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Discussion Starter #1
I am having smog problem on my 1991 yj 4.0L . failed nox I've replaced just about every thing... If any one out there has a DRB II scanner would like to work out a deal to get some time on it... I have some parts I could trade or just some greenbacks....
 

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I completely redid the emissions on an '84 CJ7 to get it to pass smog. When I took it to the smog station and told the guy what I did he said that replacing the cat will do more than most other repairs. He was impressed with the low numbers it produced.

Good luck,

Dennis
 

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I had problems with my 87 YJ passing smog, ended up dumping almost $600 to get it to pass. When it passed the guys said that it was running almost clean, and I told him it better damn well be running almost clean:flipoff2:
 

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Discussion Starter #6
ALREADY REPLACED CAT, PLUGS, WIRES, CAP, ROTOR, FUEL FILTER, AIR FILTER, O2 SENSOR, AND TIMING CHAIN. 91 HO HAS NO EGR AND THE TIMING IS ONLY ADJUSTABLE USING THE DRB II SCANNER, OR SO I'VE BEEN TOLD. I HAVE A SCANNER BUT IT JUST READS BASIC THINGS, SENSOR READINGS AND THE LIKE.
 

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get a really cold thermostat. that will lower the combustion chamber temps. how high is the nox anyways, is it about to pass?
 

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Do you have a low restriction intake or bored out throttle body? I had a problem with my NOX. It would hit 1400 at 1600-2000 RPM. I eventually put the stock throttle body and air cleaner box back on and it finally passed...barely.
Hope this helps,
Bryan
 

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gotta love oklahoma... no inspections!
but yeah i get some brown funk comin outof my 93 4banger sometimes, like ocndensation gets on garage floor and is black sometimes
 

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Discussion Starter #11
ONLY CHANGES I MADE WERE TO THE EXHAUST I HAVE A BORLA HEADER CATCO CAT AND BORLA CAT BACK EXHAUST. I SUSPECT THIS IS CAUSING A LEAN CONDITION. MY LTFT (LONG TERM FUEL TRIM) IS UP TO 46%. I PLUGGED THE VACUM LINE TO THE FUEL REGULATOR AND AFTER DRIVING AROUND FOR A WHILE THE LTFT WENT DOWN TO 40.5%. DOES ANYONE KNOW WHAT THE MAX ADJUST FOR LTFT IS ON A 1991 YJ??? MY DAD HAS THE MOPAR INJECTION ON HIS 81 CJ 4.2L AND HIS LTFT IS UP TO 58%. THOUGHT THAT MAYBE THEY REWORKED THE COMPUTER FOR THE KIT...JUST AN IDEA.
 

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Discussion Starter #13
So fast forward 9 years and experiencing same problems.

First test High NOx and HC.
Replaced plugs, tested wires, replaced cap and rotor, replaced air filter, replaced cat with ca compliant model. Long term fuel trim is still reading 46%. No codes.

Second test Hi NOx Gross polluter. HC have returned to normal.
During second test started leaking coolant. Later found out it was the water pump. Could low water level cause NOx to increase?

When replaced the plugs there was some major deposits on one of the plugs. Almost enough to bridge the gap. I am thinking the spark plugs alone corrected the hi HC.

Could these deposits be caused by a leaking injector? If only one injector is leaking could this cause the O2 to read rich, causing the computer to lean out all injectors to correct the rich reading?

Long term fuel trim is being enriched 46%. The short term trim is reading -512ms at idle.

I'm at a loss any help would be appreciated.
 

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So fast forward 9 years and experiencing same problems.

First test High NOx and HC.
Replaced plugs, tested wires, replaced cap and rotor, replaced air filter, replaced cat with ca compliant model. Long term fuel trim is still reading 46%. No codes.

Second test Hi NOx Gross polluter. HC have returned to normal.
During second test started leaking coolant. Later found out it was the water pump. Could low water level cause NOx to increase?

When replaced the plugs there was some major deposits on one of the plugs. Almost enough to bridge the gap. I am thinking the spark plugs alone corrected the hi HC.

Could these deposits be caused by a leaking injector? If only one injector is leaking could this cause the O2 to read rich, causing the computer to lean out all injectors to correct the rich reading?

Long term fuel trim is being enriched 46%. The short term trim is reading -512ms at idle.

I'm at a loss any help would be appreciated.
It must be OIL depotsit, from say a leaking vlave seal or bad ring....

oil deposit cause Hot spot in cumbustion chamber and lead to Hi NOx...
 

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Discussion Starter #16
No fix... the smog tech ran the 15 mph test in 1st gear. In 2005 moved to a county that didn't do the dyno. Now back in the Bay Area and dealing with the smog nazis again.
 

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Discussion Starter #17
It must be OIL depotsit, from say a leaking vlave seal or bad ring....

oil deposit cause Hot spot in cumbustion chamber and lead to Hi NOx...
Wouldn't oil show up as a rich condition?

The plug wasn't oily. Just really worn with some major deposits. It was only 1 plug.
 

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Discussion Starter #19 (Edited)
Don't have the plug anymore. I'll try to take pic of new plug next time I pull them. Does appear to have a valve seal leak on that cylinder. Back side of valve appears oily. Looked through injector hole with inspection camera.
 

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I would check the fuel system for correct pressure and flow. i.e. No restrictions. The pressure may appear good but drop off under a load. I had this on the GM engine and it was a low pressure/ flow causing a lean condition.
 
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