Hc (ppm) levels

I have a 1996 infini g20 I went to get a smog test and the hc (ppm) levels were double the passing level at 15 mphs, and only 8 points over at 25 mphs. I’ve been told tune up could help, but am more concerned that it might be injectors or catalytic converter. Any thoughts would be appreciated thanks !

First, check your ECU for stored fault codes. You might have a huge clue there.
Second, bring all the maintenance up to date, including a “tuneup”, which in modern cars may not be much more than new sparkplugs and filters.

Unburned hydrocarbons at your level usually come from incomplete combustion. Usually that’s just overdue maintenance. Occasionally it’s a bad sensor or some sort or other, often the O2 sensor. This is highly unlikely to be a serious problem, so get it fixed. Occasionally it’s the accumulated years of neglected maintenance and cannot be corrected. You don’t want to end up there. Remember that oil is a hydrocarbon too…

By the way, how many miles does it have on it? And does it use excess oil?

How’s the ignition system?

Plugs, coils, wires, etc. up to date?

Is the engine running smoothly?

No check engine light?

It’s at 150000 miles and the previous owners unfortunately did neglect it pretty bad, engine kinda has an unbalanced sounding idle, I just replaced a busted distributor cap and the rotor, that did help my throttle response I’m about to replace the plugs and wires and do a oil change. I have just recently also ran sea foam threw the gas tank and vaccuum line. And decently have to replace the valve cover gasket . I’m also certain to find more problems as the days go as I for. Mentioned poorly maintained by previous owners .

Also check engine light is off

Check the compression too. If that’s good, the rest is worth working on.

And make sure it is well warmed up, a short trip at highway speeds before the test can help also. A dose of techron or seafoam a tank before inspection is also worth a shot.

From what I read as long as the compression levels are less the 10 percent differential I’m ok but more then 15 percent it’s most likely a rebuild situation

Not quite true. Compression readings can be consistently low across the board and an overhaul or engine replacement is necessary.
E.G.; 135 PSI on all cylinders is a problem.

It’s also true that an engine, or a specific cylinder, can have fantastic compression readings and still burn oil past the piston rings.
E.G.; 190 PSI on all cylinders could be viewed as great but that’s not always the case. The compression rings may be fine and one glazed cylinder or stuck oil control ring can cause havoc.

There’s always a bit of murkiness in some areas but generally a lowly compression test will determine whether the engine top end has serious issues or not.
The general rule of thumb is 20 X the compression ratio to arrive at a good compression number. That number will drop over time due to wear, is affected by altitude, etc, etc.

Maryland recommends driving at least a half hour at highway speeds before having the car tested. That is ore than a short drive to me, and I would do just that before your next test.

Good comments above. I have an HC problem w/my Corolla so I’ve done a little research on this, might be helpful. Make sure all the routine engine maintenance is up to date. Remove and check the thermostat for proper operation. Codes can be stored w/out the CEL on, so have those read and addressed. Within a week prior to test, at the minimum replace air filter, spark plugs, and engine oil. Verify ignition timing and idle speed are at spec. Still a no go? High HC’s mean gasoline is going in and out without getting burned. Valve and ring problems can cause this, so have a wet/dry compression test done, and have the valve adjustment checked. O2 sensor problems can cause this too, but diagnosing those requires a mechanic experienced and with the proper tools. A clogged fuel filter might could cause high HC’s, so if it is close to due, replace it.

There’s some pre-test tricks too. A day or two prior to the test drive the car on the freeway 100 miles or so. On the day of the test, make sure the engine is fully heated. After driving to the location, park in a near by parking lot and let it idle until the radiator fan comes on might be one way to do it. If you google “how to pass an emissions test” other good ideas appear.


The smog techs in Los Angeles are wise to these “tricks” to getting cars in marginal condition to pass

They know that if you’ve got a marginal cat and drive the hell out it so that it’s at 1 million degrees when you arrive at the testing station . . . I’m exaggerating the temperature, of course . . . you may pass

I may be wrong, but I believe it’s known as overprepping

That said, the car is supposed to pass in real world conditions

So, when you show up at a smog station, the guy will tell you to “Park it over there. Turn off the engine.” 10 or 15 minutes later, he’ll get it and start his thing. By that time, the cat will have cooled down to a normal temperature.

Personally, I’ve never used any snake oil or gone to any heroic measures to get a car ready for smog inspection. Perhaps I’m not poor enough, desperate enough, or stubborn enough

Can you post a pic of your Vehicle Inspection Report? Just knowing what the HC levels were don’t really help anyone. If you can tell us what the CO, CO2, O2, and NOx readings were we might be able to point you in the right direction.

HC is unburned fuel. Many things can cause an elevated HC level. Tune-up, improper ignition timing, weak catalytic converter, vacuum leaks are a few.

db4690 … maybe the techs here in San Jose area haven’t learned we auto owners are learning some pre-testing tricks. I’ve always just pulled right in, never had to wait even 15 minutes for the test to start. The Corolla has always had to take the treadmill version, maybe that makes a difference.

