Ignition Timing
 

This may seem like a stupid question: I need some basics of timing. When setting timing, do you set to the little pin or the "0"? With vacuum or without? I am using a non adjustable light so I cannot set for advance or retard.

Timing is not adjustable on the 85 SEL.

What car?

Sixto
91 300SE
81 300SD

the 1985 500SEL

Pretty sure Dave's right then.

Sixto
91 300SE
81 300SD

Timing is adjustable on a US 1985 500SEL & should be set at TDC with the vacuum line removed.

I am curious MB DOC, how do you set the timing?

I know this to be true:

The timing is controlled by the EZL ignition control module. It gets a signal from a crankshaft position sensor located on the flywheel and is not adjustable. One way to change the timing would be to move the position of the sensor (very difficult) or change the value of the reference resistor. But generally speaking there is no need to adjust the timing, it is set by the EZL ignition module.

The EZL ignition control unit contains a microcomputer, pressure sensor and the power output stage for control of the ignition coil. It is fitted to the left wheelhouse and is installed with heat conducting paste. The control unit receives information concerning engine speed (crankshaft position), intake manifold vacuum (load condition), engine temperature (coolant), and full load (throttle valve switch).

The EZL control unit compares information from these inputs with ignition maps for typical load and speed ranges which are stored in the microcomputer. The optimal ignition timing for each operating condition is instantaneously determined from the stored maps and the power output stage switches the primary current of the ignition coil between terminals 16 and 31 of the control unit. Furthermore, a TD (top dead center) reference signal is provided to the CIS-E control unit, tachometer, fuel pump relay, and diagnostic socket.

During cranking and up to approx. 450 RPM, the ignition timing is controlled via the segment edges (fixed) of the flywheel. After approx. 460 RPM has been attained a transition from the fixed ignition timing to dynamic ignition timing (instantaneous, ignition map comparison) is made.

Various ignition characteristic curves are inhibited in the warm-up range depending on the coolant temperature in order to reach the normal operating temperature as rapidly as possible. When a full load signal is received from the throttle valve switch the control unit adapts a fixed full load ignition map characteristic. At temperatures above approx. 203°F the ignition will be retarded to counter any further rise in temperature.

I have attached a typical ignition timing map of the EZL unit. As you can see the timing has a complicated relationship to the various factors that influence it.

Except that all that applies to cars after 1986. The 1985 car still had the inductor inside the distributor and did not have a crank sensor.

The cars that had the crank sensors were 420 or 560 or 300.

Woops - Sorry for the bad answer.

OK It is at TDC no vacuum. Is that the nipple or the "0" ?

Alright, I will spell it out.

The pointer mounted in the timing cover is a refernce point for lining up the point TDC; that is top dead center. In this case top dead center of the number one piston.

TDC is occuring when the "0" zero position of the balancer passes by. The direction of rotation indicates the by function the points before and after TDC. Expressed BTDC and ATDC. The degree wheel on most Mercedes, even ones where it can't be seen, has a scale mostly on the before side. You will notice if you face the motor and turn it clockwise the scale which starts at least at 40 degrees has marks every 5 degrees. As you keep turning and the "0" aproaches you are still before top dead center BTDC.

With a light you are illuminating only when the spark occurs allowing the marks to be framed at the moment. You need to remember which way its turning as it will look stopped. If the zero lines up you are at TDC, anywhere else you will be lined up with the scale and the number represents the degrees off TDC the the spark is firing before or after by position in time.