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Mercedes Benz 190E Hard Cold Start

Q. I have an 1989 Mercedes Benz 190E 2.6 liter 6 cylinder with K-Jetronic fuel injection. I have replaced the fuel pump check valves, both of them. Replaced all injectors. Replaced cold start valve. Replaced overload protection relay. My problem is that it does not want to start when it's cold. Have to turn the engine over for more than 10 to 20 seconds before it will fire once.

Mercedes Benz 190E Hard Cold Start

Then try again and it will run but feels like its running on three cylinders. Then it feels like all of them kick in eventually. Then it runs fine. Starts fine too when hot. Checked fuel pressure at fuel distributor and I got 60 psi then I lose it after 20 or 30 minutes. Vapor lock in line?

I have lots of positive pressure in the fuel tank when the cap is removed. Tried removing the cap and leave it overnight see if that helps but same thing. Tried pinching off the fuel accumulator at fuel pump and leave it overnight, same thing, won't start in the morning. I looked and this car does not have a warm up regulator. Someone told me electrical.

Fuel distributor at return line seems to hold pressure overnight. What do you think? What could it possibly be? Sure driving me nuts. It's my own car and I am working as a transmission specialist, so I have good mechanical background and don't seem to find the problem. Also, I checked for vacuum leaks and the IACM is working, it's opening and closing. Re-tightened all the fuel lines, same thing. Could it be really electrical?

Another way to explain my problem is when you have a rebuilt engine and you want to fire it up for the first time, it takes time to get the carburetor filled and floats working. Well that's what mine is doing, but I don't rebuild my motor every night. Hope you can help me. Soon it will see the bottom of the cliff. Kidding. Please help, or did you ever come across a problem like this? Another thing I'm suspecting, accumulator cause its dropping pressure in 30 minutes. Hope to hear from you.

Thanks in advance,
Lorant

A. If you went to a Mercedes Benz dealer and bought six brand new fuel injectors, it doesn't mean you got six good fuel injectors. At the dealer we used to stock those injectors by the hundreds. It was not uncommon for me to go through 40 or 50 new injectors before I found six good ones.

The injection valves inject the fuel allocated by the fuel distributor into the intake ports directly in front of the cylinder intake valves. The injection valves are secured in a special holder in order to insulate them from engine heat. This insulation prevents vapor bubbles forming in the fuel injection lines which would lead to poor starting behavior when the engine is hot.

The injection valves have no metering function. They open of their own accord when the valve opening pressure is exceeded. They are fitted with a valve needle which vibrates (chatters) audibly at high frequency when fuel is being injected. This results in excellent fuel atomization, even with the smallest of injected quantities.

When the engine is switched off, the injection valves close tightly as soon as the fuel-system pressure drops below their opening pressure. This means that no more fuel can enter the intake ports once the engine has been shut down.

Mercedes Benz 190E Hard Cold Start

A new fuel injector opening (break) pressure is 53 to 62 psi. I have seen new injectors break at much lower pressures and just dribble fuel. There is a fuel injector tester that will not only tell you what pressure the injector breaks at, but will show if the spray has the fine mist and conical shape it should have. It also cleans old injectors.

I would run the engine and get full fuel pressure when it's running nice. Then shut it off and isolate the injectors by pinching off the feed and return lines. If the pressure drops, you definitely have a leaking injector(s).

Additional Information provided courtesy of AllDATA

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