91 420 SEL failed emissions - GA
 

My 420 just failed emissions and I need some advice. It has about 180,000 miles on it.

Here is the complete test (failed tests are in bold):

PASS - HC ppm reading was 63 of 103 on 25/25 and 34 of 107 on 50/15
PASS - CO % reading was 0.05 of .57 on 25/25 and 0.02 of 0.59 on 50/15
FAILED! - NOxppm reading was 2308 of 712 allowed on 25/25 and 3308 of 786 on the 50/15 test.
PASS - RPM reading was 1375 of a 2500 max on 25/25 and 1286 of 2500 on 50/15
CO+COe% reading was 14.6 of 6.0 min on the 25/25 and 14.1 of 6.0 min on the 50/15

The Catalytic Converter was read as: Present

Fuel Cap Test 1: Fail

I'm being told I need to replace the Catalytic Converter and was wanting some advice before I jumped into that. If a converter is needed are there any good universal afterkmarket options?

Thanks in advance!

My 420 failed emissions in GA
 

My '91 420 just failed emissions and I need some advice.
It has 180,000 miles on it.

Here is the complete test (failed tests are in bold):

PASS - HC ppm reading was 63 of 103 on 25/25 and 34 of 107 on 50/15
PASS - CO % reading was 0.05 of .57 on 25/25 and 0.02 of 0.59 on 50/15
FAILED! - NOxppm reading was 2308 of 712 allowed on 25/25 and 3308 of 786 on the 50/15 test.
PASS - RPM reading was 1375 of a 2500 max on 25/25 and 1286 of 2500 on 50/15
CO+COe% reading was 14.6 of 6.0 min on the 25/25 and 14.1 of 6.0 min on the 50/15

The Catalytic Converter was read as: Present

Fuel Cap Test 1: Fail

I'm being told I need to replace the Catalytic Converter and was wanting some advice before I jumped into that. If a converter is needed are there any good universal afterkmarket options?

Thanks in advance

Start by getting a new fuelfiller cap.
I doubt you need a catalytic converter, based on your CO & HC readings.
NOx is controlled mostly by the EGR valve.
I would check it ( or have it tested ) first. ;)

I second the EGR. If your cat was bad, the CO and HC would probably be much worse. EGR controls peak combustion temperatures and NOx formation, so faulty EGR would be the prime culprit for a NOx fail.

Here are some general tips to reduce emissions at test time:

1) Change oil and filter just before going to the test station. This reduces emissions from burning oil.

2) For my part, I would use an oil additive like STP Oil Treatment to thicken the oil a bit and further reduce emissions from oil smoke.

3) Have the car fully warmed up before testing.


And in your case it does look like the EGR valve could be responsible. Does the car generally run well? If so, I expect the EGR valve may be stuck closed - carboned up all around it. You'll need to remove it and clean out the passageways leading to and from it. Also check the vacuum hose leading to the EGR valve to make sure it is still attached. Some people disable the EGR system, and that has an impact on gasolene engine emissions testing.

Ken300D

Well Ken, in my humble opinion, all the afformentioned " Tricks " will only serve to reduce your HC numbers. ;)

Thanks for the advice. In looking at my engine manual, nothing is labeled EGR valve. Which valve is the EGR & what does MB call it? This engine has the air pump emission system with air shut off valve, (exhaust gas) check valve, switch over valve. Which is the EGR?

Could it be that rusty looking lump that I have attached to my exhaust manifold? The one I'm afraid to undo because I may break a stud/bolt?

The egr valve looks like this.
http://img.eautopartscatalog.com/live/B701084216DEL.JPG

As I said before, considering the price ( $ 330.00 ), check it and all the pieces that work with it first. ;)

Hi
You need to have your on/ off ratio checked with that kind of mileage how is you 02 sensor how is your gas mileage around 20 mph... if that is dropped off 02 sensor bad.. The mixture is controlled by a loop electronic system which controls EHa valve on side of fuel distributor.. How does the enging run smooth if its rough these engines are prone to vacum leaks if you have a vacuum leak then you will run lean.. all this will show up with on off ration check..
Bob

based on numbers that you provided,your car is running lean.you don't give the o2 reading which would confirm it.generally speaking if there is enough fuel to consume all the o2[except for maybe .1 or.2%] there will be no o2 for nox to form.your co2 numbers also suggest not running at peak efficiency[should be closer to 15%].i think richer until very low o2 reading will get the nox under control.i don't think that egr on benz is activated at those low rpm's.

Is the timing adjustable on your engine? You could probably retard it a few degrees and pass.

This engine comes w/ the timing set @ around 2-3 degrees BTDC...Very conservative.

Where in GA are you?? I'd wager with some tinkering I could get it to pass..

Jonathan

Hah, now we know your true idendity,..........you're Tinkerbell. :D

I thought the 420sel came with 12 degrees btdc?