Smog test failed - ca hydrocarbons

Failed California smog check - 99 Chrysler Sebring JXi.

  • Somewhat over HC at 15mph but at limit at 25mph. Test guy think catalytic converter. The cat monitor was not ready (state allows 1 or 2 devices saying not ready to the smog test machine). 11 days earlier the starter was replaced so battery may have been disconnected.

  • After that replaced PCV value. Did not have injector cleaning before so used a fuel system cleaner. Heard from tow trucker driver he had passed smog retest after changing PCV value & using 91 gas (which has more/better detergents). I put in 13.3 gal of 89 instead of usual 87. A little low oil to have smog done so added handy 10W30 to shop oil change of 20W50 1900 miles earlier.

  • Smog retest (6 weeks after 1st test) failed with worse HC at 15 & 25mph - cat monitor still not ready.

  • After that, so far put in 5.6 gal of 87 gas. Later put in 6.0 gal of 87 gas.

  • Through all this, no check engine light so no trouble codes.

  • Want to know:
    a) how much of the fuel cleaner shows up in which type of emissions & how much gas refilling takes the cleaner out of emissions numbers.
    b) effect of different octane gas - higher means more compression. Someone said he goes farther using 91. I read that higher octane is harder to burn implying more unburned material. Comments? How common do cars adjust for different octane gas?
    c) Spark plugs gradually get foul. Would affect all emissions? Would fuel system cleaning get material on spark plugs (if so how much get burn off & which could stay on)? 3 plugs reachable by other 3 high labor (shop 1.5 hours to change all 6 because of cover).
    d) Possibly oil getting burn in combustion chamber & the lighter oil getting thru making retest result worse? Oil level naturally go down for all cars. If dirty oil, get oil change a little before smog test? If it gets overfill, would more of it go into combustion/emissions path? if so would most get burned off & after 1 or 2 weeks be enough time to stabilize before retest?

e) Cat monitor still stayed not ready. Sign of cat problem? Devices not ready would be after battery disconnect or battery completely drained but not go low to need a battery jump?

  • Very limited budget so need info of inexpensive possibilities.


Excessive oil consumption can raise the hc value

Are you absolutely sure the thermostat is good?
Is the engine reaching the proper coolant temperature?
Does it reach proper operating temperature quickly?
Does it maintain the proper operating temperature?

If your engine’s not reaching proper operating temperature, you’re going to have a hard time getting all the monitors to run to completion

Here’s advice from a pro:

If you want to clean your injectors, you need to hook the canister cleaner directly to the rail. Disable the fuel pump. The engine needs to run exclusively on the cleaning solution until it stalls. That is the most effective way to clean injectors, short of removing them and having them sent out for cleaning . . . crazy as it sounds, there are shops that will recondition your injectors

You definitely want a tip top ignition system before the smog test

Plugs . . . OEM, preferably
Wires, if you’ve got them . . . high quality, please

With all due respect, your plugs may very well be fouled because of the oil consumption

If the starter was replaced, the battery was almost certainly disconnected. Most sane mechanics would do this

Does the rear oxygen sensor’s signal match the front?

It should NOT. If it does, you’ve got a problem.

You could always do a back pressure test to check if/how much the cat is restricted

I’m just throwing out some ideas . . .

Good luck!

How many miles on this car? Have the spark plugs EVER been changed? High HC means unburned fuel in the exhaust. Some sort of misfire or leaking valves…

I have a similar high HC problem on my 20 year old Corolla. Here’s what I do to squeak by, has worked so far.

  • A week or so prior to test, bring all the routine engine maintenance up to date, including new spark plugs, rotor, air cleaner, oil & filter change, check pcv and egr, check the idle coolant temp, and set/verify idle speed and timing, making sure timing is not advanced beyond the spec at all (I usually retard it 2 degrees for the test, then reset it after the test). Then a day or two before the test, take a long freeway drive, 100-150 miles.

  • Before arriving at the test, bring the engine to full operating temperature and keep it there for at least 20 minutes. Make sure the gas tank is close to full, use whatever octane is recommended for you car.

If you google “how to pass a California emissions test” you’ll see a couple of sites there w/some good advice.

If it still fails, it could be the cat. But before I’d replace the cat, I’d have a pro check the valve clearances and the O2 sensor(s).

If you’re burning oil bad enough to foul plugs then you may never get through an inspection.

Running a heavy oil and new spark plugs with the gaps widened a bit over the stock recommendation may help. Or not.

Another potential problem could be if the leading edge of the substrate in the catalytic converter is becoming partially clogged. That can cause the engine to have a tendency to run a bit rich; meaning high HCs.

The cat is not working so the self test is failing. A new cat will clean that up enough to pass this time. Cat monitor should be the most ready of the monitors. Yes, a diagnosis is needed to find out why HC is high. Fuel injector cleaner will not ruin the smog test.

Move out of California. Your car is among the least of things taking your resources.


Move out of state so that a car doesn’t have to pass smog

Surely you jest?

Try cataclean. I have heard it really helps. That said plugs and wires have to be good. As said before engine has to be up to temp. You may have a lazy O2 sensor that has not failed, but it causing it to run rich.