NOx Questions - Failed Emissions

[Kevin718]

I have failed my emissions test for the first time due to high NOx. The inspector suggested that it could be the EGR valve or the catalytic converter.

Test Results: 25mph result/15 mph result
HC(ppm) - 53/62 (131/134)
CO(%) - 0.11/0.10 (1.45/1.13)
CO2(%) - 13.3/13.4
O2% - 3.3/3.0
NOx(ppm) - 1029/1609 (818/893)
Dilution - 13.41/13.5 (>6/>6)

The numbers in parentheses are the standard numbers (limits).

Theory Questions:
Can someone explain the theory of NOx formation in a vehicle?
Can someone explain why a catalytic converter could affect the NOx numbers?

Here is what I think I know:
1. NOx is formed when combustion temperatures are high.
2. The EGR valve works to control combustion temp by putting exhaust gas into the intake manifold.

EGR Testing:
1. Put vacuum on valve while engine was idling, and the idle became worse and the engine stalled. This is correct per the manual.
2. Transducer - Plugged outlet. Applied light pressure to exhaust reference port. Transducer held vacuum. When pressure was removed from the exhaust reference port, the vacuum was not held. This is correct per the manual.
3. Vacuum measurements at EGR valve while driving:
Idle = 0 in/Hg
Light Acceleration = 5 in/Hg (sometimes vacuum would fluctuate very fast between 3 to 5 in/Hg)
Med Acceleration = 3 in/Hg
This seemed low given that ported vacuum (the supply) is higher than this.
4. Ported vacuum measurements between EGR CTO and TVS on air cleaner:
Idle = 0 in/Hg
Light Acceleration (40 mph) = 10-11 in/Hg
Light Acceleration (55 mph) = 12 in/Hg
Med Acceleration = 5-10 in/Hg
Med - Heavy Acceleration = <5 in/Hg


Relevant Work Done Since Last Emission Test:
1. Took carb apart for inspection, float adjustment. (11/2005)
2. Installed electric fuel pump and pressure regulator set at 3 psig (9/2006)
3. Replace exhuast Y-pipe, still have leaks. (10/2006)

Other non-relevant work:
- Rebuilt transmission and transfer case.
- Other normal maintenance.

Thanks for your help.

[jode]

Don't have a lot of answers to your questions, but the other day, I failed in my 22RE toyota. I made some adjustments and then retested and passed with flying colors. Here's how:

Changed spark plugs (they were fouled)
Changed engine oil
Cleaned cap/rotor
Adjusted valves

Not sure which of those was the big culprit, or if it was a combo of all of them, but I have a feeling it was the valve adjustment. Now, you can't adjust the valves on an FSJ like you can on a Toyota, but if your valves were burnt or damaged, they might give you some problems.

Of course, none or all of the above may be relevant to your case, but I had some time, and figured I would share. My 76 wag w/ 401 NEVER had even a prob with emissions even when it was poorly tuned. I think they just had low standards for it?

[babywag]

Those numbers look very close to mine when I failed.

I had a bad EGR valve that wasn't working @ all.

Also turned out that the vac temp switch on the air cleaner wasn't working.
Couldn't locate one, even though it was a Ford part w/ ford pn#.
It was not opening, and the new EGR valve wasn't getting any vacuum.

I just bypassed the vacuum temp switch, and plugged it directly into ported vacuum.
No other changes/adjustments and passed w/ flying colors.

[Brisdon]

I failed because of a bad CTO valve, a vacuum leak at the non-linear valve and a failing check valve on the air injection line to the catalitic converter. After those things were fixed, I passed with flying colors. The numbers turned around completely with just these changes.

[JeepinPete]

It seems to me that your carb is adjusted pretty good do to the good CO and CO2 numbers. And since your EGR tests all show good, that shouldn't be the problem. I am wondering if the timing isn't set a little to far advanced? Or maybe the vacuum dashpot on the distributor is adding too much timing. If your retests are free, I would try pulling the vacuum line off of the distributor and give it a try...

