Correct me if I'm wrong, but you did say the car uses no noticeable amount of oil? If the cylinder was out of round or rings malfunctioning enough to cause a driveability issue, wouldn't you be using some oil, at least a teeny bit? Maybe meticulously check oil consumption again before you pull that beastly head. You don't seem to have any issues regarding heat or coolant etc. pointing to a head gasket either. Your idle issues sound EXACTLY like mine, even though we have completely different cars (79 240d). The fact that they are both diesels mean they run using the same principles, so I am following this thread like a fat woman follows a soap opera...

Would anyone more knowledgeable than me like to comment on the possibility of loss of compression(?) without oil loss in regards to wear in the bottom end? If fixing the IP doesn't help, maybe you should start checking your valve train more? Also doesn't hurt to try the compression test again, could be operator error? And pull out that sherlock holmes magnifying glass and quadruple check for fuel leaks ANYWHERE.

Is there coolant consumption or indication of oil in the coolant? Is the engine back together to where you can do a radiator squeeze test? If you're taking a poll, chalk another vote for pulling the head. IMO, you should have done that before pulling the IP.

Sixto
87 300D

No coolant/oil exchange. Overflow tank is clean, no pressure in the hose. The engine exhibited these exact symptoms before the brand new (not used) #20 head was installed. This seems to exonerate the head or gasket as causal factors.

The lack of engine oil consumption also has kept me from worrying too much about #2 being ovaled. At the time of the rebuild, it was found NOT to have a bent rod- numbers 3 and 4 did have bent rods, which were replaced. The rebuilder attributed the problem to "cylinder glazing, and improperly seated rings."

Once the IP is re-installed, I'll run and evaluate the change, if any. Obviously I'm hoping that #2 will wake up. If not, I'll do a leak down test, before I pull the head. I'm pretty satisfied that it will not be the head, I already know it's not the injectors, and won't be the IP. That would leave the cylinder and piston/rings. I would tend to think a piston issue would have been obvious during the rebuild. If I have to go down this road, I will very carefully measure the bore, piston and rings.

I understand that early on, MB said the OM603.971 was not suitable for cylinder sleeves. Later, in August of '94, they issued TSB 01/32 that said it was ok to install sleeves in this block. I have not read this myself, so I am looking for a copy of this TSB to verify.

Anyway, one step at a time. I hope to have the IP installed in the next couple of days.

FYI
 

* The injection pump WAS damaged.
There where at least two major delivery valve issues found, now repaired and calibrated.

My advice when we spoke on the phone when he picked it up from the injection shop was:

* Install the injection pump and see if the issue is gone, before any further diagnosis or repair.

Until he reports back with some results, there is IMO no logic putting more time, labor, and/or money forward.

********************************************

Reviewing:

The engine was rebuilt at 40k miles:
* #2 cylinder issue has been there since then, and may have been there to some degree before.

The #14 Cylinder head was replaced with a #20:
* #2 cylinder issue was there before and after.

* The engine consumes no lubricating oil or coolant.
* Coolant system is not showing indication of combustion pressure.
* The engine started smooth when cold.
* The engine ran progressively worse as it warmed up to full operating temperature.

Engine running; His mechanic "cracked" the injector lines loose one at a time.
* Only 3 cylinders where significantly affected during this test.
* The other 3 made NO difference.

.

I understand the your logic and Roy's logic. Prefaced with IMO, any compression irregularity tells me to pull the head. I agree with not putting more time and effort without understanding the situation which is precisely why I'd have the head off immediately after the compression test results. I'm happy for the IP results but it remains an IP without a worthwhile engine to fuel. I'm not challenging the process since I know about 2% of what you know of the situation. Just, again, IMO.

And a fact check - the original head should have been a #17, not a #14. Do you have a .970 or .971? It's an irrelevant detail but a 91 SD would have a .970 engine.

Some shots in the dark to check without pulling the head:

- inspection of #2 cam lobes; visual and actual measurement of lift vs other lobes.
- do service records indicate that valves and lifters were reused on the new head?
- do service records indicate that prechambers were reused on the new head?
- can you check for a compression leak through the prechambers and lock rings?

I don't know whether resleeving is possible but Performance Products sells .97 cylinder liners for $99 each. I'm not sending you somewhere other than Phil/Pelican. Just pointing out that they exist if Phil or even MB doesn't carry them.

