300E Ignition Timing
 

I would like to check the ignition timing on my '86 300E 5-Speed. I don't have access to the shop manuals, and would like to know the timing specs.

At what setting BTDC should it be at 3000 revs?

That answer is a big "it depends on load, temp and many other things.....".

Here is a typical ignition map it looks at a lot of conditions to determine that the timing should be.

THANKS !! (I suppose)

Upon reflection, I believe I'll look around for something else on the car to occupy my time.

:rolleyes:

What a crock-o-crap, whats his name should have posted a pic of his dog, it would have been as much use. IF he can eplain that 3-d graph, I would be suprised, I have the same picture in my manual too.

I will look up timing settings in my manual whan I get home and try to post it by 10-29.

Well its clear to me that Mr. inspector1 does not know what the fudge he is looking at.

Its a three dimensional curve. RPM on one axis, engine load on another, and timing advance on the third. To find the timing number you find the intersection of RPM and load then read the timing value. Its simple but you obviously have never seen one before.

My real point was that its not easy to get an exact number.

But just for Mr. inspector1 here is a picture of a dog. Im sure he can relate to that better.

300E ignition timing
 

DANG you guys go for blood, don't you? At least the dog is smiling! (good one, Petryk)

CEO, well, need we say more? If ya wanna get into it with insults, bring it on.

I said post a picture of a DOG, not yo' girlfriend.

I wish I were a moderator on this forum.

Fine looking dog you have there Dave.

I understood the graph but I did wonder what the "Z" coordinate units were and how they are actually measured in the car.

inspector - Dave has been around here for awhile and brings alot to the table - especially when it comes to the electronics part of the equation - there is no need for the slamming.

Now now...
 

Perhaps Allen 141 asked the wrong question! (I know I have before) He should have requested the approximate timing. :) While I agree that the graph raises more questions than answers for the untrained eye, there is no need to bash it or the poster. Allen, on a 124 you should be able to find PLENTY of things to occupy your time!!:D Nice dog!!:cool:

Thanks for the support guys!

Here is how you read one of these things. For any given engine condition you are able to determine the ignition timing in degrees BTDC. Start by finding the RPM on the X axis. Then find the engine load on the Y axis. Then find the height of the intersection of the X and Y points on the Z axis (red lines). The height of the Z axis defines the ignition timing (green line). Its a simple lookup problem determined by the interesction of an X and Y coordinate value. I have red-lined the graph to illustrate how it is done. I hope it makes sense. To answer your question Jim, the Z cooridinate is the result of X and Y and not a measurement.

Now, I have to say this graph is useless to me because the engine load units is in milliseconds and I dont understand how engine load can be expressed in those units. But I am sure the Mercedes engineers do. The Z axis is in degrees BTDC which is what I would expect and the X axis is RPM. You cannot use this graph to get any precise numbers because it is not possible to arrive at the Z axis number accurately. One would prefer to have a spreadsheet form of the data represented by the 3D curve so a precise value could be looked up and read. The microprocessor in the ignition module is doing exactly the lookup function described. Its a simple and commonly used technique to control a process that is not linear or easily modeled or calculated using mathematical formulas. Its called a 3D lookup table.

I also know that the engine temperature is an input to the ignition module and if the engine temperature is to high a different map is used to avoid overheating the engine. Its a very smart module and the timing is very precisely controlled to protect the engine and deliver optimum performance under a wide set of operating conditions.

So back to original mission when I first replyed to this thread. That answer is a big "it depends on load, temp and many other things.....". This map represents the complexity of the answer and in fact is probably not the right one for the engine in question.

Thanks Dave,

I had the Y and Z coordinates reversed. I'm like you - I'm not quite sure about the Y axis "units".

Good explanation.

