Severe emissions failure - NOx doubled

[JHZR2]

Hi,

This is the same situation I had the last time I went for inspection... Nox on my 91 BMW 318i failed. Only this time, it has doubled from the accepted level!

Background:
For reference, in 2003, my emissions (dyno test) were as follows:
NOx 1114 (standard is 1134)
HC 97 (standard is 146)
CO% 0.33 (standard is 0.82)
CO2% 14.1
O2% 0.2

Failure in 2005:
NOx 1167
HC 96
CO% 0.35
CO2% 15.3
O2% 0.3

Replaced cat converter, reading that passed in 2005:
NOx 1074
HC 133
CO% 0.34
CO% 14.8
O% 0.2

My failure today:
NOx: 2126
HC:161
CO%:0.54
CO2%:14.1

As a reference, my 98 Chevy truck (owned since new) had these results on its last dyno test (currently exempted because its an OBDII vehicle, so these are a little old, but done on the same system):
NOx 16
HC 7
CO% 0.01
CO2% 15.2
O2% 0

Spark plugs are very clean and correctly gapped, etc., I even ran the new Amsoil PI through the tank just before to ensure that CCs, etc. were cleaned out. No dice.

I do have a dinan chip, Ill be removing it as of right now, to hopefully be able to pass... The car runs great and gets me good fuel economy, Id hate to have to spend $500 on senseless repairs to get a waiver, just because this car never came with an EGR from the factory (by design).

UGH!

Any thoughts or comments would be most appreciated.

Thanks

 

[andyd]

lose the chip, It prolly is giving too much advance. Maybe apples and oranges but, Motronic 1.0 ECUs in E 28s have an adjustable fuel quality switch that plays with the advance

 

[andyd]

Also how is the O2 sensor, and are there any vacuum leaks??

 

[JHZR2]

O2 sensor is rom 2005, has maybe 25k on it, and is OE. No vacuum leaks, I had a shop replace all the rubber in late 2005 as PM (IIRC the date).

We will see how the loss of the chip changes things... im hoping that is all that it is, but the effective doubling of NOx level, all other things being equal is strange to me, unless the generic cat that I swapoped in last time things failed for me is bad already...

 

[Virtuoso]

Does this vehicle have an EGR system? If so; perhaps a cleaning is in order. Malfunctioning EGR's are known to throw NOx levels through the roof.

 

[JHZR2]

No, M42 engines are not equipped with EGRs...

 

[Terry]

He has no EGR.

How about ice packs placed on intake... will they allow that?

BIO PLUS fuel additive from www.renewablelube.com

RLI BIO PLUS MAY be able to reduce the level significantly in addition to ethanol enriched Shell fuels. Tell them you are a Dyson Analysis customer.

Perfect ring seal will help to ( think a load of Auto-RX).

Seems we attacked this before with mixed results in analysis.

 

[JHZR2]

Quote:
He has no EGR.

How about ice packs placed on intake... will they allow that?

BIO PLUS fuel additive from www.renewablelube.com

RLI BIO PLUS MAY be able to reduce the level significantly in addition to ethanol enriched Shell fuels. Tell them you are a Dyson Analysis customer.

Perfect ring seal will help to ( think a load of Auto-RX).

Seems we attacked this before with mixed results in analysis.


Thanks!

Just got done Auto-Rx actually, thus why no UOAs in a while, wanted to do a double flush before going back to analyzng...

I had been running schaeffer's soy sheild quite a bit in the gas... just did PI recently because I heard it was really strong, and wanted to remove any chance of deposit-induced increased compression...

Ill have to give that renewale lube product a try, thanks!!!

We did attack this before, including using UOA, the one thing that you did mention (actually here on BITOG, not in consultation) was the fact that a dying ignition coil (my car is distributorless) could cause funny stuff like this. Those might be the next swap, if needs be.

Thanks!

 

[Rickey]

Lots of possibilites.
It appears as if the engine has always been close to the limit correct?
So it only takes little to put it over the edge.
Double...WOW! Could this be a testing error?

