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Old 08-07-2006, 10:02 PM   #1
rocketdan
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Question Smog test failed NO (ppm)

hi guys,
just quick intro been around the yahoo 318ti list since probaly around 1996. i have a 1996 318ti. i've heard the yahoo list is out of commission. So just wanted to say hi from good old So. Cal.

oh that note here's my question,
just got a smog test, and i FAILED... anyone have any experience with failing the NOx portion of the test and what you guys did to resolve the problem. i guess i have 60 days to make repairs and retest for free.

help me out!
thanks in advance.
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Old 08-07-2006, 10:09 PM   #2
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First big item is probably the catalytic converter... Was the car cold when it was tested? I've heard people say that having the car at operational temperature is the best way to pass if the catalytic converter is questionable..

Do you have a CEL?
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Old 08-07-2006, 10:16 PM   #3
rocketdan
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Thumbs up

the car definitely wasn't cold, i ran it for about 20 mins, and even the test operator ran it on the machine twice. the second time he revved the engine up for about 2-4 mins. he said the same thing that the cat probably needs to heat up.

i did have a CEL but my friend erased it w/ his scanner. i think it said something like CAT and something about threshold. so possibly failed CAT?

ran a search on google, and this forum, seems that many say that the O2 sensor could be bad too.

i'm having problems similar to the cars on this site click only reguarding the NO (ppm) portion.

thanks for the reply.
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Old 08-07-2006, 10:27 PM   #4
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o2 sensor was my next suggestion, but a bad O2 sensor should keep throwing a CEL.

I think any CEL related to the catalytic converter is either the cat itself or the 02 sensors. The only way it can tell if the cat is bad is by the O2 sensor.

Honestly it is probably best to take it to a mechanic that is experienced with BMWs. O2 sensors and catalytic converters are to expensive to just throw parts at it and hope for the best... Especially if you have a mechanic that will diagnose it for free. Chances are though with a 96 if you have never replaced the O2 sensors that one of them has gone bad. I have a 95 and mine has been replaced. Something like 90-120$ a piece. OEM cat is expensive.

If you decide to change the cat, you are probably better off getting a muffler shop special than trying to replace with an OEM cat.
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Old 08-07-2006, 11:21 PM   #5
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I just recently passed Maryland's VEIP. Since I have a '95, they put my baby on a treadmill to test (and to butcher the clutch, but that's another story)... FWIW, here are the numbers:
Code:
Standard Reading Hydrocarbons : 0.9000 GPM 0.2461 GPM Carbon Monoxide : 20.000 GPM 7.8745 GPM Oxides of Nitrogen: 2.1000 GPM 1.0841 GPM
This is with the original cat... phew - these things last
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Old 08-09-2006, 04:10 PM   #6
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bump
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Old 08-09-2006, 08:23 PM   #7
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You could try running a couple of bottles of fuel system treatment through it. I can't remember the brands, but I know there are some that say they will help with emissions. Maybe put a tank of premium in a few days before you go for the test. You could also try what I've heard referred to as an "Italian tune-up". Get the engine fully warmed up and do some 1st and 2nd gear redline runs. The theory is that this will blow any buildup out of the cat. Probaby an old wives' tale, but it's fun
Another option is to go to Advance Autoparts or Autozone(maybe Pep Boys but I'm not sure about them) and have them check your codes. It's free and they should be able to tell you if it's the o2 sensors or the cat itself. I recently replaced my pre-cat sensor after a trip to Advance. The sensor was around $75 for the Bosch. Good luck
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Old 12-10-2012, 04:18 AM   #8
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A year and a half ago I bought my '97 318ti; it had 186,000 miles. Its first smog test was marginal, barely passing.

Its smog test just the other week, at over 200,000 miles, failed miserably: Co and NO emissions several times over the limit at 15 MPH and marginal at 25. The shop I had been taking it to wanted to drill a hole in the catalytic converter blablabla and probably find something that meant it had to be replaced.

I took it to a different place. Based on the smog test numbers, they concluded that the engine had a lot of carbon build-up and thus too-high compression, leading to the excess NO. They replaced the air filter and spark plugs, poured a can of "Guaranteed to Pass" in the tank, and had me fill it up and do an "Italian Tuneup." Over the next week, I could feel the engine becoming more responsive, accelerating more willingly.

I brought it back to the smog check and got the free retest *and it passed with all values well below the limits. It drives better now!

Next time it needs a smog test, I'll do run another can of the gunk through it. Give it a week, do an oil change, and then get it tested. It's nice to have an engine that's in proper tune.
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Old 12-11-2012, 06:47 AM   #9
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You drill a small hole in the pipe ahead of the cat and use a vacuum gauge to check back pressure, it should read nearly 0.... Vacuum gauges will read a inch or so of positive pressure usually...

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Old 12-12-2012, 06:32 AM   #10
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I"d rather use a pressure gauge ;-) but I'd rather not do it at all if other diagnostic means are available, such as a vacuum gauge on the intake manifold. Run the engine wide open for a short time, the chop the throttle. The vacuum should immediately increase. If it does only slowly, then there is an exhaust restriction.

Drivability tests would also reveal really bad carbon-buildup problems. I did not know the 318Ti's "good" characteristics, so I didn't see its cantankerousness as a trouble sign. Let go the gas while in gear and it would be very choppy at engine braking. Smooth shifts were really hard to do! I felt like a total clunk driving this car; I thought it was me. But after the engine treatment all that bad behavior went away and the engine is drivable and fun.

Drill a hole in the exhaust? Not if I can avoid it and fix the problem some other way! Right?
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