Failed SMOG check

[BMSman]

Car is a 91 850i. 137Kmi. Driven <1,000mi/yr.
Since fixing up the car 4 yrs ago it passed its first smog with flying colors (results below) and passed 2 yrs ago but I don't have the results handy.
Today it failed quite miserably (results below).
The car is not driven much and I cant detect any change in performance. Intake vacuum looks normal but it seemed to do worse at low speed.
Any ideas where to look/what to try/how to diagnose?

Drawing1.jpg

[cartoonz]

you have a vacuum leak or ignition misfire... likely vacuum leak.

[tran2tran]

From my experience. Driving the car for about 10 to 15 miles to get the engine warm up enough then take it in to the smogs shop to do the smogs test. I did this on 3 of my e31. Failed smogs in the morning. Drove it to work and back at lunch time and did my smogs test and passed

1994 840 with over 200,000 miles
1997 840 with 170,000 miles
1997 840 with 120,000 miles

All failed smogs test the first time in the morning
Smog tech told me these car need to warm up then it would passed smog test

So I just drive to work in the morning and do the test by my work or take it back for the smog test on the way home from work


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[rharris99]

Try these 2 things and you should pass...I do this every time prior to doing the smog check...put a can of Seafoam in half a tank of gas and drive 50 freeway miles and take it to the test station immediately while the cats are hot.

If nothing else is wrong with with your car you should pass.

[tran2tran]

Try these 2 things and you should pass...I do this every time prior to doing the smog check...put a can of Seafoam in half a tank of gas and drive 50 freeway miles and take it to the test station immediately while the cats are hot.

If nothing else is wrong with with your car you should pass.

Yep. That’s what I did too


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[TedBobo]

Car is a 91 850i. 137Kmi. Driven <1,000mi/yr.
Since fixing up the car 4 yrs ago it passed its first smog with flying colors (results below) and passed 2 yrs ago but I don't have the results handy.
Today it failed quite miserably (results below).
The car is not driven much and I cant detect any change in performance. Intake vacuum looks normal but it seemed to do worse at low speed.
Any ideas where to look/what to try/how to diagnose?

Drawing1.jpg

Pass smog yet?

[BMSman]

Update:

Passed!

smog2020.JPG

Added a bottle of CRC guaranteed to pass to about 3/4 tank of gas this morning and drove the car to work (~15 mi). Left work at 2:30, got on the 5 and thrashed it as much as I could for about 1 hr. Drove straight to the same smog station I used last time and results improved significantly!

Hopefully I will remember this next time I have to do this...

Thanks for the suggestions!

[tran2tran]

Every 2 years


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[TedBobo]

Congrats!

I always do a "5-South" loop of at 50 miles & then it's immediately to the test site that's just off the freeway exit. Those "cats" are nice & hot!

[BMSman]

Well it's that time of year and my car failed its smog again!

IMG_5258.JPG

Although I thrashed it on the freeway for ~ 40 mi before the smog test it failed. I did not however add any 'CRC guaranteed to pass' this time... maybe this stuff really works!
I'm not concerned with the fuel evap test failure... the test station's equipment was not working correctly and he pretty much told me so!

Since I last smogged the car 2 yrs ago I've driven it 500 miles! In that time I installed a set of Wokke chips. Could it be possible for these to cause the smog to fail? The intakes are freshly sealed and the car runs great!

My plan right now is to switch back to the stock ECU's (I have a spare set), add the 'CRC guaranteed to pass' and try another test station.

Any suggestions?

[Timm]

High Hydrocarbons usually means misfires and incomplete combustion, everything OK on the HT system?

[BMSman]

Hi Timm,
As far as I can tell. The ht wires distributor etc don’t have many miles on them and all checked out good resistance wise. Plugs are correct. Coils ok. It stutters a bit at cold idle but otherwise ok. Pretty much always been this way.

[Red Racer]

Crazy as it sounds, but Seafoam has always fixed my smog issues with my car. I thought it has to do with the high alcohol in it. I don't have any experience with CRC, but mine gets a can and a good drive through Malibu Canyon every time Smog is due.

Let us know if you find anything.

California is pushing the limits on Smog giving more and more of us problems.

[Timm]

If you are having stumbles when cold then that can be caused by a vacuum leak, with single-cylinder vacuum leaks (at the manifold) that cylinder ends up too lean and the others too rich (to get the right Lambda value) - are your manifold gaskets OK?

[Auraraptor]

If you are having stumbles when cold then that can be caused by a vacuum leak, with single-cylinder vacuum leaks (at the manifold) that cylinder ends up too lean and the others too rich (to get the right Lambda value) - are your manifold gaskets OK?

+1

I had a similar issue on my 7 series and it ended up being need for a new manifold gaskets. I swear the V12s use them up every few years. I fully expect the 8 to do the same....

[dragon850]

Catalytic converters on our cars are becoming very old, I have replaced many with walker units and only then was able to pass smog.
This is on cars running perfectly some after a full rebuild.