For several days I have been testing and refining my tests of the IP timing of several diesel MBZ(s) and will now call my latest method the:

“ Karoly MBZ Diesel Injection Pump Timing Check / Test ”

My use of “ Karoly ” in the title is to give credit and respect for my independent MBZ mechanic friend Karl [Hungarian born] who’s 30+ years of experience working with these vintage diesels has been invaluable! Here are the latest steps in our procedure which attempts to squeeze out the most accuracy possible using ordinary tools most of us have:

(1) Disconnect the #1 fuel injection line running from the IP pump element to the injector.

(2) Disconnect the wire to the #1 glow plug and remove the plug. This is to remove the compression on the cylinder and improve the ease of turning over the engine, particularly as you approach the engine/IP timing pulse you are trying to detect.

(3) IF only 1 person is conducting this test, use the bolt on the power steering pump to turn the engine over [to the right as you face the engine]. NOTE – IF the V-belt slips, you will need to tighten the steering pump’s belt tension and then readjust to your liking after the test is finished. Turn the #1 cylinder until it is approaching its compression stroke which you can judge by looking inside the valve cover and see the intake and exhaust cam lobes rising up to the top. Rotate the engine until it is at ~60 deg. BTDC as indicated on the timing marks on the front of the crankshaft.

IF 2 people work together and coordinate closely, one can turn the engine from below using a 27 mm socket and long ratchet [the longer the better] and the other can coordinate verbally from above to accomplish the same as written above in this step (3).

(4) at this point give the priming pump 2 to 4 stokes to raise the fuel pressure inside the IP... and then immediately shut off the priming pump IF it is the old style that often leaks when left open… for such leaking would probably void any advantage you achieve by such pumping ! This should leave the IP’s exposed #1 element fuel outlet fitting full of diesel fuel which is actually too much fuel but we will now remove.

(5) By whatever means you desire, you need to “wick-up” or blow away excess fuel which usually forms as a “meniscus” or “bubble” in the top of the #1 element’s outlet fitting. What you are trying to do is remove the top of the “meniscus” but leave the narrow throat of the fitting full. This is another step to help improve the accuracy of this check/test. I like to use one of those computer aerosol cans that have a “swizzle-stick” nozzle. These are normally used to blow dust out computers. IF you hold the nozzle just right, you can easily blow away the top of the “meniscus” but leave fuel in the throat of the element’s fitting.

(6) As you turn the engine through it’s final few degrees seeking to detect that illusive pulse from the #1 IP element, it is IMPORTANT to use a tool with as long a handle as possible. For instance I switch over and put my longest ½ inch breaker-bar with the socket being used [ 22 mm on the power steering pump or 27 mm on the crankshaft pulley]. This extra length increases the control, thus accuracy of your check/test as you are intently watching for movement of the fuel in the IP element that indicates the IP’s timing !

And so its time to let out a “Eureka” or “voila” when you see the fuel move up in the throat of the IP’s fitting, for you will have found as accurate an indication of the IP’s timing as I can conjure up ! My completely biased opinion is that with a little practice you too can be accurate to within one degree.

So give me your thoughts as we are open to further refinements... and better yet, give this a try and see what you get for your vintage MBZ's timing. I have thus far found our 1980 240D at 20 deg. BTDC and the 1980 300D at 17 deg. BTDC. Soon I'll be working with tow 1985 300SD(s) to see exactly where they are set.

I think that most of us on this FORUM now agree that these engine will not only run, but perform well over a wide range of IP timing settings so why worry about the timing so much. Well for me I'm hopeful that fine tuning the timing on these cars' engines will give us improved fuel economy... and the first giant step in fine tuning for economy is to get the timing close to the 24 deg. BTDC most of these engines are "spec'd" at.

Then I will begin to seriously experiment with the notion that we can use the miliVolt output of the glow plugs to make that final bit of fine tuning that will allow me to give this topic some rest.

P.S. - Armed with new piezoElectric clamp sensors, our used Kent-Moore "Tach-N-Time" meter is giving fine results and with this new accuracy in manually checking the IP's timing, we are finding that 11 to 13 degrees appears to be the proper correction factor for these K-M meters... in other words when the meter/stobe light show the timing to be 13 deg. BTDC, it is actually 24 deg. BTDC.

PLEASE voice your opinion and/or share your experience IF you try this method of checking your IP's timing!
Regards,