Failed smog but this is confusing...

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nthach

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I took my car in for a smog check this past weekend and I failed the 15MPH test. HC was high. NOx and CO are fine. The spark plugs are clean - the old ones had light gray deposits on them. This points to a misfire but the car seems to run fine albeit it's been using a little more gas than usual when I do drive it. I also checked the O2 sensors and while the CEL isn't being thrown, the readings never went above .5V, it stayed between .2-.4V. I'm thinking my O2 sensors are lazy, but also I recall driving back home when suddenly I lost power due to a failed coil wire - I was running on 4 cylinders and dumping raw fuel into the cats for 5 miles. Could the cats be shot, but if they were wouldn't all the HC/CO/NOx readings be off the charts?

https://drive.google.com/file/d/0B_wxerr_NAqBMkJuMVVvX3A5R0U/edit?usp=sharing
 
Sound like the cats may be cooked.
Siamese Pad Thai
smile.gif
 
Was the car good and warmed up or did you leave home, drive a mile or two to the test center, and then have it tested? The cats need to be nice and hot to function optimally, so maybe you just need to take it for a good 10-15 mile freeway drive before having it re-tested. Similar for the O2 sensors. Since this is an OBDI vehicle, I'm guessing they are two wire non-heated O2 sensors that are only warmed up by the exhaust gases.
 
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Your car is running rich, even your 25mph HC is on the border to failure. Your O2 is fine as your NOX is very very low, it would have been high NOX as well if your O2 is bad.

I'd check your coil (did it shorted out? what's the resistance compare to spec at the same temperature?), your plugs (did you tighten them?), your wires (did they look cracked?), your distributor cap and rotor, your air filter (is it clogged?), before you decided to pay for a new cat.
 
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Originally Posted By: PandaBear
Your car is running rich, even your 25mph HC is on the border to failure. Your O2 is fine as your NOX is very very low, it would have been high NOX as well if your O2 is bad.

I'd check your coil (did it shorted out? what's the resistance compare to spec at the same temperature?), your plugs (did you tighten them?), your wires (did they look cracked?), your distributor cap and rotor, your air filter (is it clogged?), before you decided to pay for a new cat.

Did you put fresh oil and filter?
 
Originally Posted By: PandaBear
Your car is running rich, even your 25mph HC is on the border to failure. Your O2 is fine as your NOX is very very low, it would have been high NOX as well if your O2 is bad.

I'd check your coil (did it shorted out? what's the resistance compare to spec at the same temperature?), your plugs (did you tighten them?), your wires (did they look cracked?), your distributor cap and rotor, your air filter (is it clogged?), before you decided to pay for a new cat.

New NGK wires were installed after the previous wire set failed going 70MPH down 80 and running on 4 cylinders for 5-6 miles back home. I replaced one coil a few weeks ago as PM, just installed 8 new Denso platinums and they looked clean when I pulled them a few days ago(but there was anti-seize on the threads as well, I don't think that will cause HC to spike). Cap and rotor look clean, the contacts look good and there's no carbon tracks.

Oil was changed too, I used Valvoline MaxLife 5-30 with an FL400S filter. My car still uses xxW-30 oil for its age.
 
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Thought 1991 cars, incl. Cali cars are all OBD-I type (no wideband O2 sensors)?

Also: did your engine warm up quickly and holds its temp while cruising down the highway? Sometimes, high HC may be linked to open-loop operation due to failed/faulty thermostat.

Another possibility is that the cold-start injector has a minor leak but that should be minute enough for the CAT to ingest the HC and keep it low...

any oil burning issues?

Q.
 
Originally Posted By: nthach
New NGK wires were installed after the previous wire set failed going 70MPH down 80 and running on 4 cylinders for 5-6 miles back home. I replaced one coil a few weeks ago as PM, just installed 8 new Denso platinums and they looked clean when I pulled them a few days ago(but there was anti-seize on the threads as well, I don't think that will cause HC to spike). Cap and rotor look clean, the contacts look good and there's no carbon tracks.

