Help on emissions and catalytic convertors!
 

I am having problems passing the emissions test over here.. My results are consistent even after changin the PCV valve, plugs and O2 sensors. Gas mileage is great, no engine codes (it is even above rated MPG for the car) and everything seems fine so I don't suspect the EGR system.

I suspect it is the catalytic convertors and other people think so too.

My readings are:

Limit Reading
HC ppm 68 154 FAIL
CO% 0.38 0.37 PASS
NO ppm 501 1092 FAIL

Does anyone also think it is the cats? If so, are the precats important in these cars? I know in some cars they play a miniscule role. Can I get away with just changing the main cat? Also are the cats just bolted in or are the welded as well?

I think the figures you show are a bit off, not many cars from '94 will blow a 68 HC. Our limits are easier here - 220 HC, 120 CO. Most decent running cars with some miles will aveage around 110-150 HC, exceptional cars will idle at 50-55 HC and around .2 CO, with a few even lower.

Anyway, HC is raw fuel (or oil, etc. in case you have a little oil burning going on) CO is poorly burnt fuel. NOx usually stem from high combustion temperatures. We don't normally deal with NOx or O2 here so I don't pay much attention to it. Usually it falls in line if the HC and CO are good and the EGR is working properly.

You failed to mention if these are idle figures or cruise figures, that will make a difference. If @ idle, look for a vacuum leak, it can cause a lean misfire which in turns raises the HC. It can also cause an elevated NOx reading. I found a leak at a very small check valve under the manifold, just behind the right side of the alternator. You might also try disconnecting or pinching off the PCV hose to see if the HC drops. You might also loosen the oil fill cap while it's running and see if there seems to be excessive case pressure.

You're not very far off from passing, it's probably something simple. I rarely see cats go bad and causing a fail problem - maybe one or two/year at the most. Most cat failures are meltdowns, not failure to 'light up'.

Hi, thanks for replying. The limits for the SVX is unfair IMO, all the other cars I've had before have much more reasonable limits I don't know why the limits are so low.

The readings are from a running speed test (40km/h), my idle results are OK, they just barely pass.

I'm not sure what to do anymore.. I wanted to do the emissions diagnostics at the shop but their computer won't interface with the SVX, then I wanted to have to cats checked out (the drill 2 hole procedure) but they said they couldn't can't check the precats because its too close to the manifold (or something to that effect). I've can't get the car registered until the car passes emissions, and its been 2 months, it sucks bad..

The car doesn'ts seem to burn oil, and as I said gas consumption is fine. If all the readings are bad as I described, isn't this typical of cats gone bad? I was thinking of putting a cat on and hoping that in the chance that it wasn't the cat, being new it would clean up the emissions. I'm not too sure where to check for vaccuum leaks, do I just listen for leaks?

Thanks!

edit: just one thing, do you know if the cats are just bolted in or welded and bolted down?

Silly question. Are they aware the car is a 1994 MY? I wonder if running a bottle of injector cleaner thru it would help. I'll leave the technical stuff to Beav. :p

they have that snakeoil in a bottle called "Guaranteed to Pass!" at your local auto parts store. maybe it works?

If it passed idle and is failing cruise for HC I'd double check the PCV system. Like I said earlier, try removing the oil cap while the engine is idling and see if there's a flow of air coming out. A light pulsing is normal. Gas engines run dirtier at idle than cruise, I'd be hard pressed to believe the cat is bad. Not to say it can't be bad, but it doesn't make logic at this point in time.

If you failed NOx at cruise I'd be taking a close look at the EGR system. Try moving a vacuum hose over to it while it's idling, it should die when vacuum is applied at idle. If it doesn't die you have a plugged EGR port or a defective EGR valve. If it does die you may have a problem with the solenoid that applies vacuum to the valve or maybe something as benign as a disconnected/broken/leaking vac hose going to it.

It would be much simpler for you if you had access to a four-gas analyzer. Just remember that sometimes it's better to take it to a good shop and have it fixed than it is to take the 'shotgun' approach and throw lots of unecessary (and expensive) parts at the problem. Good Luck!


p.s. You did drive the car 15-30 minutes before taking in for testing, didn't you? A lot of people fail for that reason alone.

Beav has a good point about driving it before you go for the test, also change the oil before you go. I have a 92 Tercel and when I had it tested after replacing the engine it failed (Canadian Tire) then took it for a drive and took it to another private facility and passed no problems. I did nothing to the car between tests. Make sure they have the fan mechanism on to simulate cruising speed. As per the tech at the second facility he felt they had not properly tested the vehicle at Canadian Tire. If you have been going to the same place maybe try somewhere else. Also what is the ruling on only having to put out X amount of $$$ before automatically passing (I am not sure if this applies to new owners). I would check this out as it seems you have put some $$$ into repairs already.

Good Luck,

Keith

Thanks for the help guys.. I got a service centre to finally do a 4-gas/emission test on the car. Everything checks out except the cats. Apparantly the cats have been hollowed out (performance reasons I suppose) there is no difference in readings before and after the cats.

So I guess I need cats.. Anyone have any for sale? :(