1990 420SEL runs rich or bogs down - PeachParts Mercedes-Benz Forum

turbozeke418 · #1 07-14-2022, 01:03 PM

I recently purchased a 1990 420SEL with 208k. The car had a full history of every receipt from work done over the years. I love the car but it had one thing that annoyed me and that was a hard time starting. I replaced both fuel pumps, the accumulator and the filter. It started a little bit better but not perfect. I checked the fuel injectors and they appeared to be original. I replaced them and the problem went away. Now the problem was that it would bog down on WOT. I took it out for a drive and when flooring it, it would sputter a bit and then take off. I watched several videos and read tons of threads on similar issues so I adjusted the fuel distributor with the 3mm allen. In order for it to not bog down, it has to run rich. To the point that you can see exhaust and your eyes begin to water. I backed it down to lean it out and it bogs down again. I'm just trying to figure out if anyone has any experiences like this and what to look at next?

porkface · #2 07-14-2022, 01:54 PM

could be the plugs, wires, etc. if you test the fuel pressure and use pins 3 and 4 to set the co, that's the way to go. don't guess or smell. high fuel condition can be because of low spark.

dumping the throttle means a rush of air that's harder to ignite. if the spark kv is too low, it will bog. look at the coil where the bracket surrounds it. any white on the outside means the spark is escaping due to high resistance in the cap, wires, etc. any spark leaving the coil means replace that, too.

me, i'd scope the reserve kv and see if the ignition is capable. or, you can shotgun the ignition like you did the fuel system and replace everything.

turbozeke418 · #3 07-21-2022, 04:05 AM

SOLVED! I took off the EHA and adusted it a half or so turn with the 2mm. It ran a little better but still a slight bog at WOT. I took it off a 2nd time and adjusted it some more and voila! I found it's sweet spot. After that I had to back down the 3mm allen on the top of the distributor. I'm doing everything by feel and smell (which I know you shouldn't do, but without the proper equipment....) It now drives like a completely different car. Actually responds perfectly off the line with no issues. Thanks for all of the input.