Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Diesel Discussion

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 10-31-2014, 08:32 PM
mattwestm's Avatar
1977 300D
 
Join Date: Dec 2009
Location: KCMO
Posts: 73
Engine surging

With my 300SD, I noticed that when I start the engine from sitting overnight it will sometimes surge a bit. What I mean by this is that the RPMs will start out around 600-700rpm for a second or two, then drop down to about 500 for a split second, then back up to 600-700. This usually happens one or two times, then it evens out. You can feel the shakiness in the car when this happens. It has the feeling that a manual transmission vehicle has when it's about to stall.

The engine runs normally and usually has full oil pressure within a second of the engine starting.

The surging doesn't happen every time either. It's completely random.

Any ideas?


Last edited by mattwestm; 10-31-2014 at 11:34 PM.
Reply With Quote
  #2  
Old 10-31-2014, 10:50 PM
ROLLGUY's Avatar
ROLLGUY
 
Join Date: Oct 2007
Posts: 7,229
I hope you don't mean 6,000 to 7,000 RPM. That is past the mechanical capabilities of the engine. I am guessing you mean 600 to 700 RPM.
Reply With Quote
  #3  
Old 10-31-2014, 11:13 PM
Jesus'd drive a diesel
 
Join Date: Jun 2014
Location: Chicago,IL
Posts: 230
what year is your benz?
__________________
General George - 1967 Land Rover 2a SWB 1983 OM617 Turbo
Reply With Quote
  #4  
Old 10-31-2014, 11:34 PM
mattwestm's Avatar
1977 300D
 
Join Date: Dec 2009
Location: KCMO
Posts: 73
Quote:
Originally Posted by ROLLGUY View Post
I hope you don't mean 6,000 to 7,000 RPM. That is past the mechanical capabilities of the engine. I am guessing you mean 600 to 700 RPM.
Whoops. Accidentally added a zero.

Quote:
Originally Posted by interzonearts View Post
what year is your benz?
1984 300SD
Reply With Quote
  #5  
Old 11-01-2014, 12:45 AM
Jesus'd drive a diesel
 
Join Date: Jun 2014
Location: Chicago,IL
Posts: 230
Quote:
Originally Posted by mattwestm View Post
Whoops. Accidentally added a zero.



1984 300SD
Being all mechanical, i'd say maybe some elements of the governor got dirty or worn. The only thing that comes to my mind that could help without tearing the IP apart , if that's the governor in fact, would be good quality biodiesel which could clean and lubricate it better
.
__________________
General George - 1967 Land Rover 2a SWB 1983 OM617 Turbo
Reply With Quote
  #6  
Old 11-02-2014, 02:28 PM
wrench dropper
 
Join Date: Oct 2014
Location: very very very Nor-Cal
Posts: 204
Maybe air in the fuel lines?
Reply With Quote
  #7  
Old 11-02-2014, 04:39 PM
Diesel911's Avatar
Registered User
 
Join Date: Sep 2007
Location: Long Beach,CA
Posts: 51,038
Quote:
Originally Posted by mattwestm View Post
With my 300SD, I noticed that when I start the engine from sitting overnight it will sometimes surge a bit. What I mean by this is that the RPMs will start out around 600-700rpm for a second or two, then drop down to about 500 for a split second, then back up to 600-700. This usually happens one or two times, then it evens out. You can feel the shakiness in the car when this happens. It has the feeling that a manual transmission vehicle has when it's about to stall.

The engine runs normally and usually has full oil pressure within a second of the engine starting.

The surging doesn't happen every time either. It's completely random.

Any ideas?
The Emission Sticker on My Car has the normal idle at 750-800 rpms. So 700 rpms could be too low on a old Engine.
You could back off the Rack Dampern/Governor Idle Pin and adjust the Idle by way of the normal Idle Adjustment Nut and Screw to the Spec on the Emission Sticker. After that adjust the Rack Dampern/Governor Idle Pin to remove shaking but you don't want it to raise the Idle Speed so that your idle is being adjustec by the Rack Damper Screw.

As previousl menitoned a small Air Leak. Cheap to replace the 2 sections of Fuel Inlet Hose with 5/16 ID Hose from the Auto Parts Store; it is rated for Diesel Fuel.

The Valve in the Fuel Supply/Lift Pump could be worn or sticky and allowing Fuel to drain back to the Fuel Tank. Sort of a Pump losing prime.
If you pump on the hand primer before you start and it always starts like that that gives an ides that it is a Fuel Supply issue were the Fuel is going back to the tank.

The Fuel Pressure Relief/Overflow Valve Spring could be weak. If you have the type that can be taken apart you can do that and stretch the Spring to a 27mm free length; re-assemble and see if that helps.

__________________
84 300D, 82 Volvo 244Gl Diesel
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -4. The time now is 04:06 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2024 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page