Failed Emissions on 95 FZJ80: NOx (1 Viewer)

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Joined
Sep 21, 2017
Threads
6
Messages
37
Location
Boulder, Colorado
Hi all,

I've been lurking around here for a while. Back in September I picked up a 95 FZJ80 in CO Springs (150K on the OD, but a OD discrepancy on the title), and have been slowly working on it to turn it into a camper for a road trip. So far I've really only removed the interior and sound deadening, put in new drive belts, and replaced leaking power steering hoses/flushed the PS system. I also had a small coolant leak, and have a new radiator, heater hoses, water pump, and fan clutch to install this week. I dont have a garage, but it's going to be 60 here in Boulder on Tuesday, somehow.

My temp tags were set to expire, so I took a gamble and got it emissions tested despite all the work I wanted to do. It failed for high NOx (6.4 average). Just wonder where people think I should go first.

My understanding from all the lurking is that elevated NOx is from high cylinder temps. Any reason to believe that the cooling system overhaul would make a major dent in NOx? Wouldn't that be a treat?

Most commonly successful fix: new cats. (But $$$)
Usually tried before new cats: O2 sensors, EGR valve check, VSV check, new vacuum lines.
Usually used to squeak by: fuel additives, getting the cats hot-hot-hot on the highway, "sending thoughts and prayers."


(OH and PS yes, obviously I should have gotten a smog check from the PO. I hadnt bought a used car in a while and clearly should have brought a checklist with me, because I got too excited while test-driving, and remembered literally as I was driving away in the truck. Like an idiot.)
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NOx is produced in the high temperatures of the combustion chamber and the job of the EGR valve is to re-introduce exhaust gasses back into the combustion process to control the production of NOx at the cost of some engine efficiency.

Catalytic converters after the 1980's also reduce NOx, but they were primarily there to reduce carbon monoxide and un-burnt hydrocarbons by reacting with them to change them into less bad emissions.

If you NOx is not passing, do you have any codes? It would be strange that there wouldn't be codes if the EGR were stuck closed. VSV and Vacuum lines are all part of the EGR system. These should all be addressed at the same time if you are going this route.
 
No CEL, so I'm assuming no codes. Agreed it seems unlikely to be EGR w/o codes. I've heard people having problems with emissions due to O2 sensors w/o CEL, though?
 
Does your CEL light work? It should come on briefly when you first turn on the ignition.
 
I had a similar problem. No codes but high NOx according to the smog check. Turned out it was an airleak at the EGR gasket.

If you do what I did then make sure you have a fire extinguisher with you and do it with a reasonably warm motor but not hot.....fire is bad

I found it by spraying carb cleaner at hoses and interfaces and listen for changes in RPMs and watch ECU data for the O2 sensors...this was a very sight change in RPMs but a decent spike (up I think) in O2 sensor readings but when I tightened the interface and put Gorilla tape over the suspect area the engine ran different and you could see the O2 sensor change. Don't spray at the exhaust maniford or pipes
 
Coolant temp has very little to do with combustion temperature. High Nox is usually due to insufficient EGR gas. There are lots of possibilities: EGR modulator, EGR valve stuck partially closed; VSV valve leak, Obstructed EGR passage in intake and more.
 
I had a similar problem. No codes but high NOx according to the smog check. Turned out it was an airleak at the EGR gasket.

If you do what I did then make sure you have a fire extinguisher with you and do it with a reasonably warm motor but not hot.....fire is bad

I found it by spraying carb cleaner at hoses and interfaces and listen for changes in RPMs and watch ECU data for the O2 sensors...this was a very sight change in RPMs but a decent spike (up I think) in O2 sensor readings but when I tightened the interface and put Gorilla tape over the suspect area the engine ran different and you could see the O2 sensor change. Don't spray at the exhaust maniford or pipes
My favorite snoop technique...
 

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