1986 r107 (m103 engine) - Emissions right on limit

[spiderlane]

Hi all,

I have just taken our 1986 r107 with the m103 engine for MOT and happily it passed without advisories. The tester said that the emissions were right on the limit and that the car was running rich.

The car starts, idles and drives perfectly smoothly and I haven't noticed poor fuel consumption, but I'd like to understand if there is an issue.

I've read up on diagnosis via measuring the lambda on/off duty cycle on the X11 connector. I used my oscilloscope to measure the DC as follows.

1. Ignition on, engine not running - stable 69.3% (was expecting 70% here from my reading so this seems correct)
2. Engine idling, fluctuating between 48.6% and 49.6% - this seems to be about right indicating that the system is adjusting the mixture correctly according to the values from the O2 sensor.

So my question is - are the idling values correct? And does the idling value range indicate a very slight rich mixture? Should I be looking to adjust this to oscillate around the 50% value?

I look forward to any guidance.
Cheers
Mark

 

[spiderlane]

fullsizeoutput_3de9 by markelane, on Flickr

8KJPgVIWRZG+%5hUdPHb9A by markelane, on Flickr

 

[ivan1983]

Sorry I can't help at the moment as I don't have access to my computer with all my bookmarks regarding duty cycles etc

I do like your oscilloscope , what brand is it?

Also i assume the engine is getting to the right temperature?

 

[spiderlane]

Hi Ivan

Thanks for replying. Yes all gets up to temperature and then stable. I think between 80 and 90 (although I confess I can't actually remember the value now)

The scope I've had for ages - it was a cheap and cheerful one, which is probably not especially accurate but perfectly adequate for my needs and it's nice and small/light. It's almost identical to this (was about half the price when I got it as well, which seemed excellent value) :

https://www.amazon.co.uk/dp/B01LYAXCCW/?tag=amazon0e9db-21

* Edit - I loaded the open source "BenF" firmware on it which adds/improves some features.

Cheers
Mark

 

[grober]

PeachPartsWiki: Mercedes-Benz Driveability

One off the wall cause can be a faulty OVP relay which can effect the KE injection electronics supply leading to rich running.Other possibility is a faulty injection engine temp sensor underreading or the fuel supply pressure regulator need adjusting.