Increased compression from a little bit of carbon.
Itallian tune up?

Advanced timing, lean mixture, anything that would increase combustion temps = more NOX.
Brings us back to the chip I suppose.
And guessing that you are performance oriented discounts the carboned-up theory I reckon.

Tough one for sure. I will be watching this thread.

Good luck Sir.

Rickey.

 

[alanu]

2005 you swapped your catalytic. Thats meaningless because alot of aftermarket catalytic converters have less rhodium in it. For a BMW I'd spend the beans and buy an ultra catalytic from walker. They are OBDII speced have more precious metals than a "standard" walker cat. Testing a catalytic for efficiency is not really accurate because you can only really test "oxidation" not "reduction" looking at your previous test after new catalytic your readings looked worst.

Get the 02 sensor tested with a scope. Should have at least 10-12 cross counts in 10 seconds. The voltage sweep should be withing .1 - .8Volts. If its less than 8 cross counts your 02 sensor is getting lazy. If its running lean your NOX will go high.

Make sure your ignition timing is spot on factory specs.

Wierd that your CO readings are higher (richer) and you failed nox. excessive timing seems to look like more of a probable cause.

You might be able to use a colder plug as long as you dont start to foul your plug.

 

[Merkava_4]

FWIW, I had a smog check guy tell me once that elevated NOx levels were attributed to ignition issues; not fuel and air mixture.

 

[alanu]

Quote:

---

FWIW, I had a smog check guy tell me once that elevated NOx levels were attributed to ignition issues; not fuel and air mixture.

---

Change your fuel map to run lean across the board. Leave the ignition alone. I assure you that your NoX will increase dramatically.

That smog guy is not really being realistic. HIgh percentage of NoX failures is due to plugged EGR passages, defective EGR's and inefficient catalytic converters. I'd say least likely is ignition timing.

 

[nel]

Speaking from experience--both as a former emission controls engineer at GM and as an owner of a '90 BMW 325is--your conversion efficiency needs a dramatic boost. Both HC and NOx are high. HC increases with richer A/F, while NOx increases with leaner A/F. Your O2 sensor is relatively new, so the likely culprit is the converter. Was the converter nice and hot when you went in for a test? If not, try retesting after a 30 minute run on the freeway.

When I bought my '90 325is two years ago, the previous owner had trouble passing smog in California--NOx was high. He had a generic, low cost Magnaflow installed for about $100. It barely passed with the new converter. I had a more expensive Magnaflow installed (~$300) that is CARB and OBD-II compliant. NOx levels are now down to about 10% of what it was before.

 

[JHZR2]

Well, we removed the dinan performance chip and re-tested after a good highway run. With the OE chip, the numbers are now:

NOx 2700
HC 206
CO% 0.63
CO2% 13.9
O% 0.7

Getting worse...

 

[Junior]

Is the vehicle running any hotter? Maybe the coolant is running too hot?

 

[Junior]

Quote:

---

FWIW, I had a smog check guy tell me once that elevated NOx levels were attributed to ignition issues; not fuel and air mixture.

---

High NOx is caused by high cylinder pressures and temperatures.

 

[tc2468]

your chip killed the cat

 

[JHZR2]

Quote:
Is the vehicle running any hotter? Maybe the coolant is running too hot?

nope, in fact, after doing a changeout and multiple flushes to G-05 coolant, the car runs slightly cooler, about a needle width below where it usually was...

 

[JHZR2]

Quote:
your chip killed the cat


Except that it barely passed NOx when the OE chip was in there... With the chip in there it was consistent with the OE cat in the car. In an attempt for a quic fix last inspection, 2 years ago, I swapped in a new 3-way converter, which made me barely pass.

Only this time is the Nox reading crazy high... and OE chip doesnt make it go back down, in fact it has gone up!

 

[Rickey]

Ok left field... assuming that the cats are OK.
Advanced cam timing, if it was off from the factory that could explain it maybe.
Just a stab in the dark on my part really.

Good luck sir.

Rickey.