98 Corolla failed CA smog due to high NO

[LiLRiceBoi]

Hi,

My 98 failed CA smog yesterday due to high NO at 15 mpg. I drove for 20 minutes, mostly on the freeway, before getting to the test station. However, there were 3 people ahead of me, so my car sat for 25-30 min before being tested. It was started and idled for 2-3 minutes before the test began. I recently got an oil change less than 300 miles ago.

The car otherwise seems to be running fine. I dont want to spend a lot of money to fix it because the car isnt worth very much and I'll likely be getting another vehicle soon. 185k on the odometer.

I have not taken the car to a mechanic yet. Will an italian tune up help here? Any cheap maintenance I can perform to get it to pass?

Results

Thanks

 

[Jimzz]

With that many miles I would clean/replace the PCV valve, spray out the throttle body and PCV line with carb cleaner, and check for vacuum leaks.

You are not way out of spec so simple things like I suggested might be enough to get it below the limits.
After that I would clean the EGR valve and lines if it still failed.

 

[phucheneh]

I don't think he has EGR. Late 90's to early 2000's is when a lot of manufacturers started trying to meet standards without it. It's a largely obsolete thing on Japanese cars.

Low NOx emissions simply had to do with the design of the engine. Tweaking of valve timing and whatnot to hit the lowest levels possible. Tune-up stuff like mentioned will probably be enough to get it passing. It's all cheap and easy on that car...put some plugs in it, change the oil. PCV valve is a good idea. I think it's still got a distributor, so cap and rotor, too. Be careful of the dist cap gasket; people like to lose that little o-ring, and you can get misfires when it's wet outside without it.

Throttle cleaning prob wouldn't do much since they're testing at higher RPM (is this a dyno test?). A small vac leak is possible but would probably set a CEL.

 

[LiLRiceBoi]

This car doesnt have a distributor.

This is a dyno test.

High NOx means it's burning lean right? Would changing the spark plugs help lower NOx?

 

[phucheneh]

It can mean lean, yeah. HC is unburned fuel (usually indicative of a rich condition) and CO is usually the result of a rich condition and/or just incomplete combustion.

But (I know I make this point a lot) excessively lean, to the point of the ECM saying 'I am adding fuel to try and reach stoich but just can't seem to do it' sets DTC for long term fuel trim.

'Clean MAF' should've made it into my above post. That's a big one. Again, often results in a fuel trim code. But it's worth cleaning since it's quick and only costs you the five bucks or so for a can of cleaner.

It's hard to make a concrete link to plugs or other ignition parts, but passing the sniffer test is usually a lot less frustrating when you first make sure the simple cheap stuff is all up to snuff. It's worth changing the plugs if you are unsure of their condition. And I'm pretty sure you do have a distributor...it would be on the driver's side of the engine, sticking out the end of the cylinder head.

Also of note, you have a catalyst that is intended for both oxidation of CO and HC, and reduction of NOx. If I remember my car-chemistry right, different substances in the cat are responsible for making these reactions happen. So normal HC and CO, but high NOx, can still be the result of a worn cat and may not cause a 'catalyst efficiency' code. You're so close to passing that I would definitely not recommend cat replacement, though...it's just something to think about that could be a root cause of high NOx. Getting the engine into the best running order that you can should result in a pass, and you may never need to replace the cat...but one that is underperforming will always be a bit of a thorn in your side when it comes to passing smog.

 

[LiLRiceBoi]

I dont think this year has a MAF. It has a MAP near the throttle body.

 

[Mark R]

Normally, I would expect a true lean condition to give unusually low CO and HC, whereas yours are up a bit.

Possibilities are a borderline cat, or a mixed lean-rich condition (e.g. one clogged injector, or injectors with bad spray pattern giving lean and rich combustion in the same cylinder), borderline spark plugs (causing poor combustion), crud buildup on valves, etc.

An Italian tune up can sometimes help with a borderline cat. Sometimes, there can be a little bit of surface contamination, and if you can get it hot enough, you can evaporate it off. Most contaminants (zinc from engine oil, etc.), however, won't evaporate off at temperatures below cat meltdown, so this method is marginal at best.

That said, a can or two of injector cleaner in the tank, and a good thrashing down the highway at 4.5k rpm for a few miles, is a cheap and easy thing, and might just get you enough margin to pass, once any mechanical or sensor issues have been addressed.

 

[exdeath]

NOx = high combustion temps, normally regulated by EGR.

 

[LiLRiceBoi]

This car does not have an EGR.

 

[Jimzz]

This car does not have an EGR.

Some early 98's did have an EGR. 97 was the last year EGR was standard but many of the 98's were still made in 97 and had some left overs from the 97 model.

So a TRUE 98 model should not have a EGR but an early 98 model might.