Assuming your engine has a conventional centrifugal advance mechanism, +/- 2 degrees is their typical tolerance range, so retarding the initial timing 2 degrees may not make much difference at higher engine speed.

Suggest you retard the initial timing about 6 degrees from spec. The initial timing spec is on the "tuneup/emission lablel", which should be located somewhere in the engine compartment.

The other way to reduce the timing at part load is to disconnect the vacuum advance, assuming that vacuum advance is active during the test, which is may or may not be depending on the details of the emission control system and test conditions.

Duke

Thanks to Peter and Duke for your help.

Peter,
The Mass test is a dyno the NOX was the highest at the steep acceleration ramp I would assume it was full throttle and therefore full advance. The other readings were:

HC limit 2.00 actual 1.16
CO limit 30 actual 6.47
CO2 limit none reading 379 all grams per mile
and NOX limit 3.0 actual 3.6 last time


Duke
The emission label is missing I was going by the MB CD for engine group 116.962 gives the advance settings for the distributor that I quoted earlier because the test failure was at full throttle then should I retard the 6 deg from the 25 deg advance without vacumn and make it 20 probably as close as I can come at 3000 rpm. The 25 deg setting looks right as the balancer has a welded in post at 25 deg mark.

Another strange thing is that I cannot find an EGR valve on this car I have the MB SL CD and find reference to it but nothing under the hood as far as lines or valves on the exhaust manifolds. All other emissions equip seems to be in place and working the air pump etc. Was it removed or were there engines without it?

I also changed plugs they were a bit carboned up and a new air filter.
Thanks again.

__________________
Bob

1985 380SL 110k,mi
2000 Harley Dyna Conv 29k,mi
2004 Honda Element 48k,mi
1999 Honda Accord EX 156k,mi
1984 380SL 90k,mi (gone)

I would think the CD would have the spec for initial timing, but if it's not available reducing the 3000 RPM timing spec six degrees (vacuum advance not connected) would be the same as reducing the initial timing a like amount.

I'm not aware of any emission test procedures that require WOT. Even the federal/CA certification test comes nowhere near WOT on a reasonably powered car. The proper emission/tuneup label has abbreviations for all the emission control systems, so it will tell you if your engine originally had EGR. You can probably buy the correct label for you car through Mercedes parts. In not abolutely sure, but in CA lack of an emission control label may be cause for failure.

Prior to your next test you could also plug the vacuum advance line temporarily and unplug it after the test. Plug the line internally and reconnect it, so it won't be visible on the visual inspection. The car will run poorly and maybe hot, but the lack of vacuum advance should reduce the measured emissions. You don't have that far to go.

Duke

Bob,

Got a chance to go through my 84 and 85 model year books and those cars were not equipped with EGR. You should have an air pump, but that doesn't do much for NOX. Actually your overall readings look very good, and you wre close on NOX, but we all know that close only counts in horseshoes and hand grenades. It looks like you have some room to tweak up CO a little which will probably reduce HC and maybe NOX. I wouldn't mess with timing except maybe retard it slightly. Your state probably has visual specs on timing that must be met. One thing that has worked well here in Ca. to reduce NOX is to hook the car up to one of those carbon blaster machines. It's like a dialysis machine for cars. You hook the machine up to the car fuel system, draw out a gallon of fuel, add a special additive to the gallon, disable the fuel pump, and run the car at idle for 45 minutes on the machine. If you know what you are doing, there is a less sophisticated way. You can run the car on water injection to clean out the carbon.

Peter

__________________
Auto Zentral Ltd.

Don't know about other states, but CA allows a maximum of 3 degrees advance from the initial timing spec and unlimited retard.

Retarding the timing is a quick and easy way to reduce NOx due to lower peak flame front temperature. It will also reduce HC and CO (as long as there is available O2 in the exhaust) due to higher EGT that will increase converter temperature.

Duke

1985 380SL Passed Emissions
*
A big THANK YOU to Duke and Peter
*
Test Results and Summary
NOX limit 3.00 ***final 1.88 ***prior 3.60
HC limit 2.00 ** final 0.51 *** prior **1.16
CO limit 30 *** final 4.90 *** prior **6.47
CO2 limit none *** final 326 *** prior 379
all grams per mile

The key was ignition timing the MB CD had a value of 13-19*adv at idle for the 116.962 engine. The actual tested reading was 10-12* adv Duke you were exactly right the 6* retard you advised bringing the value to 4-6* was the USA certified emissions value which not having an emissions label on the car I found a picture of buried in the MB CD.

Emissions Systems FI,AI,TWC,OS Peter thanks to you I resolved where the EGR system had gone, there isn't any.

Final Test prep was new plugs, 1/2 filled tank of premium fuel, FI cleaner, all emissions systems working and being second in line I let it idle while waiting to keep it hot. Good to know that a 20 year old MB (103k) will pass with flying colors when properly tuned.

Thanks again from a new member.

__________________
Bob

1985 380SL 110k,mi
2000 Harley Dyna Conv 29k,mi
2004 Honda Element 48k,mi
1999 Honda Accord EX 156k,mi
1984 380SL 90k,mi (gone)

Bob,

Congrats and thanks for the follow up appreciation, but I think Duke is the hero. I will also remember his advive on the retard issue in my future dealings with the state.

Peter

__________________
Auto Zentral Ltd.

I think I may have mentioned before that I have a MSME from the University of Wisconsin Engine Reseach Center where I did emission related research, so I have an indepth understanding of emissions generation and control.

