Won't start when hot
 

My 1987 300E won't start when hot. I have to wait about 15 to 20 minutes untill the engine cools down and then the engine readily restarts. Might the problem have something to do with the voltage regulator gadget located behind the battery?

The engine turns over well but simply makes no attempt to fire.

I too have an 89' 300E and mine wont start in park, so i have to put it in neutral to start it. Also sometimes when i try to start my car after i have driven it earlier I have to keep my foot on the gas pedal at all time, as if there is no idle set at all. Im going to take it to the shop to get it worked on and i will ask the mechanic what the problem was.

Ok Imatation... Sounds to me like we have very different problems... yours a little more serious than mine. Thanks for the reply.

Im pretty sure my problem also has to do with the voltage regulator or some other electronic component like that. I have had similar problems like this and that is what it turned out to be.

Once I had the same problem (wouldn't start in P, only in neutral).
Replaced the neutral switch, problem solved.
No start when hot could be one of many things, do a search, you will find tons of info.

Hot starting problems for an M103 typically indicate a fuel pressure problem (leak). I'd start with the fuel accumulator. To find out for sure, you need to do fuel pressure testing.

Thanks Mike... that sounds like a good lead. However I do not know what the accumulator is or where it's located. Also... should I smell fuel if there is a leak from the accumulator? Would the leak be internal or external?

Thanks.

Check the fuel pump runs - you can hear it run (it's underneath the car under the right side rear seat) for about half a second whe the ignition is switched on. If not, fuel pump relay could be faulty.

Ok Mick... I like that lead... it makes sense. I'll check it out just as soon as I get someone to work the ignition while I stick my ear under there. Where is the relay if that should be the problem? In or behind the fuse box?

The fuel accumulator is with the fuel pump and fuel filter, underneath your car just behind the passenger rear tire.

Looks like this:
http://img.eautopartscatalog.com/live/E400024540BOS.JPG

While it's possible that the fuel pump relay could be the problem, I would think that it would affect more than just hot starting. I don't have a 300E, but on my 300SEL, the fuel pump relay is in the shelf between the battery and the fuse box, under the hood. Looks like this:

http://img.eautopartscatalog.com/live/P203733032.JPG

You may well be right, but the relay's problem is usually dry solder joints and the fault could be triggered by the rise in temperature under the hood after the car is stopped.

Relay looks the same and is under the plastic cover behind the battery. Jump terminals 30 and 87 to test run the pump(s)

Mike and Mick.... Thanks. You guys go the extra mile.... must be Camel smokers. I like the idea of possible dry solder joints but I don't know what is meant by dry solder. Do you mean corroded?.... the solution being to clean up the contact points? Or do you mean that the pins will have to be resoldered at a point inside the black box?

resolder