Timing for a M110 990 engine

SilverSaloon

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hi

I have a 1985 280SL with a M110 engine. Haynes (and other references online) give me the timing marks for all other types apart from the 990 variant. haynes has the spec for M110 989 and M110 988 etc

can anyone confirm the timing for this specific engine? M110 990?

in addition, does anyone know how to adjust the mixture? i think its running a bit rich and i'd like to reduce it very slightly.... is it the push down allan key? the thing you need to push down into the unit and then turn? i dont have any specific equipment, so was thinking of adjusting it my a few degrees and seeing how it goes.... or should i just leave well alone, without the proper kit. my method i thought of was to adjust it very slightly, remembering how much i moved it by..... if somethings up, i can just move it back..... ???!
 
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Number_Cruncher

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The adjustment for mixture is very sensitive. You really do need a CO meter to set it up properly.

However, before tinkering, I would give the rest of the system a very thorough check over. Are all the vacuum pipe connections in good nick? Depending upon whther it's K or KE, is the warm up regulator OK, or is the coolant temperature sensor working properly? Is there a cold start injector - if so, is it working properly, and sealing off properly? Is there a thermo-time switch? does it work?

As many times as not, you'll find a fault, which, when fixed will return the system to running properly without any fiddling with the mixture.

Can't help with the timing value, but in the absence of anything better, set it somewhere near, and go and find yourself a quiet road up a hill. Keep advancing the ignition until, with a warm engine climbing in a high gear at lowish revs and wide open throttle you begin to hear the engine pinking, then, retard it a bit.
 
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SilverSaloon

SilverSaloon

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thanks.

the car is running fine from acceleration point of view and isnt using any more fuel than expected.

may main reason for thinking all this is because when i bought the car the previous owner mentioned that his uncle (who did maintanence on the car) had adjusted the allan key a little bit due to me driving a long distance back to scotland. this worries me that its not set up correctly.

another reason is that is "splutters" a bit after revving, ie if you rev it at idle and then let go of the throttle it splutters a little. someone mentioned unburnt fuel?

the final reason is that there is a very slight misfire at low speed. i cleaned up the dist cap and HT leads and this went away 90% but its still there very slightly.

i've ordered brand new MB dist cap, dist arm, spark plugs to fit this week. i'm hoping they will cure the misfire. the dist cap isnt in the best of condition so is my chief suspect. the current spark plugs are quite sooty when i took them out to inspect.

i've heard if the timing is off then a 110 will run very badly - it doesnt so i think it may be fine....
 

Number_Cruncher

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It's unusual for an engine to be too sensitive to timing - especially in a fairly old fashoned mechanical plus vacuum advance set up.

The reason is that there are variations, both between engines, and between the fuels which are used in them - the timing figure from the manufacturer is a safe value which even in worst case combinations of detail engine construction, and fuel quality will still result in accptable running, providing a good margin against destructive knock.

If you look at the live data from a modern, knock controlled engine while it's running, the timing is constantly varying, and is different even in a long term averaged sense between cyclinders on the same engine.

Yes, if someone has been fiddling about with the mixture, then, yes, it needs checking. But, the point about faults elsewhere on the system still stands. In my experience both with carbs and older injection systems which could be adjusted, many times adjustments were made when faults really should have been corrected first.
 

Alex Crow

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it must be k-jetronic, the 110 engines never had ke to my knowledge. the timing we speak of is assumed to be ignition timing, as opposed to valve?

if your model is automatic trans and the figures you have available are also for automatic variants then they should be fine - beware though, often mb quote timing without vacuum connected. usually timing, being electronic, will only vary very slightly as the timing chain wears. beware also if vacuum pipes are broken/fitted wrongly (all too often the case sadly!)

you should have a basic tuning data sticker on the rocker cover (if memory serves me right) or slam panel, a white sticker with various numbers and diagrams on?

regarding the mixture adjustment, as others have said it really needs to be on a gas analyser.
 
