Hello everyone. Have been lurking here for about a year now and it's about the time to join in. I presently have '97 E320 with 150K miles and '04 E320 with 31K miles. It's the '97 model that recently failed Cal. emission test, due to Check Engine light and error codes P0455 - EVAP Ctrl Gross Leak Detection and P0422 - Main Cat Efficiency Below Threshold (Bank 1). The car actually did pass the emission portion of the test, however, failed overall. About a year ago the MB dealer had replaced the fuel tank gas cap, as the same the Check Engine light has been appearing intermittenly. They could no find anything else to cure the Evap System problem. Regarding the Cat. situation, the Smog Check technicain said that the error may be appearing due to tired Oxygen sensors, and it may not be the Cat. it's self that triggers the error code. As I stated, the car has 150K miles and it has been driven mostly by my teenage daughter for the past 2 years and I intend to keep it for her during her college years.
Has anyone have any suggestion how to approach this situations? Any input would be greatly appreciated.

Steven

 

Should be quite easy to resolve. However since you have already been to the dealer I wonder why you still have a problem.

OK P0455 (I haven't confirmed your definition) Evap Loss problem. The system senses gas tank pressure. If there is a leak you get the Evap loss warning. New gas cap temporarily solved the problem but it has come back. Need to inspect cap again. Maybe a rough spot on the gas tank neck has again damaged the gas cap gasket. If not there is a leak somewhere (need to pressure test/inspect lines to engine bay and Charcoal Cannister, or the gas tank sensor is faulty. This is likely what caused you to get a FAIL.

WRT to Cat Efficiency. Looks like you are borderline here rather than the cause of the FAIL. However the system reads the O2 sensor before and after the precat. A predetermined improvement is required in CO level (determined from O2 reading) between these two points. Could be the Cat or the O2 sensor. Need to see what the O2 readings are before and after and compare LH to RH side of car. This will help decide O2 sensor vs Cat. So what are the readings.
Hope this helps.
Stuart

 

Thank you Stuart. This weekend I will check the evap system thoroughly. I am replacing both O2 sensors (after 150K they may have had it anyway), changing plugs, air filter, oil and will see what happens

 

Hi,

It would be more cost effective to get the O2 sensor voltages first and confirm that one is bad. However if your mind is set ensure you get the correct sensors.
Low cost universal sensors MAY give you more problems than you started with!

If emission levels are OK and you don't have a misfire there is no real need to change plugs. There are 12 of them and life is usually in excess of 75k. If you do change them ensure you use a "release" agent on the threads of the new plugs and only tighten to the recommended torque (not sure what it is offhand but surprisingly low) if you want to get them out next time around. Likewise use plugs the same as those removed. Don't be taken in by all this 3 electrode / Super-duper plated / Long reach / Long life / improved gas mileage stuff. The original plugs appear extremely robust and with recommended change point 75k/100k they seem to the the job OK.

Stuart

 

Stuart, the '97 E320 I have has 6L engine with 6 spark plugs. It was the last year that engine was used, before MB switched to V6. I had the same engine in '95 E320, with 24 valves and variable valve timing. I like that engine a lot. It's higher reving with nicer sound that the 18 valve V6 that replaced it, however, the power and torque peaks are also higher in the rev range. Regarding the plugs, the existing have exactly 78 K on them, hence time is up. I'm a getting OEM O2 sensors, so I should avoid the problems you mentioned. Again, thanks for your input.

Steven

 

I hope you resolve the problem.