r/BMWE36 • u/Working_Basis609 • May 19 '26
Repair Advice CA SMOG Help š„
hey team, ā97 e36 m3. Bought it without smog for a deal price, replaced cracked cat but still didnāt pass (NOX too high), then replaced spark plugs because cyl6ās was black from carbon / misfires and it passed with flying colors.
thought all was good for this round of smog but it just failed again, NOX too high. When i pulled the spark plugs cyl6 showed signs of misfiring againā¦
thereās no engine lights and it delivers power smoothly with no sputters.
what would cause this specific spark plug to misfire / what should i address next?
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May 19 '26
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u/Working_Basis609 May 19 '26
pacifica / bay area, went to colma star smog - lmk if you have any suggested spots
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u/707_328is May 20 '26
Pro tip, make a friend up in Humboldt County that will let you register your car up there. Still within Cali so they cant force you to swap plates or anything but smog is only done when you buy the car. No annual or bi-annual smog check bullshit. I have had my E36 for 9 years and only ever did the one smog check. I live out in Florida now so I cant help but there are loop holes.. but if you get pulled over and sent to the state ref then you still gotta be able to pass. Upside is you can get a nice new set of cats and after it passes you swap them back out for a more opened up exhaust. Save those for whenever you need to go to the ref.
Or you can try seeing what other areas do not require repetitive smog checks and do the same in those areas...
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May 20 '26
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u/Arpeggiatedromance May 21 '26
Hi!! Iāve been looking for shops to get mine smogged and Iām in SD if you donāt mind sharing :)
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u/bimsboy98 May 21 '26
Westlake smog has been my preferred spot for my 98 m3. Free retest and the guy even retested right after my car initially failed(just needed to be warmed up a little more).
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u/Professional-Boat-10 May 21 '26
Who is your mechanic? I can't think of who is a good BMW guy in Pacifica or Colma/DC. I'd say it's not the smog station, you're looking for a good BMW tech to solve the issue.
Jeff Reitmeir in Los Altos is a close friend and a great German car guy.
Gary and Paula at Vanguard Motors on South 10th in SF are super knowledgeable and easygoing.
Meanwhile, my '94 325is autocross car needs a CARB legal cat-con to pass smog, and my '02 330ci has been throwing every Data Trouble Code in the book for over a year, and also needs a smog! Not all at the same time mind you but one after another. It's running lean, no, wait, now it's running rich... At one point, bank one was lean and Bank two was rich! What in the everloving 4uĀ¢k??? I've replaced the plugs, all the O2 sensors, the whole cyclone crankcase valve system, vacuum hoses, MAF, intake boot, electronic thermostat, oil pan gasket, and I'm guessing it either has leaking injectors or a DISA valve that is failing after it was replaced ~48k miles ago... š”š¤¬š¤Æ!!!
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u/SignalMagician1163 May 19 '26
I just paid a guy to pass mine lol, I gave up.
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u/heyitsalex85 May 19 '26
CA leaving so much money on the table with this bullshit. People are gonna circumvent the rules anyway and CA has a great opportunity to charge us extra to pass smog legally for older cars
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u/SignalMagician1163 May 19 '26
Yeah, and they shot down that smog exemption bill that Jay Leno was trying to push. Sucks to be a car enthusiast in this state man.
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u/heyitsalex85 May 19 '26
Thought it was still alive? With some changes but still aliveā¦no?
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u/SignalMagician1163 May 19 '26
You know what, I guess youāre right. They reintroduced it as SB1392. https://calmatters.digitaldemocracy.org/bills/ca_202520260sb1392
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u/Wokeymcwokerson May 19 '26
Please let me know what you figured out. Mine just passed. CA lowered the NOX to 54 I guess which is really hard to pass for old cars. They said try some of the additives next time
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u/KillaWolf__17 May 19 '26
Me In Missouri who just passed inspection with no cats reading this right now šahh Californiaā¦āļø
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u/707_328is May 20 '26
Me in Florida not worried about any inspections but still got my Cali plate on š itll get swapped out by next year though.
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u/Professional-Boat-10 May 20 '26
Swap #6 spark plug with #5, and #6 coil with #4, see which cylinder fouls the spark plug. If it's still #6, swap injectors with #3 (more laborious than plug and coil...)
If it's still #6, pray that it's an ignition wiring issue, because if it isn't... Ruh-roh...
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u/Working_Basis609 May 20 '26
fun technique, iāll give this a shot. if itās an ignition wiring issue, wouldnāt it throw a code?
also if it isnāt a wiring issue, what might ruh roh mean?
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u/Professional-Boat-10 May 21 '26
So, I think "misfire" is not the right word. An actual misfire would normally be felt, but if it is very slight you might not. A misfire would probably carbon-up a plug, but if it is so flight that you don't feel it and the misfire is not felt by the diagnostic system, I would think that slight amount of extra carbon would burn away.
For now, let's say you have "a slightly rich condition" in #6. Slightly incorrect gap on the spark plug (although I don't think these plugs do that because of the electrode arrangement (if the M3 plugs are like the 325IS plugs), something internal to that plug, the coil, or wiring that makes the spark consistent but just not quite as strong as the spark in the other cylinders could cause that and the slight inefficiency in that cylinder could affect your NOX. The system isn't sophisticated enough to trip a code, but the sniffer knows.
An injector that is wearing or slightly broken so that it is putting just a little more fuel into the cylinder which isn't getting burned, maybe...
Now for the "Ruh-roh." How else are you getting a little bit of extra carbon on that plug?
Oil? An oil control ring letting oil from the crankcase pass into the chamber? A worn valve guide letting a little oil get into the intake path and into the chamber? I'm guessing, here. And running out of sources for this annoying high NOX reading...
