[Kylo]

Hey there,

I have a 1989 560SEC and just moved up to the Central Interior of BC, Canada, from being on the coast in Vancouver, BC. On the way up the car started choking up and becoming sluggish. I've been informed by a few people that my air/fuel rate needs to be adjusted. When in idle it sputters and then eventually shuts off. When i pull up on the choke a couple millimeters it idles smooth. I am completely new with Mercedes and I am having a hard time figuring out how to adjust the choke.

Any help will be appreciated.

 

[maximapitko]

I never knew that the 560sec was offered with a carb...

 

[MacGyver85]

ha ha ha You know, I refrained from saying anything. I was afraid that "engineered like no other" might mean something different on German fuel injection.

 

[MacGyver85]

I AM curious though. What are you pulling up on that you think is a choke?

 

[Kylo]

I understand that it doesn't have a carb, but the plunger that acts as a choke is run on I am guessing vacuum. I am needing to figure out how to raise the it a couple millimeters. I am not mechanically inclined, but thanks for the responses anyways.

 

[MacGyver85]

If you're referring to the large plenum on top of the engine, that isn't a choke plunger nor is it operated by vacuum. That is the air plenum venturi. When you open the throttle, you essentially open the plenum, the computer senses the increased air flow and adjusts the fuel being injected into the motor.

 

[Kylo]

When I manually adjust it while the car is running with my hand it idles smoother and doesn't sputter out.

 

[MacGyver85]

It sounds like you have an air sensor problem to me.

 

[Kylo]

is there any way to adjust the plenum? My altitude changed 870 meters when I recently moved this month. which is why I am being told its my air/fuel mixture.

 

[MacGyver85]

I'm very new here and not well-schooled yet on these cars so I relinquish tech suggestions to those veterans here that are experts but I know of no manual adjustment. I think you'll end up finding you have a faulty MAP sensor, vacuum leak, or connection problem. The system (as I understand it) optimizes fuel mixture based on information received from a myriad of sensors and as such needs no manual adjustment.

 

[luckymike]

There is also an altitude sensor under the passenger side floor board. Perhaps it isn't working?

 

[LongHauler]

And Kylo, whoever those few people are who are trying to give you advice? Walk, no run away! Seriously, do not get caught up in the trap of accepting advice from every "expert" out there. These cars are not your garden variety vehicles. Join this forum, let us know who you are, what you are driving etc. Use the search function and ask away. An amazing amount of expertise here that should, no, will be able to help you through any issues you have. Welcome aboard.

 

[V12StealthHunter]

No I think they are right. Sounds like your mixture is too rich. There is less oxygen at higher altitudes. But 3000ft elevation change shouldn't affect it much unless yours was off to begin with. Your idle control valve is probably not opening up properly either. Take it to a Mercedes garage and have them put on an exhaust gas analyser and adjust the mixture screw on the fuel distributor. Don't try this at home unless you keep track of your changes. Very subtle adjustments and each adjustment takes a few minutes to take affect.

 

[Kylo]

I had the car in a merc shop a few months ago to replace a bunch of wiring, because of AirCare standards the mechanic played with the fuel mixture to see if he could get it to run cleaner, which it didn't and sat in my carport. After a couple months I bought a house up north and here there is no AirCare standards and I was able to put it back on the road where it died in my driveway one day and the mechanic had to come to my house where he said he made the fuel mixture too lean and it wasn't getting enough gas. It could be that he changed it too far the other way and the difference in altitude.

 

[V12StealthHunter]

Yeah sounds right. In the future, don't let people touch the mixture screw. Its calibrated to the rest of the car and set at factory. You can only set it correctly when all the other induction and ignition components are working at 100%. If you try to adjust it on an old car with varying degree of service life to the rest of the induction system you're bound to mess it up.

You can buy a wideband o2 sensor with a gauge for about $200. Innovate Motorsports Wideband Air/Fuel Ratio Tuning

 

[Kylo]

Unfortunately he is on the coast and I now live 5.5hrs North of him, he had all the tools needed. I heard there was a local merc mechanic in 100 Mile House, but I haven't checked him out yet.

 

[akimball442]

More important questions:

Is this a vehicle with K-Lambda- ie, does it have an oxygen sensor? Does it have an EHA valve? (google the terms and look at some pictures to answer).

Does it run equally crappy when it's cold vs. hot? Does it run better or worse cold or hot?

I'm wondering if the cold start injector could be stuck open. IF the vehicle has electronic controls and it's running crappy once warmed up, then there is something totally screwy- or someone has REALLY screwed the thing up.

Pulling up on the sensor plate definitely reduces the amount of fuel being injected. So it's certainly running rich.

To find out why, we need to know which system you have in order to help diagnose it. Feel free to take the air cleaner off and take lots of pictures. Pictures are worth 1000 words. If you have a completely mechanical system, it's entirely possible adjusting the mixture at the airflow sensor will solve your problem. If your engine has electronic controls, that's a whole different ball of wax.

 

[crickle]

At the very least, throw on new Oxygen sensors. Good maintenance idea anyways.

Check for vacuum leaks!!!!!!!!!!!