Yes.. Engine warmed up for the test. These engines burn almost no fuel at idle.

" If the shake at idle is worse after a long hard freeway run, it's probably the deliver valve seals and/or springs."

This is my exact problem ~ engine idles smooth when stone cold but shakes and lopes as it warms up to full operating temperature .

I removed and cleaned the IP's delivery valves and found much crud in the wells plus light rust on the parts i removed .

Maybe it's time to replace my IP .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

DV's can certainly cause an idle shake, but don't bet money on it being the only problem.

My SDL had a bad shake/lope (would shake the car) once at operating temp, but was smooth as glass when stone cold. All signs pointed to DV's as injectors and compression were ruled out.

Replacing the DV seals and washers got rid of the skip, but the idle is still a bit rough on occasion. Didn't 100% cure the problem, but certainly made it about 96% better - definitely to an acceptable level.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

I measured millivolts after the engine was warmed up. Using the 200m scale I had 8.8 on cylinders 1-4 and 8.7 on #5.

The dash temp guage says 80*C which is 176F

I measured the temp at flat of the glow plug with an IR thermometer mounted above the glow plug at the height of the injector hard lines.

#1 = 167
2=169.3
3= 169.3
4=172.8
5=169.6


The hood was up when the engine was shut down and the engine seemed to move more than I remember at shut down. I intend to pull and check the engine shock mounts when I have time and examine.

I'll also run the last bottle of diesel purge through from a bottle in the engine compartment.

I know the engine mounts are good as they are new Lemforders that were installed last summer with the suspension parts. The engine shocks themselves were nice and stiff when I installed the engine mounts. I'm suspicious of the engine shock mounts and will refurbish with flexane if they are bad.

Comments?

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Did you unplug the glow plug relay connector when doing the measurements? If not, the measurements are meaningless because the glow relay ties all 5 glow plugs together. Best to put the meter leads direct to each glow plug body (ground) and center electrode to avoid voltage drops of the wire harness and engine block.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I thought it strange that the readings were so close. I'll do again tomorrow and unplug the relay connection to the glow plugs.

I used a stud that holds the valve cover on as a ground and measured at the center electrode where the GP wire connects to the GP.

__________________
85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

They should be close, as long as the plugs are from the same batch and the injectors aren't plugged. These "millivolt readings" are a proxy for prechamber temperature.

What I think would be interesting would be to hook an oscilloscope up to the plugs to see if they're fast enough to measure transitions as the engine cycles. My guess is that the plugs have too much thermal mass for anything but an average reading, but tracing a cycle would be really useful information. I was going to try to do that yesterday, but 13" of snow means it will be some time before I can get out there with a scope.

Going right to the glow plugs offers no advantage. Since no current is flowing for all common sense purposes a glow plug harness leads resistance within reason are not a real factor.


If you got those glow plug milli volt readings with the harness disconnected at the controller and they represent what is really there.


There is no indication of a slack cylinder or that the injection pump has developed calibration issues over the years. In fact they indicate a far better power balance than is to be expected. So perhaps you read them wrong? Just a little too consistent on the 1-4.

Not as accurate but your thermal readings where interestingly a general verification of what is going on even if the milli volts where done wrong. Although I do not have nearly the trust in using them.


I was sitting here trying to remember when I did my scope checks if I went right to the glow plug or used the end of the harness wire. I suspect I may have used the end of a harness wire and the slight resistance at the glow plug connection may have made it pick up radiating waveforms like an antenna. Or the actual resistance of the glow plug elevates the glow plug lead from ground.



All the information I was able to to gather with my scope years ago was that it was better to use the actual engine as a ground when measuring the milli volts or there were problems.


There were voltage drops messing up the milli volt measurements and there is quite a waveform from the alternator in the system. The true minor resistance in the ground strap connections was the probable issue allowing visable waveforms to develop across the semi isolated straps suspended or isolated from absolute ground .


The only thing I really know is using milli volts can and does pick up conditions of many types in a dynamic running fashion.


Yet have a look with your scope. I at the time was just trying to find a way to get a usable reading of the milli volts. It would be interesting If something else was discovered.


Now if the readings where acquired properly. The change in the glow plug temperature indication is not fast but fairly slow. Air getting in would be my first thing to check. With those readings.


If present it provides or has the potential to randomly disperse through the elements creating a variable running imbalance you cannot read. Air once it is in the hard line compresses and reduces the amount of fuel injected. But the problem moves around so fast from hard line to hard line you do not see it represented in the milli volt readings.


The really nice thing about using the milli volts to me is it can and does also indicate sequential imbalance from the injection pump. A bad injector or internal issues in the engine. As general rule varations of .1-.3 milli volts cause no noticeable issues to us humans. At .5 mv variance or more proven by checking by swapping glow plugs. There usually is something going on to deal with.


Again if you got those readings the proper way most things in your overall engine system are really in great condition.


So if the readings were done properly the next thing I would do is introduce a clear piece of fuel line in the return from the injection pump and look for air. There of course should be none. I seriously doubt I have ever seen a better running milli volt balance indicated.


