Top Speed Is 25 MPH!

Purchased an 84 300D about two weeks ago. The first time I drove it, I had trouble getting over 40 mph. After about 100 miles, I was cruising at 65 and 70. Three days later, it slowed down again, and I had it towed back home. I just added two quarts of Trans-X, after draining two quarts of tranny fluid. Drove it about 15 miles, which was a chore as, now, I can't get it over about 20 to 25. Could it be something other than the tranny? It seems to shift, and then bogs down. I can floor the accelerator, and it doesn't seem to matter. I switched to neutral, and the engine is definitely reving. Any ideas?

[The Warden]

Wait, is the engine revving yet the vehicle not moving when in gear, or is the engine staying at low RPM's even when floored? If the latter, are you certain you're fuly fueled? If yo've definitely got fuel (don't necessarily trust the gauge), you could try changing the fuel filters...

Just a thought...good luck!

[leathermang]

LOL, I just suggested the fuel filters in an email to him...
If it is not the filters ( how many does his car have )? then what methods of responding to increased load are there ? Does his engine have a " governor" ? Is it all in the cam lobes of the fuel injection pump ? Is there an air sensor which could be giving a faulty reading ?

[jassz]

I had a similiar problem with acceleration (floor it and you barely move) and it turned out to be a problem with the throttle linkage. Probably not as likely as the fuel filters, but something else to check for. The knee bone has to be connected to the thigh bone and all that.

[84300DT]

are any of the brake calipers grabbing/stuck?
get it going, put into neutral, coast and see what happens

I would have to agree with the others on the fuel filters. You might also want to check your air filter too, and see if it is clean also. You should probally go ahead and change the filters, and run a can of Diesel Purge through the injectors. Diesel purge can help alot on these cars.
You should also check the linkage, like some others have sugested too, and lubercate the joints with some ATF.

As for the transmission, do you need to rev the engine to get it to go into gear?

Thanks for all of the input. I actually changed the air filter before I put the car on the road. I purchased two fuel filters and will install them tomorrow. The car has an inline and a canister filter. I will also try some diesel purge. I was at NAPA the other day, and one of the counter guys suggested Lucas injector cleaner.

No, I don't have to rev the engine to get it to go into gear. However, when the car bogs down, if I switch to neutral, the engine revs without a problem.

Come to think of it, when I had a problem last Friday, I filled the tank, and the car started running like a top, so perhaps it is a fuel issue.

Yes, I floor the vehicle, and I don't get much above 3000 rpms unless I switch to neutral.

I pulled the left front wheel the other day, and the brakes looked fine. Haven't checked all of them though.

Okay, tomorrow is another day. I'll keep you posted!

[JimSmith]

First Mercedes,

After following jassz's adventure, which sounds somewhat similar, I would have someone press on the gas pedal while you have your head under the hood observing the linkage. The unit on the firewall is a common failure point on older cars, and so are a few other bits of the linkage, especially those with rubber or plastic parts.

Look for a change in action at the pump compared to the movement of the shaft connected to the pedal, as the pedal is depressed and released. When these stop moving in a 1:1 ratio, something is amiss. The problems most often occur where the linear motion is converted to rotational motion, and then back to linear motion. Most of the time a problem with the linear motion is either a bent link that enables contact with something nearby or an obstruction (something has broken off and fallen in the way) that prevents further motion.

I will also relate a problem my father in law had with the tank vent. His car would actually bog down and stop, then restart ok and run for a while. He became very confused though when the reserve light would come on with the tank nearly full, while this odd behaviour was going on. Then, when he tried to open the fuel filler cap, it was stuck on tight. He has hands like vice grips and got the cap off, and noted a whoosh of air going into the tank. Once the cap was off, or put on loose, the car ran fine. He found the rubber hose connectors going to the vent box in the trunk, and then out the passenger side fender behind the bumper, were soft and gooey, and kind of sealed themselves off. He replaced them and the problem went away for good.

Good luck, Jim

[psychoman]

Well I bought a 300SD that would go over 40 unless u went down a big hill. I stoled the car. 1st question: When cranking engine does turn over real fast? If so adjust the valves. These engines close the valves as they wear. Which causes low compression, hence no power. Also change fuel filters and look for cracked hoses that would suck air in to the system. A cracked hand pump would cause this also. Good luck

[Wes Bender]

First Mercedes -

Your comment that it ran well after a refueling might lead me to believe that the fuel screen in the tank is partially plugged with dirt. When you filled the tank, the incoming fuel displaced part of it and allowed it to get sufficient fuel through to run OK. After a while, the dirt would accumulate again and restrict the flow.

I know that you said that when the car is sluggish the engine still revs OK in neutral. It doesn't take a lot fuel to rev the engine that way.

Just my thought on the problem. It will be interesting to see what you eventually find is the culprit. Keep us advised.

Thanks,
Wes Bender

[gsxr]

Wes is right - revving in neutral means nothing. My money is on the fuel filters, or possibly the fuel tank strainer (not fun to remove & clean that though). Note - when you replace the spin-on canister filter, fill it up with clean fuel or Diesel Purge, or use the primer hand pump to bleed the system. Otherwise you'll probably kill the battery trying to start the car with an empty filter...! BT, DT.

Would not hurt to check the brakes also, the old rubber hoses can constrict and cause dragging - common problem, cheap fix ($9 per hose x 4). The fluid needs changing every 2 years anyway, so plan on doing that as maintenance soon.

Also, about the power: that car should get 0-60 in less than 14 seconds (timed with a stopwatch). If it's 20+ seconds, the tubeo boost pressure line from the back of the intake manifold to the ALDA (square thingy on top of the injection pump) is probably blocked, or the switchover valve is plugged. Fix that and you'll be shocked at the power increase!


Good luck,

Changed both filters and added a can of Gumout Diesel Injector Cleaner. She's running like a champ now! Will do the 0-60 time trial to confirm turbo boost. Thanks to all of you!

[leathermang]

And now the varnish has been removed from your transmission valve body...

[Rick Miley]

I've bought it a Discount Auto Parts, which is now owned by Advance. Never seen it at Wal-Mart. If you don't find it a one auto parts store, try another.

[rivermasternc]

First Mercedes:

Now that you have her running, I recommend a good Italian Tuneup and a review your selection of diesel sources also.