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92 Sierra 5.0 L Failed Emission With High Hc

michaeld70

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michaeld70 Enthusiast

michaeld70

Posted
Posted

Hi, My truck basically sat for about 2 years, only occasionally running to move stuff etc., basically maybe an hour/month or 2, just around the yard, no road use.

 

I want it back on the road, failed 1st test, gas was 2 years old, drained and refilled, 2nd test was worse for HC, they went up slightly:

(curb idle) limit 200 reading 92

(40km/h) limit 45 reading 68 (previous was 52) (passed all other tests)

I couldnt see any vacuum leaks, did a tune up, all plugs were gapped at 35 and nice tan color, added bosch platinums.

Compression test-all were 150 psi, except for #1 which was 125, oil didnt raise it any.

When I idle it for several minutes I see blue smoke, likely valve seals I assume, oil level doesnt seem to drop much at all.

No trouble codes appear.

Any ideas on how to get the HC levels down? Any quick fixes or known issues? Chance that a valve in #1 is slightly burnt?

fbachman Senior Enthusiast

fbachman

Posted
Posted
Hi, My truck basically sat for about 2 years, only occasionally running to move stuff etc., basically maybe an hour/month or 2, just around the yard, no road use.

 

I want it back on the road, failed 1st test, gas was 2 years old, drained and refilled, 2nd test was worse for HC, they went up slightly:

(curb idle) limit 200 reading 92

(40km/h) limit 45 reading 68 (previous was 52) (passed all other tests)

I couldnt see any vacuum leaks, did a tune up, all plugs were gapped at 35 and nice tan color, added bosch platinums.

Compression test-all were 150 psi, except for #1 which was 125, oil didnt raise it any.

When I idle it for several minutes I see blue smoke, likely valve seals I assume, oil level doesnt seem to drop much at all.

No trouble codes appear.

Any ideas on how to get the HC levels down? Any quick fixes or known issues? Chance that a valve in #1 is slightly burnt?

 

These are generic comments relative to combustion/emissions measurement/ combustion engineering:

 

Generally speaking, "high" HC means "high", unburnt, heavy hydrocarbons, meaning "unburnt fuel".

 

GENERALLY, the primary cause of a high HC would be rich combustion, meaning the Fuel air ratio is well above stoichiometric --- assuming ALL ELSE is operating normally.

 

Now, if the FAR is OK, and you are STILL getting high HC, it could mean that you have a spark plug, or two, not firing, or, for some reason fuel is not burning when it is "commanded" to burn. HAve you replaced/tested all the spark plugs to make sure they are 1) clean, 2) operational...(?)

 

Rich burning can also mean too little air and the CORRECT amount of fuel. SO, have you checked your intake. Do you have an air filter that is not clogged with debris? Check all THAT.

 

A mass-air sensor with an attitude can cause off-design fuel air ratios as well.

 

SO, as a first shot, I would try/ensure this:

 

Getting spark?

 

Good spark plugs?

 

Clean Throttle body?

 

Clean Air filter element?

 

Good mass-air sensor?

 

clean mass-air sensor?

 

I mean, the possibilities are kinda endless here....

 

Could have a bad injector, or two, causing inefficient fuel delivery and subsequent incomplete combustion...

 

:cool:

 

of course, the blue smoke... if you are dumping tons of oil into the combustion chamber, this can appear as heavy HC in the exhaust as well, as it will pass through and not oxidize (burn) as the fuel does.

michaeld70 Enthusiast

michaeld70

Posted
  • Author
Posted

Thanks, but you didnt answer any of my questions, I explained everything you posted, at least I think I did.

 

Getting spark?

Good spark plugs?

Clean Throttle body?

"did a tune up, all plugs were gapped at 35 and nice tan color, added bosch platinums."

Engine runs fine, no miss fires, nothing.

 

Clean Air filter element?

Also part of tuneup, BUT, I've got a clean performance filter

 

Good mass-air sensor?

clean mass-air sensor?

N/A on a '92 5.0L

 

 

Could have a bad injector, or two, causing inefficient fuel delivery and subsequent incomplete combustion...

TBI cleaned, not multi port, seems like a decent uniform spray

 

of course, the blue smoke... if you are dumping tons of oil into the combustion chamber, this can appear as heavy HC in the exhaust as well, as it will pass through and not oxidize (burn) as the fuel does.

" oil level doesnt seem to drop much at all."

Blue smoke after extended idle time, 5-10 minutes I'm guessing. No smoke any other time.

superjim Senior Enthusiast

superjim

Posted
Posted
Hi, My truck basically sat for about 2 years, only occasionally running to move stuff etc., basically maybe an hour/month or 2, just around the yard, no road use.

 

I want it back on the road, failed 1st test, gas was 2 years old, drained and refilled, 2nd test was worse for HC, they went up slightly:

(curb idle) limit 200 reading 92

(40km/h) limit 45 reading 68 (previous was 52) (passed all other tests)

I couldnt see any vacuum leaks, did a tune up, all plugs were gapped at 35 and nice tan color, added bosch platinums.

Compression test-all were 150 psi, except for #1 which was 125, oil didnt raise it any.

