EGR - High NOx tips?

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Front Range 4x4

Front Range 4x4

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I've failed Colorado emissions twice this week so I'm hoping someone can give me some tips on tracking down the cause of my high NOx (8.0 and needs to be under 5.0) in my FJ62.

I'm guessing some component has failed. Yes, I have a FSM but no vacuum gauge yet so I'm doing the best I can with what I have. I tuned it after the first fail and managed to increase my NOx by .5 :censor:

My exhaust system is new, had the cat checked yesterday and it's fine but hotter than it should be. Pulled the EGR expecting the tube to be full of gunk but it's clean. No vacuum leaks that I can find. Running some BG44K through this tank of gas.

Any ideas? Any component a weak link?

TIA!
 
I am no expert but i would check that the EGR valve is opening with vacuum.
Check for vacuum at the EGR, i believe there should be no vacuum at idle, but there should be vacuum off idle.
 
no vacume when engine is cold

Most older vehicles which may include yours, has a thermal valve that is screwed into the engine block that will open up and send a vacuum to the erg valve. Its possible its stuck or, a vacuum leak between source to egr. Check to see if it opens up "test with vacuum after it warms up. EGR also should open up under acceleration. If I am correct, it is powered by venturi vacuum and not manifold vacuum.
 
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I think I found the problem. I didn't find any vacuum leaks and thought I did a good check of the hose from the air filter to throttle body. I did take it off and clean it during the process and apparently tore a 3" hole on re-installing which I found today when it wouldn't even stay running. Now I'm hoping it was a hairline previously that's been causing all my issues.

Duct tape and she's running fine. I'm not sure that's why I failed emissions but if it was leaking at all that's probably the problem. :rolleyes:
 
High NoX is usually and EGR problem, but a big hole in the intake tube will mess up a system pretty bad too.


Dynosoar:zilla:
 
I pulled my EGR valve out and discovered that the tube that inserts into the intake manifold was nearly completely blocked off with carbon. Since these are getting old, and the rubber diaphragms get brittle, I went ahead and replaced the egr and the other thingy that clips onto it which I think is called the modulator. It changed the way my exhaust smelled--went from kind of a dirty smell to a kind of sweet smell.
 
Dynosoar said:
High NoX is usually and EGR problem, but a big hole in the intake tube will mess up a system pretty bad too.
Click to expand...

Dynosoar, a vacuum leak is one of the causes of high NOx. I'm not sure this was my initial problem but it does seem probably since I always passed easily in the past.

slcfj62 said:
I pulled my EGR valve out and discovered that the tube that inserts into the intake manifold was nearly completely blocked off with carbon.
Click to expand...

I expected that on mine and was shocked to see it was extremely clean. Cleaned up what was there and put it back together.

I still have to give it another check for other vacuum leaks again.
 
When my old Blazer failed with high nox, I retarded the timing a few degrees. I later found that just pulling the vacuum advance on the distributer and plugging it worked as well. High Nox happens when the combustion chamber is very hot, so do what you can to cool it down. (ironically, its the opposite of all the advice usually given for passing emissions - ie, higher octane gas burns hotter)
Sorry I have no Cruiser specific advice, I don't even know if FJs have a vacuum advance, but retarding the timing was the magic bullet for me (and a very cheap fix)
 
slcfj62 said:
I pulled my EGR valve out and discovered that the tube that inserts into the intake manifold was nearly completely blocked off with carbon. Since these are getting old, and the rubber diaphragms get brittle, I went ahead and replaced the egr and the other thingy that clips onto it which I think is called the modulator. It changed the way my exhaust smelled--went from kind of a dirty smell to a kind of sweet smell.
Click to expand...

That's interesting. As far as I could determine from FSM tests the EGR is working as intended. i did pull it and clean off the small amount of carbon but that was insignificant. Same with the tube itself, much cleaner than everyone predicted.

