Car Smog Fail Help: High NO

[KC@ BRG Racing]

Generally around 2800*

However, IF I remember correctly, Spark Knock (aka PRE-Ignition) causes NOx numbers to go DOWN. Not up.

Chris not many know that. It's been a few years but I was taught 2500 your putting nox of the pipe like mad

Who cares. Are you going to put a thermometer in the cylinder to test it?

well grease monkey maybe you should care. The article below will go into much better detail than I can . It will will fill in some of the stuff that you don't know and help explain why knowing what the temperature noxs starts to develop that is important in this issue.

interesting read

http://www.catalyticconverter.org/news/news_page.cfm?Key=catalytic_converter-&News=216

apparently it's 2300*

but... never knew all this could be determined with a smog check

excellent article. Thank you for taking the time to look it up. And then post on it. The whole thing with the high readings of NOX on Chester's car is. It's very much temperature oriented you can use the nox's reading as a very accurate way of defining what combustion chamber temperatures. the higher your combustion chamber temperatures are the more Nox you will develop. It's a great way for setting ignition timing on the Dyno. It's also a great way to fail, a California smog inspection. It doesn't take much of a bump one compression to override the effectiveness of your EGR.

 

[RS250 Chester]

Here's where I'm at so far, no I'm not ruling out compression, but after diagnosing and reading numerous articles, I've found a few problems that are fixed or about to be fixed.

I took the smog test for granted after several years in being in San Luis Obispo county, no dyno or NoX readings there. Obviously I didn't come prepared, the car was pinging and I should have done a thorough shakedown before going.

After it failed, I found a leaky exhaust manifold, it was leaking quite a bit and the car was driving much better after sealing it. The next day, my cooling fan came off the clutch fan. So I'm assuming the fan was working its way loose and not fully effective during the test. In addition, when I replaced the clutch fan, I found the the water pump was on its last legs, as the bearings were making noise. The operating temps were always normal, but it seems the cooling system, with a bad fan and failing water pump probably weren't running at 100%. This probably didn't help matters on the test. Then, I found that the BPT valve on the EGR system is leaking. Since the BPT valve won't hold a vacuum, it won't open the EGR valve, even if the EGR valve is fully functional, its dependent on the BPT.

I'm pretty sure all these factors contributed to the failure. I've got one more test to run and I'll see if the EGR solenoids are working. Hopefully they are and I just need the BPT.

 

[Diezel]

I'm pretty sure all these factors contributed to the failure. I've got one more test to run and I'll see if the EGR solenoids are working. Hopefully they are and I just need the BPT.

Good luck and keep us informed. You are most assuredly on the right path.

 

[Grease_Monkey]

well grease monkey maybe you should care. The article below will go into much better detail than I can . It will will fill in some of the stuff that you don't know and help explain why knowing what the temperature noxs starts to develop that is important in this issue.

So what you are saying is you know when but now why. Understanding the "why" is way more important than know "when"

Most people know when their check engine light comes on, but most of them don't know why.

Lets put a thermostat in the cylinder, that will be the end all to this question, EGR or Carbon build up. *raise hand* how do you put a thermostat in the cylinder? Good question, Billy. YOU DON'T!!!!

Take the 5 mins to check the EGR and get a conclusive answer. Then if you want waste you time doing a compression test and assume a conclusion.

 

[RS250 Chester]

So I finally got a chance to do a formal EGR test by revving the engine on idle and checking to see if the diaphragm opens. As expected, since the BPT was leaking, the EGR did not open as the revs increased.

So I went to the Nissan dealer and got a BPT valve. Did a test on the new BPT and sure enough it hold a vacuum. Just finished installing it and took a quick drive. Throttle response seems much better and the engine actually seems quieter. But with that said, since its late, I haven't had a chance to check to see if the EGR system is now fully functioning by again checking to see if it opens during increased revs. I'll do that tomorrow, hopefully all will be ok and I don't have to test/check the solenoid valves.

 

[Motech]

Last edited by Grease_Monkey; 09-16-2011 at 08:47 PM.. Reason: Drunk post.