Oil was changed too, I used Valvoline MaxLife 5-30 with an FL400S filter. My car still uses xxW-30 oil for its age.


After replacing those parts, did you disconnect the battery to reset any ECU adjustment to compensate the broken wires?

Why replace only 1 coil for preventive maintenance and not all? What happened to it originally?
 
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At 280K miles, if that's the original engine, it could be a lot of things.

How many miles on the O2 sensors?
Did you check for vacuum leaks? When was the last time you cleaned the MAF sensor?

Having said all of that, the internet is suggesting that maybe the timing belt has slipped, some other ignition problem, a vacuum leak, a bad cat, or low compression:

http://www.smogtips.com/failed-high-hydrocarbons-HC.cfm
http://www.ehow.com/facts_5474759_causes-high-hc.html

Quite frankly, if you haven't fixed any vacuum leaks yet on this car yet, expect to find more than one.
 
Originally Posted By: PandaBear
Originally Posted By: nthach
New NGK wires were installed after the previous wire set failed going 70MPH down 80 and running on 4 cylinders for 5-6 miles back home. I replaced one coil a few weeks ago as PM, just installed 8 new Denso platinums and they looked clean when I pulled them a few days ago(but there was anti-seize on the threads as well, I don't think that will cause HC to spike). Cap and rotor look clean, the contacts look good and there's no carbon tracks.

Oil was changed too, I used Valvoline MaxLife 5-30 with an FL400S filter. My car still uses xxW-30 oil for its age.


After replacing those parts, did you disconnect the battery to reset any ECU adjustment to compensate the broken wires?

Why replace only 1 coil for preventive maintenance and not all? What happened to it originally?

The battery was replaced 2 months ago. The wire failed way before then. I replaced 1 of them since it was the one that had the failed wire. I might replace the other one.
 
Originally Posted By: zzyzzx
At 280K miles, if that's the original engine, it could be a lot of things.

How many miles on the O2 sensors?
Did you check for vacuum leaks? When was the last time you cleaned the MAF sensor?

Having said all of that, the internet is suggesting that maybe the timing belt has slipped, some other ignition problem, a vacuum leak, a bad cat, or low compression:

http://www.smogtips.com/failed-high-hydrocarbons-HC.cfm
http://www.ehow.com/facts_5474759_causes-high-hc.html

Quite frankly, if you haven't fixed any vacuum leaks yet on this car yet, expect to find more than one.


No vacuum leaks - although I did not check the injector seals, I sprayed all the vacuum lines with carb cleaner to check.
 
Originally Posted By: PandaBear
Your car is running rich, even your 25mph HC is on the border to failure. Your O2 is fine as your NOX is very very low, it would have been high NOX as well if your O2 is bad.

I'd check your coil (did it shorted out? what's the resistance compare to spec at the same temperature?), your plugs (did you tighten them?), your wires (did they look cracked?), your distributor cap and rotor, your air filter (is it clogged?), before you decided to pay for a new cat.


I agree that the car is running rich, however I wouldn't say that the O2 is okay without testing. If it is reporting .2-.4 volts, then it is indicating lean to the computer, which in turn could be richening the mixture to compensate. O/P, check your fuel trims, I bet they show positives. You can try to force the O2 rich and see if it responds...
 
Too bad you guys don't get your dilution values, you can immediately tell what's going on fuel trim wise with a dilution value.

Otherwise assuming fuel trim is correct or even reasonable, this could be an excessively retarded timing issue- over-sensitized KS? Knock detected on the drive there? False knock triggers?
Also cat efficiency. Check 'em
 
Originally Posted By: jrustles
Too bad you guys don't get your dilution values, you can immediately tell what's going on fuel trim wise with a dilution value.

