1995 E300D Weak Acceleration, Black Smoke above 2500 rpm
 

So the adventure begins with the E300D I just acquired. Was running perfectly fine for a few weeks. Disabled EGR and the flapper valve next to it by plugging the vacuum lines and disconnecting from throttle linkage, ran even better.

Now, however, at 2500 rpm, when the power is supposed to kick in, I get very weak, anemic acceleration and black smoke out the tail pipe.

Jeremy5848 has been characteristically generous with his time and has given me some pointers. He suggests that the problem may lie with the first flap change that is supposed to occur at 2500 rpm and the double solenoid valve under the IM that controls it. Need to remove the crossover pipe to get to it.

Trying to decide whether all this is above my pay grade....much is, automotively speaking.

Air filter and main fuel filter replaced...prefilter looks fine. FWIW the removal of the prefilter and replacing the throttle guide (and adjustment of the thumb wheel on the throttle cable to get idle right) were the two actions that preceded the problem.

I welcome anyone's thoughts or suggestions.

Thanks.

Before you mess with the flaps, I'd check the fuel tank strainer. If you do mess with the flaps, you should also mess with the injectors. At 300k miles, they might need some attention. Just my ideas.

But doesn't the black smoke suggest that the fuel to air ratio is too high? If it were some restriction in fuel supply, would I see black smoke starting at 2500 rpm?

Are the flaps 'stuck' in the wrong position?
--ie, closed so restricting airflow....

Flaps in the plenum and xover operate to redirect airflow not restrict it.

The flaps don't "restrict" airflow in the strictly mechanical sense but they do "tune" the pipes (as Mercedes discusses in the manual). A resonance restriction is just as effective as a mechanical restriction in reducing air flow. In any case, the OP may actually have some other problem, but in this engine the flaps are one of the items that must be checked.

Jeremy

It seems to me that it's clearly an overfueling situation. FWIW, the symptom is EXACTLY like what happens when the ALDA is removed and the accelerator is depressed too much.

Jeremy's suggestion certainly makes sense....especially since it happens precisely at 2500 rpm.

Are there other overfueling (or restricted air) possibilities I need to consider?

I might bite the bullet and get an authoritative diagnosis from my indie or, perish the thought, the dealer.

XXX Dealer XXX
 

Since the normally-aspirated OM606 engine was used for only three years and the newest is now 16 years old, most dealers will not have anyone who remembers them. Further, people with older, hence less valuable cars usually don't go to the dealer for service because of the cost.

You'd be better off with an independent wrench who has been around forever and works on older cars.

Jeremy

sounds like a flap is closing and not allowing full airflow to the engine. since you have the vac pods plugged, perhaps they need to be wired open?

Well, I could reconnect the things I disconnected (EGR and the vacuum actuated device opposite to it) to see what happens. And perhaps I should do that just to be thorough. But my recollection is that I had some period of time where things were working fine with those devices disabled. Plus nobody has ever mentioned any ill effects of disabling those two items.

Viti in Tiverton, RI has four "old guys" who've been around forever and work on the older cars. More than likely, though, I'd take it to an indie.

Today the situation markedly deteriorated. Now it's a struggle to get above 2000 rpm. Very weak, very difficult getting up even moderate inclines, more black smoke. So maybe that rules out the resonance flap?

So really can't (shouldn't) keep driving it....I'll just have to take it in.

Does it seem like this?

1995 E300 not revving above 2000rpm #2 - YouTube

1995 E300 not revving above 2000rpm #1 - YouTube

My problem was I secured the EGR flap in the closed position.

Also check the fuel shutoff valve. I tried to drive with it closed once and only got enough fuel to get to 2000 rpm and no more.

No, I can get it to go to higher rpm's....just black smoke and no power when I do so.

I'm assuming my problem has to be OVERfueling due to the black smoke.

I also wonder about the possibility of EGR stuck open....since I disabled EGR shortly before problem arose.