That's what I'm thinking, or the head. Anyone have a head for sale, just in case?

I'll know more tomorrow.

__________________
Chief

1991 350SD

Got a look at the part number on the head today- not enough light to see it perfectly, but looked like it was 20. Definately not 14.

Cylinder #2 is clearly not firing- have swapped a couple different injectors, no difference. Compression tests for #2 reveal a low while hot in the low 300's, up to about 400 cold. All other cylinders are in the mid 400's. I haven't been able yet to determine why it's low, but I just don't understand why it's not firing. MB has a min spec of around 265, so I would think with these values even though there is a problem, it would still fire. It also looks to me like someone in the past may have tried to remove/move the #2 nozzle on the injection pump using a chisel (nothing should surprise me anymore).

Talked with the PO trying to get a little more info, and I may have found the reason for the low compression. He mentioned that he thought the engine was running under temp, and he tried to get it to run hotter by placing cardboard in front of the radiator! All I found was the monovalve was inoperative. I think this was his misguided attempt to increase cabin heat, possibly sacrificing that beautiful new head!

__________________
Chief

1991 350SD

Time perhaps to have a look at the valve activation mechanisim for that cylinder. Even if the number two cylinder element was out of calibration somewhat . I cannot see the cylinder being totally dead because of it. The smoke/no smoke effect of when the injector line is loose and tight means to me fuel is being provided to that cylinder.

I doubt but again without knowing that the elements range of adjustment could let the fuel in so late there is no possibility of good combustion. So you get the smoke of heavy very partial combustion instead.

Wait and let others comment about this though. I just do not have enough knowledge.

I'm not too comfortable with the IP, but I should be able to pull the side cover and have a look without doing any harm? I have thought the same thing- there is fuel, but if that cylinder is off time (possible?) it would create that situation.

__________________
Chief

1991 350SD

The range of element timing adjustment should not be that broad I would think. Yet admit I do not know. The main fly in the ointment is the compression is lower when the engine is hot. Whatever is causing that is not the injector timing I would think. Plus the engine functions much bettter when cold. You do have 300 lbs at hot cranking speed. I have to wonder what it is at higher operational rpms. There is no way to check that out. I still might want to carefully examine the valve mechanisim for that cylinder though.

Also the more I think about it the stranger it is if not a head gasket. Maybe time for both a hot and cold bleed down test. At this stage you have to find out what the problem really is.Guessing is never a particularily productive approach.

Perhaps Mr.Hunter or another working mechanic will chime in with what he thinks. It may be run of the mill to them . It is not to me. Since youi found marks on the number two element assembly.Maybe someone tried to deal with this problem or another issue before in some way on that cylinder. Otherwise why would those marks be present?

Thanks for your thoughts. I too am at the limits of my knowledge, which is pretty frustrating- especially since I need the car!

__________________
Chief

1991 350SD

Quick alternatives.

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82 Mercedes 300SD Diesel Sedan

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1980 Mercedes 300SD


.

Yeah, the wife wouldn't be too thrilled about bringing home another car. Pretty much committed to getting this one firing on all 6 again. Thanks for the research, though!

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Chief

1991 350SD

So, specifically, is it possible for one cylinder to be out of time on the IP, and if so, how?

Thanks!

__________________
Chief

1991 350SD

Like everything, I'm trying to learn more all the time about this. While I have a compression issue, it still seems to me that at the values I'm getting I should still have ignition. So, it must be something in the fuel system. I have eliminated the injectors, so it must be the IP, right?

So far, my reading up on this suggests the delivery valve as the most likely culprit. Among the many things the PO told me was that he had had the delivery valve seals replaced. I suppose it's possible one was messed up somehow. I'm at the point where perhaps it's time to bring the IP to the Midwest Fuel Injection shop.

__________________
Chief

1991 350SD

Sorry, the answer is no.
It is not possible for one delivery valve to be out of time.
Some links for you to study injection pump internal function.