My patch of the tear wasn't successful so I'll be replacing that as soon as I find one. I don't know how much difference to expect with something like that though.

I'm really groping at this point. :confused:
 
Dynosoar said:
High NoX is usually and EGR problem, but a big hole in the intake tube will mess up a system pretty bad too.


Dynosoar:zilla:
Click to expand...

I replaced the damaged intake hose and when checking for more vacuum leaks it looks like I stumbled on the problem. I sprayed starting fluid in the vicinity of the EGR and it appears the diaphragm is cracked since the engine raced. :doh:
 
Front Range 4x4 said:
I replaced the damaged intake hose and when checking for more vacuum leaks it looks like I stumbled on the problem. I sprayed starting fluid in the vicinity of the EGR and it appears the diaphragm is cracked since the engine raced. :doh:
Click to expand...
Since you've already gone through this, could you please link me to any threads you've found helpful in diagnosing high NOx?

THANKS :grinpimp:
 
Hey Zhenya, I haven't found much that's been helpful beyond this thread. If you have high NOx as I do I can tell you to look for vacuum leaks. Bad cats are a sure cause and always the starting point along with a full tune-up. I found the one leak mentioned above and the bad EGR valve but they weren't my issue because I failed it again today. I'm replacing the O2 sensors tomorrow so maybe that will help.
 
Front Range 4x4 said:
Hey Zhenya, I haven't found much that's been helpful beyond this thread. If you have high NOx as I do I can tell you to look for vacuum leaks. Bad cats are a sure cause and always the starting point along with a full tune-up. I found the one leak mentioned above and the bad EGR valve but they weren't my issue because I failed it again today. I'm replacing the O2 sensors tomorrow so maybe that will help.
Click to expand...
Thanks for your response. I think I still do have the factory cat, but my truck is in really good tune otherwise. I get around 13-14 mpg in my 60 :wrench:
 
FWIW, I failed high NOx in Colorado (Boulder) last year. I tried most of the stuff you list, no dice. Ended up taking it to Charley's Garage in north Boulder, he replaced the thermostat (P/N 90916-03052) and associated gaskets. NOx dropped more than half and I passed.

Of course, the question is which thermostat? The MAF link shows a "cold climate" (190 F) and low temp (160 F) both under that part number, and there very well may be a standard unit (180 F) for that part # as well. I just don't remember, and the paperwork isn't in front of me right now.

At the least, you'd probably want to check that your thermostat is working correctly - if its faulty, MAF says the the rear two cylinders of your engine will run hotter than the gauge indicates. If it is working, I'd guess that you'd want to lower your engine temp if your NOx is high, but I'll defer to those who know more about such things than me (e.g. just about anyone on this site).

Cheers,
Brian

P.S. - One other thing he did was fix the speedo cable, but I don't think there's any feedback between that and the fuel mix on the 2F (could be wrong there).
 
That's interesting COHoya, confuses me further but interesting. I know high NOx is caused by high combustion temps but the thermostat never entered my mind. Now you've got me thinking I should do that while I'm at it. I'm dropping $25 a crack at the testing if I don't get in within 10 days after a fail. I wouldn't be happy if I need a t-stat instead of O2 sensors.

Zhenya, my entire exhaust system is a year old including the cat. I had it tested and it's still good as new. I'm not saying you'll have the same issues but a good running motor can still fail emissions. My truck has never run as well as it does right now.
 
To get your NOX down, check your EGR first. Then check for vacuum leaks. Check your ignition timing, too much will elevate your NOX. A Sea Foam treatment wouldn't hurt, it can remove carbon deposits which could, theoretically, create hot spots in the combustion chamber and also elevate NOX.
 
Replaced the EGR - the diaphragm was bad, found 1 vacuum leak - replaced the hose, just replaced the O2 sensors, did a full tune-up and set timing. I haven't tried Sea Foam but honestly doubt this truck has carbon build-up. I'm hoping the O2 sensors are the key.
 
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