The Corolla has always passed so far, but barely. Folks who need their car registered, have to use it to drive to work etc, and don’t pass, have family budget problems, I feel for. They get stuck between a rock and a hard place, not knowing the best course of action to effect a passing grade. And the kicker is the state gives them a time limit to get it resolved, but offers little help on how. It’s sort of a modern day Kafka-esque experience for many.

@db4690: Why would the techs WANT to fail cars? I mean, if a garage gets a rep as “drill sergeant tough,” they’re going to lose future business. My experience with emissions testing is like getting a good accountant to do your taxes: they won’t commit fraud, but they will make every effort to secure you the most favorable outcome they legally and ethically can.

I would think “making every effort” would include testing in the configuration most likely to pass…red hot, if need be. Unlike “sniffing” another car’s tailpipe, this wouldn’t be fraudulent.


I’m not making this up, unfortunately

Please don’t shoot the messenger

I’m just reporting some trends

The idea is that a car is supposed to pass under real world conditions

The smog techs don’t WANT cars to fail. They have no emotional attachment to any of the cars. They don’t get any pleasure out of failing a car

They are supposed to test the cars in real life conditions

That means testing the car with the cat at proper operating temperature, not at 1 million degrees after driving in 2nd gear on the freeway for 1 hour

Here’s another thing to consider . . . spies sometimes get sent to smog stations to make sure everything is on the level. Smog technicians go through a lot to get their licenses, and they aren’t going to jeopardize that, just because it will inconvenience somebody if their 17 year old poorly maintained car that’s burning oil like crazy and has a partially plugged cat fails

By the way, I sometimes read those online newsletters geared towards smog techs. And those overprepped cars have been brought up. What they don’t want is that crappy car to pass by the skin of its teeth, and then go right back to polluting the atmosphere for the next 2 years.

They also know about the trick with the check engine light. You know, where the problem hasn’t been fixed, but the light has been cleared. Let’s say it was an evap code, but the problem hasn’t been fixed. The light is cleared. The car is driven so that every single monitor is complete except the evap. Then it’s taken to the smog station before the evap monitor runs to completion. You’re allowed to smog a car with one incomplete monitor. So that’s your window of opportunity, so to speak.

A relative of mine had been getting some of his cars smogged that way for years. I convinced him that it would be easier for him to just bring me the vehicles. I diagnosed and repaired them, and let all the monitors run to completion. Then he brought the vehicles to the smog station. No hurry. Because there was no danger of that evap monitor, for example, running to completion and tripping the light.

That last one is a little harder to combat, though

I still don’t see how it’s unethical to test with the cat towards the high end of its normal operating range. Nothing fraudulent, no reason to worry about a license.

I wonder if the tech is trying to get a marginal car to fail so as to make bank on the associated repair. Now THAT would be unethical! Older card don’t have close-coupled cats, and were never intended to provide pollution abatement until up to temp.

Pretty easy to get an older car to flunk.

@meanjoe75fan, regarding inspections let me say this. OK does not have an emissions inspection program but in the past for many years there was a safety inspection program.

As an inspector, I did get faced with irate car owners whose cars were apparently not going to pass inspection from the get-go for blatant violations. They would insist that “it’s minor” or “can’t you let that slide. I was going to fix it next week…”.

As db4690 said, undercover people were sometimes sent out and any inspector who got caught looking the other way or cutting corners was faced with loss of license or a reprimand at best or a fine and jail time at worst.
The state surveys assumed a certain percentage of rejections at every inspection station and they looked hard at facilities with a very low or non-existent failure rate.

Well, there’s a line to walk here: too lenient could cost a license; too strict could cost you customers.

Different shops are located in different neighborhoods with customers in different economic situations. If your customers don’t drive hoopties, they ought to have a much higher pass % than customers that do. Shame to draw the ire of the state just because your clientele are well-off enough to keep current on their maintenance!

I use a shop that employs a fair bit of leeway and discretion, but will not pass an unsafe vehicle. I treat the annual inspection as a (subsidized) once-over by a mechanic.


It seems most of the smog stations here are test only

That means the smog tech has no financial incentive to fail a car

A shop doesn’t want to get a reputation as the place to go if you want all cars to pass all the time

carb knows that a lot of cars are poorly maintained, are burning oil, etc. Therefore, if a shop’s “pass rate” is way too high versus other shops in the area, that’s a big red flag

By the way, in my area, a huge portion of the population drive hoopties, because they have very meager incomes. Therefore, I expect a fair percentage of the vehicles probably fail the smog inspection

Why are you arguing with me, anyways?

I’m not the ones making the rules, regulations, guidelines, etc.

If I’m driving a car with 250K, poorly maintained, burns oil like crazy, low compression, rough idle, etc., and it fails a smog inspection, I shouldn’t be upset at the smog tech. I should have the brains to realize the car failed because it’s a POS