Topic: Failed Smog! High Nox

[Kurlee Daddee]

Went and got my truck smogged today and it failed NOx. Just barely though (1222 max / 1383 mine) @ 25mph. I have a free re-test after I fix it.

I have maintained my truck immaculately since I bought it 4 years ago. The spark plugs, wires, cap and rotor are fairly new. Air filter is brand new as of today. Ran 87 octane during the test. Everything else on the test passed with flying colors.

I read this thread that BigMike started. http://board.marlincrawler.com/index.php?topic=1119.0

So what do you guys think. Since it only failed by 161 ppm, do you think a 1/4 tank of 91 and a bottle of alcohol wil do the trick? How about retarding the timing 1 deg? Pump up my tires more? I still have 2 months until this smog test is overdue. I just don't want it looming over my head for too long. I need suggestions.

[emsvitil]

You're allowed +-3 degrees on the timing.

Retarding may help a little.   

Have you changed the exhaust behind the cat converter?    If so, more backpressure for the test should help.


I added a sheet metal gasket behind the converter (punched holes equivalent to a 1" diameter hole) to add back pressure for the smog test last time.........

[Joey88RUNR]

Egr valve controls Nox.... you should check your egr valve,  make sure it holds a vacuum, and take it off and clean it out....more than likely you have carbon build up somewhere in the egr tube, Mine was pretty bad with 400k mi

[Kurlee Daddee [OP]]

Have you changed the exhaust behind the cat converter?    If so, more backpressure for the test should help.


I added a sheet metal gasket behind the converter (punched holes equivalent to a 1" diameter hole) to add back pressure for the smog test last time.........

Yes that's basically the only difference to what I had 2 years ago when I passed. I added a new cat back exhaust with larger diameter tubing. I really like that idea with making a sheet metal gasket with a smaller hole. That would probably do the trick.

[emsvitil]

And set the timing at 2.5 instead of 5.

[Kurlee Daddee [OP]]

I was looking under my hood and noticed that the silicon vacuum lines I installed that are going to the EGR valve are pretty loose and may be leaking. I picked up some new rubber vacuum hose to replace it with. I also added a bottle of that RXP Gas Kicker stuff. Drove it the long way home and onto the freeway. My truck feels brand new again. No hesitation from a stop and idles pretty smooth again. Only put 10 miles on it at the most.

So I think I will run the rest of this gas very low. Fill up with 91 octane. Retard the timing 2 deg. Put a liter of Rubbing Alcohol in. Change the vacuum lines. Make that exhaust gasket with a smaller hole. Fill up the tires a little more and go and have the smog check again. Crossing my fingers it passes.

[emsvitil]

And make sure the converter is good and hot.........

[44magnum]

well more then likely it is your EGR.

[CrazyYota]

well more then likely it is your EGR.

X2 same problem with my dads 82 and my 83.

[emsvitil]

The EGR valve needs some back pressure to function.......   

Thus the temporary restrictive gasket..........   

[Mario]

The time info is solid but all you need for some back pressure is to install an extra muffler gasket on the outlet side of your cat. This will give you back pressure and keep the exhaust in your cat a little longer. You can leave the gasket in or remove it after smog.

[Kurlee Daddee [OP]]

I went back and PASSED smog today easily. I was really happy. One less thing off my back. Here's what I did to help try and pass smog:

Replace all EGR associated vacuum lines with new lines (don't ever buy those silicone hoses. They enlarge with heat and may be the cause of the EGR not fully functioning and me failing high nox)

Ran RXP Gas Kicker and a whole tank of gas. Once the tank was empty, I filled the tank half full with 91 octane, and a half big bottle of Isoprpyl Alcohol.

Set the timing back 1-2 degrees (timing light I have isn't digital so I guessed).

Pumped up my rear tires to 35psi.

Ran it hard on the way to the station and didn't turn off the truck until it was on the rollers.

Not sure which of these helped me pass. Could be all in a combination. But the guy said to me "Man you truck passed easy this time. What did your mechanic do to it?" I was laughing in the back of my head and told him new vacuum lines.

Thanks to everyone in this thread that gave me suggestions. I really appreciate your help. And I am now good for 2 years. W00t!!!

[Kurlee Daddee [OP]]

UPDATE:

Well I pulled my motor this weekend for a Davez Offroad replacement motor. Anyways, I took the EGR off and was inspecting it. It had some carbon build up but not as bad as I thought. I started to clean it and noticed that the lower vacuum port was completely clogged. I couldn't even push air through it. It took me almost a half hour to get all that build up out of there. So that might have been part of my NOx problem during smog. Thanks for those that suggested the EGR being the culprit.

[CrazyYota]

UPDATE:

 Thanks for those that suggested the EGR being the culprit.

  Same thing on my truck and dads truck.

[ROCKO]

if you have the same problem with the nox get a piece of exaust tubing and put on the end of the tail pipe with about a 1in. opening...(it will run like crap but i've seen it work a couple times now) and make sure not to turn off the truck when waiting to get it smogged....

[floorrunner]

if you want it to really pass put a catalitic converter on it about 100.00 from kragen auto parts. my nox was 1400 ppm and with a new cat it went down to about 18ppm almost non existant. we all had toyota pu in high school. we all pitched in on a lifetime warranty cat and then when we needed one for smog we traded in our original and welded on the new one. same with brakes, shocks and wires. worked great on our budget. but yeah if you have 100.00 and want a sure fix buy a catalitic converter.

[Plekto]

But the new cat only works for 3-6 months if the engine is having major issues.  The designs are just junk, to be honest, for the EGR equipment from that era and the narrow passages and twists and so on get clogged fairly quickly.