I've read threads on here about timing by the "drip method" and optimizing timing by reading the millivolts on the glow plugs, etc., but one thing I haven't seen is much on timing the IP with a meter.

As many already know (though some may not) there are two basic types of timing meters for a diesel - a "lumy" meter and a "pulse" meter. With no spark plugs there is no electrical "timing event" to trigger a regular inductive timing meter like ones used on gassers, so something else has to serve as the trigger.

With a luminescent (lumy) meter, a light sensing diode (protected by a quartz crystal) is inserted into the prechamber in place of the #1 glow plug. The diode registers the flash of light when the diesel fuel in the prechamber actually combusts and by comparing that signal and one from some kind of RPM sensor indexed to the crank, you can read the timing.
With the "pulse" method a piezio strain gauge element is tightly clamped to the #1 injector line and as the fuel is injected through the line it expands minutely. The piezio strain gauge registers this tiny amount of expansion and converts it to an electrical pulse that will trigger a standard inductive timing light.

NOW FOR THE REAL QUESTION... has anyone ever used (or tried to use) the luminescent type of meter for timing their Mercedes? Is there even any kind of indexing mark on the crank that could be used for the magnetic pickup? I just bought a Rotunda Tach & Time meter designed to be used for setting the timing on Ford 6.9 & 7.3 IDIs off of eBay.

I'll be using it to check the timing on my F250, of course, but I'm wondering if I can adapt it for use on my Mercedes.

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1984 300 Coupe TurboDiesel
Silver blue paint over navy blue interior
2nd owner & 2nd engine in an otherwise
99% original unmolested car
~210k miles on the clock

1986 Ford F250 4x4 Supercab
Charcoal & blue two tone paint over burgundy interior
Banks turbo, DRW, ZF-5 & SMF conversion
152k on the clock - actual mileage unknown

there is already a magnetic sensor on the crankshaft. On some models there is a dummy cap on its terminal above the drivers front wheel.

Some models have an active cap which I have yet understand.

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HEY! That's RIGHT! The earlier models used a sensor on the crank pulley and an amplifier mounted on the left front fenderwell to create a signal to drive the tach. Mine's an '84 and it uses the sensor on the bellhousing, so I'd forgotten all about the crank pulley sensor.

Hmmmn, I wonder if I should try using my meter's probe where the sensor mounts, or whether it would be easier to try to pick up the signal off one of the pins in the socket mounted on the fender.

I'm thinking I should use the sensor bracket to hold the magnetic probe for my meter. Maybe zip tie it in place. Or better yet, make a removable bracket to hold it in postition - that way it could be used on other people's engines as well.

Next I'll need to take an old glowplug, drill it out and tap it for 1/8" NPT fine threads to adapt the slimmer Ford GP sized luminescent probe to the fatter thread size of the Mercedes GP.

Once I get that far, I'm going to have to find someone who's OM617 is timed perfectly and hook the meter up to figure out what the offset and timing setting should be when measured with the meter.

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1984 300 Coupe TurboDiesel
Silver blue paint over navy blue interior
2nd owner & 2nd engine in an otherwise
99% original unmolested car
~210k miles on the clock

1986 Ford F250 4x4 Supercab
Charcoal & blue two tone paint over burgundy interior
Banks turbo, DRW, ZF-5 & SMF conversion
152k on the clock - actual mileage unknown

You should have a sensor there... no? Why cant you just tap into the lines coming from it?


I would love to see this work.

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I see.. you mentioned that already. This is what I was getting at.


I guess it depends on what kind (shape) of pickup your timer has. I wouldnt want anything too loose bangin' around down there with my engine running / belts turning.. etc.

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So, anyone ever seen instructions or equipment for timing an OM617 with a luminescent style meter?

I know on the Ford IDIs, the correct timing is around 9* ATDC versus the 24* BTDC specified for the "drip" method.

__________________
1984 300 Coupe TurboDiesel
Silver blue paint over navy blue interior
2nd owner & 2nd engine in an otherwise
99% original unmolested car
~210k miles on the clock

1986 Ford F250 4x4 Supercab
Charcoal & blue two tone paint over burgundy interior
Banks turbo, DRW, ZF-5 & SMF conversion
152k on the clock - actual mileage unknown

What I have read about the different types of Diesel Timing meters that are not made vehicle specific is that you would have to set your IP up correctly with the Drip Method or one of the other Mercedes Factory Methods first. Hook your Meter up and see which degrees it indicates.
After that; using the same degree setting you can now use your Meter for future timings.

Other random thoughts:
There is also may be a slight differance between Begin Injection and the beginning of ignition.
Also the Drip Method is non-moving static timing.
In order to create a pulse or light from combustion the Engine has to by running.
I do not know at what speed the Pump Timer begins to advance the IP. It maybe that it has some advance even within the Idle Speed range of RPMs. If so changing the Idle Speed after you get your degree setting with your Timing Meter could mess with the accuracy of your origional timing setup with the meter.

The other problem is the older model IP timing cannot be advance or retarded easily while the Engine is running.

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84 300D, 82 Volvo 244Gl Diesel