mixture control 119 engine cis-e 1990 sl500
 

I have a lean running 119 cis-e 1990 500SL. At low speeds off of idle and under load it backfires through the intake constantly until I hit 3500 rpm under load. Car has new pumps and filters.Problem did not exist prior to filter and pump replacement. Can the mixture be adjusted? If so, how?

You sure co adjustment is going to fix that? I've not seen one doing that consistently....... ever.

Anyway, you get the engine warm, remove the cap from the diag connector on the l/f fenderwell, hook a DVOM that is set to duty cycle to pin #3, positive, ground to the engine, 3mm allen in the adjuster (might be plugged, remove that) press down and turn clockwide to richen, counter to lean. You should see a duty cycle of 40 -60% with a swing of 5% or so. (it's following the o2 when it swings) Fixed cycles are indications of a failure and need to be addressed first.

You say it didn't start until after the pump and filter were changed? I wonder if they installed a bosch fuel filter, I has a bunch of those several years back that the paper exploded in as soon as they got hit with the gas, did a fine job of trashing the fuel distribitors, never had a knetch do that.

early 119's also have split ign systems with 2 caps, rotors, coils and EZL's, I'd look hard at secondary ignition while I was in there.



Joe