1980 300SD - pedal/linkage at full throttle, only idles - PeachParts Mercedes-Benz Forum

mlordge · #1 09-20-2011, 02:18 PM

driving last night to pickup my child, and car lost all power.. drifted to a stop. Restarted w/ full throttle, and could only hold idle rpm level. When I took my foot off pedal, immediately shuts down. Can repeat at will. Tranny seemed fine as I limped it (full throttle idle), in 'any' gear to get it into a residential street to check it out... changed both fuel filters under hood, inline and spin on .. no change. Today... bypassed the solenoid valve, no change.. need to check the banjo fitting on the back of the manifold later. Any ideas?? by the way.. linkage looks fine as well, with full motion and link back to tranny appears fine.

Zacharias · #2 09-20-2011, 02:47 PM

Are you certain that the throttle linkages are actually moving through their full range of travel, when the pedal is depressed? (Did you just move them by hand under the hood?) If not done already, have someone push on the pedal while you observe under the hood.

I had something similar when my shutoff valve failed on my SD. But in that case the car would idle, just wouldn't make power when the pedal was depressed.

mlordge · #3 09-20-2011, 03:06 PM

indeed.. linkage all the way to max...

Zacharias · #4 09-20-2011, 03:54 PM

Try unclamping the supply and return fuel hoses and feeding them into some sort of clean container (juice bottle, coffee can) with a quart or two of diesel, under the hood, and running the car that way. If you have some diesel purge on hand that will work as well.

jt20 · #5 09-20-2011, 03:59 PM

Great ideas so far.

just adding an inspection / tightening of the hand primer on the side of the injection pump.... perhaps replacement if you have a white handle.

mlordge · #6 09-21-2011, 01:48 PM

Jt20 and Zacharias ... can you guys expand on what you isolating.. great ideas and do appreciate your help..

I did get a chance to take off the banjo bolt w/ hose up to solenoid.. and cleared it... it did have a plug of 'gunk' at banjo.. re-installed, no change.

also took off air cleaner assembly.. including all up to inlet to turbo ... ran it (at full throttle (get's me idle RPM).. and turbo is spinning ...

there is a pressure switch on top of exhaust manifold w/ a wire going to?? ..
is it possible there is a turbo problem?

again.. thanks for you assist on this.. love this car!

kerry · #7 09-21-2011, 01:52 PM

Turbo wouldn't cause the problem you describe. It sounds as if the rack in the IP is not moving. Not sure how to check that. How does the linkage attach to the rod(?) in the IP that moves the rack? Is it possible that the linkage is moving but not moving that rod due to a loose clamp or something like that?

Zacharias · #8 09-21-2011, 02:03 PM

Quote:

Originally Posted by mlordge

Jt20 and Zacharias ... can you guys expand on what you isolating.. great ideas and do appreciate your help.

I used to own the same model and I'm going by that and my experience of reading years of fixes for similar problems on this board (and other lists). Which is to say I'm not a diagnostic whiz, but I can read

.

My suggestion was an attempt to isolate a plugged tank pickup strainer and/or algae in the tank, which is relatively common in some areas (not where I live).

If the car still runs that way, off an alternative fuel source, then the problem is somewhere under the hood.

Two questions I didn't ask before:
Has the car ever been run on alternative fuels?
Did you just fill up, perhaps not at your usual station?

Stretch · #9 09-21-2011, 02:04 PM

With engine running can you get more revs by pushing the throttle linkage that attaches to the IP?

Stretch · #10 09-21-2011, 02:05 PM

Quote:

Originally Posted by Zacharias

...
Did you just fill up, perhaps not at your usual station?

Oh oh that's a good one!

Zacharias · #11 09-21-2011, 02:14 PM

From memory, this is the range of stuff I can recall being diagnosed from behaviour like this:

1. Tankful of skunk fuel and/or plugged fuel filters
2. Plugged tank inlet strainer / agae
3. Blockage in fuel return line
4. Blockage in exhaust
5. Blocked air intake (one guy found a shop rag stuck in his air cleaner assembly)
6. Failing lift pump (from insufficiently processed/heated WVO use)
7. Shutoff valve stuck partly engaged (apparently unheard of, but actually happened to me).

mlordge · #12 09-21-2011, 02:46 PM

I like the way you guys think

.. thank you all!
will isolate fuel from back as a potential cause... same fuel stop.. never problems before.

Algae.. I doubt it.. am in NorCalifornia.. and this machine get's a fresh tank of fuel about every 3 weeks.. driven daily... but will make sure.

*Kerry.. throttle moves full range (at least linkage does).. so ....

no SVO, or veggie has ever run in this car.

will check hand primer also...
.. and any clamps... didn't see any.

and.. once fuel flow is verified/isolated.. will re-check solenoid (by by-pass)

kerry · #13 09-21-2011, 02:53 PM

Quote:

Originally Posted by mlordge

*Kerry.. throttle moves full range (at least linkage does).. so ....

Not the throttle linkages. Look at the final attachment point to the IP and see if the rod the linkage attaches to is moving.

Diesel911 · #14 09-21-2011, 07:32 PM

If you can get the Engine running pump on the Hand Primer while it is running and see if it improves. If it does you Fuel Supply Pump is having a problem.

Connect a Vacuum Hose to the Shutoff Valve and blow into it (not with compressed Air); if it is stuck that may bolw it back into position.

Codifex Maximus · #15 09-22-2011, 01:58 AM

Something to check...
Have someone actuate the pedal and observe the firewall mounted gizmo (forget what it's called) that connects the pedal rod to the rod going to the engine. Sometimes, it just wears out on the inside or the plastic gives way. Without it, you have no control over the throttle. I never can remember the correct name for the thing.