Ok here we go again.
Calling all smog techs or good auto techs in general.

I take my '75 Chevy K-10 in for a smog and it fails the NO section.

All the ignition stuff has been replaced, new oil , clean K-N air filter , timing is ok , runs good .

here are the numbers


%co2 %02 HC(ppm) .Co% NO (PPM)
15 mph 13.8 1.6 252(290 max) .14(3.6 max) 3233(2030)
25mph 14.1 1.1 278(240max) .34(3.4max) 2843(1890)

%CO2 %O2 HC CO% NO
15MPH 13.8 1.6 252 .14 3233
25MPH 14.1 1.1 278 .34 2843
MAX 290 3.6 2030


Can anyone suggest what is wrong ???
Sounds like maybe too lean???
both of these tests were on a treadmill at approx 1480 RPM
Thanks for any help:eek: :eek:

More NO is produced by higher combustion temperatures. The EGR system is designed to lower NO emissions on a '75. Is your EGR valve opening? Lean mixtures also burn at higher temperatures. Vacuum leak? What do the plugs look like? HC is also high, while CO is low. This can be caused by misfiring.

Sorry I should give more info.
The engine is a 350 Federal, so no EGR , no smog pump.
just PCV and warm air snorkel
I'll check for vacum leaks tommarow
it does have a miss at idle in gear ( auto ) but runs fine off idle
seems that the high HC contridicts the lean theory,
but I'm not a real auto tech.
could it be just simple carb. adjustment???

With no Smog pump and no EGR your engine will require a very efficient catalytic converter to clean up NOx. It will also bring down the HC's.
If you need further help call my shop and ask for John or Adam. We specialize in this area and drivability problems. (among other areas.)

I'm in Sac also.
Rosemont Automotive
366-9191

i'm a smog tech in the south sac area. bring that pig on by ,
i'll get it to pass.

Did you have them do a pre-test? If not won't it have to go to the referee station now as a gross poluter? ?s for the smog pros on here.:confused:

doesn't matter if it is a gross polluter i can still smog it. i work
at a test only station.

Originally posted by JP4WHLR95
doesn't matter if it is a gross polluter i can still smog it. i work
at a test only station.

I thought once you got the gross polluter thing it had to go to a referee station? I always have a pretest done, I don't want to deal with the other crap. Do you have smog check one or two up there? And just wait till the diesel pickups get the "snap idel test" they do to the big rigs, a lot of hopped up tow rigs are gonna fail big time.

payton sure loves indiana...

whats smog.. whats a smog test.. hahahahaha

good luck



payton says..

Heres one better.... MOVE OUT OF THAT STUPID STATE, and get back to somewhere that doesnt test! Look at me, the ARMY sends me to Colorado where half the people are from California and they brought their laws and real estate prices with them!! Lord help me:( . Luckily being in the Army I can keep my Oklahoma tags and Im exempt from testing my C3500 Diesel!!

Just yall register your trucks out in basic smog check areas... no dyno no varoom varoom putt putt test ;)

i planing on reging my trucks at my grandma's house in Bishop California, NO MO SMOG ! Unless its sold or change of ownership ;)

Well it didn't make 'gross polluter ' status, but it's in a 'high polluter ' profile so it'll always go to test only.

Oh and everyone that's smirking about no smog, it's only a matter of time for you .
You know that Kali. is the leader in stupid ideas that eventually spread across the whole country.

JP4WHLR95 pm me your shop name address etc. so if I can't get by this I'll look you up.

thanks for everyones help.
Tom

916-992-6698 home
916-428-2884 work
rpm smog
6190 freeport blvd.

i cannot do any repairs at work.
but i can at home after work.
should be a simple fix.
about a half hour.
you bring the beer.
oh yeah ask for Al when you call

or resgister in Vermont to title issues no other smog crap check it out and you don't have to be a res of the state (http://www.aot.state.vt.us/dmv/dmvhp.htm) ...............ltr

Originally posted by misfitcj
or resgister in Vermont to title issues no other smog crap check it out and you don't have to be a res of the state (http://www.aot.state.vt.us/dmv/dmvhp.htm) ...............ltr


Doesn't your local state have issues with out of state registration? I have heard Utah is pissy about having out of state plates and a local driver license. Even Vermont seems to require local reg if you live or work there. I'll probably reg my junk in a non-smog county to get around it as we are dumber than Kali on engine swaps. If I can get away with this, I think I'd like it better.

I have had no problem so far I have suggested this to a coiple people and they had no problems just like the web site says submit paper work and vola your smog free.......you may wind up paying state tax and some " registraion" fees but all and all no worry's...........it is the vechile that your are regesitering not you.......give it a shot your just a phone call away from being smog free............

Update.....
I rigged up an O2 sensor to use as a carb tuning tool, so I think the excess HC may be much better.
I also found that the vaccum advance was pulling too much advance ( I think anyway ) like 20 degrees.
So to all you experts ...
Could the vaccum advance have been putting the engine into pre-ignition, and causing the high NOX readings???

bump

Originally posted by Arrow
Update.....
I rigged up an O2 sensor to use as a carb tuning tool, so I think the excess HC may be much better.
I also found that the vaccum advance was pulling too much advance ( I think anyway ) like 20 degrees.
So to all you experts ...
Could the vaccum advance have been putting the engine into pre-ignition, and causing the high NOX readings???


Since you haven't gotten any responses, I'll add my .02. I'm not an expert, just been doing some reading.

Sounds like you're on the right track with the O2 sensor. Were you running lean or rich? Probably rich if you had high HC. How is the mixture now? Where is your timing set now? What's the spec on that motor? You should also be able to get a spec for the advance setting as well.

Did you hear any knocking at high RPM? You should if the advance was set too high. Have you tried rigging a knock sensor to the engine so you can monitor it? That might be a good idea. Pre-ignition would probably cause higher combustion temps which would raise the NOX levels. That's what EGR is for, it cools the combustion to lower NOX. Water injection can do it too, but I hear that's something only forced induction engines can use. IIRC, a catalytic converter can help there too.

About all you can do is make sure the mixture and timing are right then test it again. Add EGR or a cat if needed. You might want to take up JP4WHLR95 on his offer to help you out if you can't get it passed.

The O2 sensor had it real rich , I was able to adjust the idle mixture down to what should be pretty good.
Yes I would hear pinging sometimes ( although the tire noise drowned most of it out )
The engine itself is a very basic 350 , mostly stock, Q-jet, RV cam, headers.
I think I'll take it back to smog again, and see what happens.
Does anyone know how a knock sensor works??? ( voltage level, on/off etc. )

Thanks all

Originally posted by Arrow
Does anyone know how a knock sensor works??? ( voltage level, on/off etc. )

Thanks all

Knock sensor tells the ECU to retart the spark. Drop in an EFI engine and that will solve the problem. :D

Looks like you have two problems. the HC is a little high and NO is high. HC is most commonly due to a misfire. If you think it is running lean, check the plugs. If the tips are white or burned it is lean. Mocha brown is just right.

It is hard to believe that this engine never had an EGR or that you will be able to get the NOx down without an EGR or a 2-way catalytic converter or boths.