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  #1  
Old 05-25-2003, 06:59 PM
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300 SDL Vacuum Questions

Perhaps you veterans could help me resolve an engine surge problem (+/- 200 rpm) that occurs above 3000 RPM during hard acceleration with my newly acquired '86 300SDL (California Model)?

For test purposes, I plugged the open vacuum line going to the inline air filter and then to the EGR. On a short test drive it seemed to resolve the rpm fluctuation problem.

I'm actually begining to wonder if the vacuum lines on this car are properly configured? Is the '86 California 300 SDL supposed to be plumbed like 07.1.10.III-500/2 on the CD? Or like 500/1?
Mine appears to be a hybrid of both.

Any feedback would be appreciated

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  #2  
Old 05-26-2003, 12:21 AM
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As a follow-up I can say that the vacuum lines are now all correctly routed and the two BBs have "fallen" into the appropriate hoses.

Now my question is, in the event of continued head bobbing during hard acceleration, what would the effect be of blocking the ambient air source coming from the cabin and going to the vacuum transducer for the EGR valve?

Thanks for any help...
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  #3  
Old 05-26-2003, 02:18 PM
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smoke gets in your eyes
 
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Location: Eastern TN
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To your last question, nothing. That's just a vent or reference outside-the-canister pressure.

The surging was probably caused by a leaky air recirculation valve (ARV) controller if plugging the ARV line stopped it. I don't think a bad EGR system causes surging.

Sixto
91 300SE
87 300SDL
83 300SD
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  #4  
Old 05-26-2003, 04:38 PM
turbodiesel
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I've been living with a very subtle surging problem at highway speed since I've owned the car. I have done all kinds of tests, replaced vacuum lines and connections and replaced the hose on the turbo. I now suspect it may be a leaky ALDA, in which case I'm going to live with it.
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Old 05-26-2003, 07:29 PM
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Thanks sixto and turbodiesel for your replies. I had a chance to do another test drive again this evening and, unfortunately, the rpm fluctuation is less (+/- 50 rpm) but still noticeable above 3k rpm in 2nd and 3rd gear. No surge was noticed in 1st and I'm too far away from the highway to check it out tonight in 4th . I guess it must have wishful been a combination of tiredness and wishful thinking, on my part, when I stated yesterday that the rpm fluctuation had gone away after plugging the ambient air intake.

Hearing what turbodiesel said about his SDL, I am not content long term to be mistaken for a "giggle head" as I roar by other drivers.

Is there anything I can do to test whether the alda is the problem with this car?

How about other possibilties? I noticed a little wetness at the base of the #2 injector. Could a an injector problem cause the rpm fluctuation?

I have not changed the main fuel filter since acquiring this car. The inline filter appears to be spotless. Could fuel starvation produce these symptoms?

Thanks again for any more ideas...
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  #6  
Old 05-27-2003, 06:05 PM
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smoke gets in your eyes
 
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Wetness at the base of an injector is probably a leaking return hose. Cheap and easy fix.

Sixto
91 300SE
87 300SDL
83 300SD
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  #7  
Old 05-28-2003, 10:42 AM
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neue Dieseler
 
Join Date: Feb 2002
Location: san francisco - immer kalt, immer windig, I want to move
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surging

At least in my 87 sdl, there was a fair amount of literature that described surging with the cruise control at highway speeds. I never noticed it, but supposedly it is a problem (maybe like you describe).

My vacuum lines near the switchover valve that go to the charge air pipe and the vacuum amplifier were completely shunted or incorrectly routed. I read some about simplifying that vacuum wiring (can't remember where) and modified the lines to closer to the original.

One of the diagrams that I followed was from the CD.

Maybe that helps....

alec
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  #8  
Old 06-01-2003, 01:16 AM
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Alec,

Thanks for your input. The Cruise Control is currently inop and on my punch list but at a lower priority. It will engage and acclerate the vehicle but will not maintain a set speed. I tried accelerating the car with the cruise control stalk in different positions and it seemed to have little effect on the "surge problem". When I get some time, I will try isolating and blocking the vacuum lines for the cruise control and see if that has an effect on the surge.

Dave

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