[letank]

i passed w a disconnected non linear valve (it is off the circuit, just looks installed w all the spaghettis)

timing

the CTO is a good lead... as you tested the egr to pass, time to test the CTO, those tend to fail and the wells (autozone) more than the other brands, go for a borg warner

[Rogue]

Originally Posted by letank

the CTO is a good lead... as you tested the egr to pass, time to test the CTO, those tend to fail and the wells (autozone) more than the other brands, go for a borg warner

yes, you've proved the EGR will work and the passages are clear when you stalled out the engine. the problem is with the EGR controls. if they don't actually check your equipment, hooking the EGR straight to ported vacuum like suggested will get you past the test anyhow but the CTOs and temperature switches are for best all around perfomance at all engine temperatures so I wouldn't recommend it for a permanant fix

[Kevin718]

The CTO works. Today I bypassed the TVS and connected the transducer directly to ported vac. Here are some results:

Vacuum measured at EGR valve:
Idle = 0 in/Hg
Medium - Heavy Acceleration / Slow Speed = 5-6 in/Hg
Light Acceleration / Fast Speed (30-50 mph) = fluctuates rapidly from 0 in/Hg to 5 in/Hg

Based on this, I think that the EGR passage is restricted. The transducer passes vacuum when the exhaust pressure is 1-2 psig, and it vents the vacuum when the exhaust pressure is less than that. So I think the following happens:
1. Exhaust pressure exists.
2. Transducer passes vacuum to EGR valve.
3. EGR valve opens and exhaust gas flows.
4. Due to restriction, the exhaust pressure drops.
5. Transducer vents vacuum due to pressure drop.
6. EGR valve closes and exhaust gas flow stops.
7. Exhaust pressure builds back up.
8. This process repeats itself.

And this happens very fast, so the vacuum gauge needle swings back and forth.

So I would like to clean this exhuast passage, but I have never had the intake manifold off, and therefore have not seen the passage and where it comes from.

Please describe these passages, or post pictures if you have them.

[Kevin718]

I "cleaned" the exhaust passages in the intake manifold last night and verified that a reasonable amount of gas could flow through the passages to the EGR valve.

Put it back together and tested it, same result.

So then I bypassed the transducer this evening and routed the vacuum line from the TVS directly to the EGR valve. This did not work well at all. As soon as the CTO opened up, there was a significant engine stumble everytime I hit the gas.

Has anyone else monitored the vacuum at the EGR valve while driving with a setup like this 91 GW?

[andy d]

I had all kinda problems with my 88 passing NOx . I took it to a mechanic who bench tested the EGR with some sorta test rig. I dont know the particulars, but IIRC, the test involved vacuum to test one action and air pressure to test another. Anyway, the EGR was bad, Finding the exact replacement was impossible. I ended up with a universal eplacement that used different sized orifices to work as the original was supposed to work. Once it was set up the 88 has passed 2 MA emmissions with great numbers.

[Kevin718]

After looking around on the web, I found that the problem may be due to an exhaust leak since this EGR valve has a backpressure transducer. So I found and fixed the most significant leak. The vacuum to the EGR valve was much more stable. It basically operated between 0-5 in Hg without all of the vacuum fluctuation that I was seeing before.

I was also concerned about carbon build up causing higher combustion temps, so I put some water down the carb while it was idling, trying to use the "steam cleaning" method. But the GW pinged before and after this was done.

So, I thought that perhaps at least the EGR problem was fixed. I had it retested, and here were the numbers:

Test Results: 25mph result/15 mph result
HC(ppm) - 44/41 (131/134)
CO(%) - 0.01/0.02 (1.45/1.13)
CO2(%) - 12.3/12.7
O2% - 3.3/2.8
NOx(ppm) - 1168/1639 (818/893)
Dilution - 12.31/12.72 (>6/>6)

Failed again. NOx actually got worse, but only by a little. So it would seem that my EGR valve has nothing to do with this. Everything else looks good.

I guess my next steps are to replace the cat and try to retard the timing some. With respect to retarding the timing, won't this cause an increase in unburned hydrocarbons?

[Hubjeep]

I had very high NOx, replaced the cat and it passed; no prob.

[Kevin718]

Good news, the Jeep passed emissions. Here are the latest test results:


Test Results: 25mph result/15 mph result
HC(ppm) - 20/34 (131/134)
CO(%) - 0.01/0.02 (1.45/1.13)
CO2(%) - 13.5/13.7
O2% - 2.4/2.1
NOx(ppm) - 199/89 (818/893)
Dilution - 13.51/13.72 (>6/>6)

I made the following changes:
1. Replace catalytic converter.
2. Retarded base timing from 11.5 degrees to 5 degrees.

I only wish that catalytic converters would last more than just a few years.

[shimniok]

EGR helps to lower temps. Too much advance can cause high NOx also. I want to say the AIR system can help but I don't see how further oxidizing oxides of nitrogen will help in any way but then I took one semester of chemistry in college almost 20 years ago. Great, now I feel old. Hope you're happy.

Michael