Need Advice: Failed Smog High HC & Nox

[Gordon@EDGE]

"Enhanced" Emissions Testing has arrived here in Northern California. I am hoping that some of you So Cal guys might have experienced this problem and can help.

My wife's '95 525i, which runs very well despite having 180,000 miles, failed the 15 MPH test because it was slightly too high in both HC and Nox.

The failure is a bit of a head-scratcher because as far as I can tell elevated HC can indicate low combustion temps and elevated Nox can indicate high combustion temps.

The mechanic who tested it said basically "dunno, maybe a vacuum leak affecting one cylinder". Okay, whatever.

The advice that I have received so far says:
1) Get the converter hot, hot, hot and immediately onto the dyno
2) Make sure you have fresh oil and air filter
3) Run a can of Techron through the engine before the test

Any experience or advice?

Thanks guys,
Gordon

[MR 325]

All that advice is great.... Try to go right before the shop closes so they will do your car right away, and before you get there, beat the hell out of it [or at least redline it] to get everything good and hot.

[MDR]

I follow the advice of others (though run the techron through about 2 tanks before the test) and also put in new plugs before I get my emissions check.

[NoSoup4U]

BG Moa is the engine thing I would recommend. I would also consider running higher octane fuel such as 104 ... I've run 104 octane fuel, no cats ... and I can pass emissions :D

[shragon]

1) Get the converter hot, hot, hot and immediately onto the dyno

my car even failed smog-I because they let the car sit and the cats were not hot enough. drove the car for a bit, retested, passed.

[uberM5]

just keep the car warm and you should pass. Its very easy to fail with a cold cat

[BlackIce]

Changing your oil is probobly the most important thing to do in order to pass.

[Mark85]

um, if you have a high HC reading its because there is unburnt fuel getting to your exaust...so either your running too rich, or maybe you have a misfire, either way you shouldnt have to run your car for a while to pass the HC level

a high hydrocarbon level could also cause your cat to fail because cats dont like unburnt fuel

[Ben Carufel]

How does oil help you pass? Seriously?

My '85 325e did the same thing a few weeks ago. Failed twice, then I did this:

-- Fill up with Cheveron 91.
-- Add a can of TURBO 108+ octane booster.
-- Run it like a BITCH for a few days. Just drive it to the redline, keep it at 5500RPM's on the freeway for 10 minutes at a time, etc. This will help clean all the shit out of the engine.
-- Run a fuel system cleaner through if you can.
-- When that tank is done fill 1/2 way with Chevron 91 and put another can of TURBO 108+ in.
-- Drive 25 miles.
-- Change plugs and O2 sensor.
-- Heat up well (keep it at 4000 RPM's or higher) and take it straight to the smog shop.

I still barely passed, but hey I'm good for two years. Hell the car will probably have a different VIN in two years ;)...

[Gordon@EDGE]

Thanks, guys for all of your advice. I will provide an update when I get the re-test in a couple of days.

[NicolasW]

Any update on this??

My car (1995 M3 with 138,000 miles) just failed for having too high HC and NO.

However the guys let it sit for 10 or 15 minutes before testing so maybe that was it.

Wes

[Mark85]

yea HC is unburnt fuel so a misfire or running rich could be your problem...the cleaner id try is called an Emission System Cleaner and comes with 3 bottles, one for the gas tank, another for intake, and the last is for your oil

[Gordon@EDGE]

OK,
So it took a few months rather than a few weeks, but the car won't pass smog no way, no how.

I tuned it and changed the oil and filled the tires and poured in a can of "guaranteed to pass" snake oil and made an appointment with the smog guy, who tested it immediatley after I had heated the cats on the freeway in 3rd for 30 minutes. The result was worse than before: the car failed badly enough to be labeled a gross polluter and I was told to go to the mediator or some such thing.

Basically, I guess the cats are shot and need replacement

The good news? My wife got fed up with the car, and wanted a new one pronto so...I didn't even have to fix it. The 525 is now the proud possesion of the local stealer, and we have a (smogged and registered!) Aspen Silver E39 540 in the garage.

-Gordon

[NicolasW]

I've got an update. If you see my previous thread, I failed with excess HC and NOx.

I finally passed by getting the car GOOD AND HOT before getting it re-tested. Also, I told the tester to not let up on the gas quickly (causes unburnt fuel to go into the pipe...leading to high HC readings) so he said he would only do the test in 2nd gear. I think one of the reasons I failed initially was (1) the cats weren't hot enough, and (2) the succesfull test was done in 2nd gear only instead of having the tester shift from 1st to 2nd gear (as in the failing test).

I drove the car for 1 hour on the highway and while I was waiting in line (for 20 minutes) I revved the car at 2000 RPM.

Car has 140K miles.

Good luck,

[phiberteam]

After reading all of the replies I had to write and tell my horror story. Basically the same story high HC, ran the crap out of it tried several cans of Techron, removed injectors sent out for cleaning/testing, found two that wouldnt clean up, replaced with two new Bosch units, oh and checked the fuel pressure before removal of the injectors and found that it was reading too high, replaced fuel pressure regulator, new spark plugs and boots from the coil to the plug, replaced the coolant temp sensor to be sure it was going into closed loop, 02 sensor is current and working like it is supposed to .2-.8 volts at idle. After all of that I still get a reading of 280-310 at idle. After I open the throttle and hold it there for 3-4 seconds at the rev limiter, when it returns to idle I get about 89-100 HC at idle long enough for it to pass. As soon as I open the throttle above idle the HC will climb back up to the 300 range. It has me baffled, thought it could be a vacuum leak, checked for that with a smoke test no smoke leaking besides if it had a vacuum leak the 02 would go rich .8 or above. I was thinking maybe something with the VANOS and the cam timing. Anyone have any ideas?

[325bob]

Changing your oil is probobly the most important thing to do in order to pass.

Huh? I was wondering how an oil change could help at all, and you say it's the most important thing!(maybe if your rings are shot,and you went from synthetic 0w20 to real 20w50)

[kellie]

After reading all of the replies I had to write and tell my horror story. Basically the same story high HC, ran the crap out of it tried several cans of Techron, removed injectors sent out for cleaning/testing, found two that wouldnt clean up, replaced with two new Bosch units, oh and checked the fuel pressure before removal of the injectors and found that it was reading too high, replaced fuel pressure regulator, new spark plugs and boots from the coil to the plug, replaced the coolant temp sensor to be sure it was going into closed loop, 02 sensor is current and working like it is supposed to .2-.8 volts at idle. After all of that I still get a reading of 280-310 at idle. After I open the throttle and hold it there for 3-4 seconds at the rev limiter, when it returns to idle I get about 89-100 HC at idle long enough for it to pass. As soon as I open the throttle above idle the HC will climb back up to the 300 range. It has me baffled, thought it could be a vacuum leak, checked for that with a smoke test no smoke leaking besides if it had a vacuum leak the 02 would go rich .8 or above. I was thinking maybe something with the VANOS and the cam timing. Anyone have any ideas?

Generally high HC indicates a misfire. Something that would prevent fuel from burning in the cylinders. What are the rest of your readings? They are just as important in diagnosis as HC. Without looking at the other readings, and just based off of what you said, I would say you have a bad cat.