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1975 K10 Emissions Failed- Help please

mini_mull

mini_mull

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Hi guys, I haven't been here much, since I sold my burb, but now my 16 yr old nephew bought a 1975 K10 and needs some help, so I'm starting this post for him. I haven't gotten under the hood yet, but he tells me it's mostly stock, except for the intake and dual exhaust. He finally got it running decent with the help of his dad and a mechanic friend and took it for emissions.

It failed with high hydrocarbon and high CO. He needs help knowing what to check on this year truck in particular and what, if any emmisions equip should be on it.

It doesn't smoke and has a new air filter, plugs, wires, and he just had the timing reset.

He's going to get on here, too, as soon as his mom gets off his computer.

Thanks,
Kristi
mini_mull
 
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I don't believe 75 had CAT's, unless it was a CA truck.
CO being high means it's choking for air, they might have a stuck choke or lose flapper.
mini_mull said:
Hi guys, I haven't been here much, since I sold my burb, but now my 16 yr old nephew bought a 1975 K10 and needs some help, so I'm starting this post for him. I haven't gotten under the hood yet, but he tells me it's mostly stock, except for the intake. He finally got it running decent with the help of his dad and a mechanic friend and took it for emissions.

It failed with high hydrocarbon and high CO. He needs help knowing what to check on this year truck in particular and what, if any emmisions equip should be on it.

What about a cat? Everything I read says it should have one, but he said it has dual exhaust and doesn't have cats, just mufflers. Could that be the problem?

He's going to get on here, too, as soon as his mom gets off his computer.

Thanks,
Kristi
mini_mull
Click to expand...
 
OK, now he says it does have cats. He actually looked instead of just asking his dad. ;-)
Would a stuck choke or loose flapper make it run rough? He says it's pretty smooth.
 
mini_mull said:
OK, now he says it does have cats. He actually looked instead of just asking his dad. ;-)
Would a stuck choke or loose flapper make it run rough? He says it's pretty smooth.
Click to expand...
No, it can run prestty smooth but you probably will not like the smell and your eyes might get watery if you are standing close to the exhaust.
 
I thought AZ didn't have smog, much less a '75. CA doesn't require smog for '75.

Is the original smog sticker on the rediator core support? That will tell you what is should have for smog equipment.
 
Yo brad, pet peev of many folks here is punctuation. If there isn't any, it's really hard to read.


Have you taken a look at the choke assembly? Make sure the little flapper is all the way open when the truck is hot. Is the choke electric or manual?
 
K85 Octane said:
Yo brad, pet peev of many folks here is punctuation. If there isn't any, it's really hard to read.


Have you taken a look at the choke assembly? Make sure the little flapper is all the way open when the truck is hot. Is the choke electric or manual?
Click to expand...

"CO being high means it's choking for air, they might have a stuck choke or lose flapper"

:whistle:
 
A 1975 should not have a catalytic converter. It seems odd that someone would install one on something that does not require it.

Martin
 
82355 said:
A 1975 should not have a catalytic converter. It seems odd that someone would install one on something that does not require it.

Martin
Click to expand...

Found this

1975
In 1975, GM changed its model line around a little... HEI ignition becomes standard equipment, catalytic converters were also made standard equipment on all trucks under 6,001 gross vehicle weight (GVW)...

So cats came on this truck, which means he has to keep them.
 
Actually you are correct. I was thinking 1976 was the first year for cats, but it was 1974.

Martin
 
I'd like the tested results along with the legal passing results since every year haa different limits.

But I'm going to pretty well guess you're going to need carburetor work, regardless if It's running "fine"... I've had several vehicles in the past that ran great, but would not even come close to passing the emissions testing.
 
Yep, time for a carburetor rebuild.

Change the oil, new air filter, new PCV

Do you happen to have any way to read the Air/Fuel ratio?
Wide band O2 sensor type?
They are a little spendy, but worth it if your going to be doing this alot.

And, if it's been running that way for a while, you might need to replace those cats. Only way to tell if they are any good is read the temperature fore and aft of them after getting them good and hot. The Aft temp will be considerably hotter than the fore side.
 
loaded result for (hc) is 452 the standard is 250/ idle result for (hc) is 203 the standard is 250/ loaded result for (co) is 10 the standard is l.5/ idle results for (co) is 3.85 the standard is 2
 
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