i failed my smog test today. i passed everything except nox at 25 mph, but i passed at 15 mph.

15 mph ~~~~~~~~~~~~~ 25 mph
max is 1010 ~~~~~~~~~~ max is 870
ave is 260 ~~~~~~~~~~~ ave is 217
meas is 710 ~~~~~~~~~~ meas is 1160

so do i need a new EGR? or is there something i can do to make it barley pass? i barley rebuilt the engine with new head only about 700miles on it. it has fresh oil, new dist. cap, rotor, wires, PCV valve, timming is correct.

oh and the valves do need adjusting, just been too lazy to adjust them . would adjusting them help any?

 

How old is the 02 sensor?

 

i have no idea...just bought the truck

 

How many miles are on it?

 

204,000

 

Personally, I would do two things:

1. Go to your local Autozone and see if they can pull any codes (even if you don't have a CEL, some may be stored)

2. Get a new 02 sensor. Just the primary since you might have two (not sure about that though).

 

Valves won't help this.

If your hydrocarbons are acceptable, you have a non-functional EGR. This could just be due to a clogged or torn vacuum hose. If you trace the EGR lines to the intake, you will see some rubber vacuum lines. Make sure they are Ok and spray some intake cleaner into their ports to ensure they aren't plugged. Make sure the EGR valve holds vacuum. And, I can't help you on this next one because I don't know much about it, there is this valve of sorts inline with the EGR vacuum, it's on the front of the motor passenger side. It could be malfunctioning. I don't know how to test it. Hopefully someone else will chime in.

If you have high hydrocarbons and high NOX, you have a bad catalytic converter and maybe a bad EGR.

I would not look at the O2 sensor yet as bad O2 sensors cause rich running and rich mixtures, all things equal, lead to lower NOX but higher hydrocarbons and CO's.

Frank

 

My brothers truck is in the same situation. I am going to run a can of sea foam through the gas tank on a fairly empty tank. Run the truck until the gas tank is bone dry. Then add 99% isopropanol (alcohol) to the gas tank targeting a 20% alcohol 80% gas mixture. Then head to the smog station. I am going to do this on monday add I will post the results. Do a search on this and you find my previous trends about this subject. Use this method at you own risk and no garuntee it will work.

 

At 202K, its a good time to take care of the 02 sensor. Regardless.

 

thanx for the responses guys

im gunna post the rest of the results to get a better understanding

NO (PPM)
15 mph ~~~~~~~ 25 mph

max: 1010 ~~~~~~ max: 870
ave: 260 ~~~~~~~ ave: 217
meas: 710 ~~~~~~ meas: 1160

HC (PPM)
15mph ~~~~~~ 25mph

max: 122 ~~~~~ max: 102
ave: 34 ~~~~~ ave: 23
meas: 78 ~~~~~ meas: 22

CO (%)
15mph ~~~~~~ 25mph

max: 0.72 ~~~~~ max: 0.91
ave: 0.11 ~~~~~ ave: 0.10
meas: 0.04 ~~~~ meas: 0.00

 

Good, your catalytic converter and O2 sensor are fine. You just need to zero in on the EGR. You can replace the O2 sensor but don't expect it to make a bit of difference.. except in lightening your wallet. (They aint cheap)

Honestly, replacing something like the O2 sensor, which is not only clearly operating flawlessly, but is also expensive makes no sense especially since when it does go it will turn on the check engine light and/or make your gas mileage decrease. It will not disable the truck or catastrophically. You might as well get your use out of it.


Frank

 

Ca sucks!!! They don't even sell diesels in cars. Glad I live in Carollton, Ga. No test here at all. all you need is a tag and ins.

 

Actually we have VW TDI's.

Frank

 

I didn't know that. Those are great little car with that tdi motor.

 

Frank –

I do not agree with you completely about the 02 sensor.

If the air/fuel ratio deviates from its preprogrammed swings, catalyst efficiency falls dramatically, primarily the reduction of Nox emissions. Therefore, a test of the O2 sensor should be performed at the minimum. It is possible to test the 02 sensor by running the engine at 2500 RPM for at least 2 minutes to ensure the sensor is at normal temp. Then, the 02S signal frequency can be tested. It should be at least 8 cycles in 10 seconds (.8hz). The signal should also exceed 550mv on the rich swing and fall below 400 mv on the lean.

Contrary to popular belief, 02 sensors can become degraded without tripping a CEL, which will effect signal frequency and/or amplitude – and ultimately effecting NOx emissions. It is possible.

 

If his O2 sensor was bad, the first thing you'll see is hydrocarboms and CO's go up. His are very low. Even if it was marginal, and could function better, it won't be enough to measure so why bother with it?

As for cat functionality, it might not be able to catalize all those hydrocarbons when an O2 sensor goes bad, but the increased richness decreases combustion chamber temps while raising the temp of the cat. The lower combustion temps produce LESS NOX. The higher cat temp simple provides more fuel for the fire so to speak as far as the heat of reaction is concerned. The result in the short run is it only more easily breaks up the nitrous oxide molecules. Long term it will damage the cat.

But, none of his numbers suggest a bad O2 and it isn't exactly like changing an air filter or spark plug. They are expensive. I mean if he wants to do it for the heck of it's his truck but at least he should fo forward not expecting any improvement.

Frank

 

We can agree to disagree I guess.

 

Elripster , is right .High Nox is usually caused by high combustion chamber temps.Egr is probably the number one cause,but with that kind of mileage he could have a plugged passage way also(although he said he did have a vavle(?)job just done).Or maybe the cam timing is slightly off.Or ?