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?

__________________
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

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.

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

Attached Thumbnails

 

These are very good numbers for a M103 other than HC, and the fact that O2 is 0.0 means the O2 sensor and catalyst are working well.

That leaves excess misfires as the source of the high HC.

What make/model of spark plugs are in the car?

The ignition system is designed for non-resistor plugs (lots of archive discussion on this issue), but they are getting hard to find. Resistor plugs alter the voltage wave form and reduce spark energy at the plug, which can lead to exess misfires - often not enough to notice, but it can show up in the emission test.

RFI resistors are built into the spark plug boots and the distributor cap. The wires should measure about 2K ohms. Pull and twist on them slightly them while testing. It's possible that the plug wires on a lot of M103s have been damaged by pulling the wires off the plugs by hand. I have a special tool that I bought way back when that grabs the metal RFI shield, so no stress is placed on the wire iteself.

There is also a 1 or 2K ohm resistor in the distributor cap towers. My OE cap had a "flaky" tower that would show the proper resistance when holding the cap loosely, but then go to infinity if I put some thumb pressure on the side of the tower, so I replaced the cap.

The combination of resistor plugs and the flaky cap almost caused my car to bust the 100 ppm HC idle limit in the 1995 two-speed no load test. A new cap and going back to proper Bosch non-resistor plugs dropped the idle HC from 100 ppm in '95 to 22 in the '97 two-speed no load test.

Concentrate your effort on testing secondary ignition system components and make sure you have OE equivalent non-resistor plugs installed.

BTW, use periods instead of spaces to line up the data under the proper headings. The software ignores extra spaces but will recognize periods to keep the columns reasonably aligned for easier reading. These are the ASM test results for my '88 190E 2.6 five-speed, done about two weeks ago.

...............CO2....O2............HC...................CO..................NOx
test..rpm..meas..meas..max..ave..meas..max..ave..meas..max..ave..meas

15...1587..15.0...0.0....116...27.....55...0.74..0.09..0.28...791..255...32

25...2638..15.1...0.0.....91...18.....17....0.62..0.07..0.13...730..223...42

Duke

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

__________________
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:

http://www.peachparts.com/shopforum/tech-help/298724-300te-failed-az-emissions-nox-close.html

http://www.peachparts.com/shopforum/tech-help/123674-passed-smog-barely.html

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

-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)

__________________
1) '04 S500 Gold/Beige......120k Miles
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

No Im not 100% sure about after market cat. Just been giving a few opinions from people who have tried and didnt work. Geuss Im just gonna take it to a test and repair and run the diognostic and see what the computer says. Thank you everyone for your input.

Ok thank you very much for the spark plug info. I did just have the plugs changed when the head gasket was donr and they might not be the right ones. Im gonna pull them and buy one of the recommended make and models in my owners manuel. Thank you