Om603 extremely low on power - PeachParts Mercedes-Benz Forum

sunstealer · #1 08-07-2014, 04:19 PM

Hi all

I bought this car about 3 months ago. It's my first MB diesel.
It's an '81 280SE which has been refitted with an OM603 engine from an unknown donor car. The car has 320 000 KM on it, I am not sure about the milage on the motor.

It has been running horribly weak ever since I bought it. However it is extremely easy to start and it runs cleanly without misfiring, caughing or anything like that.

When I first got it, it was barely running at all. Approximate 0-60 time was 35 seconds. It was a total dog uphill, barely able to climb without stalling.

I have done several things to it since then. Biggest difference so far has come after cleaning in-tank filter (thx for great write-ups here on the forum, made the job a million times easier).

So to put up a list of things done/checked so far:

- Changed both fuel filters in engine bay
- Cleaned in-tank filter -was COMPLETELY clogged
- Checked/cleaned vacuum hose to ALDA
- Opened ALDA, verified spring/plunger inside moved easy and freely. Turned set screw 1 turn CCW
- Installed boost gauge -reads ~0,8bar ~11psi @ roughly 2200 rpm->
- Checked air filter
- Pulled return line and verified that fuel flows steadily out. Used maby 20 seconds to push out 1 liter. Did not foam when I had return line into a clear bottle

Having done these things, the car still feels very sluggish. 0-60 time is down to around 24 seconds now

, but it is still seriously lazy uphill.

According to prev owner cylinder head was replaced or refurbished along with valves and seats around 2010.

When I pulled the in tank filter it was completely clogged. I don't know, but might it be possible that running with such a restricted filter over many years could somehow have caused damage to IP or engine?

I would like some input regarding what should be the next on my checklist.

I am thinking the next natural thing would be to pull the injectors and clean them.
I am unsure if I should send them to a shop to be tested?
The engine runs smoothly throughout the entire rpm band, which IMO would reduce the chance of any big injector troubles.

I am quite sure that the problem must be the fuel delivery. I noticed that the last of the return hoses on the injectors have simply been plugged (pic).
Could this be the cause of some trouble?

Is there some vacuum line or some other sensory input that could be messing with the fuel delivery from IP?

I included some pics from the engine bay as well. Maby someone might notice something that is off.

Will be very grateful for any help!

Go to my imgur site for the fullsize pics:

MB - Imgur

winmutt · #2 08-07-2014, 05:07 PM

Put a jug in the bay and throw the to and fro fuel lines into it with some fresh fuel and report back after a drive. Also did you try without the ELR plugged in just for good measure?

scottmcphee · #3 08-07-2014, 05:55 PM

Release the parking brake?

...seriously tho..

plugged return hoses from injectors won't cause this, that may cause leaks.

If you're seeing 11psi at 2300 rpm then much is right with fueling and turbo.

Take the ALDA off temporarily, just unscrew it and let it rattle around on the top of its mount.

Maybe you're running in the wrong gear, auto is shifting up too quickly. Adjust the bowden cable. Try manual shifting to hold the gears down.

NJ300sdl · #4 08-07-2014, 06:01 PM

Might be excessive exhaust backpressure. Remove plug on exhaust manifold at number 1 to check.

sunstealer · #5 08-07-2014, 06:40 PM

Quote:

Originally Posted by winmutt

Put a jug in the bay and throw the to and fro fuel lines into it with some fresh fuel and report back after a drive. Also did you try without the ELR plugged in just for good measure?

That is quite smart. I will be working on the car tomorrow, will try this and a few other things and report back with results.

I just learned by reading here on the forum, that the IP have a fuel pressure valve situated inside the banjo coupling on engine side of IP.
Will try to clamp the line that attaches to banjo and see if there is any noticeable change.

Thanks for all the suggestions!

winmutt · #6 08-07-2014, 07:18 PM

Quote:

Originally Posted by scottmcphee

Release the parking brake?

...seriously tho..

plugged return hoses from injectors won't cause this, that may cause leaks.

If you're seeing 11psi at 2300 rpm then much is right with fueling and turbo.

Take the ALDA off temporarily, just unscrew it and let it rattle around on the top of its mount.

Maybe you're running in the wrong gear, auto is shifting up too quickly. Adjust the bowden cable. Try manual shifting to hold the gears down.

Parking brake is no joke. First TD I bought cheap because the engine would slow and cut off after a few miles. The dealer told her it needed a new IP. In reality brakes were frozen, warm up expand and lock solid.

sunstealer · #7 08-08-2014, 12:10 PM

I have tried a few things today. Put a bottle inside engine bay and routed both supply and return lines to it. No difference. I tried clamping the return hose from IP. No difference. Even pulled the pump between the two filters and cleaned it and lubed up the o-ring.

I have yet to try to run it with the ALDA completely disconnected. Will try that next time I work on the car.

Regarding the brakes, the car rolls easily when in neutral, even after long runs. I have not noticed any excess heat radiating from them either, so I think I can rule out that possibility.

Something is def troubling the transmission as well.
After paying a bit more attention, I noticed when I floor it from standstill in "D" 1st gear reaches 4,5k rpm, while second gear only reaches 3,5k. I have never droven 3rd gear to its max as it takes to bloody long😂

Could it be that the car has a gear ratio that is all wrong for a diesel, being as it is originally a gasser. I am not sure how many components was changed when rebuild was done. The gearbox is a 4-speed auto. What kind of rpm range are common when driving @ say 80 km/h?

snorider · #8 08-08-2014, 12:23 PM

The differential has a tab on the drivers side rear which extends out from the cover the gear ratio is stamped on it.

sunstealer · #9 08-08-2014, 01:30 PM

Quote:

Originally Posted by snorider

The differential has a tab on the drivers side rear which extends out from the cover the gear ratio is stamped on it.

Cool, will check that next time. Did a new 0-60 manually shifting from 2nd to 3rd at about 4,5k rpm. Still used about 21 seconds.

Considering the head have been worked on recently, I'm considering the idea that maby cam or IP timing might have been distorted.
Will try to check IP timing next time as well as run it without ALDA and report back.

If anyone's got any new suggestions please share

scottmcphee · #10 08-08-2014, 01:42 PM

Quote:

Originally Posted by sunstealer

I have yet to try to run it with the ALDA completely disconnected. Will try that next time I work on the car.

not just disconnected (hose), but fully unscrewed from its mount

As you look down on the ALDA the nut below it is rotated clockwise to loosen, the nut will stay on the IP, the ALDA is freed

27mm nut on my car

barry12345 · #11 08-08-2014, 03:54 PM

Assuming that you are in the top gear at 60mph. What revs are you seeing? Eighty kilometers an hour is about 48 miles per hour. I never owned a 603 engine but suspect you should be seeing maybe 2200-2500 at that speed in third gear. Not sure but many owners on site will know what should be indicated at 60 mph with this engine.

That said the 603s came originally with a football type device in the exhaust system. Is it still there as it can be problematic?