om617 Starting and Running Issues - PeachParts Mercedes-Benz Forum

SlowJon · #1 08-17-2014, 12:09 PM

Hi everyone! I'm new to diesel engines and just bought a 1983 300D with an OM617 and an automatic. It's not in perfect condition, but it's serviceable.

The problems: It's slow to start and when it does, it is clearly not firing on all 5 at idle until you drive it and get some heat into it. Also, the previous owner said that when you turn it off, you have to wait a minute or two before restarting or it'll just crank and never fire. He claimed it was a vacuum problem... Weird! Also, it's sloooooow. I mean, you have to floor it to accelerate at all and top speed seems to be about 55. It sounds good at idle, but it's just super down on power. Almost like a gas turbo engine with a roached turbo. I tried spinning the turbo by hand it feels fine with just a little shaft play. When I drove it home (about 20 miles) it got slower and slower. Then, after I turned it off for about 10 minutes it wouldn't restart so I gave up and went to drink a beer.

Any suggestions on where I should start looking for my missing power? I really want to drive this nice old car, but I need to get it running a little better first!

vstech · #2 08-17-2014, 09:21 PM

Remove fuel cap. Repeat drive...

On the intake between firewall and air filter is a hard plastic line that is supposed to be connected to a valve and the device on top of the injection pump. Carefully clean all these fittings. Next is the fuel filters themselves. The clear one is the primary, and the metal one by the power steering pump is the secondary. Replace them both, one at a time, starting the car between each change.

tyl604 · #3 08-17-2014, 09:24 PM

Does that car have a switchover valve like the SD? If so that could need replacement.

cooljjay · #4 08-17-2014, 10:08 PM

Sounds like a lot of stuff...

fuel filters
linkage
valve adjustment
glow plugs
dirty tank screen?
oil change
air filter
injection timing
alda needs cleaning
shifter bushings?

Its impossible to tell you one thing to fix, it sounds like the typical neglected car....just need to go down the list...

SlowJon · #5 08-17-2014, 11:18 PM

Thanks for the help. I know my way around a gas machine, but this diesel stuff is something I'm going to have to learn new! We have several diesel trucks in the family, but this Mercedes is way outside my comfort zone!

psaboic · #6 08-17-2014, 11:46 PM

With the help from the folks here and your knowledge of engines in general, you will not have much trouble at all. First and foremost, do NOT be afraid to ask a question about anything (general or specific). We have all been there and there are lots of friendly and knowledgeable folks willing and able to help you with just about anything.

Welcome to the M/B diesel world!

Glenn

mach4 · #7 08-17-2014, 11:49 PM

Just take it one step at a time, do the troubleshooting and fixing starting with the easiest first in order to build your confidence and knowledge and before long you'll not only understand these things but also have a good running vehicle.

Diesel911 · #8 08-18-2014, 12:46 AM

I spell poorly and have bad grammar.

If your idle speed is too low the Engine will be rough at idle. There should be an Emissions Sticker on the Top of the Front Cross Member in front of the Radiator. On mine it is on the Drivers Side. It has the Idle Speed, timing and the Valve Adjusment info on it.

If the idle speed is OK. Injector cut out test-Loosen one Fuel Injection Line Nut at a time and see what happens to the Engine. If you loosen a Fuel Injection Line Nut and there is no change in how the Engine runs you have identified a problem on that Cylinder.
Cutting the Fuel off to a good Cylinder shouuld make the Engine run rougher. Cutting the Fuel off to a bad Cylinder does not have as much of an effect on the Engine.

If you found a bad Cylinder remove the Injector from that Cylinder and swap it with an Injector from a good Cylinder.
Do the Injector cut out test on those 2 Injectors that were swapped. If the problem follows the Injector from the bad Cylinder you have a Bad Injector.
If the Problem stays with the original bad Cylinder you have a problem in the Engine.

I had a scay slow Car when I first stepped on the Accelerator. Once going like on the Freeway it was OK but when I slowed or stopped at an Intersection it was scary again.

It turned out My Throttle Linkages were out of adjustment and it simply was not shoving the Throttle Lever on the Fuel Injection Pump far enough. Another reason for that can be the Linkage Bell Crank at the Fire Wall can be worn out or the Rubber rotted out.

Valve Adjustments are often a big help as former Owners seldom do them.

Repair Links
http://www.peachparts.com/shopforum/diy-links-parts-category/

http://www.peachparts.com/Wikka/DoItYourSelf

SlowJon · #9 08-18-2014, 08:50 AM

Thanks for the warm welcome, all! I love learning new things and this car is full of opportunities to learn... meaning it needs a LOT of work!

