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Old 07-12-2006, 01:21 PM   #1 (permalink)
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Date registered: Jun 2006
Vehicle: 82 300TD Turbo Diesel Wagon
Location: Beautiful Northwest Oregon
Posts: 49
STUMPED: strange throtle response - vacuum issue?

After giving the fuel system a once over - ie: replacing primary and secondary fuel filters - replacing primer - running 2 cans of diesel purge - repacing secondary (main) fuel filter again, I'm at a loss, and clearing my brain - looking to other areas for the problem...

1982 300TD Turbo - 280K. The engine starts and idles fine. If I push the accelerator down until it starts to gain resistance (3/4 to 7/8 of the way down), the engine will idle for aprox 5 seconds, then take another 10 seconds to reach 3K.

If, from idle, I 'floor' the pedal, the engine instantly responds as it should.

If I 'floor' it, from idle, and the engine winds up, then let the pedal back to the spot 3/4 of the way down, the engine speed will drop back to around 1K before starting its slow climb once again.

Any ideas? Could this be a vacuum problem?

If I try to drive the car, I have to 'floor' it to get any engine speed, which in turn locks the transmission in low or 2nd...

Looks like I may have to trailer it the 30 miles to the mechanic...

HOPEFULLY you will all have a mountain of answers for me
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Old 07-12-2006, 01:41 PM   #2 (permalink)
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Date registered: Oct 2005
Vehicle: 1985 300TD Wagon
Location: Belgium
Posts: 408
Narrow it down; with the engine running disconnect the throttle linkage at the injection pump and try again but this time with your hand pushing the linkage at the IP. I bet it's a lot better now.
Hook a part of the linkage on and try again until you find where it's goes south.
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Old 07-12-2006, 01:47 PM   #3 (permalink)
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Location: Racine WI
Posts: 1,552
How's the linkage bushing on the firewall; and the one that the long rod goes into just in front of the other?
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Old 07-12-2006, 03:07 PM   #4 (permalink)
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Date registered: Jun 2006
Vehicle: 82 300TD Turbo Diesel Wagon
Location: Beautiful Northwest Oregon
Posts: 49
The throtle linkage 'looks' good to me, but then, I'm a newby to MB's.

The mounts/bearings for the long rod forward the firewall are both in good shape. All the linkage appears to be moving as it should...

I have good clean fuel in the primary filter - note: a very small amount of fresh diesel does appear around the head of the secondary fuel filter bolt...

Thanks again, Steven, for the primer!
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Old 07-12-2006, 03:23 PM   #5 (permalink)
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You're quite welcome for the primer pump. I still think you have an issue with your throttle linkage, you have no vacuum that does anything for the fuel system other than shut it off. If your throttle linkage is in good order, then I'd investigate your fuel system; make certain that you don't still have any air leaks, and make sure your tank screen is clean (if you haven't already). Did you remove and inspect the large plastic-like bushing that's bolted to the firewall? When you do remove that, make sure you reinstall it's retaining bracket in the same orientation. Have you enlisted an assistant to work the pedal so you can watch the linkage and make sure it's all moving at the same rate?
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Old 07-12-2006, 03:47 PM   #6 (permalink)
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Date registered: Jun 2006
Vehicle: 82 300TD Turbo Diesel Wagon
Location: Beautiful Northwest Oregon
Posts: 49
As far as the tank screen: I blew compressed air back into the tank - I also have seen NO evidence of algae in the primary filter, either in the one that was on it when I bought the car, or in the new one. I cut apart the old secondary filter, and found no evidence of algea in it.


A local area MB mechanic ( nearing retirement age ) says he has NEVER had to remove an replace a tank screen in 30 years of specializing in MB's - so maybe an indication that is unlikely the problem in our part of the country.

I have had my wife running the pedal, while I watch the linkage. "full throtle" opens the VDO (what-ever that is), and opens the IP control levers almost to the stop...

Steven: did you ever find your air leak?

Could this be a fuel pump issue?
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Old 07-12-2006, 03:56 PM   #7 (permalink)
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I doubt if your issue could be in the fuel pump itself. If your tank screen were clogged, I doubt blowing air through it would properly clean it.
I haven't found my air leak for certain, but since my fuel line holds vacuum end to end, I've decided to replace the tank screen, it's o-ring, and the fitted fuel hose. I've recently had to drain my tank several times, as well as remove the tank screen; so my theory is that all the dissasembly/reassembly has caused a small leak. I should get my new parts tomorrow; weather permitting I'll know more about an hour later.
The good news is, with as little as I've been able to drive, I've got a lot of WVO piling up in my garage; and quite a bit that I can go collect.
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Old 07-12-2006, 07:51 PM   #8 (permalink)
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Im with steven on this one...I would disconnect the 2 bolts on the firewall and check it out. Mine was broke and caused really erratic throttle response. I pulled one off a junker....I asked how much at the yard and Bob answered the next time you come in here you bring me a 6 pack....i said fair enough...:P
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Old 07-12-2006, 09:42 PM   #9 (permalink)
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Vehicle: 82 300TD Turbo Diesel Wagon
Location: Beautiful Northwest Oregon
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Thanks for the help!

OK, when the wife pushes the pedal to the floor slow, I see about 3/16" between lever and stop. If she snaps it down, it's more like an 1/8".

Is this possably enough to cause the engine the afore mentioned response?

I will try to get in to town Thurdays, and pick up a new copper washer for the fuel filter bolt...

I do see a little slop around the plastic looking bushing up top of the valve cover - the "pin" which slides/rides in the slightly "J" shaped slot - and pushes the linkage which ends up at the IP (hope this makes sense)...
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Old 07-13-2006, 05:03 AM   #10 (permalink)
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Vehicle: 83 300D, 90 300TE
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Quote:
Originally Posted by Goldenvoice
After giving the fuel system a once over - ie: replacing primary and secondary fuel filters - replacing primer - running 2 cans of diesel purge - repacing secondary (main) fuel filter again, I'm at a loss, and clearing my brain - looking to other areas for the problem...

1982 300TD Turbo - 280K. The engine starts and idles fine. If I push the accelerator down until it starts to gain resistance (3/4 to 7/8 of the way down), the engine will idle for aprox 5 seconds, then take another 10 seconds to reach 3K.

If, from idle, I 'floor' the pedal, the engine instantly responds as it should.

If I 'floor' it, from idle, and the engine winds up, then let the pedal back to the spot 3/4 of the way down, the engine speed will drop back to around 1K before starting its slow climb once again.

Any ideas? Could this be a vacuum problem?

If I try to drive the car, I have to 'floor' it to get any engine speed, which in turn locks the transmission in low or 2nd...

Looks like I may have to trailer it the 30 miles to the mechanic...

HOPEFULLY you will all have a mountain of answers for me
Let's make it easier. Rule out the simple things first.

Check the throttle linkage, usually it's just a 10mm bolt that's worked loose on the turbodiesels.
Check the bowden cable of the transmission, make sure it's adjusted properly.
Check the accelerator pedal for freeplay and the bushing behind it.

With this I would imagine your car's response is similar to mine, except it doesn't chug at 1000rpm when you let it go at 3/4 throttle. I'm thinking if you floor it all the way, you create enough boost. But once you let go, you immediately cut off the boost build up and it just chugs at low engine speed until it takes off.

My guess is it's a loose bolt on the throttle linkage. I've done a write up on it, hopefully it helps you too: http://www.benzworld.org/forums/w123...age+adjustment
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