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?