Smogtips
CHOOSE YOUR CITY OR ZIPCODE:
Within:
SELECT SMOG CHECK TYPE:  

Join the community and post your question. Use our Ask-A-Tech for free now! ASE experts standing by.

Forum > Failed Smog Test > Question

Ford Crown Victoria Failed Smog Check For High HC

The vehicle in question is a 1995 Ford Crown Victoria. I think the smog technician may have caused an error with the exhaust ventilation hose which was kinked. The car passed everything except HC (44) at 25 mph (max 33). At 15 mph HC passed with a 36 PPM measurement (max 57). All other results passed and were essentially same as last year. During emissions tailpipe test, the technician put a long hose over the tail pipe to help direct the exhaust away from the shop. This hose was moved during the test and became kinked with a 90 degree bend. I am wondering if that obstructed the outflow of exhaust. I pointed this out to the technician who didn't fix it, and said "no problem". My question is could this kinked exhaust hose have restricted exhaust outflow and artificially increased HC PPM at the probe site? Is it reasonable to get a retest (no charge) at the 25 mph rate with un-kinked (or no) hose? Other measurements were: CO% 0.27/0.26: NO 120/71 (15/25 mph). The smog technician said either oxygen sensor or catalytic converter is the likely problem. Thank you.
Answer:

What causes high HC on the Ford Crown Victoria?

Before determining where to start the diagnosis for a Ford Crown Victoria high HC failure, we'll need to first observe the vehicle's CO (carbon monoxide) and NOx emissions. It is important to learn whether your vehicle is in proper fuel control. Usually high CO and HC faults are due to engine management systems not being able to regulate fuel delivery correctly. When not fuel management related, high HC problems are more often due to defective ignition components and ignition timing.

Where to start the high HC diagnosis?

The diagnosis should begin with inspection of the air/fuel "feedback" system. This includes ensuring the oxygen sensors are working properly, the emissions computer system is receiving signals from the oxygen sensor/s, the computer is computing the data properly and sending the correct signals to the fuel injectors to either increase or decrease fuel delivery to the combustion chambers. 

The feed back test will utilize a 5-gas analyzer (the smog machine can be used for this test) and propane. The smog technician will introduce propane to the intake system and ensure the oxygen sensor is sensing the propane as an increase in CO (carbon monoxide), and ordering the emissions computer to decrease fuel delivery the instant propane is added to air intake stream. This test should be done after the engine has sufficiently warmed up and while it is running at idle. If no change in fuel delivery is seen there is feedback problem. The diagnose then should turn to which part of the feedback system is not working right.

Using a multimeter voltmeter the smog repair mechanic should observe the voltage output of the oxygen sensor as propane is added. The voltage coming from the oxygen sensor should increase. If no voltage increase is seen the O2 sensor is not working. The sensor should be replaced and the test started over. If voltage increase is noticed the smog technician needs to ensure voltage increase is also present at the computer input terminal. If voltage is present at the terminal as well next the technician must ensure the emissions computer output to the fuel injectors are lowering "injector pulse rates". At the end of the fuel system feedback test it will be know whether the high emissions your vehicle is producing is an electronic or mechanical fault. The technician can then further diagnose the failure.

Other important emission sensors also determine air/fuel ratio

The additional sensors which should be inspected for proper operation (and which also play a significant role in determining air/fuel ratio) are the Engine Coolant Temperature (ECT) sensor and the Manifold Absolute Pressure (MAP) sensor. If the coolant temperature sensor is not operating properly (not sending the correct voltage signal to the Engine Control Module) the ECM will not be able to properly calculate how much fuel to deliver to the combustion chambers. When the engine is cold the ECM is programmed to deliver a richer fuel mixture (more fuel). As the engine warms up, the ECM will lean out the mixture. Ensuring the ECT is sending the correct voltage to the ECM is important for correct air/fuel ratio (optimum is 14:7). The MAP sensor measures the amount of intake manifold vacuum/pressure. This sensor must send accurate information to the ECM as well, in order for the ECM to calculate exactly how much fuel to add to the air entering the combustion chambers.


posted by SmogTips Support

 

View SmogTips.com in: Desktop / Mobile