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SilverSaloon

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thanks everyone - i'll probably leave the timing then (it seems to be running fine) and the cars done 175,000 so is quite worn i'd imagine, so original spec probably wont be valid anyway.

my spark plugs are sooty black so i think i may try to reduce the mixture by 1/4 turn and see how it goes.

at next MOT i'll get them to adjust it better on their machine

cheers

derek
 

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I have to agree that the timing will not alter the mixture by much. When setting the screw, it is best done with a exhaust meter. Do take care when adjusting it, using no downward pressure. You turn clockwise to increase the CO content and anti clock to decrease it.


As Alexander says its K injection
Some figures here for you.

Idle speed. 700 +-50
CO level. 1983 to86 0.8+- 0.4%

You know that your idle adjust screw is by the side of the distributor.

I do have the complete workshop info for this engine,,it is in book form, but I will try and get this photo coppied
 

Number_Cruncher

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1/4 turn is WAY too much - that will probably take you from one extreme to the other - the mixture setting is very sensitive on these systems.

Ring your local MOT place, and ask how much it will cost to get 10 minutes time of their gas analyser, and simply drive there and set it up properly.

EDIT: To back up Malcolm's advice about not pushing down while making the adjustment, I tend to;

- make a small adjustment
- withdraw the allen key (this is a VITAL step)
- give the engine a rev
- let it settle to a good idle, and let the analyser settle
- take a reading
- if necessary, go back to the top of the list, and repeat

For good smooth running, I would tend to aim for the upper limit of CO, 0.8%
 
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television

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As I have all of the information for these systems and the testing and adjustments, I am going to have them photo copied and I will send you a set. No one ever before has ever offered this info.

I can cover all fuel injection on most MBs from 1980 to 1990

It tells you how to test and set up every component,,it would be a terrible waste if I wake up dead one day,,as it would all get wasted
 

Alex Crow

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good advice posted above. i would personally aim for a steady co reading of 1.5 to 2%, they always run a little happier at this.

there are many potential gremlins with your injection system though, so if your mixture is way high and you find the car will not start when cold after correcting you could be looking at a shot `warm up regulator` or metering head - for instance! my point being that simple jobs on classic cars all too often turn into complicated and frustrating voyages of tragic and regretful discovery. a pessimistic view perhaps, but pessimism makes me a better engineer.
 

Number_Cruncher

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I agree with two of your points Alexander.

1) Set the mixture towards the rich end of the tolerance - even erring a little beyond on the rich side as you suggest

2) There's no place for optimism when working on cars - it's almost never "just an adjustment" or "a simple tweak" as vendors of cars and those found propping up bars often like to make out.
 

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2) There's no place for optimism when working on cars - it's almost never "just an adjustment" or "a simple tweak" as vendors of cars and those found propping up bars often like to make out.


Everything that ever came into me to be fixed was always the switch, as it would not turn on,, thats what the customers tell me when they bring things in.:D
 

Alex Crow

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on a slightly different slant i am often told that `it feels like the fuel is not getting through` or `it feels like it`s not sparking` by my helpful and well meaning customers. i smile politely and then gently ask the pertinent questions.

generally the guys are worst for this, the very worst is the boss! it goes something like this...

me - what are the symptoms boss?

boss - it feels like the gearbox.

me - but what are the symptoms boss?

boss - you`d better check the oil level.

me - but what are the symptoms boss?

boss - not sure, could even be the air mass sensor.

me - but what.....etc etc

you get the idea, he`s a lovely chap though.
 

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This thread contains information most relevant to an issue I have...

79 280 SLC won't idle. Started a few days ago for the first time in about a year (when it did run, albeit with noisy top end and slightly erratic idle).

It started and ran so long as the revs were kept to about 1k rpm. If left to its own devices revs dropped and it just died. Running very rich; in order to restart it I had to remove and dry the plugs.

Can anyone give a few pointers and/or a diagram showing the various components. I want to try to determine what the issue is so I can get it running well enough to get to someone who can check the adjustment and timing.

(I got the car 3 years ago and drove it 80 miles... then parked it to restore, where it's been since.)
 
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SilverSaloon

SilverSaloon

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Hi

you're best getting a C02 machine and a timing gun or getting a mobile mechanic out to set the timing and the mixture for you.

i bit the bullet and took my car to a trusted mechanic. Cost me an hours labour but the car is now running very sweet.
 


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