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1990 Mercedes 300TE, hard to start

This car belongs to a friend who has no internet access, and for some reason considers me to be something of an automotive guru. No I’m not. I have some ideas but don’t know where to begin. I also have no manual for the car. The car will start (sometimes) after much cranking before the battery runs down. If he uses ether to help it, it will start and once started runs well. I don’t think that’s good for it, especially on a daily basis. Once it is warm it will start easily every time. My suspicion is that there is some sort of sensor that tells the fuel system to prime the injection system with a bit of extra fuel during a cold start. Is that plausible? If so, what and where is the sensor? If not, what do you think the problem may be?

You’re probably on the right track in your thinking. Without knowing more about the car’s maintenance history, here’s a short list of good places to start.

  1. Spark plugs and plug wires (plugs must be non-resistor type, and wires should have a resistance of not more than 1K Ohms)
  2. Distributor cap and rotor
  3. Overvoltage protection relay (OVP)
  4. Fuel accumulator
  5. Fuel pressure regulator
  6. Temperature sensor (for CIS and EZL controllers)
  7. Crank position sensor (CPS)
  8. Electrohydraulic actuator (EHA)

The ignition items are normal maintenance things that should be done regularly anyway. A good indy will run a simple pressure test first, and that’ll tell him a lot about the fuel components I’ve listed. All of the things I listed are not terribly expensive. On the other hand, if it turns out to be the fuel distributor or the CIS or EZL controller, those are big $$. Try the easy, maintenance items and a fuel pressure test first.

OK, that’s way too many abbreviations for me. What are CIS and EZL ? Where are these located?

He has access to an '89 three liter gas engined parts car for low cost parts. Hopefully they are the same for the next year. He says the engines “look alike” but he doesn’t know engines. At least they’re both gas.

CIS = constant injection system, the Bosch Jetronic KE controller that’s on your friend’s car. It is the fuel management computer that controls the fuel injection system.
EZL = ignition control unit (EZL is its German acronym), the computer that controls the ignition functions of the engine.
Together, the CIS and EZL controllers are the electronic brains of the motor. But any reputable indy specializing in Mercedes will know all of that, and should have the tools and equipment to do the fuel pressure test and the electronic diagnostics to check out the sensors and controllers. It’s not difficult, but you have to know what you’re doing, and have access to the testing procedures and the specs to compare your test results against. A 1989 parts car with the M103 motor will have interchangeable parts.

Where are the CIS & EZL located?

Where’s benzman when we need him?

Are we looking for silver boxes?

Geez, nowmaybe, you’re not really into doing any research for yourself, are you? I gave you a primer on the ignition and fuel system of the M103 motor you asked about, and you still can’t do anything with the info. Just take the car to someone who understands it. You’re in over your head if you can’t even search for a couple of terms without someone’s help.

So what you are telling me is that you know the theory behind the system and all the acronyms, but you don’t really know much else about it, right?

We’re in a small town where no one knows much about “foreign” cars. The little library has no generic manuals that cover much, and certainly nothing that covers this specific model. I doubt there’s a qualified Mercedes tech within 90 miles of here. I’m seeking help here as I don’t know where else to turn.

Thanks for what help you’ve offered.

Hard cold starts can be caused by many different issues.

The first place I’d look is are you losing fuel pressure.

Prolonged cranking on a car that’s been sitting a while usually points to the fuel pump accumulator.
It’s function is to maintain some fuel pressure in the system so it stays primed for cold starts.
When defective, the engine won’t start until the pump re-establishes pressure,hence the cranking.

The accumulator is a cylindrical metal assembly adjacent to the fuel pump. They cost around $70 and are not hard to install. You will probably drip some gasoline when making the change out so make the proper preparations. Once you buy the new part, you’ll know what you’re looking for underneath the car. One hose in-one hose out.

I believe the wagon accumulators have a specific part number so make sure you let them know that when you buy the part.

Manuals for the 124 chassis are readily available on line in the CD format.
These cars are much easier to work on with the manuals.