Need NOx help

[Six Banger]

Failed overall test due to too high of NOx at 25mph , passed at 15mph. These are the numbers:

25mph/ allowed 15mph/ allowed

HC 117 152 110 157
CO .65 .97 .50 .88
NOx 1678 1082 546 1184


I tested the EGR valve by disconnecting the selenoid vacuum line at idle, then applied vacuum to the EGR and the car died. Doesnt this mean the valve is operational? and is this the cause of my high NOx. Thanks for any help with this.........

 

[Six Banger]

Also, meant to add, the tester felt like if the car had been driven for about 20 minutes, instead of 10 like I did, that it would have passed. Is this likely?

 

[gofstbuick]

Originally posted by Six Banger
Also, meant to add, the tester felt like if the car had been driven for about 20 minutes, instead of 10 like I did, that it would have passed. Is this likely?

Probably not. But you may have a cat going bad. Hook a vacuum guage to the vacuum line at the EGR, and take your car for a drive. You should see vacuum readings on the guage while cruising down the road. If you see vacuum reading under the above circumstances, try turning your attention to the cat. You could do a temp test o the cat. Because it's a NOx problem, you may only be limited to a intrusive test of the cat. You're almost at the mercy of the repair station, unless you have access to the smog dyno. I'll try to look up some test.

 

[ijames]

Your test showed that the egr valve itself is okay, but doesn't prove that the control valve is working or not. That's what teeing in a vacuum gauge between control valve and egr valve and going for a light throttle steady speed cruist at say 30-50 mph will show. If you see vaccum then (or if you have direct scan or turbolink or another scan tool, whenever they show a non-zero egr duty cycle) then the egr is functioning. What chip are you running? There are a couple that disable the egr, most notably the thrashers (but since they are open loop idle most people don't try to pass emissions tests with them ) and the max efforts. Oh, last thought, do you have a plenum spacer or one of the power plates without the egr hole drilled? You may be inadvertantly blocking it off.

 

[Six Banger]

I have not been able to tee in a vacuum line yet to check the selenoid function at cruise, but I did notice that the vacuum line going to the EGR valve from the selenoid was cracked, scammer, and possibly leaky (original line). Hopefully this is the problem. I will do the cruise test as well though. Also, was wondering if EGR passages could be clogged with carbon causing a restriction? As far as modifications, the car is all stock (80k miles), chip included.

 

[gofstbuick]

Originally posted by Six Banger
I tested the EGR valve by disconnecting the selenoid vacuum line at idle, then applied vacuum to the EGR and the car died. Doesnt this mean the valve is operational? and is this the cause of my high NOx. Thanks for any help with this.........

That means the passages are clear. You now need to be concerned about the vacuum signal.

 

[Six Banger]

I was able to tee in a vacuum guage at the EGR valve and while driving I only saw 5 inches of vacuum (max). My guage is kind of old and sticky but it should be close because it reads engine vacuum at 20-22 inches. Should I have engine vacuum at the EGR valve at cruising speed? If not, how much should I have at the valve? Thanks again......

 

[Six Banger]

I was able to tee in a vacuum guage at the EGR valve and while driving I only saw 5 inches of vacuum (max). My guage is kind of old and sticky but it should be close because it reads engine vacuum at 20-22 inches. Should I have engine vacuum at the EGR valve at cruising speed? If not, how much should I have at the valve? Thanks again......

 

[gofstbuick]

I don't remember what amount of vacuum it takes to fully lift the EGR, but you could apply 5 inches if vacuum (using a vacuum pump) and see if it lifts the valve fully. It does seem a little low, so it is quite possible that the solenoid may be defective.

 

[ijames]

An old Chilton's or Haynes manual I have says the valve needs 10" of vacuum to open. I checked mine once with a hand MityVac pump and it needed right at 10" to open. There is a little paper filter under that round cover on the control valve also. Might try removing that and seeing if your vacuum gauge reading goes up while cruising - maybe that's plugged? Otherwise, sounds to me like it's time for a new control valve.

