HELP Huge Power Loss 83 300DT - PeachParts Mercedes-Benz Forum

rmmagow · #1 06-12-2003, 05:55 PM

83 300DT
While stuck in traffic today I experienced a very very heavy power loss while trying to accelerate from having been stopped. The car acted as if the turbo had failed or the transmission bit the dust. After getting out of traffic it was no better could barely accelerate and got completely bogged down on a minor hill. I did get it home, looked under the hood but can't see anything obviously wrong. Nailing the pedal with the car in park the engine was VERY slow to spin up. Now the strange part, I shut it off and re-started it, engine spooled up quickly so I took it back out and it ran fine, no acceleration problems, it felt good. What happened? Is there a possible electrical explanation? What do I check?
Thanks for any advise.

engatwork · #2 06-12-2003, 05:57 PM

Sounds like a fuel delivery issue. Check the tank screen. When was the last time the filters were changed?

R Leo · #3 06-12-2003, 06:21 PM

Was it at <2000 rpm or >2000 rpm? Excessive smoke?

If an unexpected low power condition occurs at engine speeds in excess of 2000 rpm, make sure that the overboost line is properly attached to the overboost switch/valve and that the rubber adapter pieces on the valve are in good condition and not cracked.

The overboost valve is mounted to the firewall, behind the brake booster. Just glancing into the engine compartment might not reveal a loose or leaking pressure line.

Sometimes the tubing from the manifold or from the ALDA will come loose from the overboost switch/valve and prevent the proper boost pressure from reaching the ALDA and thus preventing the ALDA from augmenting the fuel delivery when the turbo is producing boost.

Otherwise I'd start by replacing fuel filters.

my .02
R Leo

rmmagow · #4 06-12-2003, 06:35 PM

No, car didn't smoke that I noticed although I was very pre-occupied trying to get the thing moved out of the way. Could the fule filters act like that, suddenly plugging up then unplugging just by shutting down and re-starting? I'm gonna change the big filter as well as the little clear filter just in case. As far as I can tell all that is supposed to be hooked to the ALDA and the ting in back of the booster looks/feels OK. I've got vacuum since the door locks are working as is the power brake booster. Is there anything that would make the wastegate suddenly stick open? I do have one or two other things wrong with the car, it's been running a little warm, 95~105C not boiling over though and just this morning my brake wear indicator light came on again. It came on last week, I pulled all wheels and there lots of pad left. Can't see how any of this is related but I've seen stranger things. Car is running fine now, just blasted around the block (about 4 miles) and all seems normal.

engatwork · #5 06-12-2003, 06:56 PM

I still think you may have either a fuel tank screen issue or a filter issue. Drive it on the interstate 70+ mph for a little while and see if it looses power after a couple miles. This is kinda how poor fuel delivery shows up.

rmmagow · #6 06-12-2003, 07:45 PM

Come to think of it, fuel is pretty low, not empty exactly, but 420 miles on the tank load. Maybe I'm picking up some crap. Where's the tank filter and how is it accessed? Via the sending unit business or under the car? I use it every day on the hiway, 90 mi a day and in fact had just come off the hiway before slowing down in traffic. Filters shall be changed !

R Leo · #7 06-12-2003, 09:51 PM

Sounds like you might have been low on fuel. Marlene gets truly sluggish when she's really low...shakes, misses and no power. I don't make a habit of running my cars out of fuel but noticed this one time while running Marlene waaaay down to PM the tank strainer.

Low fuel coupled with a partally plugged fuel tank strainer could easily cause the problems you are describing.

The TD's strainer is the big, hexagonal 'plug-like' thing screwed into the bottom of the fuel tank.

The sedan's strainer looks similar and can be seen by crawling underneath the car and looking up above the rear axles.

WARNING!! WARNING!! WARNING!!! When you take these strainers out, you are opening a 1" dia hole in the bottom of your fuel tank.!!!

Do not attempt to remove these strainers unless you are confident that the tank is almost empty (less than 1 gallon left) and you have sufficient catchment and storage for whatever fuel is left in the tank because it is coming out!!!

If it's dirty, you can clean the strainer with some diesel and toothbrush.

R Leo

rmmagow · #8 06-13-2003, 09:21 AM

Filled it this morning and drove 40 miles on the hiway w/no problems. The ALDA, I know in general it's purpose and generally how it works. Is this someting that could act up and need rebuilding? Is it rebuildable? Should I just concentrate on fuel delivery issues. It really did run pretty flawlessly this morning with a full tank but it only took a little over 15 gals so there was plenty left. Thanks for all the advise.

P.E.Haiges · #9 06-13-2003, 09:42 AM

Rmmagow,

My 300SD would run fine when 1/4 full or more but when less than 1/4 full it would act weird: run good sometimes, no power other times, especially on corners or steep inclines.

I took out the tank filtter and it was plugged with a black goo (algae?) about 1/2 way up. So I cleaned and replaced the tank filter and it has been working fine since.

The other 2 filters will not act like this. Once they are restricted enough to impede the fuel flow, they not clean themselves.

P E H

Rick Miley · #10 06-13-2003, 09:44 AM

Don't overlook the possibility of the tank vent being partially clogged and causing a vacuum in the tank. If it happens again, quickly check for vacuum by taking the fuel cap off and listening for air rushing in.

BTW, when my 240D gets low on fuel, it won't idle well but above idle it still runs great. Exactly backwards from the way it should be.