1995 Saturn SL2 1995 Saturn SL2 narrowly failed smog HC tes

Tiny
TALKINHORSE
  • MEMBER
  • 1995 SATURN SL2
  • 4 CYL
  • FWD
  • MANUAL
  • 125,000 MILES
My HC measurement was barely out of range; CO and NO were fine:

15 mph
HC Max 93; Ave 21; Meas 94 - FAIL (BARELY)
CO Max 0.57; Ave 0.06; Meas 0.10 - PASS
NO Max 720; Ave 150; Meas 369 - PASS

25 mph
HC Max 59; Ave 13; Meas 59 - PASS (BARELY)
CO Max 0.55; Ave 0.05; Meas 0.04 - PASS
NO Max 774; Ave 136; Meas 74 - PASS

My question is, what's the easiest approach that will most likely pass the test? I'm asking here because everyone has an answer, but the answers are different; I figure I'll treat the 2carpros answer as definitive.

Background: My 1995 Saturn SL2, with about 125,000 miles, runs well and has received recommended service. Oil is fresh and the spark plugs have less than 5,000 miles. Driving is mixed. Sometimes on the freeway; sometimes in town. Historically, now that I think about it, the previous HC tests have been on the high side, but have always passed.

I figure some combination of the following:

1) Techron gas treatment or the like? That's what I hear most often, although some people have their other favorite fuel additives.

2) The smog inspection guy said to fill it with high-octane gas for the re-test, although others say to stick with regular; that high-octane would burn more slowly and thus might worsen the incomplete combustion and raise the HC measurement. Some people advocate filling up with a high-ethanol fuel or something else exotic (even if that were a good idea, I'm not sure where I'd get it in Southern California).

3) I see your Smog page suggests: "Drive at least 30 minutes before arriving at the Smog Check test facility to ensure the car or truck has reached full operating temperature." I didn't do that the first time (I drove enough to warm the engine, but less than 30 minutes); I'll be sure to get 30 minutes for the re-test. You also note: "The week of the Smog Check test, take the vehicle out for an extended drive"; it had been on the freeway in the recent era, but not immediately prior to the test.

So there it is: What's the best bet? Gas treatment? Gas grade? Or something else?

As a bonus question, are these relatively high HC numbers reasonable, or should I eventually take it to the shop and ask if they've got any bright ideas to improve combustion?
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Sunday, September 6th, 2009 AT 1:09 AM

9 Replies

Tiny
MERLIN2021
  • EXPERT
Here's the scoop on HC's


http://www.2carpros.com/forum/automotive_pictures/62217_HC_1.jpg



http://www.2carpros.com/forum/automotive_pictures/62217_HCa_1.jpg



http://www.2carpros.com/forum/automotive_pictures/62217_HCb_1.jpg

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Sunday, September 6th, 2009 AT 8:22 AM
Tiny
TALKINHORSE
  • MEMBER
The general information about excess HC is interesting, but it doesn't answer my question, which was about what quick practical step I might take to nudge the HC down by 1 PPM to pass the test. In particular, is a Techron (or other) gas treatment likely to be helpful, or is there a recommended octane or variety of gas that will improve combustion slightly? (I acknowledged your general advice on your smog page to do some hard driving and bring in the car for the test after at least half an hour on the road.)
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Sunday, September 6th, 2009 AT 3:04 PM
Tiny
MERLIN2021
  • EXPERT
OK let me ask yopu, what does your owners manual say about octane? Some 4 cylinder engines are high compression and require premium fuel. On newr cars it actuallt has a sticker in the fuel door stating what octane. Use a quality gas no matter what the rating is. I dont mean higher, I mean MOBIL, SHELL, EXXON, vs. Unbranded fuel. Burn several tanks of quality fuel then take the test. As stated injector may be partially clogge, especially trua if unbranede gas is constantly used. Vacuum leaks and any LEAN burn conditions are the concern! If the motor is tight (no oil burnibg) then the two important sensors here are the MAF(controls injector pulse width) and ECT(acts as a choke) for SEFI engines, Either can be slightly out of range, and not set a trouble code(DTC) or turn on the MIL. Of course this all is with a good running engine, good fuel pressure, no oil burning!
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Sunday, September 6th, 2009 AT 9:24 PM
Tiny
TALKINHORSE
  • MEMBER
Manufacturer specifies regular 87 fuel, which is what I've always used. Bought it it new in 1994. Been feeding it brand-name fuels. Exxon, Chevron, Union76. Not burning oil. It's been maintained and runs smooth. Spark plugs replaced 5000 miles ago. In sum, if it's malfunctioning, it's an internal thing that doesn't manifest in any overt symptom.

I guess I'll be taking the test results by the shop and see what they think. But, as I say, for the moment I was hoping I might squeak by with a passing test score if I nurtured the car properly. Then I'd worry about whether there was a problem later.
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Monday, September 7th, 2009 AT 1:53 AM
Tiny
MERLIN2021
  • EXPERT
How often do you do oil changes? And how much burns between changes?
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Tuesday, September 8th, 2009 AT 6:30 AM
Tiny
TALKINHORSE
  • MEMBER
Lately driving has been very light, so I changed the oil after 6 months (which was only a couple thousand miles). If it burned oil, it wasn't enough for me to notice it being low. But it's possible that, with low mileage, I wouldn't have noticed.
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Wednesday, September 9th, 2009 AT 2:00 AM
Tiny
MERLIN2021
  • EXPERT
Is it a clean oil? Or does it seem a bit black for the low mileage? Oil burning is one of the causes of your problem, maybe on the next oil change put in a heavier oil, like sae 30 non detergent, then see if it will pass.
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Wednesday, September 9th, 2009 AT 2:53 AM
Tiny
PLUS2COM
  • MEMBER
Try going a Step above premium to what is called by BP Premium Clear 91 non oxygenated, or non ethonal. Cars were not designed to run the ethonal products especally at a older age ( its typically label with something that says for use in collector, vehicles eligible to be collectors or in small engines only. Your car being a 95 is close enough to be needing a higher octane rating like this. Also the non ethonal will be easier on the motor granted the fuel is traditionally 20-40 cents more per gallon, but it works

also what oil are you putting in the vehicle?
When you replaced the plugs did you replace the wires as well? Have you ever thought to check your coils?

As a side note name brand gasolines dont really mean much it all comes down to the quart of detergent that is mixed in with the tanker before it leaves the refinery
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Friday, October 16th, 2009 AT 7:52 PM
Tiny
MERLIN2021
  • EXPERT
Could be the Feds should re caclculate the pass/fail numbers if ethanol would have that effect, but it's worth a shot! MBTE's where removed, and replaced by alcohol.
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Friday, October 16th, 2009 AT 8:03 PM

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