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 > Tech Help

LinkBack Thread Tools Display Modes
Old 06-01-2010, 10:54 AM
Registered User
Join Date: May 2010
Posts: 15
Setting idle mixture and testing o2 sensor - '87 190e

Hi all, you may remember that my new-to-me 16v has problems starting when hot, and likes to stall when hot and coming to a stop. I am trying to diagnose this myself, as I don't have a local mechanic who can work on it for me in any near time frame.

This weekend I have tried to check the duty cycle, as I know the previous owner was playing with the idle mixture screw. I have a meter with duty cycle and these were my readings:

- Car off, ignition on. 50.6%
- Car idling, cold - 50.6%
- Car idling - hot - 95%

Adjustments of the mixture screw do not change this 95%.

It is my understanding that these readings (50%, and calling 95% 100% for fault code purposes) point to a faulty lambda sensor. With that in mind, I set out to read the voltage from the lambda sensor directly. I plugged in to the sensor under the passenger seat with a home-made harness. I got the following readings.

- Start the car (already warm) - 0.48v
- As the car idles, it climbed slowly to 0.78v where it stays steady
- If I give the car gas, it drops in a linear fashion to ~0.7v, then climbs back up to 0.78v at idle.

I am not sure if this indicates a bad lambda sensor or not.

Any suggestions on what I should do next based on these readings sure would be appreciated.

Thank you.

Reply With Quote
Old 06-02-2010, 09:10 AM
Join Date: Mar 1999
Location: Tucker, Ga USA
Posts: 12,153
Those readings show that the O2 sensor indeed is inop.

Start with the obvious & replace that sensor
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator
Reply With Quote
Old 06-03-2010, 09:22 AM
Registered User
Join Date: May 2010
Posts: 15
Thank you very much. I have a new 02 sensor, but had a heck of time getting the old one out. Will get it to a shop and report back!
Reply With Quote
Old 06-04-2010, 03:05 PM
Registered User
Join Date: May 2010
Posts: 15
Ok - new sensor is in. Old one was covered in black. Unfortunately, I am still reading 50.6% key on, car off, and not much different when hot and idling. One time I get ~50%, another time I get 95% again.

Any thoughts Doc?

Edit: Voltage at o2 is now 0.49v and doesn't change.

Last edited by zhenya; 06-04-2010 at 03:20 PM.
Reply With Quote


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 05:21 PM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page