Diesel911: Thanks a ton for the reply and the information! The idle speed seems to be pretty good, at least according to the tach. It definitely seems like one or two cylinders just aren't firing at idle when it's cold (braap...braap...braap...braap...). That shaky idle seems to go away once it warms up, but the idle speed stays the same. We have an old 7.3 Powerstroke farm truck that does the same thing, but only for a few seconds... on that truck we always suspected it was one dying/dead glow plug but we never cared enough to really look into it. I'll definitely do the fuel injector tests you described and check my throttle linkage, along with the stuff recommended by the others above.

One other question: how long do the timing chains typically live on these? I've read that a stretched timing chain can contribute to low power and hard starting. This car has about 300,000 on it and on a gas engine it should probably be on it's second or third chain! I recognize that the other things listed above should be done first, but should I prepare myself to do a timing set in the near future?

mach4 · #10 08-18-2014, 11:27 AM

With that many miles you'll definitely want to do the timing chain....but first things first.

Get the fuel sorted out first - filters, air leaks
Get the injectors sorted out - do the injector line test
Get the valves sorted out - adjust them to specs
Get the linkage checked - look for any slop
Get the glow plugs tested - pull and test with battery
Get the compression tested - DIY with HF kit
Get the injectors pop tested - replace nozzles as needed
Get the ALDA line cleaned -
Get the boost tested - hook up a boost gauge to the ALDA line
Get the chain stretch checked - use 2mm method

The chain stretch test will tell you if it needs to be replaced or if it's already been done. If you've got low compression it might be an indicator the engine is shot in which case replacing the chain would be an exercise in futility.

Diesel911 · #11 08-18-2014, 07:53 PM

Quote:

Originally Posted by SlowJon

Thanks for the warm welcome, all! I love learning new things and this car is full of opportunities to learn... meaning it needs a LOT of work!

Diesel911: Thanks a ton for the reply and the information! The idle speed seems to be pretty good, at least according to the tach. It definitely seems like one or two cylinders just aren't firing at idle when it's cold (braap...braap...braap...braap...). That shaky idle seems to go away once it warms up, but the idle speed stays the same. We have an old 7.3 Powerstroke farm truck that does the same thing, but only for a few seconds... on that truck we always suspected it was one dying/dead glow plug but we never cared enough to really look into it. I'll definitely do the fuel injector tests you described and check my throttle linkage, along with the stuff recommended by the others above.

One other question: how long do the timing chains typically live on these? I've read that a stretched timing chain can contribute to low power and hard starting. This car has about 300,000 on it and on a gas engine it should probably be on it's second or third chain! I recognize that the other things listed above should be done first, but should I prepare myself to do a timing set in the near future?

You can get some idea on the Timing Chain by lining up exactly the Timing Mark behind the Camshaft Drive Gear with the Mark on the first Camshaft Bearing Tower. You need to be as exact as possible as any error up there doubles when you look down at the Pointer and the marks/Numbers on the Crank Damper.

When the Engine was new it was supposed to be set at OT (Top Dead Center).

If you want to be precise you need to do the 2mm Method that is in the Repair Links.

Mercedes has no specific spec on when to change the Timing Chain and there is Offset Woodruff Keys to restore the Camshaf Timing.

Who has or knows someone that has experienced a timing chain breakage/failure?
http://www.peachparts.com/shopforum/showthread.php?t=203364

MY Question on Timing Chain Failure
http://www.peachparts.com/shopforum/showthread.php?t=203364&highlight=timing+chain

Thread showing Timing Chains compared to Japan one
http://www.peachparts.com/shopforum/showthread.php?p=2545669#post2545669

Vacuum Pumps destroyed timer Bushing Identified as the problem
http://www.mbca.org/forum/2013-12-29/why-are-these-vacuum-pumps-being-destroyed

broke new vacuum pump
http://www.peachparts.com/shopforum/showthread.php?t=258062&highlight=vacuum

Opinion- If the former owners did not do regular Oil Changes there will likely be more Timing Chain Strech per Engine Milage.
I think the same if the Engine was overheated, Oil got too hot or contaminated.

leathermang · #12 08-19-2014, 02:55 PM

""Mercedes has no specific spec on when to change the Timing Chain and there is Offset Woodruff Keys to restore the Camshaf Timing. ""

What they say is that when the offset keys are no longer able to bring it into spec then you replace the chain.

leathermang · #13 08-19-2014, 02:57 PM

As Mach4 said.... do one thing at a time... then test to see if that fixed the situation. Otherwise you will not know what it was the next time it occurs...