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I have a 79 luv that I am trying to get to pass smog the numbers and on the 15mph are co2% .2 hc 222 which failed co% 2.27 failed No 46
the 25 mph are co2% .1Hc 109 co% 1.29 no 48
any help out there would be great it passed the first time but failed the visual due to the missing exhaust heat shield , but just barely but took it into the shop today and it failed the 15 mph test , the guy said that there is no adjustment for this since it is at cruise speed, do i need a rebuilt carb ????

Hrm, heat shield? Is that referring to the heat stove that sits over the exhaust manifold? It is less a shield, and more to give hot air to the carb when the truck is first warming up. That helps it run cleaner during warm up. Should not be hard to find one of them on a junkyard truck.

It sounds like you failed for CO2, so the other stuff like NO2 is ok? CO2 could be elevated due to a bad/worn smog pump too. The pump dumps air into the exhaust so it actually can drop the numbers of all emissions. (more air in there "dilutes" the other crud) Check the vac line that leads over to the smog pump and make sure it is in good shape as it can keep the pump from working right. You might also gain from new plugs, disti cap and rotor, points. Better spark could help get better burn of fuel/air mix and get you through. General tuneup stuff should help some if you are at least close.

I'll have to look for link I found once before. It looked at each emission test component and gave ideas for what could be causing it. I'll see if I can dig it up.

It would also help if you could explain it all out a little better. I don't have to smog test where I live, so it would help me understand if you could describe what failed and any info you got from them about why it failed.

thanks so far giving me some ideas to consider, ok the reason why it fail was due to the stove pipe, but i put it on and brought it back the following day for a retest and it failed while on the dyno @ 15 mph cruise speed on the HC (hydrocARBONS) and the CO the hc was at 222 the max is 221, Co was at 2.27 the max is 1.62 he told me that there is no adjustment for this since it is at a cruising speed , I put a set of points in before i took it down to the shop and that made a big difference on the way it was running before it used to back fire while shifting and have low power out of first , but I just want this truck to pass smog

HC emissions being high could be helped by the smog pump. From what I recall that is the purpose of it, to add air into the exhaust to try to burn left over hydrocarbons.

The last time I redid the head on my truck I found that one of the ports of the smog pump AIR manifold was clogged solid. Maybe it would help to pull that off and make sure it is clear on all 4 tubes. I ran water and degreaser through mine to break stuff loose. Greased Lightning really cuts the crud well for me. I had to jam a wire up the #4 port to break the clog out though.

I'll have to look on the CO, I think that is more a function of the carb and the air/fuel mix. Checking for vac leaks is always a good suggestion on a LUV, seems like there is always one somewhere.

might sound funny but, how old is the oil?

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Resident lurker

HC is unburned hydrocarbons (usually unburned gas). CO is carbon monoxide, which comes from partial combustion. (Full combustion yields CO2, carbon dioxide).

Usually, this is tuneup. You said you put new points in. How about plugs and wires. Also, anything that restricts air flow, like a dirty air filter can have a big effect on HC and CO. Make sure your air filter's new.

The other thing is timing. The truck will burn a little cleaner (but run crappier) if you retard the timing just a little from spec. I've done this to pass smog in California, then cranked it back up after.

If all that doesn't work, and if your motor's otherwise tight, it's probably the smog pump or catalytic converter.

Hope this helps.

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You went there in that?!?!

Yeah i Just bought a new smog pump today along with new plugs and wire's just don't know the gap they are at 36 right now just need to take a closer look at my vacuum lines for this california monster, I am going to get an extension on my truck for the smog date to give me time to fix all of this , probably going to change the oil the morning that I decide to get it smoged thanks again for everyones help so far, I just want to keep this truck on the road

Gap the plugs at .44.

I live in a state that needs a visual, nothing more. So I just put the pump up there and it helped with the smoke.

The heads will be replaced this summer cause it blows oyl out the tail pype unburned.

If I had to hook it up I know it would never pass cause of that darned stuck valve, so your prob could even be valves.

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definitely replace the oil if it needs it. I failed a few years ago in an 86 4x4 toyota and the tester told me to change the oil. came back after and passed. He told me that more than half the cars that fail just need to get the oil changed. ... worked for me anyway. + its easy and pretty cheap.

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Well I got an extension on my smog so it will give me time to repair what is needed, Thanks for all the help so far