Calif Smog Test Failed (again);

[BlackOnBlack]

Hi, can any of my fellow California bimmernuts provide advice on what might cause HC and NO to be over the limit on the low speed test (15 mph)? 25 mph passed;
1992 525i manual trans.
241,000 miles; new plugs; air filter; fresh oil; 70 degree weather; normal operating temperature;
Cars doesn't noticeably burn oil.
When warm, Has been idling @ 1,000 for the past few months. When cold, it idles ok at @ 700;
Last smog test in 2011 it originally didn't pass as a gross polluter in both low and high speed tests.
Guy put on a new set of cats and it passed.
Just wondering what would burn out the cats and if it might have happened again.
also, my car suffers from the no hot-start syndrome. I replaced the relay but didn't fix it.
I'm trying to track down a fuel line check valve but they're hard to come by.
Thanks,
Steve

[shogun]

Three Reasons for Gas Analysis, from Bosch, I copied that in 2008


5 Gas Analysis

Bosch Technologies Group

Three Reasons for Gas Analysis

* Identify engine performance and mechanical problems
* Test the running efficiency of the engine
* Test for exhaust emissions against state and federal standards

Combustion Chemistry and Gas Analysis.

* The combustion process releases the energy stored in the fuel
* Fuels consist basically of carbon(C) and hydrogen(H) referred to as hydrocarbons (HC).
* Under ideal conditions all of the HCs would be converted to H2O, CO2 and heat.

Combustion Chemistry and Gas Analysis.

* Unfortunately this complete combustion is rarely if ever achieved
* Short burn times, continuously changing mixture ratios and air temperatures, and combustion chamber quenching produce conditions which give rise to the formation of pollutants

Pollutants

* Incomplete combustion produces carbon monoxide (CO)
* Unburned fuel produces hydrocarbons (HC)
* High combustion temperatures produce oxides of nitrogen (NOX)

Other Exhaust Gases

* Carbon dioxide (CO2) is a product of complete combustion. Therefore the higher the level of CO2 the more efficient the engine is running.
* Oxygen (O2) level in the exhaust indicates the fuel-air mixture.

High O2=lean

Low O2=Rich

Gas Analysis as a Diagnostic Tool



Gas analysis

* Is a quick and accurate way to determine the running conditions of an engine
* By observing the 5 gas readings and understanding their relationship to each other you can diagnose the 3 major engine areas:

Fuel delivery

Ignition

Engine Mechanics


High HC Only


Hydrocarbons are unburned fuel. This can be caused by:

Ignition Timing (base and advance)

Vacuum Leaks (hoses, brake booster, manifold, evap. etc.)

Ignition (misfires, coil breakdown, etc.)

Mechanical (low compression, bad cam, etc.)

Catalytic Converter Failures


High CO Only


* Carbon Monoxide is a result of incorrect fuel/air mixtures. Causes include:
* For Carburetors (float level, power circuit, choke circuit)
* For Injection (injectors, pressure regulator, temp sensor, MAP/MAF sensor)
* For Both Systems (air filter, PCV, Evap, O2 sensor, air injection

High Nox Only


* NOX is caused by high combustion chamber temperatures. Check:
* EGR (valve, controls, solenoids, passages, vacuum hoses)
* Ignition Timing ( base and advance)
* Engine Temperature (cooling system, fan restricted exhaust, Thermostat)
* Vacuum Leaks (hoses, booster, evap, etc)
* Mechanical (carbon deposits, converter, etc)

High CO and HC


* Normally, when HC and CO are high it is the result of a CO failure driving the HC high.
* Correct for high CO first (Excessive fuel, restricted air, Evap., etc.)
* If HC is still high, test as high HC (ignition, timing, mechanical, etc.)



High CO and Nox

* These problems are normally incompatible. If they occur on the same test they will most likely occur at different points on the drive cycle
* Correct CO failure first
* Retest and locate NOX failure in drive cycle and correct as NOX failure only

HC and NoX

* High HC and NOX normally occur as the result of a lean misfire. Check for:
* Lean run (vacuum leaks, mixture problems, fuel delivery, etc.)
* Mechanical (oil burning can cause high combustion chamber temperatures)

CO, HC and NOX

* This is a complete breakdown of the emission systems or multiple failures.
Check:
* Catalytic Converter (missing, damaged)
* PCM (closed loop, wiring, etc.)
* Drive cycle ( if failures occur at different points diagnose each failure separately)

[BlackOnBlack]

Thanks Shogun. I'll start some troubleshooting. maybe as simple as a vacuum leak...

[Rustam]

what gasoline do you use? if this is m50 engine, it has higher compression, you cannot use 87 or 89 octane, but should do 91. low octane number can result in detonation or preignition and this can damage the catalytic converter...

put 91 octane, and also wet the air filter in water, not to the point of dripping, but moderately soaked. this will make the intake charge cooler and help avoid detonation further. also make sure that you go for a good drive before smog test so the catalysts are well warmed up.

[bennyg]

What mpg does your car get and is it abnormal and do you have OBC figures to compare with

The ~25% my OBC was not accounting for vs pump fill volume was helpful in diagnosis. I got an injector clean as well as a new fuel pump and lambda sensor (I suspect got gunked up from unburned fuel?) and it ran sweet again, I always suspected a dirty injector was leaking too much fuel into a cylinder - if you get desperate this is something else to consider. One cylinder with bad AFR might cause the pollutants to show in the exhaust gases but not affect the overall AFR enough to be detected?

Though for your particular case nox and hc are according to the Bosch list above indicative of lean misfire rather than rich, plus I only know that stuff from an organic chemistry background as we dont have emissions testing in Aus since theres too many 20yr old big six barges driving around half the traffic would be off the road in some parts if we did!

[Tiger]

I would pull the injectors and send them in to get it thoroughly cleaned.