well,
i FAILED emissions testing again!

on LOW IDLE (1090RPM), failed with 516HC and 5.07CO on the 220/1.0 standard.
on HIGH IDLE (2450RPM), failed with 534HC and 4.13CO on the 220/1.0 standard.

disappointing, but a marked improvement over my previous results (7708HC / 13.6CO)!!!!!

anywho, i could really use some help getting the rest of the way.
i know MBBUFF suggested 'leaning out' the mixture screws and retarding timing, but maybe some advice on how much?

right now, my mixture screws are turned out 2.5 turns, my timing is set to 32º BTDC @ 4500RPM w/ vacuum hoses removed (per spec), and my spark plug condition is light gray / borderline white.

also of note, apparently it's rare for the HC content to not decrease significantly on the "high idle." mine increased.

thoughts?
what would you do now?

__________________
-lee
'83 300CDT (286k)

former proud owner of:
'85 mercedes euro 300TD
'80 mercedes 300TD
'77 mercedes 280e
'80 mercedes euro 250
'82 mercedes euro 250

Lee, why did you richen the idle mix screws from your original 1 1/4 turns out to the current 2.5 turns out? Not knowing the condition of the rest of your engine, ignition, carburetion, etc. it'll be tough to accurately figure all this out. I'll give you my best shot to get you past the emissions though. First verify that each idle mix. screw is out the same amount. I'd start at about 2 turns out. Warm up the engine to operating temp and let it "heat soak" for a little while, maybe 10 minutes or so. Make sure the choke is completely in the off position. (Also do this before going to the emissions place. Take it out on the highway and run it in third gear (hi RPM) for a little while.) (Note: To verify that the mixture screws are indeed functioning, slowly turn each one in all the way. The engine should die, or at least nearly die. Back it out to the original initial beginning setting. If it doesn't die/almost die, there is a problem with the idle circuit.) Now turn one screw in until the RPM just begins to drop. Turn it back out about 1/8 turn. Do the same with the other one. With this setting it may not run that well because of the leaner mixture. Adjust the idle speed so it will run (should be about 800 RPM), especially in gear. Don't want it to stall on the way to the emissions joint. Set the timing to about 0 degrees at about 2500 RPM. The vacuum canister on the distributor (at least mine with emission controls) is a retard canister, not an advance canister. Since yours doesn't have emissions equipment, yours might be advance. Verify which it is. If it is advance, temporarily plug the hose at the canister. I use a small BB (really a carburetor check ball). If it is a retard can., leave it alone. You'll probably have to readjust the idle speed again. It'll probably run like crap, but should pass the test. If you want to do a little more to further lean it out, create a small, non visible vacuum leak (i.e. unhook the secondary air valve damper canister hose at the back of the carb. base and set it so it looks like it is hooked up, but not. Idle speed should slightly increase.) This should for sure get you in the ball park. I think most, or at least part, of your problem is that there is no emission stuff on your Euro. engine, yet "they" expect you to pass emission standards for vehicles with emission controls. Does your engine have the vacuum governor? This controls (or should) your idle speed, with engine warm, under all conditions (curb idle, in gear, A/C on, etc.), except when the choke is on. Good luck, and keep us posted. Oh, also make sure your air filter element is clean.

it turns out the '80 model takes hotter plugs than my '82...so i replaced/renewed them. plug condition is "white," so i richened the screws up to hope i'd start getting "tan" plugs...hasn't happened.

yep. dies. weird thing is that vacuum stays the SAME everywhere from 1.5 turns out through 2.5, 3.0, 3.5 turns, etc...doesn't drop as you continue to turn out.


book quotes 0º ±4 Timing BTDC at 850RPM. does your timing suggestion still apply?

mine's got both advance and retard ports...should i leave it alone for emissions?

so, just manufacture a vacuum leak from a line from the manifold? they don't do any kind of 'visual inspection' at the emissions place, other than verify you've got a catalytic convertor...

yep. why? something i can do w/ that?

__________________
-lee
'83 300CDT (286k)

former proud owner of:
'85 mercedes euro 300TD
'80 mercedes 300TD
'77 mercedes 280e
'80 mercedes euro 250
'82 mercedes euro 250

How are you reading your plugs? It's tough to get a real true reading when you're stop and go, idle, power and cruise. I think I'd just use what the factory says, make sure all is well with ignition and carb., and call it good. Mine run pretty white too, with just a hint of tan.

Does the idle quality change as you screw the mixture screws out....i.e. rough, lope, chug, etc. It should. The farther out I go on mine, all of the above start happening. Anyway, for your emissions test, screw them in (lean) as far as possible, as I indicated before. I think mine are now at about 1 1/2 out. Recently mine were out about 2.5 too. I just had a rough idle problem and slight off idle flat spot that were not there before. With my hand vacuum pump I checked all vacuum components and hoses. All was good, with just very slight bleed down on the storage tank in the right fender well. The only thing I couldn't check with the hand pump was the power brake booster and vacuum pump. I finally rigged a hose setup that bypassed the vac. pump and allowed me to hook up my vac. gauge. Presto, bad (internal leak) vacuum pump. Parts are now on order. I guess my point here is that if all the systems are not "tight" you're going to have to compensate in ways that may be adverse. Now that I am temporarily bypassing the vac. pump all is well. I had to readjust the idle speed and mixture, and will have to lower the float level in the carb.

Yep, I'd go for zero degrees at 2500 RPM. I chose this because this is the RPM you said they check the emissions at higher RPM. You can reset it later if need be. If you're set at zero at idle, chances are you're going to be advanced by "X" degrees at 2500 RPM, depending on the advance curve set in the distributor.

It depends on how the vac. lines are run from the carb. Do you have a hand vacuum pump? I'd still verify which is the retard side and, if anything, hook that side up and temporarily plug the advance side. Again, if the vac. advance is working at the higher RPM, you're going to get more advance and more emissions.

Yes, you're manufacturing a "small" vac. leak. That is why I chose the air valve damper canister hose. It makes very little difference in idle quality or speed when it is disconnected, and doesn't impact any carb. components during the test.

The vacuum governor is suppose to control your idle speed under all conditions, except when the choke is on. If it is not set properly, your curb idle, in gear idle, A/C on idle will be all out of whack. You'll have to run a higher idle speed (out of gear, A/C off) to allow it to idle properly when in gear and/or with the A/C on. Mine varies 100 RPM under any of the different conditions. My curb idle is 800 RPM and it drops to 750 RPM in gear, and 700 RPM in gear with the A/C on. Once you get everything set up the way you want (idle speed/mixture, timing, etc.), then you can set up the vac. governor. I've got the instructions in the shop manual and turn you on to them when you're ready.

Good luck on the emissions test. Hope you pass.

hello guys!

I'm reading though out this post, I have float problems in my '72 280S W116. Is the new "hip roof" one is resistant to ethanol-mixed(E10) gasoline? The float in my 280S was destroyed by this fuel with E10! thus the engine idles rough but held idle nicely under load (when placing the stick in D with AC on), but high fuel consumption b/c of dripping fuel inside the primaries.