smog/NO failed worse on new catalytic converters, help 95 m3

[everbruin]

hi, my 95 m3 failed smog HC so I got 2 new cats [walker, carb approved] that now fail badly on NO.

each time I drove on highway 10 mins about 5k rpm on stock 235/40/17 rear, intake, exhaust, taller 255/40/17 front tires.

station1, old cats, ebay chip like dinan, 5 min wait but idled at 1500
15 mph/1667 rpm HC 99>85 FAIL, CO .12<.50 ok, NO 91<695 good
25 mph/1872 rpm 50<=50 borderline pass, .12<.47 ok, 21<717 good

then unplugged battery, installed stock chip & new cats

station2, new cats, stock chip, no waiting
15 mph/1688 rpm HC 41<85 now ok, CO .0<.50 good, NO 991>695 FAIL
25 mph/1889 rpm 12<50 good, .01<.47 good, 937>717 FAIL

so again unplugged battery, swapped back in ebay chip like dinan,
drove 25 highway mi

station2, new cats, ebay chip like dinan, no wait
15 mph/1688 rpm HC 29<85 ok, CO .0<.50 good, NO 1168>695 FAIL
25 mph/1889 rpm 9<50 good, .01<.47 good, 937>717 FAIL

stock chip beat ebay chip on NO [stock slightly worse on HC] but old cats did much better than new cats on NO.
Does obd1 need some # of miles before it's good to smog?
Help, any advice?
thanks!
An.

[RRSperry]

If it were me, I'd change the O2 sensor, and the plugs. Use the stock chip, and go do the test again. Also check to see of you have any stored codes. (do the OBD1 stomp test)

[nick325xit 5spd]

Most aftermarket cats (including the cheap Walkers) are utter garbage. Switch back to the stock cats and you will probably pass. Edit: Dunk them in citric acid before reinstallation. You may be surprised by how much crap comes out after a citric acid soaking.

That said, you were running rich with the eBay chip. High NOx is frequently a sign of lean running. It's too bad that you threw a bunch of parts at this with a very marginal result. You probably could have put a few gallons of E85 in the tank and passed that way. (A bit of E85 mixed in trades HC for NOx. You had plenty of NOx headroom before you messed with it.)

[everbruin]

prior cats were walker too; anyway I reverted to stock chip, mechanic cleaned valve carbon, fixed crack in new cat installation then passed smog on 0 NO w/ 1 day before reg expires =)

[bluptgm3]

I have heard to run 20 mins before testing. New aftermarket cats might have high flow and not get HOT easy.


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[BMW 750]

I cannot believe you are actually trying to legally smog your e36 m3.

[bluptgm3]

I cannot believe you are actually trying to legally smog your e36 m3.

Which city/state do you reside and what ‘opportunities’ are you offering?


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[RRSperry]

I cannot believe you are actually trying to legally smog your e36 m3.

why not? Mine passes the tailpipe treadmill test every two years.

[marvinstockman]

Does car run hot? Any other mods?

[yurisuika]

I have to have my '97 SMOG'd, but the CEL has been going off again and again. I had a track pipe on it and post-cat O2 sims and after I took it to the shop to get a sheered header stud replaced in the Spring, the CEL had come on just before I picked it up and immediately came back on after he cleared it. So now in having it fixed up to pass SMOG this year I put the cats back on and I had the code cleared, but it came on after 55 miles. So then we found one pre-cat O2 sensor was not oscillating so it was replaced. Then the CEL came on after 35 miles and so the other pre-cat went out. Picked it up this afternoon and drove 85 miles today, hard up the canyon roads sticking it on redline in 2nd often, and all seems good finally, no CEL.

Finally I can get my tags and be compliant.

So $460 in parts and labour to have it fixed on the sensors... I guess isn't that bad to know it is running perfect now. Else I could have dropped $300 on "The SMOG Guy" to have my tags and a rough idle and excessive afterfire and have everyone think I was cammed.

I just wonder if those sensors are gonna die again after I put my track pipe and sims back on. Maybe it was because they were too old and they couldn't take it? Who knows.

So I guess my point is take a look at the pre-cat oxygen sensors. I know the OBDI is a bit different but should be a starting point.

[RRSperry]

The post cat sensors are only monitored to tell you if the PRE cat sensors are having a problem. There is no control function associated with post cat sensors, So yes, Pre cat is the place to start. If one is bad, change both (obd2). Since there is only one sensor for OBD1, I'd change that. Vacuum leaks, (unmetered air) will cause your car to run rich. That will kill the converters too, along with rough idle, and drivability problems.