Good thing lest you too get banned for making sense.

 

[Motech]

So I finally got a chance to do a formal EGR test by revving the engine on idle and checking to see if the diaphragm opens. As expected, since the BPT was leaking, the EGR did not open as the revs increased.

So I went to the Nissan dealer and got a BPT valve. Did a test on the new BPT and sure enough it hold a vacuum. Just finished installing it and took a quick drive. Throttle response seems much better and the engine actually seems quieter. But with that said, since its late, I haven't had a chance to check to see if the EGR system is now fully functioning by again checking to see if it opens during increased revs. I'll do that tomorrow, hopefully all will be ok and I don't have to test/check the solenoid valves.

PM sent.

 

[RS250 Chester]

PM sent.

Replied, thanks.

Update:

Removed the solenoid and performed test per FSM. Everything working per FSM. Changed several hoses due to age (no cracks): 2 hoses from BPT to EGR, Charcoal canister hoses and EGR solenoid hoses.

Still not sure if it is opening while the revs were increased to 2300 rpm, not sure if I still have a leak somewhere. I have a couple more hoses to change out, hopefully that will be it.

I also changed the plugs, pcv and air filter. The car is driving much better, no pinging, steady idle and responsive throttle. But still not sure if the EGR is functioning.

 

[Diezel]

Replied, thanks.

Update:

Removed the solenoid and performed test per FSM. Everything working per FSM. Changed several hoses due to age (no cracks): 2 hoses from BPT to EGR, Charcoal canister hoses and EGR solenoid hoses.

Still not sure if it is opening while the revs were increased to 2300 rpm, not sure if I still have a leak somewhere. I have a couple more hoses to change out, hopefully that will be it.

I also changed the plugs, pcv and air filter. The car is driving much better, no pinging, steady idle and responsive throttle. But still not sure if the EGR is functioning.

If you are raising the idle slowly, you may not notice the valve actually move. A good solid throttle snap up to 3000 rpm, should make a noticeable change in the EGR's position.

 

[Dubbington]

we have run into this very problem with hi mileage cars. 95000 and above. The customer don't drive the care hard. carbon builds up over time. kicks the comp up 2 points. blows great numbers cats are clean. But through s nox out the pipe like crazy. Seafoam or water alcohol mix thought a small vacuum line drive 3 to 500 miles
chips the carbon out comp drops and your good, retest and our good to go.
Now it could be the EGR but tying some water alcohol mix i think would be easier to do and if it works wow you just saved a boat load of effort. the only reason for the comp test is to see if the comp is higher then stock. You know if your stock comp numbers are 150 and your at 185 well then you might have this problem. the only way to tell is a compression test.

Any chance the Seafoam would hurt a BRAND NEW CAT?

My '87 Dodge Ram 50 wont pass. I replaced the cat 4 years ago but its the old style and no longer CARB certified with the new CA laws. I just barely failed CO my last run.

To the OP...

Find the EGR and clean it out. Mine was clogged and caked black. I replaced the hose that went from the EGR to the computer after a quick shot of carb cleaner dumped black crap everywhere. I'm hoping wit my cat my truck passes now.

 

[Dubbington]

Replied, thanks.

Update:

Removed the solenoid and performed test per FSM. Everything working per FSM. Changed several hoses due to age (no cracks): 2 hoses from BPT to EGR, Charcoal canister hoses and EGR solenoid hoses.

Still not sure if it is opening while the revs were increased to 2300 rpm, not sure if I still have a leak somewhere. I have a couple more hoses to change out, hopefully that will be it.

I also changed the plugs, pcv and air filter. The car is driving much better, no pinging, steady idle and responsive throttle. But still not sure if the EGR is functioning.

When idling if you hook up a vacuum to the egr and give it 10lbs or inches of suction the car should start to die and shake.

 

[Grease_Monkey]

Find the EGR and clean it out. Mine was clogged and caked black.

Already confirmed the EGR passage is not clogged by manually pushing on the EGR diaphragm and having the car want to die. BPT stand for Back pressure transducer, if there is not enough back pressure in the exhaust (like at idle) the EGR wont open on vacuum to the diaphragm alone.

