300e Cold Start Issues

[wabenze]

Hello All:

I have a 1991 300E which has a cold start problem which began after the car was unused for a few months. It takes about 1/2 hour to start the car when cold. It will fire up instantly if I spray carburetor cleaner into the fuel distributor. It idles at 500rpm and will die if any attempt is made to press the gas pedal. Once it warms up (2 minutes), it runs normally.

I have changed the OVP relay. The old one was corroded and probably had water in it (has been sitting for a while). The fuses are good. I have also changed the cap, rotors and wires and have cleaned the EMA. With the 4-prong temperature sensor bypassed with two 10 k-ohms resistors, I am getting 6-8Volts at the cold start plug-in, but, in opposite polarity. The ground get the power and will not actuate the cold start in any direction. Resistance of the CSV is 13 ohms. Will spray normally with battery voltage applied.

I need help!

[psfred]

You need to replace the fuel pump relay, fuel filter, and check the accumulator.

I would NOT expect a car sitting a couple months to fire up without some cranking, as the fuel pressure will be low. However, it should run once started if the fuel is good.

You cannot "store" modern gasoline in the tank for months on end, it will be hard to burn and make the engine run badly.

Check for vacuum leaks.

Check for severe rich running, too -- may be a bad fuel distributor.

You should really check the fuel pressures for a better diagnosis.

Peter

[wabenze]

Can you please tell me the location of the fuel pump relay? Around the battery area I see two relays; one being the OVP and the other I am assuming is the fuel control relay?? Besides the OVP and the temperature sensor are there any other inputs for the actuation of the cold start valve?

Thanks

[JEdwards]

The fuel pump relay on the m103 engines are located behind the battery and should be right next to the klima relay. The ovp relay is along side the klima and fuel pump relay. However on the m104 engines, I believe the fuel pump relay is located in the trunk on the passengers side towards where the tank is. It should be behind those plastic walls.

The cold start valve is only activated at a specific temperature (I think when the ambient temp is below 50, but I am probably wrong). If its warm out when this is happening then you should be able to rule out the cold start valve.

[wabenze]

Another few long hours spent trouble shooting i did the test at the MAS connector plug and all was good
Terminal 1-12v
4-Ground
10-batt voltage start/run
12-10v
16-4.5v
21-11.5v in on position
OVP will start a 300e 1988 cold start works normal during crank.(on test car)
in on and start position get 12 v from the -ve prong of the cold start plug will actuate valve if i jump the plug to the +ve side and give it an external ground no action if pluged in normally .
I get the 12v even with the temp switch cable disconnect (open no resistors) i hate giving up so pls some one help .The fuel pumps run normally.

[wabenze]

Update - Found the engine control module transistor fried. With a replacement module, the car idles instantly and has no hesitation to accelerate. Still trying to trace cold start valve short.