Ok just took my 91 300E in for smog. Failed the 25 mph emissiin test.80 hc(ppm) allowed. Ran at 100. Need advise.

Slightly high HC can be caused by many factors.

ASSume that the ignition system is in perfect condition?

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Yes it should be. All 20 components checked like catalytic converter PCV EGR Vacuum sensors oxygen sensors says ignition timing is N/A due to computer controlled etc etc. passed without incident. I did a smog background on it and for the past 12 years or so it passed. I bought it at auction as a salvage so i need smog and lamp and brake to get plates. I had head gasket replaced, head resurfaced, tune up done .I filled it with cheveron supreme and drove it home from mechanic. It just runs 20 ppm over on the 25 mph at 1615 rpm test. It did probably sit for a couple years. Do I just need to drive around a bit more to clear out the crap from sitting? I have noticed there is still some sludge residue in the coolant from the head gasket blowing so Im taking out the radiator today and flushing it but I didnt really think that would make it fail.

Any opinions you might have would be greatly appreciated. Thank you.

Slightly high HC is normally caused by very slight misfires.
You could open the spark plug gap to .040" & see if that helps

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MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

A better diagnosis could be given if you posted the type of test and complete test results.

California has tagged the M103 engine family as "high emitter profile". The KE fuel system is a factor, but catalyst aging is likely the primary issue.

There are a couple of easy "tweaks" that can significantly reduce emissions that are discussed in the folloing threads:

300TE Failed AZ Emissions...NOx close...

Passed Smog-barely

Emission testing has been extensively discussed, and I've posted a lot of test data and analysis, so you should do some more archive searching.

Duke

post the results for the complete test. That will us give a better idea of the problem.

__________________

Chris
84 280sl
82 300d euro

My emmisions were high and I switched the Cat. and all was good. They just visually check the Cat. The smog tech. cant really tell if it is working properly or not. It will just give a bad smog reading like high HC. After My car barely passed I ended up hearing the Cat rattle around soon after. I tuned the car with the bad cat as best as possible then got a new one.
MY readings are now pretty much around 0% CO and 7ppm HC. Before the new Cat. 0.5% CO and 170ppm HC.

__________________

Chris
84 280sl
82 300d euro

You are expecting too much from the emission test, those checks are only to verify the parts are on the car and not a function test.

Did you drain the 2 year old fuel?

A lean condition will cause high HC due to random miss fires that you might not feel.

Clogged injectors ( from old fuel ) will dribble rather than spray, this will cause higher HC.

thank you all for your help. I tried the spark plug gap and yes it has all new cheveron supreme feul. I drove it for 120 miles still fails. Ive been asked by you to post results. So.. ASM Emission Test Results are:

%CO2 %O2 HC ppm CO% NO ppm
test rpm meas meas max ave meas max ave meas max ave meas
15 1582 14.6 0.0 105 41 101 .69 .05 .04 530 175 55
25 1609 14.6 0.0 80 30 103 .56 .05 .05 487 138 52

15mph passes the 25mph fails.
SORRY THIS THING WILL NOT FORMAT THE PAGE RIGHT. i WRITE IT OUT SO ITS LINED UP BUT WHEN IT POSTS IT DOESNT STAY

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Those are interesting numbers. You have high unburned HC, but low CO, and zero oxygen in the exhuast stream. So the fuel that is burning is burning completely and all the oxygen is being consumed. But you have too much fuel for the available oxygen. You would seem to have a mixture problem - either too much fuel or not enough air. Have you checked the air filter element lately to see if it is dirty or restricted? Cars that have sat tend to have rats nests in such places.

Ya i had the head gasket changed a tune up put on it. new plugs new air filter. new oil new gas. Could it be the cheveron supreme doing that. I mean its suppose to use supreme gas, so I wasnt really factoring that in. I just dont want to go to a test and repair and them try to tell me its the most expensive thing before I get some opinions. I know the cat is a very real possiblity but I hear they are around 1,000 dollars and you cant put an after mrket so Im hoping to hear its not the cat.

Changed the Cat. and all was good. Does the cat rattle. You could get a Ca emissions Cat. more expensive but also will last longer. It may work better as well. I am not saying for sure it is the Cat but I would bet on it if it were mine.
Actually, I look again and yours are high HC on the 25 mph test and the idle test HC is close to failing as well. My readings were high on the Idle test only.

__________________

Chris
84 280sl
82 300d euro

-Run guaranteed to pass/seafoam bottle through your tank
-Smog your car hot...Really Hot...
-Remove Air filter before smog.

it will help a bit.

To compare

1. When I Failed


2. After Doing above (Engine heat was so much that you feel it 3 feet away with Hood open)


3. Last year First attempt (Changed plugs, New oil day before smog test, Ran through half bottle of seafoam through intake)

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2) '93 300E 2.8...Green/Tan MBTex..........202k Miles(and going)
3) '89 420SEL...Light Blue/gray Leather....155k Miles (Retired )

Are you sure you cannot get an aftermarket Cat?

__________________

Chris
84 280sl
82 300d euro