When I idle it for several minutes I see blue smoke, likely valve seals I assume, oil level doesnt seem to drop much at all.

No trouble codes appear.

Any ideas on how to get the HC levels down? Any quick fixes or known issues? Chance that a valve in #1 is slightly burnt?

 

 

Something you might try as a temporary measure...just to get it to pass emissions testing.

 

Change the oil and put a pretty heavy oil in it to minimize the leakage into the combustion chambers. Maybe a 15w-40 HIGH MILEAGE oil if you can find it. The high mileage oils have seal conditioner in them and it may help the blue smoke problem.

My guess is the blue smoke issue is what is causing it to fail.

 

After changing the oil...and BEFORE taking to the inspection station...take it out on the highway and drive several miles...maybe getting on it just a bit.

It needs to be TOTALLY warmed up to pass testing.

michaeld70 Enthusiast

michaeld70

Posted
  • Author
Posted

Theres an idea, I usually add a liter (20-30%) of 15/40 diesel oil to all my engines, even lawn mowers lol, just for the extra wear protection additives. I figure if a tractor trailer can get a million miles on an engine with it...lol Shell rotella was good, but I guess they changed the formulation recently. I never used it strait in gas engines because it gets pretty thick in the winter, but I have friends that do.

fbachman Senior Enthusiast

fbachman

Posted
Posted
Thanks, but you didnt answer any of my questions, I explained everything you posted, at least I think I did.

 

Getting spark?

Good spark plugs?

Clean Throttle body?

"did a tune up, all plugs were gapped at 35 and nice tan color, added bosch platinums."

Engine runs fine, no miss fires, nothing.

 

Clean Air filter element?

Also part of tuneup, BUT, I've got a clean performance filter

 

Good mass-air sensor?

clean mass-air sensor?

N/A on a '92 5.0L

 

 

Could have a bad injector, or two, causing inefficient fuel delivery and subsequent incomplete combustion...

TBI cleaned, not multi port, seems like a decent uniform spray

 

of course, the blue smoke... if you are dumping tons of oil into the combustion chamber, this can appear as heavy HC in the exhaust as well, as it will pass through and not oxidize (burn) as the fuel does.

" oil level doesnt seem to drop much at all."

Blue smoke after extended idle time, 5-10 minutes I'm guessing. No smoke any other time.

 

 

I mean, like I said, could be many things.

 

Does the truck have the original Catalytic Converter. Maybe a spent catalyst could be causing this as well.....

 

I dunno, just trying to help. I like the bigger tip idea.....that might indeed fix it faster than anything. :lol:

michaeld70 Enthusiast

michaeld70

Posted
  • Author
Posted
Does the truck have the original Catalytic Converter. Maybe a spent catalyst could be causing this as well.....

 

I dunno, just trying to help. I like the bigger tip idea.....that might indeed fix it faster than anything. :lol:

 

Not sure on the converter, I've only had it about 3 years, and it basically sat for 2 lol.

Problem was, after I got it in the 2nd time they were about to close by the time they finished me so I'm likely stuck with a 3rd test and not many ideas on what I can do quick to get it in for the next test without costing me a pile of money, but there is the $450 repair limit at least. They didnt get a chance to look anything over or run diagnostics.

 

Tip? Its a Canada wide chain, I shoulda went to the smaller guy, but they are almost always busy lol.

hockeypro1411 Senior Enthusiast

hockeypro1411

Posted
Posted
Does the truck have the original Catalytic Converter. Maybe a spent catalyst could be causing this as well.....

 

I dunno, just trying to help. I like the bigger tip idea.....that might indeed fix it faster than anything. :lol:

 

Not sure on the converter, I've only had it about 3 years, and it basically sat for 2 lol.

Problem was, after I got it in the 2nd time they were about to close by the time they finished me so I'm likely stuck with a 3rd test and not many ideas on what I can do quick to get it in for the next test without costing me a pile of money, but there is the $450 repair limit at least. They didnt get a chance to look anything over or run diagnostics.

 

Tip? Its a Canada wide chain, I shoulda went to the smaller guy, but they are almost always busy lol.

 

 

Honestly I wouldn't even bother with emissions if you never drive it on the roads. Report it as destroyed/salvage and keep it on your private property.

superjim Senior Enthusiast

superjim

Posted
Posted
Theres an idea, I usually add a liter (20-30%) of 15/40 diesel oil to all my engines, even lawn mowers lol, just for the extra wear protection additives. I figure if a tractor trailer can get a million miles on an engine with it...lol Shell rotella was good, but I guess they changed the formulation recently. I never used it strait in gas engines because it gets pretty thick in the winter, but I have friends that do.

 

 

Some of the guys on the Cadillac board with really high mileage engines, run the Shell Rotella 15/40.

 

Just saying... :lol:

 

You don't have to LEAVE it in there...after it passes inspection. :lol:

txab Senior Enthusiast

txab

Posted
Posted

I had always heard the older vehicles really didn't like platinum plugs that much. Something about the older ignition system didn't fire as hot as the plug needed. I've always run the copper core plugs in my old trucks and never had a problem. Another thing to look at would be a lazy O2 sensor. It could be allowing the engine to run way too rich.

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