Californa Smog Issues - The Unofficial BMW M5 Messageboard (m5board.com)

M5KIKO · 7th April 2008, 03:00

Looking for assistance, recently gave my son my 93 325i. In prep for the CA smog, I changed the plugs, oil, filters, cleaned mafs, ran a tank of additive that ensures you will pass, then filled up with 91 oct and ran it hot prior to having it smogged. It failed the 2nd part of test @ 25 mph, below are the results;

Test M1: 15 MPH Results = Passed
rpm %co2 %02 hc(ppm) co(%) no(ppm)
meas meas meas max ave meas max ave meas max ave meas
1842 14.6 0.2 86 21 51 0.50 0.06 0.18 697 150 263

Test M2: 25 MPH Results = Failed
rpm %co2 %02 hc(ppm) co(%) no(ppm)
meas meas meas max ave meas max ave meas max ave meas
1813 14.0 0.6 51 13 183 0.48 0.05 0.59 724 136 1050

No mod's done to exhaust system, didn't know if I should chng out the 02 sensors. Appoligize in advance for posting it here, but it's where I trust the information received. Fyi my 00 M5 passed with flying colors. Any assistance would be much appreciated. Located in the east bay of the sf bay area.......thnx Kiko

Need4Spd · 7th April 2008, 03:27

Either tired cats or marginal or failed O2 sensors, I would guess. Changing out O2 sensors is cheaper and what I would try first. If they've never been done, that's most likely the cause, though I thought bad O2 sensors would throw a code. '93 and you didn't say how many miles but that's what, 15 years, so we can't expect O2 sensors to last quite that long (of course if they were replaced in the last few years, that's a different story). Hope it's not the cats.

El Diablo · 7th April 2008, 06:18

+1 Bad O2 sensors will make you run lean or rich and will cause high CO or high NOx. But since you failed in both, I will guess that your cats will most likely need to be replaced IMHO. Let us know what it was. I'm also due for a smog test in June

. Good luck!
-Roberto

Quote:

Originally Posted by Need4Spd

Either tired cats or marginal or failed O2 sensors, I would guess. Changing out O2 sensors is cheaper and what I would try first. If they've never been done, that's most likely the cause, though I thought bad O2 sensors would throw a code. '93 and you didn't say how many miles but that's what, 15 years, so we can't expect O2 sensors to last quite that long (of course if they were replaced in the last few years, that's a different story). Hope it's not the cats.

M5KIKO · 7th April 2008, 06:30

The 02's and the cats are both orginal equipment, the car just turned over 200,000 miles, thinking I may have gotten my money out of them. I'll give the 02's a shot first, then the cat's if it still fails. Thanks for the feed back Need4Speed & El Diablo, I do appreciate it. Anyone know where the best deals are for both the O2 sensors and the Cat's?

tstaples · 7th April 2008, 07:09

As a fuel systems and engine calibration engineer, with quite a bit of experience, including the BMW M50 engine in your 325i, I can assure you the original O2 sensors stopped functioning long ago, and your car has been running a little rich for a while (i.e. the calibration goes to something safe, but not optimal.) Running rich will slowly degrade your cats. You almost assuredly need to replace both.

I would never run O2 sensors longer than 70-80k miles. They are consumables, like spark plugs. They slowly degrade with use. Once they stop functioning, the ECU will still run the motor, but with slightly rich settings to ensure you don't burn up valves. On OBD or OBDII equipped vehicles, it will set the SES light once that happens. Since yours is pre-95, hence pre-OBD, you get to drive in total oblivion to the problem, and unless you are very sensitive to how your car runs, you most likely won't notice the slight degradation in performance.

FWIW, it's a 50-50 chance that your car has fuel injectors in it that I had a hand in designing and manufacturing. I previously worked for an OEM supplier, one of two injector suppliers for the M50 engines back in the early-late 90's. Good luck!

alijonny · 7th April 2008, 07:45

"Since yours is pre-95, hence pre-OBD"

pre 95 OBDI, 96+ OBDII

i've got nothing better to do.

tstaples · 7th April 2008, 08:18

alijonny,

You are technically correct. However, most people who work in the industry refer to OBD-II as just OBD. Sorry for the confusion. Prior to the OBD standard, which came to be know as OBD-II, there were multiple schemes used by various ECU's or OEM's as On Board Diagnostics. The OBD-II standard became mandatory in the US starting with the '96 model year, in the 1995 calendar year. The earlier systems have become known as OBD-I or OBD 1.5, but technically, there was no overall standard, as these various schemes are proprietary. They have one thing in common, they generally won't set the Check Engine, or SES, light for much of anything short of a major problem.

M5KIKO · 7th April 2008, 10:27

Tstaples & alijonny thank you both for the information you've shared. True, I didn't know the O2 sensors were alike the plug's in that they do ware and now I understand the impact that they have on the cats. I did notice the reduction in performance, but I assumed it was do to the age and the mileage of the car. Also since my normal tune ups provided me only a slight improvement in mile per gallon verses overall performance. I've never had a check engine light come on, execpt in the early days. Again thanks! I'll begin my seach for O2s and cats.

paypalbid · 7th April 2008, 11:38

do you need to go to smog only place ? if not you should approach the local racers and see where they get their cars smogged and slip the cash and get your car passed.