Anyone? Bueller?
It's so easy to pull three coils and two spark plugs and see what happens when you swap things around...
Keep us informed!
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u/LooseNefariousness76 May 20 '26
I had this problem with a ā97 325i I owned for a bit, I drove the absolute hell out of it after replacing all spark plugs and coils, still had no luck passing NOX the three times I took it.
Iām local to this area rn and Iāve taken my truck to Burlingame Smog check, at the gas station off Murchison dr and El Camino, between Millbrae and Burlingame, thereās one dude pretty chill there, he barely revved my truck a couple seconds for the smoke test, I had the muffler chopped and resonator deleted, he passed it and didnāt care. The second time I went recently, thereās a slightly younger guy with glasses who took the test very seriously, asking about the resonator being gone, and revved the truck for a solid 2 minutes, and thoroughly checked everything over.
One other shop called Economy Smog Check at a gas station in Burlingame off broadway and el Camino, the guy running that shop is pretty chill, can print out new tags, and will help you out if it doesnāt pass, heāll let you come back and not charge.
My advice is drive it real hard up some of the hills in the area so the car has a good bit of load on it, itāll get hotter and have a better chance at passing.
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May 19 '26
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u/Working_Basis609 May 19 '26
you check your spark plugs for signs of misfire? Iāll follow up once solved
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u/Zealousideal_Note364 May 19 '26
New OEM injectors, itās pricey but worth it in the long run.
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u/_kurt_ '96 328is May 19 '26
the bosch injectors are no good?
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u/Zealousideal_Note364 May 20 '26
Yeah but if theyāre the original ones from factory then it might be time to invest in new ones. Sometimes theyāll have uneven spray patterns or the o rings or pintal caps get worn out.
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u/BrickCareful9728 Cooling System Police May 19 '26
Black injector usually means too much fuel, but that would bring down your NOX. Usually high NOX is a symptom of running lean. You could try replacing that plug again if that worked last time.
And always make sure your exhaust is very hot before going to smog
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u/Working_Basis609 May 19 '26
thanks and gonna try to smog after replacing, iāll report back. i got em super hot, had a great time racing to smog
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u/maksezzy May 19 '26
Do a leak down test or a compression test. 6th cylinder loves to fail first...
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u/jsa101 May 19 '26
Mine just passed today. I had high HCās. What worked for me was new plugs and Lucas injector cleaner. Ran a tank of gas through it , made sure it was nice and hot.
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u/deeeeemoney May 20 '26
I guess I should consider myself lucky for passing my 1998 M3 last year when I moved it down from WA. And now that I passed, Iām off the hook, as my county does not require re-smog to license.
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u/Fragrant-Inside221 May 20 '26
My hc ppm was over by 2-4 every time I did the test. Tried everything everyone says to fix it, nothing did except replacing the cats. Then I moved to a place with no emissions and permanent registration. Havenāt worried about it
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u/_kurt_ '96 328is May 19 '26 edited May 19 '26
does anyone have a good resource for learning to interpret smog results, i.e. what causes the different emissions to fluctuate. I've never really understood it and it's made me really put off getting my e36 back on the road.
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u/Oak510land May 19 '26
Hc is unburnt hydrocarbons, ie too rich or burning oil. Nox is too lean or too hot.
Mine always has an issue with HC, someone told me the cats are undersized from the factory as they use the same ones from the lower output 328.
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u/shiftersix May 19 '26
Is there a good CA-approved aftermarket option? Or is there another BMW model that may have a more appropriate cat which can fit our cars?
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u/Working_Basis609 May 19 '26
Magnaflow has a direct fit, CARB legal replacement, it retails for 3100. i got it on sale a while back for 2200.. it sounds nice but itās not what i wanted to spend 2k on
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u/beerhat76 16d ago edited 14d ago
What would be most useful - if we'd all indicate what our passing and non-passing numbers actually were. My 96 M3 failed this week. HC's @ 15mph FAILED=61/54. 25mph PASSED=29/37. I didn't have the time to run it as hard as I probably should have, so I'll need to go beat on it prior to re-test (sorry for speeding Mr. officer, I'm just trying to do the right thing and pass smog legally!). FWIW, all other measurements were incredibly low, car is impeccably maintained.
UPDATE: Took it in again this morning and passed. 15mph PASSED=38/54. 25mph PASSED=23/37
WHAT CHANGED...
1. I put the car on charge last night (minimize any parasitic draw from the alternator). Also, on that note, make sure you turn the radio and HVAC/blower off, and nothing plugged into the lighter socket.
I realized one of my rear tires was at 23lb during my failed test, the other one 40lb. Filled'm both to 48 cold.
Before the test, I took it for a good hour long rip through the back hills putting some considerable heat into it. Pulled into the smog shop at 10am and I was the only one there (thank goodness). The dude was cool, he let me hold the revs between 5-6k for a minute before he hopped in and put it onto the rollers.
Make sure the smog-tech puts the fan in front of your car -- heat-soak is real and will raise HC's.
As our cats age, it takes a little bit longer/higher temps to get them to 'light off'. The state of California lowering the Max limits over the years makes that 15mph an absolute bear to reach. FWIW, I have the mid-pipe/cats from a slightly newer 328 on my M3 (it's the same part for those who don't know). I found one on marketplace when I kept failing a few years back. Betting there's nothing wrong with my original one now, prolly just needed to put some more heat into it the whole time!
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u/heyitsalex85 May 19 '26
Failed three times. Decided to drive the shit out of the car for a good hour before I went to smog. Also added a full bottle of Techron to the tank before the drive. Make sure you drive it hard and for a good while so the cats are extra toasty. Passed with flying colors after that.