Question about 1986 Mercedes-Benz 300

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Cold start injector is not energizing. When i do get it started it runs rough until it gets warm.

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I am assuming this is an 86 300 e. first see if you are getting voltage to the cold start valve. this valve is fairly simple although it is hard to describe to someone how to test it and also there are other things that happen when these valves fail. assuming you do not have excessive cranking and you know that this valve is not working i'll just give you the most likley problem. on these earlier cis systems there was a 2 pole tempurature senser( 4 pole in the later version) on the in line six motor. if you look to the intake side of the engine it is the last senser located on the top of the head to the side of the valve cover. There will be 2 seperate wires going to the senser. both the cis and the idle speed computers use this senser. I would usually think the check engine light would be on but these earlier systems are not as sensitive. most likley the senser is giving false info to the cis unit which grounds that solonoid(cold start valve). take a ohm meter and test each pole form ground to the senser pin. compare the 2 readings. I know the 4 pole sensers cannot be more than 10 ohms differense. To make things easier on yourself just get a new senser and install it with a new crushwasher. ask for the pcm engine coolant temp. senser. The other sensers are used for your gauge and aux. fan.

Posted on May 17, 2009

  • Ryan Jasper
    Ryan Jasper May 25, 2009

    unfortunately in 86 $ 87 model years the cis computer did not have fault storing capabilities so it has to be failing at the time of code retrieval there are no hard faults

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You need to check all the factors that can affect cold start.

Check the AIF Sensor, check the air intake and the air filter. The air intake sensor can also affect cold start.

Also check your spark, and have a code reading done at your garage to scan car computer, this will tell more on the fault.

Posted on Mar 07, 2009

  • Ginko
    Ginko Mar 07, 2009

    If your car is a 1986 mercedes, things may be different if you have a carb model.
    In that case check primarily the idle settings and air settings on carb, the air intake and spark plugs.

    As you mentioned the injectors, I assume you have a diesel or an electronic injection model.
    In that case do an injector cleaning, replace air filter and spark plugs, if the problem persists check the AIF, check the air intake and the air filter. The air intake sensor can also affect cold start.
    Also do an injector cleaning, and test your fuel pump (test fuel pressure), fuel pump can also be cause for rough start.




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