Mercedes-Benz: E300 Diesel Hesitates

I believe this is a non-turbo engine, right? If so, that eliminates the
possibility of the turbo, wastegate etc.
So that leaves only the fuel system and its controls. You say the engine
hesitates upon light acceleration at speed - much like a "flat spot" in
a gas engine.

Since diesels don't have "flat spots" I suggest the accelerator linkage
should first be examined for looseness - somewhere. The accelerator is
attached to a cable, check the security of the cables ends - that the
cable's case is attached firmly to the mounting point and then that the
cable's ends' ball and socket are not binding. Follow the linkage all
the way to the injection pump for IMHO the problem is in the linkage,
not the engine.

To answer your algae question, a black paper element inside the fuel
filter is the symptom of algae. The older cars used a small clear
plastic fuel filter, perhaps yours does too.

You are correct - the engine is non-turbo. The throttle linkage looks
perfect - tight and smooth. The ball joints were lubricated a month ago and
upon inspection today the cable and case look and feel excellent.
The fuel filter is sealed in metal housing - much like regular oil filter,
but during the weekend I'll split it open and look inside for the signs you
mention. Will also clean the injectors and fuel system with Lubro Moly
diesel purge.
Thanks for your help! You posts are always most informative and up to the
point!

D.

"T.G. Lambach" <net> wrote in message
news:net... 

I thought ALL diesels hesitate.

Just kidding.

Algae in the fuel tank and filters sounds familiar.

Satish



"DCM" <com> wrote in message
news:atLeb.7103$.. 
and 
you 

I reread your first post and have second thoughts - but no remorse.

When driving at a 60 MPH constant speed the engine suddenly lags but the
lag can be overcome by pressing the accelerator.

That means there's lots of fuel to the injectors or the lag couldn't be
overcome by accelerating the engine. It's not a fuel problem.

I suspect the emission control system which, on a diesel, is mainly the
EGR valve. As a test I'd plug its line and see if the problem showed
itself. If not, the controls for the EGR would be my first suspect for
after 87K miles a bit of dirt could have lodged in a vacuum line or
control valve or a rubber connection may have split causing erratic EGR
operation.

Another thought.

This car has a 5 speed electronic transmission with a lock-up torque
converter. The car might FEEL like the engine was lagging if the lock-up
disengaged, but the engine is not the culprit. If the lock-up feature
failed, the engine's RPMs would rise about 3% to maintain the car's
speed. The lock-up feature gives one a "direct drive" feel, especially
in 5th gear which is an "overdrive" ratio. I own a '97 E320 and can
imagine how this would feel but have no personal experience with a
lock-up failure. The test of this theory is if the engine's RPMs rise or
fall when you perceive it lagging. A RPM rise indicating lock-up
failure, falling RPMs true engine lag, perhaps due to EGR.

So those are a couple of ideas for your consideration, I hope one or the
other solves the problem.

Tom