Well, my '94 945 has failed emissions.
High NOx reading (about 35% over MAX).

I ran a bottle of Techron through w/premium gas and did a minor tune-up (cap, rotor & plugs, it was due).

Upon re-inspection, the NOx readings were somewhat higher than before. Differences between inspections were; the tune-up, premium gas, longer engine/CAT warm-up period & higher ambient temp.

Engine is running fine otherwise, smooth & strong.

I'm figuring it is time for a new CAT. Any dissenters? Am I missing something obvious?
--
1999 E320 1994 F150 1989 560 SL 1986 560 SL (deceased) 1988 300 TE (departed) 1994 945T (daughter's) 1988 244DL (fallow) 1986 242Ti (fallow) 1968 GT500KR (under restoration)

I'm liking the cat idea, but also, higher ambient is a factor, as is carbon buildup. Maybe do a water torture, then take it in on a cooler day. And leave the heater on with the fan running.
I saw a car at the JY that had something like a 71 thermostat and have wondered if that could make a difference also, that is putting one in for the test.

For every degree increase in engine temperature, the HC emissions decrease around 1 - 2%

Check out this info from the EPA on the ambient temperature vs. Hydrocarbon emissions. Most interesting is the final analysis at the end of the report.

http://www.epa.gov/oms/regs/toxics/420d06001.pdf

Hmm; yes, so there's the HC down, NOx up nexus; as one goes down the other up, and finding the point/area of best of both is what the cat is for, I suppose.

Jerry,


Actually, the NOxs are caused by high combustion temperatures. You can burn cleanly without burning leanly. As M said, advanced timing and higher compression engines generate higher exhaust temperatures.

Switching to a fuel with higher latent heat, and / or adding water to the combustion mixture would probably almost eliminate the NOx production.


Goatman

You may try CRC Mass Air Flow Sensor Cleaner to make your sensor more sensitive. In other words, it sends a signal to computer to inject the correct amount of fuel. Before cleaning, your sensor detects less amount of air than the actual air due to the dirt on the sensor. That is why your engine is burning lean.

After cleaning, you will feel a little more power. Give it try and it won't hurt (Note: Be sure to follow the instruction). You only pay around $7 dollars.

http://www.youtube.com/watch?v=vPT8rL0noYg

Hello,


It is likely running lean. You should check that there are no intake air leaks, like from a broken intake manifold gasket, or old hoses.


Goatman

I should have mentioned my A/F gauge looks to be displaying normal but point taken, I'll poke around the intake plumbing.
--
1999 E320 1994 F150 1989 560 SL 1986 560 SL (deceased) 1988 300 TE (departed) 1994 945T (daughter's) 1988 244DL (fallow) 1986 242Ti (fallow) 1968 GT500KR (under restoration)

On second thought, my HC's are not elevated so an intake leak is not a primary suspect. I'll spend some time and effort looking at exhaust connections. I do know there has been a crack promulgating in the back of the exhaust manifold. Maybe that has grown to the point air is infiltrating.
--
1999 E320 1994 F150 1989 560 SL 1986 560 SL (deceased) 1988 300 TE (departed) 1994 945T (daughter's) 1988 244DL (fallow) 1986 242Ti (fallow) 1968 GT500KR (under restoration)

I found one of those laser temp readers, the ones you can point and get a temp reading to be very helpful in a situation like this. I found the Cat was pretty much the same temp as the rest of the exhaust. I changed the cat and the car passed. Not saying that's your problem but the gauge is cheep at harbor freight.

Hey,


That argument is inconsistent! Just because you have no elevated hydrocarbon reading, does not mean that the mixture is not lean!

I expect you to provide evidence that it will; after asking for my help and then telling me I'm wrong.


Goatman

I just did a little googling and it appears you are likely correct in your intake leak/lean theory. Here tis:,
"NOx emissions are the result of high combustion chamber temps pure and simple. NOx readings go up whenever there are hot spots that exceed about 2400 degrees. Things like high compression and lean mixtures contribute to high chamber temps, as does over-advanced ignition timing."

That being said I dont think he was deserving of the "tude" you took with him.
Peeps are allowed to disregard your advice(without chastisement), even if you are correct. IMHO
Matt

Matt,


Thanks. I was just wondering if the OP had a different theory. In my opinion, people have the right to believe whatever they want. It is when someone else might be hurt by the incorrect technical arguments I become defensive. If someone were to passively or even actively use the faulty statement, "This can't be a lean condition, because the hydrocarbons are low" and be misdirected or even hurt, then I feel responsible for not challenging the argument.

Who knows, the poster might have a perfectly valid theory for his argument. But the facts are, he didn't offer one, and nether did I.

I also have a bad tendency to use Ad Hominem. It's something I need to work on.


Goatman

Everyone needs to take a deep breath.

Goat,

1) I did not rule out an intake leak, just said it was not a "primary suspect".
2) I did offer an alternative suspect in possible exhaust leaks & earlier, the CAT.
3) "This can't be a lean condition, because the hydrocarbons are low" is YOUR quote, not mine.

I stand by my posts. I've been posting here a long time, have owned 5 red blocks, have taught auto mechanics in a NY State BOCES, some of my diagnostics have made it into Steve's FAQ's, I've been turning wrenches a LONG time.

I value the combined knowledge lurking on this forum which is why I continue to return. I steer clear of other unnamed forums due to the incessant backbiting on them. I would hope this one will remain an open source of informative sharing while avoiding thin-skinned responses.
--
1999 E320 1994 F150 1989 560 SL 1986 560 SL (deceased) 1988 300 TE (departed) 1994 945T (daughter's) 1988 244DL (fallow) 1986 242Ti (fallow) 1968 GT500KR (under restoration)