Hey guys, I'm new here so sorry if this is the wrong place to post. My truck failed emissions today because of a high NOx output. Everything I've read online suggests that it's the ERG valve, but my '94 doesn't seem to have one. I'm not entirely sure where else to look, short of dropping some cash to replace the catalytic converter. It's dark now so I haven't checked the vacuum tubes, or cleaned out the MAF sensor. I'm just hoping that somebody else had a similar experience they could share. Thanks in advance!
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'94 V6 4.0L Failed Emisions NOx Output. No EGR Valve
- Thread starter bwdedgar
- Start date
NOx is produced when cylinder temperatures are high, like when engine is under load or running a bit Lean.
Did you have high NOx at low speed or higher speed?
If its the original Cat converter then I would plan on replacing it.
EGR systems were used because adding a bit of exhaust gases to intake air causes a slower burning air/fuel mix, which lower cylinder temps.
That is why EGR system would popup if you were searching "high NOx"
But it can also be old cat converter.
A vacuum leak will cause Lean mix which causes higher cylinder temps so higher NOx
Higher cylinder temps doesn't mean overheating in this case, but if engine is running a bit warmer than "normal" because of cooling system issues then that could raise NOx emissions during a test, because cylinder temp is right at the edge of low and high NOx and adding load(dyno) during testing brings on the higher NOx.
Did you have high NOx at low speed or higher speed?
If its the original Cat converter then I would plan on replacing it.
EGR systems were used because adding a bit of exhaust gases to intake air causes a slower burning air/fuel mix, which lower cylinder temps.
That is why EGR system would popup if you were searching "high NOx"
But it can also be old cat converter.
A vacuum leak will cause Lean mix which causes higher cylinder temps so higher NOx
Higher cylinder temps doesn't mean overheating in this case, but if engine is running a bit warmer than "normal" because of cooling system issues then that could raise NOx emissions during a test, because cylinder temp is right at the edge of low and high NOx and adding load(dyno) during testing brings on the higher NOx.
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Sorry for not responding earlier, I had finals for school. I was failing the high speed and barely passed the low speed. I expect to have to change the Cat converter soon, I was just hoping there was something else(less expensive) I could try first. It has been a while since I've changed spark plugs and plan on checking that tomorrow to see if they look bad. I have checked the vacuum tubes that I've been able to trace (like I said I'm new to this whole thing) and they seemed fine. Thanks for your input and breaking it down for me a little better!
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I am pretty sure if the ignition timing is advanced too much it can also increase NOx. If it is retarded too much the HC can go up. It is a fine balance. That is where a good catalytic converter helps a lot.
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And, I have heard (on here) that there are different cat converters for those trucks with EGR and those without. So beware!!
The guy said he was failing NOx, replaced the converter and it tested worse. He/they/someone figured out the wrong converter was installed.
The guy said he was failing NOx, replaced the converter and it tested worse. He/they/someone figured out the wrong converter was installed.
Ok, so I did an entire tune up and tried all the less expensive things first. I retested today and I still failed. The emissions technician said everything he has seen similar to my results have been the EGR failure. Before I look into replacing the Cat, is there anything that "replaced" the EGR valve that I could try looking into first?
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Don't want to tell you what I think of a technician that tell you something useless like that. On those without EGR valves, NOx was controlled by the computer and the cat.
No nothing "replaced" EGR system.
Some engines needed it some years and others didn't, also local emissions standards in some places required EGR system period, like California.
I assume your Ranger is from a local source, not an import, so you need a new Cat.
Emissions technician is correct, high NOx is usually an EGR system issue, but NOT if you don't have an EGR system, lol.
Some engines needed it some years and others didn't, also local emissions standards in some places required EGR system period, like California.
I assume your Ranger is from a local source, not an import, so you need a new Cat.
Emissions technician is correct, high NOx is usually an EGR system issue, but NOT if you don't have an EGR system, lol.
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