I have a 93 190e 2.6 that has a real hard time starting when it's cold. You have to hold the gas down when you crank it and let off the gas for it to try and kick. I was told the cold start system wasn't functioning.

What I've checked so far is the voltage at the cold start valve when cranking the engine. It's reading about 2-3 volts for a few seconds when the engine is trying to get started and drops down to 0 volts after a few seconds.

I have replaced the cold start valve with a used one that is suppose to work. I have also replaced the fuel injection thermo sensor (picture: http:www.belletc.net/temp.jpg) because I was told this might be the culprit. But the problem with this sensor is that it has no directional groove or specific way to plug it in. So it will plug in any of four ways. And although the plug from the harness is numbered, the original sensor had no numbering on it, and the new unit has a number two stamped on the side, but it's exactly in between two pins. So if that's suppose to tell me where pin two is suppose to plug in there's no way of knowing.

So I tried plugging it in 4 different ways, but the result is the same... I always get 2-3 volts at the cold start valve. So it leads me to believe that this sensor has nothing to do with the cold start valve.

So my questions are; which is the right way to plug this sensor in? And where should I look now for my cold start problem?

Thanks to anyone who can help me out here. I'm pulling my hair out tring to figure this thing out and spending money on unneccasary parts in the proccess. Two things I don't like doing

Seem's like this is the answer everyone gives for every problem but in your case it's the first answer I have. Check the fuse in the overvoltage protection relay located behind the battery.

Perhaps a bad fuel pressure regulator.

Not likely but possible

I checked both 10 amp fuses on the relay and they're both good.

I just had somthing happen. I was starting it cold and it was doing it's usual thing sputtering up to where I could get it to idle while holding my foot on the gas... and then somthing "clicked" under the hood and the idle smoothed out and shot up to about 1000 RPM, like it's suppose to be. I think at that exact moment the Check engine light flashed on then went off. The "click" sounded like it came from the passenger side of the engine compartment.

Any ideas what this could be?

That doesn't mean the relay is good. The fuses protect against an overcurrent condition that could occur if there is a short on the power buss that the OVP controls. The relay itself protects against overvoltage that can occur due to, for example, a charging system fault.

You need to check the OVP relay function in addition to the fuses.

Duke

How can I check to see if it's functioning properly?

What I'll suggest may not be considered scientific, but in my case it worked.

Pull the OVP out. Make sure the flap is closed and holding the flap closed, shake the OVP. If you hear any rattling, something has come loose inside and the device is faulty.

I read about this technique here and also had it recommended to be by an MB tech - local independent shop.

Some part of the internals had apparently come loose as I heard rattling when I shook it. My problem was stalling after restarting a warm engine after sitting for 20-30 mins.

Replaced OVP; it hasn't reoccurred since. That last stall was about 2 months ago. My issue may not be related to the original posters, but the infamous OVP was brought into the conversation.

See Steve Brotherton's remarks in this thread:

an OVP question

__________________
'91 300-SEL

Go here and download all the service information for your car:

http://mb.braingears.com/201_Chassis.htm

You should also look at the 124 and 126 CDs since they have additional diagnostic and other procedures that can apply that are not in the 103 engine manual or 201 chassis manual. You can download individual procedures that look like they might apply and add them to your service information folder.

Duke