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Unread 08-20-2013, 05:00 PM   #1
huntingheep
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1990 YJ Wrangler 
 
Join Date: Aug 2013
Location: stockton, ca
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90 yj howell fi help

I have a 90 yj 4.2 auto that has a howell fi kit ca smog legal. it has failed smog a half dozen times due to high nox. howell sent a new throttle body and it still is having issues. hoping someone can tell me how much vacuum you have at port A at an idle and 1500 rpm

already put new cat/muffler, distributor, radiator, gas cap, ecm, plugs wires cap rotor,


too much in it to stop now! help


Last edited by huntingheep; 08-20-2013 at 07:15 PM.. Reason: updating
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Unread 08-21-2013, 04:07 AM   #2
Old4X
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1990 CJ7 
 
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We need the full emissions test results to get an idea where the problem is.
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Unread 08-21-2013, 07:16 AM   #3
Que89YJ
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1989 YJ Wrangler 
 
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High nox is a lean burn. You either have a exhaust manifold crack/leak or an issue with the O2 sensor itself. Check your manifold for cracks by the collecting tubes and double check all the manifold bolts torque. Check the egr tube too.
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Unread 08-22-2013, 04:05 PM   #4
timatoe
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I'd also bet your leaking at the manifold. Mine did the same. You may be money ahead to call around and find a shop that can do a smoke test, they basically pump a fog machine into the engine and you'll see anywhere it's leaking. Found an entire end piece was cracked on my intake this way that I couldn't see with it on there. I think the local guy charged me $45 to do it.
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Unread 08-22-2013, 06:00 PM   #5
YJ4LIFE
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1989 YJ Wrangler 
 
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damn go to a different smog shop. they should tell you why its not passing not how to rebuild your whole jeep. my friend has a shop and the only thing i've ever changed to pass was a rebuilt carb, gas cap, 02 sensor, or egr diaphram. All things that eventually fail with age.
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Unread 08-24-2013, 09:12 PM   #6
huntingheep
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1990 YJ Wrangler 
 
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the o2 sensor is new with the howell kit and a mechanic put on a new intake gasket which i think includeds the exhaust side at the same time. Thanks for the ideas keep em coming!
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Unread 08-24-2013, 09:18 PM   #7
WNUNEZJR
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I don't mean to be a ******* but my 2.5 passed with flying colors today I didn't think it would pass at all.
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Unread 08-24-2013, 09:20 PM   #8
huntingheep
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1990 YJ Wrangler 
 
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last test results
15mph 1396 rpm co2%14.2 %o2 0.4 hc 30 co% 0 nox 1027 fail
25mph 1404 rpm co2%14.2 %o2 0.3 hc 23 co% 0 nox 900 fail
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Unread 08-24-2013, 09:23 PM   #9
huntingheep
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1990 YJ Wrangler 
 
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smog shop says its egr system including the cat, that controls nox gas, its on its 4th egr and I put a new cat on a year and a half ago, no egr tubes are clogged, vaccum is run correct for the howell diagram
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Unread 08-24-2013, 10:04 PM   #10
Que89YJ
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1989 YJ Wrangler 
 
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Lean burn is the cause for high nox. The question is why. Fuel pressure
being regulated low by the control systems or running low because your fuel pressure is low. Check your fuel pressure.

The cylinder temp too high. The EGR it's responsible for lowering the chamber temp by porting the exhaust into the intake to lower the combustion temp.

Timing being too far advanced. The timing will cause the combustion to run too hot if it's advanced too far. Again I am not familiar with the hesco but the advance on the standard setup is controlled by the map sensor vacuum. If it is setup already you need ported vacuum for it.

The cat is the final stop for nox that is left. Start by checking your fuel pressure. You can try hesco
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