Otherwise assuming fuel trim is correct or even reasonable, this could be an excessively retarded timing issue- over-sensitized KS? Knock detected on the drive there? False knock triggers?
Also cat efficiency. Check 'em


timing is fixed on this car - Toyota says if it is off, replace the ECM. And I've been reading up on capacitor failure.

The smog shop said bring it on by and he'll do some diagnostic work - his hourly rate is $90. I'm trying to do as much as I can but I'm willing to pay the diag fee to see what the BAR-97 analyzer says in test mode.
 
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Originally Posted By: nthach
No vacuum leaks - although I did not check the injector seals, I sprayed all the vacuum lines with carb cleaner to check.


I use a Mityvac to check for vacuum leaks. It's not just the lines that can leak (BTW, EFE lines have gas vapor in them and seem way more prone to degredation). Devices that consume vacuum can leak vacuum and often do, and unless you test them with a Mityvac you will not find them.
 
My Infiniti had almost the same smog results. two tests ago,
I used a can of guaranteed pass and was right at the limit
- my 99 measured 54 for HC after initially failing.
last time I ran several cans of various fuel system cleaners
and dropped the HC to 14 or so. my car is about to hit 200K
miles.
 
Originally Posted By: nthach
Originally Posted By: jrustles
Too bad you guys don't get your dilution values, you can immediately tell what's going on fuel trim wise with a dilution value.

Otherwise assuming fuel trim is correct or even reasonable, this could be an excessively retarded timing issue- over-sensitized KS? Knock detected on the drive there? False knock triggers?
Also cat efficiency. Check 'em


timing is fixed on this car - Toyota says if it is off, replace the ECM. And I've been reading up on capacitor failure.

The smog shop said bring it on by and he'll do some diagnostic work - his hourly rate is $90. I'm trying to do as much as I can but I'm willing to pay the diag fee to see what the BAR-97 analyzer says in test mode.


Yes, it's not user adjustable, the computer has complete control over the timing. What I mean though is that maybe the computer is hearing knock via the knock sensor, which it uses to adjust timing thresholds. It could be that there is knocking and the timing is being pulled back, or that there is false triggers being picked up (perfectly common at that age) and the computer freaks out and pulls timing. Especially at low RPMs where th test is taking place, that will be the first area of RPM for timing to be pulled.

Something to check for
 
Originally Posted By: jrustles
Originally Posted By: nthach
Originally Posted By: jrustles
Too bad you guys don't get your dilution values, you can immediately tell what's going on fuel trim wise with a dilution value.

Otherwise assuming fuel trim is correct or even reasonable, this could be an excessively retarded timing issue- over-sensitized KS? Knock detected on the drive there? False knock triggers?
Also cat efficiency. Check 'em


timing is fixed on this car - Toyota says if it is off, replace the ECM. And I've been reading up on capacitor failure.

The smog shop said bring it on by and he'll do some diagnostic work - his hourly rate is $90. I'm trying to do as much as I can but I'm willing to pay the diag fee to see what the BAR-97 analyzer says in test mode.


Yes, it's not user adjustable, the computer has complete control over the timing. What I mean though is that maybe the computer is hearing knock via the knock sensor, which it uses to adjust timing thresholds. It could be that there is knocking and the timing is being pulled back, or that there is false triggers being picked up (perfectly common at that age) and the computer freaks out and pulls timing. Especially at low RPMs where th test is taking place, that will be the first area of RPM for timing to be pulled.

Something to check for

And the knock sensors are in the V-bank, which also requires the intake to be pulled. I might be able to check them out at the ECM connector.
 
Try watching your timing with a light.

Start up, fix your timing light up, and have someone bring the revs up and down unloaded, see if the computer does anything with the timing while listening for knock. Then put the car in gear and lightly load it (preferably reverse) while you look at the timing again and note any movement/listen for knock.

It's best if you put high octane in, so that you can be more assured that any timing pulled would be erroneous, on top of not hearing any. Good luck
 
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