Sixto
87 300D

Can't tell you guys how much I appreciate all the the thought that has gone into this so far!
As Roy said, Once the IP goes back in, I'll go from there.

Lastly, thanks for the fact check. It's a 603.970. Never saw the original head. WHen the new head was installed, there are also reciepts for new exhaust valves and 2 new injectors, but not for anything else.

Early on I pulled the cam cover to inspect the cam, etc. All cam lobes look absolutely new, and everything in the cam chamber is clean, bright and shiny, just like new.

The injector pump installation is now complete. No joy.

Leak down test is next, then off with its head.

The Head is Off. All is Revealed
 

So I spent some time at my mechanic's shop today, and helped pull the head ( a #22 by the way, now that I could see the casting mark clearly). First things noticed- The head gasket was perfect, no sign of any problems there. Proceed to looking at the piston crowns and bores. Since #1 is already at TDC, I saw a very light, uniform carbon soot deposited over its surface. Number 2, the real problem cylinder- dead clean! Number 3 was also pretty clean, while 4, 5 and 6 were nicely carboned like #1.

All cylinder bores look fine. No ridges, scoring etc. Just what a good bore should look like, so we rotate the crank to look a little deeper. As #1 descends, I watch #2 come up to TDC and guess what? It is at least 1mm shy of where it should be! A friggin bent rod! Number 3 appears to crown slightly off kilter, but crests the bore. 1, 4, 5 and 6 all fine.

There it is. I'm assuming the fact that there is so much head space between the piston crown and the head explains the low compression and lack of ignition. In anticipation of a fatal flaw, I found an OM603.96 with 140k miles. I'm going to listen to that engine tomorrow, and if it is as described I'll acquire that engine. My plan is to freshen it up with a set of rings, swap over all the good bits like the head and injection pump from the 3.5 and end up with a solid car. I will be searching the site for threads on this swap, but please, any tips as to what I should be looking for, what changes I need to accomodate etc. would be SO welcome!

There is nothng like diving into mess like this to really learn a lot. While it IS pretty inconvenient, I know that when I'm done I will have a 126 that I can have real confidence in.

Jim/engatwork is going through that right now - http://www.peachparts.com/shopforum/tech-help/311554-pulling-head-1991-350sdl.html

Sixto
87 300D

Thanks- I missed that thread.

My 3.5 has lots of new parts, like the oil pump and of course my newly overhauled injection pump. As I undestand it, the injection pump and head will swap right on to the 3.0 without any problems. Since I am going into it this far, I want to use the best of what I have, like the new oil pump, the later timing cover from the 3.5, check out the vacuum pump, etc. I appreciate you all helping me avoid the pifalls that can accompany this sort of thing!

I checked out the 3.0 OM603 engine today. It is currently in a Chevy Tahoe, which is why it is for available. The installation is a bit crude, and it broke the flex plate so the owner who acquired the truck this way is going to repower it with a GM engine.

Engine started right up from cold, running on all 6 cylinders. It sounded good, no funny noises other than a squeaky idler and a noisey K&N air filter. Revved up and held rpms smoothly too. There is a thin wisp of steady blue-grey smoke, and some apparent blow-by with the oil filler cap off. The owner tells me the engine is supposed to have 140k miles, and by his testimony used 1.5 quarts of oil over the 4k miles he has actually used the vehicle. It has good oil pressure, and runs cool with no overheating. The price of the engine, complete is $700, with a money back guarrantee should it have any issues once I get into it.

My plan is to re-ring the engine, and transfer all the best bits from my 3.5 to this engine, selling off what remains. I'll keep everyone posted, and as always welcome the wisdom of the board!

Were you able to drive the Tahoe with 603 power?

Sixto
87 300D

It was offered, but I declined. This vehicle is out in the puckerbrush, and with its cracked flex plate, I just listened to it run.

How can you tell it doesn't overheat if you're just listening to it idle in February?

Can you do a radiator hose pinch test?

Is there a chance for compression test before it's yanked from the Tahoe? Is there time to send an oil sample for analysis before you decide?

Sixto
87 300D

All good points. The problem I have is there aren't any other engines locally available, and I'm going to pull it apart anyway. If it doesn't measure up on disassembly, I get my money back. At least I have more info on this option then if I had to go with a used engine from the internet.