gasket was leaking wouldn't that be a vaccum leak that would show on a vaccum gauge????

Thanks

Quote:
Originally Posted by ujoint View Post
also look down the throttle body and see if you can see oil in there you may have a plenum gasket leaking and burning up oil. if it has bean sitting for a long time it may also be the old gas in the tank
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Unread 05-21-2010, 02:54 PM   #5
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is the cat working?
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Unread 05-21-2010, 03:11 PM   #6
Indslpwr04
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If it sat for a long time and the battery was dead it could just take some drive time to get the comp to relearn. My 97 4.0L would not pass when i first bought it. I drove it for a year with an expt sticker and did nothing else to it and it passed the following year.
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Unread 05-21-2010, 03:25 PM   #7
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Quote:
Originally Posted by Bossanova View Post
is the cat working?
Is there anyway to test the cat?????
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Unread 05-21-2010, 03:29 PM   #8
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Climb under and shake it around a bit with it COLD. If you hear stuff rattling inside (not the Shield) it may be broken up and done. If it glowing red its clogged but that doesn't sound like your issue.
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Unread 05-21-2010, 03:30 PM   #9
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Make sure that engine is warm. And don't do an emission test and then a tune-up, do a tune-up and then the emission test.
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Unread 05-21-2010, 03:36 PM   #10
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Yeah I know but it runs so well and no exhaust smells or anything I thought I would get lucky........ smooth acceleration, idles smooth correct RPM etc...

Quote:
Originally Posted by LordHobbit View Post
Make sure that engine is warm. And don't do an emission test and then a tune-up, do a tune-up and then the emission test.
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Unread 05-21-2010, 04:35 PM   #11
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The purpose of the EGR system on your 94 is to reduce NOx emissions. Do indeed check the EGR system as you said you would be doing.
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Unread 05-21-2010, 05:05 PM   #12
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Quote:
Originally Posted by twmart View Post
We just purchased a 1994 Grand Cherokee with the 5.2 engine 160K. Went to get the emissions test done and it failed for high Nox. I found the old test from 2008 in the car the car only has 2,000 more miles now, so it looks like it sat for a while.
I did a vaccum test to see if it was good after the failed test we had 16 inches of vaccum it was steady no jumping around.

Old readings 2008 (passed)
HC .9684 limit 2.00
CO 8.8775 limit 20.00
CO2 602.2
NOx 2.6876 limit 4.0

My readings are
HC 1.2983 limit 2.00
CO 18.5306 limit 20
CO2 660.53
NOx 4.1738 limit is 4.00

We have not yet done anything to the Jeep since we bought it. I was looking at giving it an oil change this weekend and a tuneup (plugs, cap and rotor) I will also be checking the EGR to make sure it is working correctly.

Thanks
1) Did you fail at high speed or low speed, or do you just have a single-speed test (if so, what speed(s) - this is instructive.)

2) If you have a two-speed test, what were the results for the other speed range? Also instructive.

3) High NOx is typically a function of failed EGR or clogged passages, but that is also accompanied (typically) by a massive reduction in HC and CO (increased combustion temperatures = more compleat combustion. HC and CO are "partially-burned fuel.") Ergo, you may want to check your catalytic converter as well.

Quick-and-dirty EGR test - find your EGR valve. Remove the hose from it and cap it off. Attach a hand vacuum pump to the valve vacuum nipple. Start engine and let it idle. Apply vacuum to the valve - the engine should stumble almost immediately. This checks operation

With the engine OFF (stalled or shutdown,) apply 15-18" vacuum to the EGR valve and hold. The gage should not move appreciably for at least two full minutes - if it does, you have a vacuum leak (which will interfere with EGR operation.)

This doesn't change the fact that I think the EGR is a stupid idea and there are far more efficient ways to solve the problem (EGR causes more problems than it cures...) but the Air Police won't get out of my hair and let me do it. I could probably delete everything except the PCV/CCV, play with the tuning a bit, add a water/MeOH fog, and my 22-year-old XJ with the AMC 6-242 would run cleaner than a 2010 KK with a four-cylinder engine. Yes, that includes getting rid of the catalytic converter, and yes, that means that it would still have lower emissions than the new KK!
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Unread 05-21-2010, 06:00 PM   #13
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EGR is what controls NOx. Change that out and put the old ring back in the hole. And put new vacuum hose on it. You're readings should come right down.
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Unread 05-21-2010, 06:02 PM   #14
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Quote:
Originally Posted by 5-90 View Post
1) Did you fail at high speed or low speed, or do you just have a single-speed test (if so, what speed(s) - this is instructive.)

2) If you have a two-speed test, what were the results for the other speed range? Also instructive.

3) High NOx is typically a function of failed EGR or clogged passages, but that is also accompanied (typically) by a massive reduction in HC and CO (increased combustion temperatures = more compleat combustion. HC and CO are "partially-burned fuel.") Ergo, you may want to check your catalytic converter as well.

Quick-and-dirty EGR test - find your EGR valve. Remove the hose from it and cap it off. Attach a hand vacuum pump to the valve vacuum nipple. Start engine and let it idle. Apply vacuum to the valve - the engine should stumble almost immediately. This checks operation

With the engine OFF (stalled or shutdown,) apply 15-18" vacuum to the EGR valve and hold. The gage should not move appreciably for at least two full minutes - if it does, you have a vacuum leak (which will interfere with EGR operation.)

This doesn't change the fact that I think the EGR is a stupid idea and there are far more efficient ways to solve the problem (EGR causes more problems than it cures...) but the Air Police won't get out of my hair and let me do it. I could probably delete everything except the PCV/CCV, play with the tuning a bit, add a water/MeOH fog, and my 22-year-old XJ with the AMC 6-242 would run cleaner than a 2010 KK with a four-cylinder engine. Yes, that includes getting rid of the catalytic converter, and yes, that means that it would still have lower emissions than the new KK!
This is a multi speed test I have a page that lists IM240 Trace Diag. type of failure. If that helps here are the numbers
CO 71% Accel 28% High Cruise
NOx 81% Accel 5% Low Cruise 12% high cruise

Thanks
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Unread 05-22-2010, 11:08 AM   #15
twmart
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Quote:
Originally Posted by ujoint View Post
also look down the throttle body and see if you can see oil in there you may have a plenum gasket leaking and burning up oil. if it has bean sitting for a long time it may also be the old gas in the tank
Ok I have done some troubleshooting this morning and the EGR work perfect holds 15 vac for about 2 min, when I apply vac to the EGR the engine stumbles and dies at around 6 on the vac gauge.

I just looked down the throttle body any there is oil down there so my next step is to replace that plenum gasket. Will that increase the vaccum reading or is 15 a good number for a 5.2 with 160k miles?

Thanks again for all the help..

next step is a/c.... lol good thing it was cheap..

Tom
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