Duty Cycle adjustment mistake! Doh! - PeachParts Mercedes-Benz Forum

Merkey · #1 06-02-2006, 10:01 AM

My sons '88 300TE recent purhase... attemping to fix stalling and odd misfire...

Ok, so I buy a Sears multimeter with duty cycle....
Figure out how to connect it.... Black pin to pin 3 on the connector..
Its reading steady 85% with ignition on.. and engine off.. so California car...
Starts car... reading varies 78 to 90 ish, so assume 85% ....
Figure I can adjust it down a bit... to 70%ish....
Put in the allen wrench...push down... turn it a bit... one way..... no difference.....
Turn it a bit more.... and a bit more..... maybe half to one turn.
Engine stalls.
Now it wont start!
Cant remember which way I turned it!
Turn it back... I think about one turn...
Still wont start!
:Thumps head... shuts hood and goes indoors:
Ideas?

mctwin2kman · #2 06-02-2006, 11:48 AM

Clockwise is Rich, Counter is Lean! You do this in small adjustments, like 1/32-1/16 of a turn!

You need to remember the last way you turned so you can go back. Pin 3 should be the red wire and Pin 2 the black.

Merkey · #3 06-02-2006, 09:48 PM

This morning, from cold... well 70 deg here in the OC, it did start, but ran very roughly.
So, I will connect the meter as you say, and see what it says.... then I will turn it to push it back to at least 85%, to start with.... but is 85% rich or lean relative to where it should be at 50%?
So if its reading say 95%... to bring it back to 85% do I go richer or leaner?
If that makes sense?

falconsprint · #4 06-02-2006, 10:16 PM

You don't supply the year and model of the car you have.

Perhaps this is your issue:

"For California cars, starting in 1988: Press the push button switch on test connector X92 (passenger side, between the two firewalls) for two to four seconds. The LED will flash once, indicating no fault code is stored in the system. Now press the switch again for two to four seconds. The LED will be on continuously, and the injection control is switched over to an on/off ratio output. "

These instructions come from the following helpfull website: http://www.landiss.com/mixture.htm

If you don't get the system in test mode your multi-meter may be reading noise in the circuit if it is auto-ranging. Be sure to also manully set the multi-meter to the appropriate range (~12V).

Another suggestion: First adjust the CO mixture without looking at the on/off ratio. You should be able to get somewhere close when the engine smooths out.

Merkey · #5 06-03-2006, 01:53 AM

I did quote the year and model in my 1st post...
But I did miss that important reference to CA cars in the text... thanks for pointing it out... that will help!

Merkey · #6 06-10-2006, 01:18 PM

Ok, found the time to look at it this morning.

I have a craftsman meter, I put the black lead that is in the port labeled COM into pin 3 and with the ignition on and the diagnosic LED ON as per the instructions I get a steady 85.1% reading.

I started the car, it ran a little rough at first, but started fine with a little gas applied. I warmed it up whilst seeing the following.... The meter reads with the engine running at idle also about 85%.
When I rev it, it goes down to 45/50% and if I hold the revs steady it comes back up slowly to 85%.

Here is where the fun starts.

It is warming up nicely... I shut it off to read the Landis instructions.... and now it wont restart!
I have a good healthy spark, before anyone asks!
Its still warm at the moment, so it wont start... it does not even fire at all... just spins.

HELP!!!!

Merkey · #7 06-10-2006, 04:57 PM

Ok, so now it wont start cold.

Is there a baseline point that I can set the car to get it started?
On carbs, you can set it like 5 turns from the stop or something?

Merkey · #8 06-12-2006, 01:40 AM

Got it running!
I tried it today, no go.
I spun it without touching the gas, pulled the plugs, and they were wet.... too rich!
So, I started by tweeking the mixture 1/4 of a turn anticlockwise to lean it out.
Nothing.
Repeated this 3 times, until I heard it almost start, then I knew I was getting close.
The next 1/4 had it running, and the next one was an 1/8 turn.
It started and sent out a lot of smoke...
I warmed it up and set up the meter.
After a couple of smaill adjustments I had it running at 50% reading!
Yeah!!!!!
I will see how it runs the next day or two!

BENZ-LGB · #9 06-12-2006, 03:02 AM

Merkey, congrats on getting the car running, I bet your son is happy.

I sent you a couple of PMs on the stalling issue.

Merkey · #10 06-12-2006, 10:48 AM

Thanks LGB, I got them.
I am working on it!
He is not that concerned... yet, because he has not passed his test... he has another month to go!
In the meantime, he drives my jeep when he can, so he is not complaining!