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Old 07-16-2010, 09:37 PM   #1
gunner0352
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86 s10 smog fail, high HC. please help

Hi all,

I have an 86 s10, 2.8L. I just got it with low miles considering the age. Only 94k. Anyway, it runs well, But when i tried to smog it for title transfer it failed.

The report shows failed fuel cap, failed ignition timing, and high HC at low and high rpm. I was told to go to a "test only" shop. So the guy just said it failed. No reasons. So I took it to a local smog shop and the guy there showed me that the timing is dead on. It seems the first guy didnt unplug the wire under the dash before checking it.

So that should fix the functional ignition timing failure. But i still have high HC. I also had the plugs checked and replaced for the hell of it, but they all looked good. Old maybe, but not caked with carbon.

I really don't have the money to shotgun it by replacing one part at a time. I'm really hoping someone here can help me out. There is no stink or rttle from the CAT, so I don't suspect that. Ignition seems to be in good shape. I assume that if the rotor, distributor or wires were bad, then it would show with carbon on the plugs.

The previous owner was the only owner, and took very good care of this truck, so im hoping its just some small part somewhere that I can fix for cheap.

Any ideas are appreciated. Thanks
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Old 07-17-2010, 10:37 AM   #2
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Re: 86 s10 smog fail, high HC. please help

Quote:
Originally Posted by gunner0352 View Post
Hi all,

I have an 86 s10, 2.8L. I just got it with low miles considering the age. Only 94k. Anyway, it runs well, But when i tried to smog it for title transfer it failed.

The report shows failed fuel cap, failed ignition timing, and high HC at low and high rpm. I was told to go to a "test only" shop. So the guy just said it failed. No reasons. So I took it to a local smog shop and the guy there showed me that the timing is dead on. It seems the first guy didnt unplug the wire under the dash before checking it.

So that should fix the functional ignition timing failure. But i still have high HC. I also had the plugs checked and replaced for the hell of it, but they all looked good. Old maybe, but not caked with carbon.

I really don't have the money to shotgun it by replacing one part at a time. I'm really hoping someone here can help me out. There is no stink or rttle from the CAT, so I don't suspect that. Ignition seems to be in good shape. I assume that if the rotor, distributor or wires were bad, then it would show with carbon on the plugs.

The previous owner was the only owner, and took very good care of this truck, so im hoping its just some small part somewhere that I can fix for cheap.

Any ideas are appreciated. Thanks
Any codes or check engine lights?
Jumper A&B for codes.

If any codes post back code no.

You do not need special shops.

A good major tune up by a good repair shop usually fixes them.
Check around Ask around
Word of mouth.
Family friends coworkers neighbors business people and delivery people.
Mailmen and parcel delivery people get around and notice a lot of stuff.
Even a good parts house knows what shops are good and not good.
Chamber of commerce and better business bureau and city hall.
If you find a good referral to a repair shop go look them over and talk to them.
Look for a clean looking busy place with nice people running it.
Ask a few questions and ask about their qualifications and training.
Not all places have trained tech/mechanics.
If they do not find a place that does.
Even all dealers do not have all trained techs/mechanics.
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Old 07-17-2010, 10:50 AM   #3
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Re: 86 s10 smog fail, high HC. please help

Hi MT,

Thanks for the reply. I have not checked for a code. But there is no light on. Should i still check for a code? I know the O2 sensor could be an issue, but wouldn't i get the check engine light if it was bad?

Aside from a slight hesitation when i first start driving in the morning, it runs great.

Someone did mention that maybe it wasnt hot enough. I only drove about three blocks to the shop after it sat for about 4-5 hours.

I'll check the code anyway. I'm also thinking I might just get a new air filter and oil change to see if that helps. Tha big issue is, how do I know if I fixed it without going back for the test again? I only get one free retest. Not sure wht happens if I fail again.
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Old 07-17-2010, 11:15 AM   #4
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Re: 86 s10 smog fail, high HC. please help

Start with codes and a good secandary ign tune up.

Did you get the timing set good?

A good engine scanner read out may point to problems.
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Old 07-17-2010, 11:19 AM   #5
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Re: 86 s10 smog fail, high HC. please help

As I said in the first post. The test only guy said timing failed, but i went directly to another local guy who showed me step by step and pointed out that the timing is dead on. He assumed that the first guy didnt unplug the wire from under the dash before checking it.... on the fan shroud under the hood it tells you to unplug the wire before checking the timing...
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Old 07-17-2010, 11:26 AM   #6
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Re: 86 s10 smog fail, high HC. please help

I just checked the codes and it did come up with one... code 24. Makes no sense though.. "vehicle speed sensor circuit fault".. meaning my speedometer? That works fine, and shouldnt have anything to do with the high HC right???
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Old 07-19-2010, 02:36 AM   #7
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Re: 86 s10 smog fail, high HC. please help

i had an 88 suburban 5.7L 500k+ miles that burned oil like a mofo. i bought it for $300 because it ran without needing major work.

it passed the smog test every year, i had it (i think 4 yrs). the keys seemed to be:

new gas cap right away
plugs, dist cap, and rotor.
new air filter and oil change the day of test.
check for proper tire pressure.
take off and clean egr valve.
run some seafoam through the throttle body.
a bottle of "guaranteed to pass" in the gas tank ($8 from autozone)
REGULAR unleaded gas.
drive around on the freeway for about 30 mins before the test.

it was kinda funny, because on the dyno for the smog test, white smoke would be POURING from the exhaust, but the HC levels were low enough to pass.
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Old 07-20-2010, 05:37 PM   #8
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Re: 86 s10 smog fail, high HC. please help

Im glad I live in Iowa and we dont have "smog tests" or emissions tests, or inspections, or anything.
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