Inline diesel Injection Pumps
FYI: Inline diesel Injection Pumps - PeachParts Mercedes ShopForum

OM616/617 Injection Pump.
How to adjust the Naturally Aspirated Injection Pump.
OM616/617 Injection Pump - PeachParts Mercedes ShopForum

'75 240 D M-style IP Theory - Help!
'75 240 D M-style IP Theory - Help! - PeachParts Mercedes ShopForum

Fuel injection pump diagrams???
Fuel injection pump diagrams??? - PeachParts Mercedes ShopForum

Delivery Valve Leak issues thread
Delivery Valve Leak issues thread - PeachParts Mercedes ShopForum

Fuel only dribbles from removed injector line when cranking at WOT
Fuel only dribbles from removed injector line when cranking at WOT - PeachParts Mercedes ShopForum

How forcefully will fuel come out of injector lines
How forcefully will fuel come out of injector lines - PeachParts Mercedes ShopForum

Leak-down Tester and ?'s
Leakdown Tester and ?'s - PeachParts Mercedes ShopForum


It is possible someone has screwed up delivery valve calibration while replacing seals = roughly $950.00 for re-calibration.

With the compression numbers; and especially reversed temperature compression numbers of cylinder #2. The LEAST you have is a BAD head gasket.

Cylinder compression (on a good engine) is always higher when at operating temperature.
If the compression test numbers where wrong, possible gauge damage, operator error, then it could still be a delivery valve issue.

The reversed numbers indicate thermal expansion; of a crack, or bad head gasket.

I am sad to say
IMO: The cylinder head must come off for further diagnosis.



.

Certainly possible for one element of an in line injection pump to be out of proper sequential order with the others as to exact position. Thats what the adustment is for to compensate for production tollerances etc. Actually totally out of sequence is impossible. The only way that could be accomplished is swapping injector lines to the cylinders.

To find out if it is possible to be as far out as yours would have to be. I would talk to an injectioon pump shop about that.

Personally I still do not like the fact that the cylinder tests lower compression wise when the engine is hot. This is abnormal to me. I could see the same or higher. But lower?

I would do a leakdown test just to see with the engine hot and cold.

As you suggest I would still expect the cylinder to light off .In fact it does until the temperature rise gets going. It may be a total waste of time but I still would want to critically inspect the valve train for that cylinder. As Mr.Hunter alluded to it could be just a head gasket as well. The leakdown test may help there.

Really though things are not adding up well here. If you are determined to check out the injection pump you may live in an area where a cheap one from a pick and pull is an option. The pump shop may or may not be reasonable in cost. Although you could also talk to them before taking it in. One certainty is the compression lower when hot will not be changed.

I was sitting here trying to frame an example of one possibility. At say 60 degrees the compression is 400. At less than 200 degrees it drops to 300. Is there not a probability that the heat of combustion or compression takes the cylinders compression way lower?

That heat of combustion/compression is multiples of the temperature and pressure spread you are observing. You have to consider that the heat of compression alone at higher revolutions may take the cylinder pressure down further .

The fact that the #2 cylinder seems to run well when first started up cold indicates to me the injection pump may still be fine. The exception being the delivery valve seals on your type injection pump can be a little flakey. I am getting way beyond my knowledge depth here though.

I assume you have checked for any bubbling in the coolant when the engine is up to temperature? And done the upper coolant hose test the next morrning? The hose should be flacid the next morning. If it is still very firm definatly forget the injection pump. I really would forget the injection pump for now anyways. You have enough fish to fry with the falling compression.

Great replies- lots to read and think about, Thank you!

The head comes off tomorrow.

__________________
Chief

1991 350SD

Question
Answer
That is incorrect!

It most certainly is possible and is part of the normal calibration procedure to set start of delivery on each individual cylinder within Spec.

__________________
Beagle

I have just read through this thread. Can you explain logically why you have decided to pull off the head??

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Beagle