Emissions

[BiXLL]

I have a 93 KA24DE in my 240sx. It runs smooth, no shaking or missing. I am getting 25 to 27 mpg city driving. I stay on top of the maint., air filter is new, oil was just changed. I went to have my State inspections done yesterday and was floored when they told me it failed emissions.

On the CO, I am allowed 1% and I showed a reading of 5.13%.
On HC (hydrocarbon) I am allowed 130 ppm and showed 320 ppm.

I have no engine lights on, spark plugs are year old platinum tipped. I am absolutly stuumped. I would think that for the readings to be that far off the car would have to be barely running?

I have put a can of Seafoam fuel system cleaner in the tank and am running it through, but I really don't expect it to change anything. Any ideas/suggestions????

[Infinitiguy19]

Seafoam is useless for everything except waisting money. Use Redline S1 fuel system cleaner.

Sorry I can't help more.

[rioredstang]

You need to check your ignition timing and set to spec. Also check idle speed make sure it is correct. I would idle it up to the max allowed idle speed for your state. Make sure engine is nice and hot when they check it. I don't know how many miles are on it, but the cat could be going bad.

[BiXLL]

I am starting to think it may be the cat. Timing is good, car has 143,000 miles. Car was only driven about 1 1/2 miles to the inspection station the day they did the test, perhaps not warmed up enough?

[rioredstang]

I don't think it was warmed completely. I normally crank and idle till operating temp is reached. Then drive about 4-5 minutes. At the station I will idle up to about 1200-1500 rpm till I pull into the lane. This keeps the cat warm and clean.

[BiXLL]

Well, I ran half a can of carb cleaner through the vacuum hose to the air box thing where the idle adjustment is, changed plugs, and ran a can of Seafoam though the gas tank. My air filter is new and the oil was just changed. I just got back from the inspection station and not only did it not pass, the numbers were worse!

It is idling as smooth as silk, has no misses, runs great! No codes have been thrown, but the exhaust does have a strange smell to it. Not the rotten egg smell, but strange. I am at a loss once again, as if either the O2 sensors were bad or cat bad it show throw a check engine code????? I don't know where to go from here!

I just do not know where to go or what to change from here to get it to pass. I hate to go and change the cat or O2 sensors only to get the same results, which I have a feeling I would get because of no codes thrown for those items being bad.

Any ideas guys?

[SteveTheTech]

You most likely will not get a code...being a pre OBDII car your cars lacks logic and is simple rationality based dtcs. Which for the day is pretty advanced.

Since your retest numbers were worse your cat might be toast. Partially burning more chemicals (Seafoam, Carb Clean) might have actually taken it out. If you have a multimeter nearby check the O2 sensor cycling rate while holding the rpms steady at 2k for 30 seconds. The post catalyst number should be fairly steady. If it is cycling frequently the oxygen retention capabilities of the catalyst are no longer sufficient.

You also might want to check the fuel pressure regulator. (Too much fuel not being burned=high HCs)
If you already have a fuel pressure gauge it would be a perfect time to bust that out.

[BiXLL]

I am sorry, I forgot to get back to this thread. I replaced the 02 sensor and the car breezed right through the test with great numbers!

[SteveTheTech]

That's great news. props