I thought it was a contour map of my property!:D My house is at the intersection of 1680 and 1.465!;)

I am using as a reference "MERCEDES W-124, OWNERS WORKSHOP MANUAL, 1985-1995" first published in 1994 by Dellus, Klasing & Co. Bielefeld Germany.

page 58, "IGNITION TIMING"- testing states:
" The ignition timimg does not normally change. It should be checked if the fuel consumtion is too high or, in vehicles with the TSZ system, if the distributor has been removed and refitted. The ignition timing does not need to be checked in vehicles with direct ignition.

page 60 chart " Ingnition Timing Values", indicates that a 300E. with emissions control (catalyst) has the EZL ignition system and is timed at 650+/- 50 RPM with BTDC at 6*+/- 11* with vacuum hoses connected. a timimg value is listed for 300E. @ 3200 RPM@ 25*+/- 2*BTDC, non catylyst models.

The EZL system, in vehicles since 9/86 ( Retrofitted and OEM catalyst) has a EZL equalizer plug with fuel settings that can correct timing for gasoline quality.

In closing, it seems in general, not nessasary to mess with the timing.

To read the graph:

Since you are checking under no load (NLD) conditions, the Y-axis on the graph collapses to the NLD 'isobar' line. Timing scale is indicated as 5 degrees/div, so draw lines parallel to the X-axis to find their intersection with the NLD line. This will give you - to the precision of this graph - the rpm that corresponds to each 5 degrees of advance.

Steve

My question is...
 

How does the computer know how much load is on the engine?

Vacuum?

The EZL unit has a pressure sensor which measures manifold vacuum. High manifold pressure means high engine load. Low pressure - low load.

I suspect the graph Y axis is manifold pressure in some metric units.

explanation of milliseconds in defining load
 

Quote #1- from DEPETRY
"...Now, I have to say this graph is useless to me because the engine load units is in milliseconds and I dont understand how engine load can be expressed in those units. But I am sure the Mercedes engineers do...."

Quote #2
"... inspector 1 must not know what the fudge he is looking at..."

The graph is called the "DRIVE MAP"

Load expressed in milliseconds is in reference to the INJECTION PULSE WIDTH ie. time injector is open.

As we all know,INJECTION PULSE WIDTH is controlled by the ECU which at idle/low load seeks to maintain a lamda =1, it does this by monitoring the O2 sensor and adds/subtracts approx. .001 millisecond to the INJECTION PULSE TIME (ti).The amount of increase or decrease in INJECTION PULSE WIDTH is called the ADAPTIVE VALUE and is the value output by the ECU when reading live data stream from the O2 sensor in closed loop and the other various sensors at load.

At higher load- high RPM- larger volumes of fuel and air are needed (duh :^)). In order to maintain a lamda =1 the ECU monitors the upstream O2 and calculated load and compares it to the optimal values for the FUEL INJECTION PULSE WIDTH stored in the DRIVE MAP, If this INJECTION PULSE WIDTH does not equal 1 at the O2 sensor for the amount of air that the MAF sensor is sending to the ECU, it increases or decreases the PULSE WIDTH by a percent that is defined by the difference in lamda from optimal (1). This is defined as the SHORT TERM FUEL TRIM MULTIPLICATIVE If this value exceeds about 25% for more than apprx. 10 seconds a DTC is set for lean or rich state.

But in my enthusiasm, I digress.

Short answer, the Z axis of the graph- DRIVE MAP- is the programmed INJECTOR PULSE WIDTH

I really enjoy this tech forum, I have collected an entire library from the intelligent input from so many folks, I also find it challenging to try to understand the subtle factors that effect engine performance, and you guys are a great help.

Peace to all in the upcoming Holidays.

All hats off to inspector1. Looks like he has solved the mystery.

I was confused because the 86 300E uses CIS injection (Continous Injection System) often refered to and operates much like a "sprinkler system". There is no timed injection pulses used on that car.

The map can easily confuse people because it is used in context with the CIS system. I agree that the map shown is indeed for a pulsed injector type of system. However in CIS systems, I know the EZL unit monitors vacuum as an input for engine load instead of pulse width.

Can't resist suggesting that Inspector1 do a search and find the thread about removing the resistor thus allowing full advance and taking advantage of premium fuel. Many of us have done this and it does provide a nice kick.

[
I was confused because the 86 300E uses CIS injection (Continous Injection System) often refered to and operates much like a "sprinkler system". There is no timed injection pulses used on that car.

My guess (95% Confidence Level) is, based on the above fact, is that the -ms, millisecond- measurement is the plug firing time.