Mercedes-Benz Owners' Forums  

Go Back   Mercedes-Benz Owners' Forums > Technical > Electrics, Vacuum, Ignition and ECU
 

Reply
 
Thread Tools Display Modes
  #1  
Old 07-12-2015, 09:07 AM
d215yq d215yq is offline
Senior Member
 
Join Date: Mar 2008
Location: Barcelona
Car: 1987 W124 300D 200k
Posts: 1,386
Default Strange rev counter behaviour a clue to cold idle not working?

Have been having a rough cold start from my car ever since the temperatures have got lower than 10 degrees. Although the glowplug light never lights (i assume bulb broken), if i wait 15 seconds for the glowplug cycle to work, and press the accelerator a bit the car starts perfectly. However now the temperature is near zero, releasing the accelerator after 5 seconds will see it stall, it needs about 10-15 seconds at 1500rpm before release to idle.

So I am thinking it isn't a glowplug issue but is a cold start idle issue. I've already played withthe relays behind the battery and switch cleanered them/changed all fuses in fusebox. One thing I notice is that when the ignition is on and I am waiting for the glowplugs, the rev counter acts like a temperature gauage! (6k rpm is when it is near zero, 4k when it is about 5 degrees, 2k when it is 10 degrees, above 10 degrees rev counter is on zero). There is also a clicking from the relays behind battery while car is cold. Once the car starts the rev counter works as normal (although soemtimes mid journey it works intermittently). So does this suggest that somehow the rev counter is shorting out/interfering with the feed to not allow the relay to do its job of making the car put more fuel in when cold?

If so is there a particular wire or relay or circuit that needs further investigation?
Reply With Quote
  #2  
Old 07-12-2015, 09:13 AM
television's Avatar
television television is offline
Senior Member
 
Join Date: Mar 2005
Location: Daventry
Car: 2002 SL500, 216 CL500, all fully loaded
Posts: 163,814
Default

The rev counter cannot interfere with the running of the car. when they do not always work it can be a sticky stop pin.

The glow plug lamp should be on when the key is turned to ignition.
__________________
Malcolm

Don't worry, it only seems kinky the first time
Reply With Quote
The Following User Says Thank You to television For This Useful Post:
d215yq (07-12-2015)
  #3  
Old 07-12-2015, 09:30 AM
d215yq d215yq is offline
Senior Member
Threadstarter
 
Join Date: Mar 2008
Location: Barcelona
Car: 1987 W124 300D 200k
Posts: 1,386
Default

Quote:
Originally Posted by television View Post
The rev counter cannot interfere with the running of the car. when they do not always work it can be a sticky stop pin.

The glow plug lamp should be on when the key is turned to ignition.
Thanks as ever for quick reply. Perhaps I phrased the question wrong, is the fact the rev counter is somehow getting a feed from something that measures cold temperature a clue as to why the actuator or whatever it is that increases the fuel when cold is not getting this signal/not working?

The glowplug lamp hasn't worked for a long time, but does the fact the car starts first time with the accelerator down a bit show they do work and it's actually a not enough fuel at idle problem rather than a glowplug one? Also on start up there is nothing more than a puff of white smoke the instant it starts, nothing more after.

Last edited by d215yq; 07-12-2015 at 09:34 AM.
Reply With Quote
  #4  
Old 07-12-2015, 10:41 AM
television's Avatar
television television is offline
Senior Member
 
Join Date: Mar 2005
Location: Daventry
Car: 2002 SL500, 216 CL500, all fully loaded
Posts: 163,814
Default

You have an air temp sensor and water temp sensor that set up the fueling mixtures.

The rev counter was an extra on most diesels and it takes the reading from the engine CPS, often from the front one on a diesel, so this cannot be the problem.

Just pulling the connector off either sensor would put the car in the max cold mode
__________________
Malcolm

Don't worry, it only seems kinky the first time
Reply With Quote
The Following User Says Thank You to television For This Useful Post:
d215yq (07-12-2015)
  #5  
Old 07-12-2015, 12:40 PM
d215yq d215yq is offline
Senior Member
Threadstarter
 
Join Date: Mar 2008
Location: Barcelona
Car: 1987 W124 300D 200k
Posts: 1,386
Default

Thanks,

Could you tell me where these two sensors are and I will try disconnecting them.
Reply With Quote
Reply


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 Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
SEC Idling Question Francois Engine, Drivetrain, Fuel and Exhaust 31 20-10-2008 11:34 PM
94 e420 idles at 1400 rpm gtnit Engine, Drivetrain, Fuel and Exhaust 9 29-08-2005 08:33 PM
Cold Idle kiwi_bloke Engine, Drivetrain, Fuel and Exhaust 9 26-01-2003 08:38 AM
190E idle speed when cold jacjam Engine, Drivetrain, Fuel and Exhaust 3 02-01-2003 06:45 PM
500 sel cold start idle - rough idle on cold start DENNIS Engine, Drivetrain, Fuel and Exhaust 1 22-11-2001 02:06 AM


All times are GMT. The time now is 10:54 PM.


Powered by vBulletin® Version 3.8.6
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.