rolf morrow

just failed california smog,15 mph fail,25 mph passed.

NO (ppm) reading at 15 mph on a dyno read 2299,at 25 mph read 944

HC " 15 mph read 179,at 25 mph read 46

CO " 15 mph read .87, at 25 mph read .37

why such different readings at minimal speed increase?
bad cat?
bad o2 sensor?
i rarely drive 15 mph,so whats the big deal?
i know this common thread,but any help appreciated.

thanks,
rolf morrow
1986 951

docwyte

Move to Colorado, where you can pass emmissions without a cat.

rolf morrow

well that was a waste of time,
sometimes you get tech help,sometimes people from colorado.
thanks.
rolf morrow

Kelly Chiu

Likely your car hasn't warmed up fully yet so the effectiveness of the cat isn't optimized. You should do a pre-test after a long highway run to heat everything up. I would also ask them to use a fan to cool the radiator while on the dyno, this lowered my NOx emissions enough to pass last time around.

Legoland951

I agree with the above post. Make sure they warm up the cat first.

docwyte

hehehe. Drive the living $hit out of the car for a good 30 minutes before brining it to the smog place. Keep the motor running if there's a line.

Legoland951

30 minutes is unnecessary. Rev the engine up to 2500 rpm for 60 seconds immediately before the test will be more than sufficient. You may be surprised that 60 seconds of high revs can make your headers glow.

docwyte

60 seconds isn't near enough to light off the cat, particularly if you haven't done much of a drive to get to the smog station.

michaelathome

Going through the same thing here in VA. My car's NO was at 2200 as well. After some reading high NO can be a sign of lean condition. Check your O2 sensor and make sure that it is plugged in and working properly. Also check your plugs as a lean condition may be visible as white plugs vs dark when running rich. You may also look at the fuel pressure at the rail and fuel filters to make sure that they are not clogged.

Good luck!

Michael

rolf morrow

thanks for help.
i did drive for about 20 miles,at some speeds between 60-90+,
before test,to make sure nice and hot.
just ordered new o2 sensor from paragon.
i will check plugs,cat is only 2 years old.

i am having a diagnostic done,since it was flagged as a GROSS POLLUTER,
by the state of california. if they find something interesting will post.
anybody living in CA.,knows that they will try and retire your car for failing badly.
are the other states,Except Colorado as strict ?
can you buy universal fit catalytic converters for 951?
thanks again,

rolf morrow

1986 951(never will let them retire it)
1983 944

docwyte

Don't think they made a bolt in universal cat, you're going to have cut and weld probably. High NOx readings are usually O2 and cat, so you're on the right track.

MA and NY use very similar programs to CA, but I don't think they have the gross polluter bit.

Legoland951

I guess the California smog standard cat warm up time all the smog stations are supposed to abide by is not enough for your car. I don't know what to say...

Yes we do have the gross polluter designation too.

nickg

your car is most likely running a bit lean. high nox readings are because of high temps, otherwise you would be off all the time if the cat was bad, i would suspect that you have vacumm leaks on the car. when you move off idle it still is hot and lean and it takes a bit to transfer to a more complete combustion from the lean condition as the computer richens the mixture with throttle. this would explain your problem, as an overly lean idle will cause these types of emmission problems.

Porsche-O-Phile

Tell the tech to run it in a lower gear so the RPMs are higher as well. Sometimes that helps.