The actual milli volt readings do not give any indication of the injection pump timing. I have never seen the effect of what too advanced timing seems like on these engines but it might impact the idle. General wear will only retard the timing. To be advanced someone would have had to do it.


I have to add as well. That I have never given much thought to how exactly that damper adjustment impacts everything. If it is deficient it seems that after a long hard highway run the idle is really pretty bad usually. It is deemed both an adjustable and wear item.


I guess my final comment is just that at this time. With an indicated power balance that good. The engine just might be at a sub standard idle speed. We as a general rule never check it out. Smooth running at low rpms is partially a function of inertia.


The weather here also is such that I would resist doing much service work outside. You could easily have a non engine issue.


I noticed today that someone put a lot of new parts into their front end fifteen thousand miles ago and is now having issues with them. They were lemforder parts that we respected back when he installed them. The original parts lasted probably about 150-200k.


I hope it is not reaching the point where a good used part in the suspension system from another car. Is a better option than a new one. I had to wonder when you saw the engine move more than normal on the shutdown if one of your newer motor mounts was bad.


Also keep in mind that I am getting pretty old now. Two really good women would tucker me right out or kill me. Without a doubt.


Unfortuantly it is just something else that I cannot get the opportunity to prove.

The test has to be done with the relay connection unplugged, otherwise the relay will connect the plugs together. That just makes it easier, as you can do all your tests at the connector.

The IR test is unlikely to tell much, because the injector and head temps will average out. I like the idea of the millivolt test, because it's essentially a thermocouple probe right at the ignition point. If the reading is fast enough, it would be like scoping the coil on a gasser.

I took new readings. The ground was connected to the front driver side stud that holds the valve cover or the entire test. The pos lead was to the plug on the wiring harness when the plug was disconnected from the GP relay. A 2nd set of readings was taken at the plug. Both readings at the GP and through the wiring harness were almost the same.

At the GP: 1 thru 5: 9.3, 7.0, 9.0, 9.5, 7.0

Thru harness 1 thru 5: 9.1, 7.2, 9.0, 9.5, 7.0

This was a several year old Greenlee brand meter using the 200m scale.

Next move?

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Those are not good numbers in relation to the spread of some of them to each other. I need a little time to think but a compression check might come next.


Since the glow plugs are recent. Swap out one of the low reading cylinders with the glow plug from a high reading cylinder. Read the cylinders again. Just to verify it is not a difference in the glow plugs.


This is pretty much an absolute first. The injectors where redone reciently so I am ignoring them in my suggestions. But had they been old. I would have swapped a couple of then also to either condem one or give it a clear bill of health in general.


If I assume the glow plugs are as they should be in a new batch. Although you cannot under any condition assume that. Because this is where I found people took a very dangerous shortcut. The compression checks out favorably as well. Then there is an issue with the injection pump. This actually is a better thing than finding low cylinder pressures in some cylinders. Personally I feel you might find this but I suspect not.


Anyways keep going taking no shortcuts and things will get nailed down. Those voltage readings where too far off for an engine to idle well. Try to not work too much in harsh weather conditions. This thread will be rechecked often enough. You have a two volt milli volt spread and that is really substantial from my past memories. You might also weigh running a solvent through the injection pump just in case you have a couple of really dirty delivery valves after just a couple of things are done. That is a long shot though.

Well going to take the wife out to supper now.. So if you have any questions directed towards me that others do not answer. I will check the thread later this evening.

It will take a couple of days to move the glow plugs. Millivolt readings were taken with neg lead connected via alligator clip to the stud that sticks up through the valve cover and goes directly to the head. I'll check that as a ground by measuring battery voltage from there but I think it is good.

The other thing that I thought of is that I don't have a glow plug reamer and have no idea how carboned the chambers are or whether they are different. The odometer works and shows ~185,000 mi. The engine starts and runs easily always on the 1st glow unless really cold then I glow twice as a matter of course. The oil cap barely moves when loose. My only engine complaint is the shake. Even power is good.

Unfortunately, time moves on. A friend of mine says "you can remember it any way you want". I say "the only way I'll see something like that is if I buy it".

Reminds me of the saying "To soon oldt, to late schmart."

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

I repeat, you want to take the readings the same way, same distance for each glow plug. Cast iron has a certain resistance/ foot. The further away, the higher the resistance. Why would you choose one ground point where the distance will be different for each glow plug? You want the ground point to be the same for each glow plug, that's the hex on the glow plug. Besides, that stud you were using is all rusty.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

If it was a thin iron wire, maybe, but the block presents an enormous flow path cross section. There isn't enough distance for the resistance of the block to matter. My observations so far are that a common ground point is just fine, and I've been using an injector line for my experiments. You can see that just from the distribution of his readings: if block resistance was a significant factor, you would expect the readings to drop in proportion to the distance to the common ground. Instead, the highest reading is four cylinders away from the ground.

Tell you what I would do next. Use the same ground point and the same technique of measuring at the relay plug. Measure the resistance to the common ground of each plug. That may tell you whether the variations are related to the plugs or the cylinders.

I'll measure as you suggest. Stud itself isn't rusty. Intermittent external oiling system takes care of that. Besides, valve adjust has cleaned it also.

__________________
85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.