After reading all of the warnings against adjusting the delivery valves, or "cam phasing", I found a few threads in which adjustment of the valves via the millivolt method produced good results. Here's one:
fuel delivery valve adjustment

Understanding that a 10 dollar multimeter is no substitute for an IP calibration bench, is there any validity to this test at all? If I carefully mark the position of the valves before I start, will placing them back in their original position leave me back at where I started, or will damage be done simply by moving them in the first place?

Thanks

Only Barry can answer that question.

Get ready for some serious reading............

No it was never intended to do a complete rephasing of all elements. More to find out if that was a problem in itself. A guy might pull it off but we never considered your possible approach seriously.

If my memory serves me right that was one of the earlier posts on this subject. We did move somewhat further with time. It was pretty discouraging to find that because of the stiffness of the injector lines this system was not suitable for dynamic overall injection pump to engine timing on in line mercedes injection pumps. The only really worthwhile way in my opinion to time old diesel engines. You can compansate for all sorts of wear within reason. Static timing is no substitute.

I tend to reserve this appraoch for an injection pump that obviously by proper prior millivolt testing is going to the shop otherwise. There is then no risk. You are right in that quite a few apparent problems were done away with by this method. Far more than the ones you quoted.

One problem is the effort to really establish the testing properly. Plus the interaction at the adjustment. For most it should be reserved for just finding the problems if there. It was meant to be another tool.

If the problem is confined to one element and the testing was really done properly with no short cuts. Only then consider the adjusting of an element. The problem will be gone then.

Funny thing is it worked out every time that I am aware of when reasonable proceedure was followed. Suprised me even. Perhaps people were just kind but were they happy.

As you suggested you could return to where you where otherwise with caution. You have your markings and the milli volt reading you recorded previous to the move to guide you back. Again though we never considered more than one element as the amount of fuel as well as the time of injection is being changed. There is a good chance you could land up all over the place by what in your mind is basically just a tune up.

One reason I went with this was the chance that at some period when an unskilled person was trying a drip test the first element adjustment got moved. Or was moved previously. Simple enough to get it back with that senario. In my opinion it is not suitable to sequentially phase all elements in relation to each other. This does sound like what you want to do.

A more recent related development not fully explored yet. A very low fuel pressure in the injection pump supply might duplicate certaun element problems. So before tweaking any one element from this point forward I would verify the fuel pressure under load was present in the pump.

I think people are treating the lack of proper fuel feed pressure present in the injection pump under load too lightly. It also can effect fuel milage and power it seems. No doubt very low pressure does effect idle smoothness.

To really stretch this at present it may be the cause of the number one bearing failure on four cylinder 616 engines. That is a reach though with present knowledge. Still I would not drive around in a 240d with really substandard fuel pressure in the pump. Better safe than sorry and this is too difficult to prove but something has made those 240ds destroy the number one bearing. This kind of fits.

Anyways if you feel you have a related problem post it and people will guide you. As the expression goes the proof is in the pudding.

Quite a few other people decided to do it by email. It was reasonable they did not want to expose themselves to public ridicule I imagine. To my knowledge all were resolved well with about one draw if I remember.

I actually became wary of people taking short cuts or not doing all the important steps in proper sequence. Another way to look at it. There is no sounder approach available to us on site to my knowledge. Other than pulling your pump and taking it to a shop. This is the only way to really isolate it to the pump first though in most cases.

The subject of the milli volt system will always bubble to the surface from time to time.

It is America...And it is YOUR Injection Pump...

(BUT,if T'were me...)

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'84 300SD sold
124.128

Does it matter whether the plugs are pencil or loop-style?

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Tomas, Sweden
1966 Mercedes Benz 230S with OM617.912, automatic. Disk brakes from W108
1983 Mercedes Benz 300TD grey, OM617.912 and 5-speed manual
1983 Mercedes Benz 300TD blue 7-seater, OM617.912 and 5-speed manual

No, but you will have much easier and quicker starts with the pencil style GPs

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

The glowplugs are NOT sensors and should not be used for anything but to satisfy curiosity as to what might be happening inside the combustion chamber.

Use the pencil plugs, if you already have the relay, winring, etc in place, and it will work off the key correctly.

It would be more work to swap them around to verify things. They are not designed as thermocouples as mentioned but do generate voltage from their different operating temperatures. I still see them as just a comparison type device.

You have to be thinking at each step of the process to retain accuracy. As long as the filament loop is made of dissimular metals there should be some reaction. I am pretty sure to the best of my recollection. That no person posted after reading the loop type plugs. Or of anyone reading them. I could be wrong.

As some poster mentioned it is your car. I just would not like to see anyone get in over their head. I see post after post that the milli volt method could be used to at least partially isolate a problem.. Or more importantly clear something of suspicion.

If the actual operating temperature of any given cylinder is really higher or lower than another there is some sort of problem lurking. Interpretation is probably the difficult part combined with being thorough. That means using one glow plug as a standard at least and moving it from cylinder to cylinder.

You are almost forced to use one plug as a standard as their individual response voltage wise can and does vary from plug to plug. I am really glad to see someone brought up the milli volt method again. I was at a loss to find a reasonable method to prove my suspicion that a low fuel feed pressure might take out the number one rod bearing over time on 616 engines.

Now I will describe the test for someone perhaps to try. I have no ideal when I may get the time myself. Yellit is already geared up partially. Start a 616 engine and know the fuel feed injection pump pressure. Read the glow plugs milli volt voltage from front to back. Lower the feed pressure by removing the return valve spring for example. The engine will still run. Read the voltages again from the front of the engine back.

If the voltages show a trend to be higher on number one and taper off more than they did with fuel pressure as you progress down the line. In my opinion it is then almost conclusive that this is the cause of the ultimate failure of the number one rod bearing with time on 616 engines. Less so but still prevelant on the 617 engines as they have more power strokes and the loading on number one can never reach the 616 engine dynamics.

What this proves in my opinion is happening. Either the timing of the elements or amount of fuel in various elements has changed with low fuel pressure to the injection pump. Number one cylinder is forced to overfuel at the same loads in comparison to an engine with good fuel feed pressure. This would be reflected by a higher than normal milli volt reading on the number one cylinder. Or a gradual lowering of the voltages present on the other glow plugs as you went down the line.

What has occured is simply stated. The number one cylinder is then forced to carry a much larger percentage of the operating load than was originally intended. . I will drop Yellit a note to see if he might do the test. I know he has at least one gauge hooked up to his injection pump fuel feed pressure. At this point he is the man if anyone is in this area.

The problem with the milli volt method is one thing seems to always lead to something else over time. Even Yellit if he is thinking will realise this might prove certain other things that are suspicious at the same time. Like abnormal loading of the elements for example. Or the whole basic engine to pump timing has been shifted with the low fuel pressure.