 

[joespeedfast]

Already confirmed the EGR passage is not clogged by manually pushing on the EGR diaphragm and having the car want to die. BPT stand for Back pressure transducer, if there is not enough back pressure in the exhaust (like at idle) the EGR wont open on vacuum to the diaphragm alone.

If the car has a free-flowing exhaust, it might never happen.
We used to put em on jack-stands, power-brake them(lightly) in 2nd or 3rd gear @ 20mph or so and even stuff a sock in it sometimes to get them to work...

 

[Diezel]

Any chance the Seafoam would hurt a BRAND NEW CAT?

My '87 Dodge Ram 50 wont pass. I replaced the cat 4 years ago but its the old style and no longer CARB certified with the new CA laws. I just barely failed CO my last run.

To the OP...

Find the EGR and clean it out. Mine was clogged and caked black. I replaced the hose that went from the EGR to the computer after a quick shot of carb cleaner dumped black crap everywhere. I'm hoping wit my cat my truck passes now.

Knowing those trucks a bit... I would say most likely your issue is NOT a CAT. It's most likely the carb is leaking internally.

 

[Dubbington]

Knowing those trucks a bit... I would say most likely your issue is NOT a CAT. It's most likely the carb is leaking internally.

New rebuilt Mikuni replaced 4 years ago. Wish a diagram was available so I knew where the mixture screw was I could lean it out, pass and be done!

 

[Diezel]

New rebuilt Mikuni replaced 4 years ago. Wish a diagram was available so I knew where the mixture screw was I could lean it out, pass and be done!

Well the carbs for the D50 were pretty notorious for CO issues. And leaning it out might help, but it could screw you on NOx numbers too.

 

[RS250 Chester]

Yeah...IT PASSED

A week ago, I took it in to have a pre-test done and it failed, even after all the repairs. The repairs helped reduce NOX to 700 on the 15mph test, but it stayed the same for the 25mph test. But as mentioned, the car was running so much better. I finally took out the EGR and cleaned it, but it actually was very clean and it wasn't clogged.

Finally took it to a shop and they said the CAT went out. Got that replaced an the car passed, NOX actually went down to 25, HC down to 9 and CO% down to .01. Its running clean.

The only issue that the tech mentioned was NOX climbed on the actual test for the 25mph test, it got up to 490. But his pretest after the CAT was installed measured 25. He measured it again a few hours later and it was down to the 20 range. He thinks it might be the MAF, any suggestions.

At least I can sell the car now with a smog or restore it and not worry about for another 2 years.

Again guys, thanks for all the help and suggestions.

 

[DannoXYZ]

If the EGR is operating properly, I would say look at the cat next. I have seen cats with one out of the 3-way catalytic action being dead.

A week ago, I took it in to have a pre-test done and it failed, even after all the repairs. The repairs helped reduce NOX to 700 on the 15mph test, but it stayed the same for the 25mph test. But as mentioned, the car was running so much better. I finally took out the EGR and cleaned it, but it actually was very clean and it wasn't clogged.

Finally took it to a shop and they said the CAT went out. Got that replaced an the car passed, NOX actually went down to 25, HC down to 9 and CO% down to .01. Its running clean.

The only issue that the tech mentioned was NOX climbed on the actual test for the 25mph test, it got up to 490. But his pretest after the CAT was installed measured 25. He measured it again a few hours later and it was down to the 20 range. He thinks it might be the MAF, any suggestions.

At least I can sell the car now with a smog or restore it and not worry about for another 2 years.

Again guys, thanks for all the help and suggestions.

The cat was probably not warmed up enough. Car probably sat around for a bit between the pre-test and actual test and cooled off.

MAF failing can result in low-output voltage and cause lean-mixtures, with high NOx. You can catch that by monitoring MAF output-voltage at 25mph test and correlate with emissions numbers. Do two tests to catch NOx at high and at low levels. If MAF voltage is same @ 25mph for both tests, it's OK. Something else was different, probably cat temp.