Failed emissions...........again

[marc_gti]

hi peeps

 

need ideas on what may be the problem.

 

car went for mot re-test after failing on emmisions, so on the advice of the mot centre i changed the cat and lambda sensor, its gone back in for the retest and failed again on emmisions.

 

the garage changed over to a different MAF sensor and it is still the same..

 

what is the next step to check??

 

cheers

[Craig855S]

how is the rest of ur exhaust? is it burning oil? how recent are ur spark plugs?

 

was it a new cat and lambda u fitted?

 

u could run redex through it?

[marc_gti]

hi craig

 

not burning any oil, new spark plugs and leads not long ago. brand new cat and lambda fitted also

[sidrick]

Were the cat and lambda sensor new?

[reaper tw4]

Were the cat and lambda sensor new?

 

brand new cat and lambda fitted also

[escort4x4]

has your car got a exhaust blow, that will make your car fail an mot as aswell,

was your car red hot before being tested

 

also id take to another garage mate, see if fails there

[charlie74]

new airfilter and a good dose of injector cleaner and then go cane the tits off it,, make sure you take it for the retest with the engine hot,,

[speedy]

put fule system cleaner in check ur air filter if dirty replace it

check exhaust system for leaks

sort out any missfires etc if it has any

remove any shitty ebay chips that cause over fuleing

give the car a fooping good ragging get it hot befor testing the emissions

[stoney]

Would actualy be nice to know on wich part of the emissions it failed on to give more of an accurate diagnosis, was it,

 

hydrocarbons?

 

lambda?

 

carbon monoxide content?

 

carbon dioxide?

 

pm me and i can telll u wat you need to do

[marc_gti]

pm sent

 

gave the car a bit of a serice today, new plugs, oil + filter, fuel filter and air filter. any thing else i may need to do??

 

been looking around and have read that the EGR Valve may need to be cleaned? and maybe replace the coolant temp sensor? also forgot to mention that the car did have a superchip fitted, this has now been removed and have reset the ecu.

 

any ideas or help would be great car goes back in wednesday for test again

 

thanks

Edited March 15, 2009 by marc_gti

[MikeyRS]

post up the emission figures bud

[marc_gti]

fast idle CO fail

 

second fast idle CO Pass (on limit)

 

natural idle CO Fail

 

everything else passed

[MikeyRS]

Need the actual figures to see how far out they are

[marc_gti]

fast idle co fail 0.59%

 

natural idle co fail 0.58%

 

the limit is 0.50% so its not miles out

[escort4x4]

High carbon monoxide (CO) emissions are a telltale sign of a rich fuel mixture. On older carbureted vehicles, fuel-saturated plastic floats, incorrect float settings, leaky power valves and misadjusted chokes are often responsible for the rich mixture. On newer vehicles with feedback fuel controls and fuel injection, leaky injectors, excessive fuel pressure and sluggish or contaminated O2 sensors are all possibilities to investigate.

 

Harder to diagnose are elevated oxides of nitrogen (NOX) emissions. Causes here may include a defective EGR valve, EGR vacuum solenoid or motor, plugged EGR ports in the manifold, over-advanced ignition timing or engine overheating.

 

In areas with I/M240 programs that require an evaporative emissions check, problems with the charcoal canister, purge valve and evap plumbing may cause a failure. A leaky gas cap is an often-overlooked cause for leaking fuel vapors into the atmosphere.

 

EMISSIONS FAILURE

Since loaded mode testing is the most demanding in terms of emissions performance, let's see what happens when a vehicle fails this type of emissions test.

emission failure

 

A loaded mode test uses a dynamometer to simulate actual driving conditions. During the test, pollutants are monitored during idle, acceleration, cruise and deceleration. The pollutants are typically measured in grams per mile (gpm) rather than percentage of concentration (%) or parts per million (ppm) which makes it hard to translate ordinary 4 and 5-gas analyzer readings into gpm readings. Software is available that can do a fairly accurate conversion using additional inputs such as vehicle weight and engine displacement. Without the proper software, there's no way to know if a vehicle's HC, CO and NOX readings are within the required gpm limits or not.

 

In any event, the motorist is usually given a printed form that indicates which portion of the test their vehicle failed and by how much. The form may also provide additional diagnostic readings such as carbon dioxide (CO2) and/or oxygen. Some forms also plot the data on a graph so you can more easily see which part of the test produced the highest levels of pollution.

 

In an I/M 240 test, the vehicle is run on a dynamometer for up to 240 seconds. The drive cycle is broken into two phases. Phase One lasts 93 seconds. The test starts at idle, includes two minor accel/decel curves before attaining a "low speed cruise condition," then decels to a stop. Phase 2 includes three high speed cruises: One at 47 mph and two cruises in the 54 to 56 mph range. During the drive cycle, the emissions are gathered and recorded second-by-second.

emissions testing

 

The I/M 240 software calculates the total amount of HC, CO and NOX produced for each portion of the test. If emissions are low enough during the first 30 seconds of the test, the test may be ended early with a "fast pass" issued. But if emissions are high or borderline during the first part of the test, the test will go the full duration to determine an ultimate pass or fail grade.

