300ce mixture adjustment

[anfieldassasin]

Hi guys i want to adjust the idle mixture on my car, smells as though it's running a little rich. It's an 88 300ce.

I'm a little confused though, the car has no O2 sensors that I can see. It has the diagnostic port with pins 2 and 3 that people use to adjust duty cycle but I also have a CO2 reader. Which one should I use to adjust?

It has a slight miss at idle and oddly is slower or perhaps more lazy than my previous 230ce to accelerate, although I'm aware the 6cyl is a lazy-er engine by nature. It wakes up above 3k rpm and reaches 110mph fine before I give up as it wanders slightly on the road(plugs and wires are new original bosch non resistor ones and Beru silicone leads and cap and arm OEM nearly new in good condition)

Ta

 

[anfieldassasin]

So co2 a Analyser showing 0.26% with engine at operating temp duty cycle showing 50.6% at pin2 no fluctuation but I'm assuming that's because I don't have an 02 sensor.

Running lean? Odd as car smells rich after a hot run

 

[grober]

http://www.mbclub.co.uk/forums/electronics/124900-diagnostics-older-mercs.html

 

[190]

0.26% is lean for an engine without a cat. The spec for my 89 190e was 1.0%

 

[anfieldassasin]

0.26% is lean for an engine without a cat. The spec for my 89 190e was 1.0%

Yeah I agree, maybe my nose is off as I think it smells rich. Mine should also be at 1%, hmm will try and adjust and see what happens

 

[190]

0.26% might also explain the lazy acceleration.

You may have done the adjustment before but if not be aware it's quite sensitive and only needs fractions of a turn on the allen key.

 

[anfieldassasin]

I think my adjuster is broken turned felt it engage but nothing happens when I turn it! Odd

 

[stwat]

Are you pushing down against the spring?

 

[anfieldassasin]

Are you pushing down against the spring?

Yes! I can feel it engaging the spring but nothing happens as I rotate!

My Co meter is also fooked I can't get it to calibrate which is annoying. Checked on ebay and new meters are over a grand!

 

[anfieldassasin]

0.26% might also explain the lazy acceleration.

You may have done the adjustment before but if not be aware it's quite sensitive and only needs fractions of a turn on the allen key.

Yeah done it on my 230ce I usually do 1/8tb turns at a time.

NB does any one know if adjusting the idle mixture is the only way to raise an idle speed? Mine idles at 600 in D or R and I can feel a slight miss. But in neutral or park it idles at 800 and engine runs smooth

 

[alabbasi]

You can buy the tower with the adjuster on it's own aftermarket. They're quite cheap. Look under the car and see if you have cats, if you don't then 1.0 as everyone has said. You can't really adjust the idle speed, it's controlled electronically. Fuel distributors start going bad after time which could create a slight miss but as you'd indicated 0.26% CO, you're running lean which could cause a miss.

These systems are also very vacuum sensitive, if you have access to a smoke machine, I'd use it.

 

[anfieldassasin]

You can buy the tower with the adjuster on it's own aftermarket. They're quite cheap. Look under the car and see if you have cats, if you don't then 1.0 as everyone has said. You can't really adjust the idle speed, it's controlled electronically. Fuel distributors start going bad after time which could create a slight miss but as you'd indicated 0.26% CO, you're running lean which could cause a miss.

These systems are also very vacuum sensitive, if you have access to a smoke machine, I'd use it.

No cats so 1% it should be. I don't have a smoke machine but there must be a vac leak somewhere as the vac operated fuel economy guage doesn't go all the way to black at idle in both the old and the replacement cluster I installed. It also fluctuates with changing from. E to s on the gear box. With e it sits almost at the middle

 

[190]

If it's basic Bosch Ke Jetronic with no cat then idle speed adjustment is the big screw that bypasses an air bleed around the throttle butterfly.

 

[alabbasi]

If it's basic Bosch Ke Jetronic with no cat then idle speed adjustment is the big screw that bypasses an air bleed around the throttle butterfly.

They still use that on the 6 cylinder cars? That was replaced by annidle control module on the V8s from about 1981.

 

[190]

They still use that on the 6 cylinder cars? That was replaced by annidle control module on the V8s from about 1981.

I don't know when idle speed stabilisation was introduced on the 6 cylinder engines. Bosch Ke on 4 cylinder engines didn't get it until 1990. From what little work I've done on Ke injection I know for certain that the "book" description of what the setup is supposed to be doesn't always match reality. There is no substitute for looking at the physical system in font of you to see what's installed. The idle speed stabilisation module bypasses the throttle butterfly same as the manual adjustment.

 

[anfieldassasin]

If it's basic Bosch Ke Jetronic with no cat then idle speed adjustment is the big screw that bypasses an air bleed around the throttle butterfly.

Can't seem to find this but will have another look. With my 230ce m102 I could just adjust using the mixture tower and the cog wheel on idle control Valve but the icv on the m103 doesn't have any cogs.

I think as someone else said I need to find vac leaks I'm sure there is one as the economy guage isn't working (same behaviour on both old and new cluster). I guess adjusting whilst having a vac leak would give an inaccurate adjustment.

No smoke machine and cigar smoke revealed sweet FA. So needs a proper smoke test

 

[alabbasi]

No smoke machine and cigar smoke revealed sweet FA. So needs a proper smoke test

Well at least you got to enjoy a good cigar . Try to figure out the fuel mixture first and worry about the idle as one can affect the other.

 

[estate-agent]

Finding vacuum leaks can be identified by using something like aerosol "easy start", if you give it a little blast around your vacuum pipes and inlet manifold at idle any air leak will suck in the easy start and the engine will rev up on its own. It will basically enrich the mixture for a split second. If you find a spot that revs up then you've found your vacuum leak. As a word of warning try to keep the easy start away from you spark plugs and dizzy cap, should be no problem but a leak of high tension spark would cause ignition of the easy start, only last a second but will scare the crap out of you and may singe your eyebrows Also avoid it going through your airbox/filter as it'll give a false enrichment rather than finding an air leak.

Used this method on so many occasions, works a treat. If you don't have Easy Start you can use any flammable aerosol to good effect like deodorant etc.

Don't worry about adjusting mixture screw until your sure you have no vacuum leaks.

If it is a vacuum leak that is causing the rough idle and weak mixture at idle then it should have little effect in the cars performance once going as a little vacuum leak will not have any effect once your on the throttle as you'll be letting a bucket load more air into the engine.


.

 

[anfieldassasin]

Well at least you got to enjoy a good cigar . Try to figure out the fuel mixture first and worry about the idle as one can affect the other.

Haha my. Misus did wonder why I've suddenly taken up cigars. Will try the aerosol trick as mentioned.

 

[anfieldassasin]

So tried with some brake cleaner aerosol and nothing, sprayed around all vacum lines injectors intake manifold area idle valve area, area under air flow plate where the big rubber boot is but nothing.
I did notice I have strange whistling almost turbo like sound coming from the interior as I accelerate seems to be coming from somewhere in passenger side area.