COLD RUNNING
 

I have a 1990 500sl. Runs great when warm. When cold it starts fine but will hardly come off idle. When you push the gas pedal it coughs etc. If you let it idle for a minute or two it runs fine. Like a carb car with a stuck choke! My conclusion is that cold run mode is wrong.. I pulled the cold start valve out and it doesn't seem plugged. Olease offer any ideas

thx

Has nothing to do with the cold start injector!

On any engine with CIS fuel system, cold running is all about fuel pressure.

For that car to perform correctly cold, the fuel pressure in the lower portion of the fuel distributor must get a signal to be much lower than the upper portion.


OF course if the secondary ignition system is weak, like bad distributor caps & rotors or wires then that needs to be fixed first.

cold running
 

So what signals the pressure differential for cold running? Shoulsd i look at fuel filter etc

cold start valve?
 

what the heck is a cold start valve? Where is it?

don't confuse
 

the Cold Start Injector with the Idle Control Valve....2 different things....

Cold Start Valve = Cold Start Injector

:rolleyes:

Actually....
 

based upon your description it sounds like a vacumn leak. Do you have that giant 1964 Ford looking air cleaner on yours like I have on my 1990 300? I swear, if any of you play golf, here is my analogy....Augusta National wants to appear traditional while updating...Mercedes, same thing...they want/need to appear traditional to maintain existing customer base yet upgrade to maintain leadership technically...*****! Anyway, I would take the aircleaner and look all the stuff.....

The lower chamber pressure is regulated by the electrohydraulic actuator which is a solenoid valve controlled directly by the CIS-E control unit, which sets running conditions based on feedback from the temperature sensors (among other sensors, switches, etc). The CIS-E fuel injection system is the result of taking a bullet-proof mechanical injection system and adding whiz-bang gizmos to make the system run leaner to yield better fuel economy and extended service life without adjustment. Do a little research on the system, there should be some good online info available (I've got the MB CD's at work with the testing procedures and how the injection system works, its a lot of information but impressive the engineering put into this injection system - I'm pretty sure I've seen the CD's linked here before).

I wouldn't think this through too far
 

Start at the basics....

Here's the deal
 

Professional mechanics go right to the most obvious point of the problem at hand, they are being paid by the hour, and they keep going until the issue is resolved, that's it. But mechanics always start with the most obvious and common problems...alot of times they find it really quick and it costs nothing to fix....enter quandry

CIS system
 

And an automotive technician (which is neither of the two stated above) understands the system, common failures, and zeroes in on the root cause of the problem in a competent and hasty manner.

of course
 

sorry for the percieved slight...I was a Computer Programmer and all of a sudden I was a Senior Systems Analyst...doing the same thing....goofy

No sleight taken, just a little friendly banter:D

And I'm not trying to be snobbish about the mechanic vs. tech thing, To me a tech is the next step/evolution of mechanic work. I drive what I work on for a living (as do the rest of the techs at the shop - I've got a 300E, a BMW 528i, BMW 325e, a VW cabby, and an Audi A4). I spend time in the evenings and on the weekends in training, going to training classes, digging up info in manuals, and participating in discussion on paid tech websites. Working on these cars for a living is more of a lifestyle (and mental illness) than a career choice.

As a computer guy, you will find this interesting. The latest BMW factory diagnostic program (ISTA) assigns each car an IP address and works through an ethernet port on the car. A scan involves downloading ALL of the cars coding as a file structure and then loading all of it back up after fixing the car.