Excess CO2 - MOT fail 124 300 24v

[David124T]

My 1990 300TE 24v (non cat) failed it's MOT yesterday with excess CO2 exhaust emissions, 3.81% where the limit is 3.50%. They told me that they do not have MB diagnostic software and I would need to take it to a dealer or MB specialist to have the problem sorted. Checked the Haynes manual last night and it seems that the CO2 can be adjusted manually with an allen key inserted through a hole in the air cleaner (if only everything was that simple!).
My question is, should I take it back to the test centre and ask them to do the adjustment or are they correct and I should take it to a specialist/dealer?
I am not sure if excess CO2 can be an indication of something else that might need attention.
Thanks

David

 

[television]

If you have got the adjuster,take off the filter box, and if you have the plug in the top of the little pipe on the air flow sensor you can adjust it,this was deleted on later cars during 1990.

Insert an allen key down the tube and locate the screw once located, do not press down as this will open the throtle plate.

to decrease the Co2 content turn screw anti clock wise, no more than 5 degrees at a time. Only do it when hot 85c and best do it in the MOT garage while hooked up to the tester.

Do not press down when turning,do not turn more than 5 degrees at a time.

Malcolm

 

[David124T]

Thanks Malcolm. There isn't a plug on the tube so I assume that it has been removed to adjust sometime in the past. The Haynes book says do the adjustment with the air filter in place. I don't need to take it to a dealer/specialist as suggested?

David

 

[124coupe]

try some simple stuff first - is the air cleaner clean? Leaves in the intake before the filter?

 

[David124T]

There were leaves and a small variety of wildlife residing there until a few weeks ago! Airbox is clean and the filter is new. I am going to look at the injectors this morning just in case.

 

[television]

Let me have the VIN first 6 numbers, in 1990 the cars went over to Motronic.

Malcolm

 

[David124T]

Let me have the VIN first 6 numbers, in 1990 the cars went over to Motronic.

Malcolm

Here you are Malcolm. 1240912
In a previous post you said you may consider getting a 124 (again). If so, which model would you go for?
David

 

[television]

http://www.detali.ru/cat/oem_mb2.as...GM=717.450&CT=M&cat=520&SID=07&SGR=015&SGN=01

If its KE its in the small picture 38

http://www.detali.ru/cat/oem_mb2.as...GM=717.450&CT=M&cat=520&SID=07&SGR=030&SGN=02

if its LH it could be the MAF

http://www.detali.ru/cat/oem_mb2.as...GM=717.450&CT=M&cat=520&SID=07&SGR=040&SGN=03

item 5 the MAF on motronic.

do you know what you have on the car.

I fall in love with all 124/6 cars. the is a near mint 124 at a breakers near me, I will put up some pics and get a price.


Malcolm

 

[David124T]

It is KE - item 38.
I think that this car I have was near mint once. As well as near Ash, Birch, Oak, dandelions, etc. etc.
David

 

[124coupe]

Hi, I presume you mean CO level (not CO2) ad this engine should run at 1.0% (+-0.5%) so its seriously rich....

Is it engine type 104.980?

 

[television]

Hi, I presume you mean CO level (not CO2) ad this engine should run at 1.0% (+-0.5%) so its seriously rich....

Is it engine type 104.980?

If it is item 38 there is a hole in the middle of that stand up pipe.

Malcolm

 

[David124T]

Hi, I presume you mean CO level (not CO2) ad this engine should run at 1.0% (+-0.5%) so its seriously rich....

Is it engine type 104.980?

Just had another look at the emission test printout. Yes, it is the CO % that it failed on, not CO2 that I said earlier. Sorry for that error. And the engine is 104.980.

 

[124coupe]

OK. The adjuster affects idle mixture - did the car fail the idle test?

If so, you adjust like this (ideally with a CO meter in the exhaust pipe or you are guessing!)

Insert hex driver through the hole (where the anti-tamper plug should be)

Press down against the spring pressure and rotate slightly until you feel it engage with the mixture adjuster.

Then left = leaner; right = richer. Blip throttle to clear the pipes between each adjust/measure cycle.

 

[124coupe]

Next is to check the inputs the ECU uses to trim the mixture.

you have no KAT so there is no O2 Sensor input.

Therefore, the biggest influence is the engine temp - you should check that the coolant sensor is alive and well and that it's wiring to the ECU is intact.

Also check that the electo-hydraulic actualtor unit that the ECU powers to alter the mixture is free and working. If this unit fails or goes open-circuit, the car will run at all times on the basic mixture map (rich enough to start and to keep running but too rich for the current MOT test).

 

[124coupe]

You may also have a temp sensor in the air intake - if this fails it can also cause enrichment (the ECU thinks the incoming air is cold).

Last thing to check is the resistance trimming plug (round with numbers 1-7 on it and usually has a merc lead seal).

This is used to set the KAT or non_KAT map and to "tune the map......someone might have tweaked it to give more fuel thinking they might go faster!

Post back with the type and current position of the plug - it "probably" should say "ECE" on the front and be in position 1.

 

[David124T]

You may also have a temp sensor in the air intake - if this fails it can also cause enrichment (the ECU thinks the incoming air is cold).

Last thing to check is the resistance trimming plug (round with numbers 1-7 on it and usually has a merc lead seal).

This is used to set the KAT or non_KAT map and to "tune the map......someone might have tweaked it to give more fuel thinking they might go faster!

Post back with the type and current position of the plug - it "probably" should say "ECE" on the front and be in position 1.

Is this plug next to the ECU behind the battery?

 

[124coupe]

Not sure on your car. My slightly later HFM car has the plug in front of the battery on the firewall rib. Shaped like a cotton reel with the numbers on the rounded end.

Did they also do the HC tests or just stop when the CO idle test failed?

 

[124coupe]

Yours may be behind the batt sort of "above" the ECU?

 

[Ian B Walker]

Always a good idea before an MoT top take it for a "spirited" run, cleans out the system.

 

[124coupe]

the famous "italian tune-up"