1977 280SE (W116) Failed Colorado Emissions Testing - Mercedes-Benz Forum

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post #1 of 19 (permalink) Old 05-18-2016, 02:51 PM Thread Starter
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1977 280SE (W116) Failed Colorado Emissions Testing

Hello all!

I recently purchased a 1977 W116 280SE from New Mexico and drove it home to Denver, Colorado. I have always worked on our cars (standard things like fuel pump, heater core, brakes, suspension, etc) but have never owned a classic car or Mercedes before.

Today I took the car in for emissions testing and it failed. The results are listed below. The car runs well but does seem to idle on the low side at about 600-700 RPM. Also, sometimes when coming to a stop the oil pressure gauge will drop from to top (45) down to near 0. Any thoughts? Are these issues related? Thanks!


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post #2 of 19 (permalink) Old 05-18-2016, 03:00 PM
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You are so close it shouldn't be hard to make it pass. Is the oil old and thin?

If you haven't ever messed with the mixture, you might now want to. Perhaps some fine tuning of the idle will be simpler. But altering the fuel mixture is pretty easy on a k-jet. We can guide you through that after you confirm the oil condition.

Also, the warm up regulator could be getting stuck causing a rich running condition. Some people like to whack them lightly with a hammer.

And it's always good to give your car the old "Italian Tune up".

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post #3 of 19 (permalink) Old 05-18-2016, 04:23 PM Thread Starter
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Thanks for the insight Fonzi.

The oil is starting to show its age. I will change it tomorrow.

I have not adjusted the mixture at all. Any tips you have about the procedure would be greatly appreciated.

I've heard about the "Italian Tune-up" from my father-in-law but have never done it. Anything special I need to keep in mind with this specific model?

Thanks!


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post #4 of 19 (permalink) Old 05-18-2016, 04:33 PM
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There's a 3mm Allen screw in the tower in the fuel distributor. Don't mess with it until you've covered the basics. You'd be going for the BFH right from the start of are messing with the mixture. I might do that on a JY condition car with unknown history or previously messed-with mixture, not one that I knew was fine before though.

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post #5 of 19 (permalink) Old 05-18-2016, 04:45 PM
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Take the idle up with air screw to about 825 that should lean out the idle mix a little if it is not enough then you could turn the mixture screw slightly leaner (counter clockwise) not alot you only need a little to lean can make hc go up. make sure engine and cat are heated up good

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post #6 of 19 (permalink) Old 05-19-2016, 12:32 PM Thread Starter
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I'm going to be changing the oil this evening and report back. Any recommendations on oil weight and brand? Summers here in Denver are usually hot and dry (80-90F) and winters are anywhere from the teens to 50s (not really as brutal as most people think Denver winters would be). The car does not leak but the previous owner did state the engine could use a top-off every 500 miles or so.

Thanks!
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post #7 of 19 (permalink) Old 05-20-2016, 07:28 AM
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June 5th is the Colorado Concourse. You should enter your car or at least come by. I will have my 250S entered.

Colorado Concours 6/5/16 Exotic Car Show Denver


I use Rotella 10-30 in all my older cars.
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post #8 of 19 (permalink) Old 07-15-2016, 01:25 PM Thread Starter
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Hi, everyone -

I'm still having trouble passing the Colorado emissions/smog test. Below are the results of all three tests. After failing the first test I changed the oil and filter (Rotella 15W-40), changed the plugs (NGK BP6ES), and changed both the air and fuel filters. I also did an "Italian Tune-Up" two separate times a couple days before the second test.

As you can see from the test results, I also upped the idle speed for the second test. I know I overshot it a bit but was hoping it would help. For the third test, I brought it back down but that didn't seem to help either.

Also, I can't seem to find the fuel mixture screw on the carburetor. There is a flathead screw on top of the fuel distributor that seems like it could be it. I can't get it to budge though so maybe it's not it.

Any ideas? Thanks in advance!

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post #9 of 19 (permalink) Old 07-15-2016, 02:19 PM
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1977 280SE (W116) Failed Colorado Emissions Testing

You won't find a mixture screw on the carburetor of a factory 280se because there is no carb. the E in the name is for some German word for injected I'm pretty sure. But you sound like you are on the right track.

Normally there's a screw or plastic cap on top of the hole/tower for the mixture screw, which is normally a 3 mm Allen bolt. Righty-richy, lefty-leany. Don't go nuts! A 1/4 turn could mean burnt valves. I suggest taking the Allen wrench to DMV with you. Don't leave the Allen key in there. The Weight of the Allen key itself can cause it to run richer.

I think the simple way to do this is turn it left (counterclockwise) until it starts stumbling (lean), and then turn it about an 1/8 of a turn back clockwise.

After messing with the mixture you may need to adjust your idle, possibly even your timing. When you mess with your timing you will probably need to adjust your idle. I view these as: mixture > timing > idle.

I am not a mechanic or expert, just a hobbyist, and I am VERY often wrong.


Edit:
PS: I had a similar experience with my 450slc 5.0. I could have gotten it "antiqued" but I wanted to make sure it was running right and used DMV for its free emissions tests. I was getting really rich running with 4% CO and higher. First I knew I had fuel pressure issues because the car had trouble starting often. It turned out that my accumulator was so horribly bad and leaking back to the tank that it caused the car to not start. Low fuel pump pressure in a k-jet leads to a rich running condition. I had hope that the accumulator would fix everything and get the mixture back to the way it should be. I was very surprised to see it had little-to-no effect on the emissions tests. Finally I turned the mixture screw and came up a total "0.00" on the CO and maybe even the HC too. When I got home I turned it just the slightest bit to rich. I should take it back through for an emissions test one of these days, but I kept it just a little more rich than those 0.00 because the engine in my car is one of the things that makes it special being an early 5.0 alloy engine. Richer is safer than leaner I think.

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Last edited by Fonzi; 07-15-2016 at 02:25 PM.
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post #10 of 19 (permalink) Old 07-15-2016, 02:27 PM
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the mixture adjustment is done with an allen wrench.


This doc will show you where it is.

http://handbook.w116.org/Engine/110/07_3-100.pdf

do not increase engine speed with the wrench in there, it will ruin things.

make small adjustments only.

If you dont have emissions measuring equipment it may be best to have a mechanic dial it in.

PS E = Einspritz (Injection)

Last edited by rumb; 07-15-2016 at 02:29 PM.
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