How I got my 300TE to pass smog in CA

[3L33ter]

I just wanted to share how I got my 1989 300TE to pass smog. It has the m103 engine. Luckily I work at a German auto shop and we have a (old) smog machine so I could do all the pretesting I wanted. I live in a "non-enhanced" zone meaning smog checks here don't check for NOx and there is no dyno. Basically all I was looking at was the HC. Before doing anything, I put in the sniffer. I was getting numbers between 800 and 3000 ppm, where the limit is 120. LOL, for a second I thought I brought the wrong mercedes (my other one is a diesel). I ran some seafoam, half in the fuel (1/4 tank) and half in the dirty old oil. I changed the oil 75 miles later and ran out the remainder of the fuel. Then I tweaked the fuel mixture of the CIS using the 3mm allen in the airbox while the smog machine was sniffing. I got the HC down to around 180-200. It would wander near 300 sometimes (when the idle would dip). I took off the airbox and tightened the throttle linkage, so the throttle would always be partially open. This was my quick and dirty way of raising the idle. This lowered the HC a little and kept the reading from bouncing around. I noticed actual smoke from the tailpipe. I switched the synthetic (burns less smoky) of the heaviest weight I could find (so it doesn't leak past seals as much) which was 15w-50 Mobil 1. I also ran it a quart low so it would have less pressure and leak less into the combustion chambers. I also checked the air filter, it was filthy, so I just took it out and left it out for the smog tests. HC went down to about 120 but I wasn't sure if it would actually pass, riding the limit like that. Finally I replaced the WRONG bosch resistor-type spark plugs with the correct non-resistor type NGK plugs. The HC went down to 25. The car has an aftermarket cat, and an exhaust leak before the muffler. True, these are advantages, but I think even without them I could have passed with just doing these: 1. fuel mixture 2. spark plugs 3. air filter 4. idle/throttle (you'd be amazed how much lower your emissions are at 900rpm instead of 650) 5. Clean thick oil might help Other things to consider before giving up: O2 sensor fueling problems, like leaking injectors or leaking CSV injector After I got my smog check done and I passed, I put the old air filter back in (until the new one arrives) and I set the throttle linkage back to normal. I hope this helps someone.

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[OJ's DNA]

Thanks for sharing man, I had a 86 2.3-16V that always needed to be tweaked at my local MB mechanic before a smog check. I always wondered what it was that he did to make her pass, maybe he did some of what you noticed. Nice info...

[ps2cho]

That is great to know that the resistor-type plugs raise hydrocarbons.

[i6h000]

What's the number of the NGK's you used? Thanks.