 

[Six Banger]

I was able to connect a Mighty Vac directly to the EGR valve, and really anything over 5 inches of vacuum does not raise it anymore. I could tell by feeling the diaphragm from underneath. Also I teed in the guage at the EGR valve, had someone put the car in drive with the brake on and applied light throttle. I could feel the diaphragm raise and I watched the guage go to around 5 inches. So, I guess that I can assume the EGR system is functioning properly and maybe should turn my attentions to the cat? If so, what features should I look for in a new one?

 

[Six Banger]

Did a search, and I guess that I need a three-way cat to help control the NOx. I also read about a quick fix homebrew fuel. 4 parts high test gas, 1 part methanol, and 1 part G2P. Any thoughts on going the cheap/quick route? Thanks.......

 

[gofstbuick]

IMHO, I'm really not a fan of the use of chemicals to to pass smog. That's not to say that it won't work. I just have little faith. What kind of cat is on the can now? What are the O2 readings from your emissions test?

 

[Six Banger]

The cat on the car, as far as I can tell, looks to be the original one that came from the factory. I have no records of it ever being changed. The other test results that I have are:

25mph / 15mph
co+co2 % 14.6/ 14.7
min% 6.0/6.0


Do these numbers help?

 

[gofstbuick]

The CO2 looks good, but there wasn't a oxygen content reading? Something like 0%-3.0%.

 

[Six Banger]

No, there is nothing about that on the printout. Do you think that my cat is just old?

 

[gofstbuick]

I would think your cat may be worn out. How old is your O2 sensor? What kind, GM I hope. If your O2 sensor is fairly new, I would suspect that your cat is wearing. My car barely pass a two speed idle test when it had 78000 miles on it. After I verified the sensors were functioning properly, I installed a new cat and the readings dropped to zeros across the board. Now with dyno testing, it bacame a little more difficult, but the cat was still fairly new and the emissions passed real clean. If you have eliminated all possibilities of NOx failures, then the cat would be the next logical solution. I usually will not consider a cat replacement until all other options have been exhausted. A competent technician can perform a cat test for you. If you have access to a 4 gas analyzer I could explain. You could try to temp test the cat. Requires a portable pyrometer. Get the engine into closed loop. then run it down the freeway for a least 5 minutes and look for a safe place to pull off (that will allow you to lay along the side of the car), after stopping, immediately test the inlet temp and outlet temp of the cat. The outlet should be at least 100* hotter than the inlet. The cat accelerates a chemicle reaction and therefore creates heat. So if the inlet temp is 250*, then the outlet should be 350* or more.

 

[TurboJim]

I dont think a cat would cause a NOx failure in one of these cars. My car passes NOx at like 690ppm with no cat. I'd question your EGR operation first.

When you apply 5in hg, how far does the pintle move? Theres ~3/8" of movement in an EGR valve. If yours onmly moves 1/16 or so, its possible you have a leakjing diaphram hat movement uncovers.

What I would do is apply engine vacuum to the valve to see how far it moves. If it barely budges, then theres a problem with the valve. As Joe says, hook up a vacuum gauge to the solenoid. You dont NEED to T it if you cant. We just want to verify the solenoid is passing engine vacuum to the valve. Hook up a gauge and situate it so you can see it from the drivers seat. Brake stall the car slightly. To like 2000-2500rpm with a light load. Dont mash the throttle. You should see at LEAST 10" hg being applied. If so, that part of the circuit is working and you need t diagnose why the valve isnt moving sufficiently

Just fwiw

 

[Six Banger]

Just thought that I would post a follow up. The joke was on me. I removed the stock catalytic and found that it had been gutted. Funny thing is that it was close to passing like that. With the new cat (3-way) the readings are:

25mph-tested/allowed 15mph-tested/allowed

HC- 47/152 35/157
CO%- .01/.97 .01/.88
NOX- 69/1082 15/1184