After narrowly passing on HC a couple years ago (sharky was too cold), I went in for my Bi-annual smog test today.....I was a little worried...so I take sharky for a slight Italian tune up prior to the test....a couple runs to redline, 10 minutes on the freeway in 3rd gear..etc...

Get to the test place and it passes no problem.....but still a smidge more HC than I would like..... Max at 15mph is 110, last time I got 107...this time I got 79..but the average is 31?? 25mph was better with 85 max, 43 last time, 37 this time with an average of 20? NO was very low at 36 (15mph) and 63 (25mph) with a max of well over 700 on both...so clearly I am not running lean!!!

So it appears to me that my cats are working properly...the engine is NOT running lean & might be slightly rich.... Not enough to fail, but maybe a factor in my slightly lower mileage?

But since it passed and runs well...who cares right!!

 

Hi Brian,
I assume your running with all the stock smog fittings??? I have been curious how some are faring without their pumps.

 

Well you did better then I did. I passed the HC (18/16), CO (.02/.01) for both 15
and 25 mph, and the NO for the 15 mph (761!) and FAILED the NO for 25 (926!!!).
So either my cat is bad, or I'm running too lean... I guess I'll try installing another
cat (mines the original one).

 

Brian:

You might be running just a bit rich. MAF might be slightly out of spec. Man, that NOX is low! Mine was in the 400s last time, but my HCs are low normal, like George's. Guessing old cats. We should have good set for George by this weekend.

 

Pumps are for warm-up only. The output is diverted to the air cleaner once the engine is warm/closed loop, and has no affect on emissions after warm-up. You will fail a functional test here if the pump and it's associated hardware are missing, assuming of course the tech knows what to look for.

 

My 928 is 100% stock + an RMB...so the airpump is on and working (I guess)

Interesting my CO% numbers are both .15-.16 (25mph higher)....I wonder what that means? Its still well unuder the max of .71-.59 In the test where my car was very cold the NO was much higher at 211...which is still below average?

My fuel pump-filter-injectors are all new since the last test.... My MAF seems fine, since we tested it in Bills car a few years ago and Bills actually ran smoother with my MAF than his?

I do think my 928 was up to operating temp...but I'm sure the I could have driven longer to really get the cats up to temp.....

 

I passed last week, just for a base line here are my numbers

15 MPH, HC 27, CO 0.14, NO 366
25 MPH, HC 20, CO 0.02, NO 155

88 S4 5 Speed, Stock w/RMB 147K on the clock

 

Brian--

Ask your smog check guy to do the rolling 25mph test in second or third. My car ('89 with 2.54) rolls right into top gear on the rollers since there is such a small load applied. Yours with 2.20 will be worse. Have them hold it down a gear or two, and the NOx reading will be a lot better. The low RPM's, combined with the slight load on the motor mean that it's running pretty lean. Not enough airflow change at the MAF to tell the engine management to richen up a smidge. The lower gear selection makes it balance out a little better.

 

This makes sense. I also have a 2.2 (with big tires), so the rpm was way down
when doing the dyno tests. I'll suggest that when I go back after installing some
new cats (and maybe a MAF?).

 

George: How many retests will they allow for free? You might just try Dr. Bob's good suggestion as I don't know when we will be able to swap parts. I should have the cats Saturday but I am tied up. Sunday is a possibility, but if Dr. Bob is right, as I suspect he is, it would save the hassle of doing the swaps.

 

this does make sense......since the rpms were 1322rpm at 15mpg and 1821rpm and 25 mph...but 1821rpm at 25.....that has to be 2nd gear? Since 4th would be under 900rpm at 25mph?

 

Bill, I don't know how many times they'll let be retry. The place I went last time wanted $25
for each retry after the first. I was hoping I didn't have to go through that here. Any way,
using a 2nd gear pull at 25 mph would only be 1550 rpm (vs 1000 in 3rd), so it might not be
that much of an advantage. 1st gear would be around 2700 rpm, but might be too much.

 

George--

Try it in third, and tell the guy to abort the test before completion if it isn't going to pass. Have him restart the test in second, same drill. If it isn't going to test, have him abort before completion. Th etest guy can see the actual realtime results on his display, and knows almost instantly if your trace is in the red zone as he's testing. It's painless for him to abort the test, very important for you. If you rack up a series of 'fails' the state has the option to send you to a state referee, with a 'gross polluter' flag attached to your car's records. The referees tend to be a lot less flexible. If the tester aborts before the test is complete, there's no 'failed' record in the system for your car.

 

So Bill and I put on the new cats Sunday evening and I took it in to be smogged this morning.
It pass, everything was way better then the limits, but the NO at 25 mph just barely passed.
Here are the numbers (15/25mph):

HC 8/8, CO .01/.00, NO 553/703

Max allowed on the NO at 25 is 706, so it was very close. Thanks all, now it's time to get back
to work.

 

That is close! I think you could be lean as the HC and CO are VERY low and being lean raises NOX. Maybe not a real concern since we are going to change everything - except the MAF and LH.

Anyway, so now we can re-install the SC. Weekend is tight, but we could do week day and/or nights before SITP.