Duty Cycle 99% M103 - PeachParts Mercedes-Benz Forum

ps2cho · #1 05-08-2011, 08:44 PM

The airflow potentiometer is supposed to 0.85v +- 0.1v so not sure where you got that spec from. Yours is fine.

Engine running is more important than engine off....

Duty cycle is NOT in closed loop at 99% -- that is open loop! Closed loop is an oscillating duty cycle which shows the system has the ability to compensate for change.

Still looking too hard for problems!! Concentrate on the meter tower and adjustment. It may take a good 30mins before you get the right place. The initial turn will cause an increase in % because you are (physically) pressing the plunger allowing more fuel in (hence the momentary change). If its heading in the right direction away from 99%, then keep doing it. eventually it will either find its way to 50% and oscillate around there, or go to 0% in which case you need to go CCW (or vice-versa...some Craftsman DMM's read opposing duty cycles). It may need 1-3 full turns to find the correct height.

Think of the mixture unit as a log see-saw....Your allen key screw is simply changing the middle log so that the height at its maximum extension is higher or lower. The higher the log goes, the more the plunger on the fuel distributor is pushed in, more fuel, and the less it is pushed in, the less fuel. If the see-saw is sitting too low its not even making contact with the plunger, showing excessively lean mixtures at idle (which I bet is what is happening). Keep turning the screw to raise til the plunger finds its happy level at idle and it might be your golden ticket.

Once you have the duty cycle at or around 45-50% with it increasing no more than 10% at WOT, you have found the correct spot.

As I said in the previous thread though, I know you were fiddling with the fuel distributor, so if you did also the EHA, you need to return it back to its original position or direction.

This is why I don't advocate touching or adjusting anything but the duty cycle (for future readers/researchers) because if it ended up being something simple, like the vacuum leak, you now have issues returning multiple, fine adjustment units back to where they were originally. It's tough

350SL4spd · #2 05-08-2011, 09:12 PM

Quote:

Originally Posted by ps2cho

As I said in the previous thread though, I know you were fiddling with the fuel distributor, so if you did also the EHA, you need to return it back to its original position or direction.

This is why I don't advocate touching or adjusting anything but the duty cycle (for future readers/researchers) because if it ended up being something simple, like the vacuum leak, you now have issues returning multiple, fine adjustment units back to where they were originally. It's tough

FD or EHA were never adjusted. The FD is new (which is probably the source of the car being out of adjustment) and I have a spare EHA that was swapped out just to rule it out.

I've gone as far as 1.5 turns with the lamda tower so far for exactly the reason you mentioned: I wanted to be able to get it back to where it was if that wasn't the problem. I'll take it a bit further and see what happens.

The 1.5 turns didn't move it even a hint off of the 99% that's why I didn't push it further.

350SL4spd · #3 05-08-2011, 09:42 PM

OK. Got the car fully warmed up & very slowly turned the lamda screw in 1/2 turn at a time, every 3-5min or so. Same result every time. Brief journey to the 40% range, followed by a drop all the way down to 99% (.1v). I didn't dare go any farther after 5 full turns, lest the damn screw fall right out.

However, if I manually push the AF plate just a millimeter, the idle smooths right out & Duty Cycle shows around 45% & oscillating. Is it possible that something is wrong with the screw?

Or do I just need to adj the height of the AF Plate with the drift-pin on the top of the mixture unit?

I'm pretty surprised that moving the screw that far didn't get me anywhere...