PeachParts Mercedes-Benz Forum - Retarding Ignition Timing (to improve emissions?)

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Retarding Ignition Timing (to improve emissions?)

Reviewing the archives and found this excellent post from ann old thread on retarding timing... to improve emissions.

Quote:

Originally Posted by Duke2.6 (Post 1105063)

...

I don't know where the R16/1 resistor is located on your model. Maybe someone with a 126 can help out. Remove the resistor and replace it with a home made shorting plug - like a short piece of 12-gage wire with the exposed ends folded over so they make good contact with the pin receptables.

On my car there is a short piece of rubber tubing that connects from the manifold port to the nylon line that routes to the EZL module. This can be replaced with a piece of 1/8" vacuum hose with a slug of silicone sealer that is allowed to set up.

With these temporary mods, the car will feel VERY sluggish at low revs, but the retarded timing will considerably increase EGT, which will help keep the converter hot. The substitute parts can be removed and replaced with the OE parts when you are done with the test. Once you know the drill it only take of couple of minutes to configure and de-configure for emission testing.

Duke

I'm a little unclear on replacing the vacuum hose. Is this just for EGR equipped vehicles, as my '89 M103 is NOT EGR equipped. If it applies to non-EGR vehicles, I'd appreciate it if someone can help me isolate this hose as I'm not certain which hose Duke is referring to here.

Also, do I need to check the timing BEFORE I retard it? What is the ignition timing spec on these cars?

Thanks again.

Yes, retarding (like to 2 degrees or hey, even zero while you're at it) makes a huge difference and lowers emissions considerably. But you'll have difficulty driving to the testing center!!!

Curious if the only thing added to the '90+ cars was JUST the EGR for lower emissions or if the cam and such was changed. :confused:

Quote:

Originally Posted by stevenstevensteven (Post 2259987)

No, it's not just for EGR-equipped vehicles. The vac hose described in the post by Duke2.6 is pictured in the photo below. Leading edge of intake.

Quote:

Originally Posted by Hit Man X (Post 2260112)

Curious if the only thing added to the '90+ cars was JUST the EGR for lower emissions or if the cam and such was changed. :confused:

Cam was changed and air (smog) pump also added.

If this is just to get past the emissions testing, I'd go for it. I wouldn't leave it that way all the time, unless you want poorer fuel economy. I've had to do this for years with my old Jeep to get past the "smog nazis". I retard the timing about 4-6 degrees, lean out the idle mixture (it's carbureted...won't work with F.I. unless you can control idle mixture) and put a BB in the vacuum line going to the vacuum advance on the distributor, and readjust the idle speed. You can also create a temporary small, non visible (to the smog tech.) vacuum leak to further reduce CO and HC emissions. If your state checks for NOX emissions, this won't work very well, as the NOX will increase. Some Benzes don't have vacuum advance (like mine), just vacuum retard. Others have both advance and retard. If yours just has retard, you don't have to plug the line. So far, I haven't had to do anything to my old Benz to pass, knock on wood.

Quote:

Originally Posted by Cal Learner (Post 2260227)

No, it's not just for EGR-equipped vehicles. The vac hose described in the post by Duke2.6 is pictured in the photo below. Leading edge of intake.

Thanks very much for the pic...is that your vehicle? If so, boy is your engine clean! I'm jealous!

So, this vacuum hose controls ignition timing advance... so blocking it keeps the engine from advancing. And shorting the resistor retards the timing? So, I'm retarding my timing and keeping it from advancing. Is that correct?

Quote:

Originally Posted by Cal Learner (Post 2260229)

Cam was changed and air (smog) pump also added.

Yeah the air pump I know of (mine fell off mysteriously), figured they went to a diff cam profile that doesn't self EGR like the '89 and older did. Now I know.

Now I wonder if the '90+ have a hotter cam profile (somewhat) and just used the EGR to drop the NOx lower than the '89 and earlier.