HELP??!! 94 e420 FAILED Emissions : How To Correct??!!
 

Hello Forum Friends;
My 1994 MB e420 w/238,436 miles FAILED State Emissions Test Today.....
Car Runs very good, Smooth idle ; No misses; quick throttle response and No visible/smoke exhaust.
Please advise on what the included Emission Test Failure Data Requires me to correct to PASS .....

Test Parameter ... Result .... Additional Information if available

Idle Speed CO ... 8.56 % ... GREATER THAN 1.20 %
High Speed CO ... 4.40 % ... GREATER THAN 1.20 %
Idle Speed HC ... 623 ... GREATER THAN 220 parts per million
High Speed HC ... 373 ... GREATER THAN 220 parts per million

.....Please Help /Advise on items Needing Attention for a Passing Test
THANKS ; In advance for All Replies!!!! Chance

Could really be a lot of things. First off, at 238k miles, I'd guess you are still on the original cat? Next time you get it tested make sure you take it on the highway and get it nice and hot. The cat cools down quickly once the car is parked and reduces its efficiency. From then on, it's mostly fuel and timing tuning.

The function of the oxygen sensor is the most important thing in smog testing.

If it isn't working then you can get that type of results.

MBdoc do you know the threshold for tripping the CEL for these O2 sensors? Something I was wondering not too long ago with my 300E. I know in other cars I've owned, they trip the CEL quickly (IOW not much variation until it trips the light).