The simple act of retarding initial timing is very effective at reducing emissions readings, and can often turn a marginal failure into a solid pass.
I only wish we could do this for M103 engines being as how they are often on the ragged edge of the HC limit and California has identified them as "high emitter profile". Unfortunately, the electronic timing control system built into the EZL ignition module does not allow the initial timing to be adjusted.

Duke

Just to concur, my 1994 Infiniti G20 failed the smog inspection the other day.

The tester noticed that my timing was off. It was at O degrees, but it should've been 15 degrees BTDC.

It took it home, and set the timing to 15 degrees, took it back to the smog inspection "test only" station, and it passed.

He said my timing was at 13 degrees, not 15, but he said you are allowed to be off 3 degrees + / - .

I noticed when comparing both inspection sheets that the 15 degrees made a surprising difference.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

I am following this (old) thread sice I have to go get my M104 smogged today and since I am new to the board. Autozen - the bridge you are referring to is the Tacoma Narrows Bridge. It was built in 1940. It fell down right after it was completed, and I mean right after. The failure mechanism was resonant vibration leading to huge displacements ("it moved too much"). The root cause of the vibration was wind blowing through the channel. The wind induced harmonic forces on the bridge structure and the forces then excited the bridge at its natural frequency. It fell down. There is a video that shows the whole event. Here is a link: http://www.civeng.carleton.ca/Exhibits/Tacoma_Narrows/

The bridge was designed using the best theory that the guys had at the time, which told them things like how thick to make the support columns and how many bolts to place in the connections. What they did not know (much) about at that time was something called flow-induced vibration, nor did they have the (computer) models necessary to estimate whether it would have been a problem for this bridge.

The point is - the theory works. If it didn't, no bridge anywhere would be standing. The designers of the Tacoma Narrows bridge used the best information and theory they had at the time. The bridge in fact stood up to the loads they designers had anticipated and that they had the tools and skills to deal with, again at that point in time. The problem was they did not have the skills or ability to deal with the vibration, and when it occured, the bridge became overloaded and failed.

As a design engineer in the fluid flow business I often am amused by plant operators, craftspeople, or other hands-on types who will immediately place blame and denigrate a system and its engineer/technician who designed it because it quit working or otherwise failed. When you get into it to see why it failed, many times it turns out that it's something that they did (improper or infrequent maintenance), didn't do (opened the suction valve too fast or didn't enable a shutdown device), or it was something that the theory behind the system does not address, for example, plugging or clogging of sensing lines. Of course this does not exclude design or engineering failures - I've been involved in plenty of those also. That is where experience must be married to theory to make a successful installed design. But to throw all theory and science out the window under the claim that art or operational experience is the only way, is indefensible. It is unfortunately true that a lot of engineers and scientists have arrogantly rammed designs down people's throats simply because they thought they knew better. The best design takes into account the experience and training of all team members: engineer, operator, and mechanic. - Pete

I grew up in Seattle and got my BSME from UW. I remember a class where we watched the film of "Galloping Gertie" in its final death throws and then the road structure began to disintegrate.

Analysis was done at UW, which determined the probable cause of failure. One of the "aesthetically pleasing" aspects of the original bridge was the "thin" road support structure that consisted of fabricated solid beams beneath the road rather than an open truss structure such as the Golden Gate Bridge. It was an aerodynamic problem caused by this solid girder road support structure that caused the road structure to begin twisting - an oscillation would set up. It's analagous to the sound that's created when you blow across the top of a bottle since sound is just a pressure wave oscillation. The name "Galloping Gertie" was applied shortly after the bridge opened as movement was quite noticeable to users, and I think it failed only about two months after it opened in a relatively modest wind that was less than 40 knots - far below what the designers believed the bridge could easily stand.

The replacement bridge upped the total lane count from two to four and an open truss road support structure was used instead of the solid girder structure, which allowed the wind to pass through without creating significant displacement forces.

One other interesting anecdote that I recall. The State of Washington bought an insurance policy on the bridge, but the insurance broker, thinking that the chances of ever having a claim were remote, pocketed the premium and never established a policy with the underwriter. I don't recall if the state was able to collect anything, but I think the insurance broker went to prison!

Duke

Well the M104 passed smog barely and I do mean barely. Allowable HC is 82 ppm and the measured amount was... 82 ppm. The other four gases were waaaay below max.

Great anecdotes Duke on the bridge. I first saw that video when I took vibrations and then again in a grad-level failure analysis class. Don't you know every engine school in the country has gotten a lot of mileage out of that old movie!

I saw in an earlier post that you did your MS at Wisconsin - did ya ever go to the Superior or Waukesha plants? I took a trip to the Waukesha plant once for a couple days to observe run-in and bench testing on a couple 1000 hp 900 rpm natural-gas engines I bought to drive gas compressors here in Kalifornia. One was a lean burn and one was a clean burn, both turbocharged. Long story there! I also used to witness emission testing of large stationary IC engines and fired equipment. We used to test for NOx (and SOx) way before they ever started doing it on cars. Makes for some interesting discussions with the smog techs when you take your car in. The principles are all the same, combustion is combustion. - Pete

That was a really interesting explanation.

wb, BSEE 1975.

__________________
Regards

Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.

Nope, just visited the GM Research Center in Warren, MI. GM sponsored by research assistant fellowship.

Duke