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.

I thought ALL diesels hesitate.

Just kidding.

Algae in the fuel tank and filters sounds familiar.

Satish

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

Yesterday I replaced the air filter, the fuel filter and pre-filter. Run a bottle of Lubro Moly diesel purge through the engine. Took apart and cleaned the air intake manifold and the air control valve and sensor. The difference was surprising - now the engine runs very quiet and smooth. There is noticeable improvement in power and acceleration. I haven't checked the air filter for a little bit less than a year (about

15K miles) and it was in surprisingly bad shape - very dirty and deformed. I don't know the reason. Obviously should be checked more often. Just FYI while at it I decided to replace the fuel return lines. Good move - while taking the old ones out they were breaking and falling apart in my hands.

Now everything is back to normal. Thanks to the group and Mr. Lambach for all the valuable advice.

D.