 

In states that use a simpler "hump" drive cycle, the vehicle accelerates at a given rate from idle to a predetermined cruising speed (30 to 33 mph), holds at cruise for a given number of seconds, then decels back to idle.

 

There are some preliminary checks that should be made any time a vehicle with an oxygen sensor feedback control system fails an emissions test:

Always verify that basic engine compression, vacuum, fuel pressure and ignition timing are normal;

 

The air cleaner is clean and unobstructed;

 

The engine is running at normal temperature;

 

All emission control devices are installed and appear to be connected properly; and

 

Is the "Check Engine" light on? If the light is off, cycle the ignition to make sure the bulb is not burned out. If the light is on, there are stored trouble codes that can help you make your diagnosis. If the computer doesn't use LEDs to display the code, a scan tool or other diagnostic tester will be needed to access the codes.

 

On 1995 and newer vehicles with OBD II, the OBD II system is usually capable of detecting most of the problems that can cause an emissions failure. If the light is off, check for history codes that may reveal a part problem.

emissions test

 

IDLE EMISSIONS

A vehicle that has sharply elevated HC or CO emissions at idle will usually have a noticeable misfire and/or rough idle. The most likely causes here would be:

Fouled spark plug(s);

 

Shorted spark plug wire(s) or defective plug boot(s);

 

Vacuum leak;

 

EGR valve stuck open;

 

Burned exhaust valve;

 

Misadjusted throttle body air/fuel mixture; or

 

Misadjusted carburetor idle mixture.

 

An extremely rich fuel condition can also cause elevated HC and CO at idle, while an extremely lean condition will only cause HC to rise abnormally. A leaky EGR valve can act like a vacuum leak and cause a lean misfire at idle.

 

HC and CO will be somewhat higher as a cold engine warms up because the fuel system may still be running in open loop. Until the engine reaches a predetermined temperature and/or the oxygen sensor gets hot enough to produce a good signal, the PCM will supply a relatively rich mixture while the system is in open loop. A faulty thermostat that is stuck open or a defective coolant sensor may prevent the system from going into closed loop.

 

NOX emissions are always lowest during idle and decel because that is when engine load and combustion temperatures are lowest.

 

ACCELERATION EMISSIONS

During acceleration, the engine momentarily drops out of closed loop and receives a richer fuel mixture for more power. During this time (depending on the system), the MAP or Airflow Sensor and the TPS sensor play critical roles in controlling the fuel mixture.

 

Most fuel-injected engines have either a throttle position sensor or switch that indicates when the engine is at idle. When this device indicates that the engine is no longer at idle, the on time of the injectors is increased to temporarily richen the fuel mixture. The same thing happens any time the engine comes under load and manifold vacuum drops. The MAP sensor tells the computer the engine is under load, and the computer responds by adding more fuel.

 

It is normal to see some spikes in CO during acceleration, but unusually high CO readings indicates that the fuel mixture is too rich. Possible causes might include:

 

Flooded charcoal canister or a leaky purge valve;

 

Leaky power valve (older carbureted engines);

 

Defective mass airflow (MAF) sensor, manifold absolute pressure (MAP) sensor, or vane airflow meter (VAF); or

 

Defective throttle position sensor.

 

If the feedback fuel control system is working properly and there are no apparent sensor or purge valve problems, the catalytic converter may be contaminated or not functioning.

 

Elevated HC readings during acceleration indicate ignition misfire under load. The causes could be:

 

Defective knock sensor;

 

Weak ignition coil(s);

 

Excessive resistance in spark plug wires;

 

Arcing inside the distributor cap;

 

Worn, fouled or incorrectly gapped spark plugs;

 

Over-advanced ignition timing; or

 

Lean air/fuel mixture.

 

NOX readings will rise sharply during acceleration and will peak a few seconds after the cruising speed is reached. If the EGR system fails to recirculate exhaust back into the intake manifold, combustion temperatures will rise causing an increase in NOX. The higher temperatures may also cause some detonation (spark knock) to occur, which may be audible when the engine is under load. Causes of elevated NOX emissions during acceleration include:

 

Defective EGR valve;

 

Leaky EGR valve plumbing or control solenoid;

 

Carbon deposits in EGR manifold passageways;

 

Carbon buildup on pistons and in combustion chamber;

 

Over-advanced ignition timing;

 

Defective knock sensor;

 

Engine overheating (check thermostat, fan, coolant level);

 

Exhaust restrictions.

 

Check through that mate few ideas there