1991 500SL "Cold start injector Relay"

[jsauto]

I am having some difficulty with starting my vehicle (1991 500SL from Europe), it will crank for a long time when it is cold but not start. If you keep cranking for about 5 minutes (not non stop) it will fire up, but is very unsteady and will stall if you try and give it any gas. If you get it going a few more times it will start to smooth out a little and then after about another 5 minutes of running or once it warms up it will run perfectly smooth. I can then stop and restart with little difficulty.

I have another 1991 500SL (from Europe) that runs great, so I have been interchanging parts. I started by buying and replacing the distributor cap. I have also changed over the crank position sensor, OVP relay and MAS unit.

I also took out the cold start valve to see if there was any fuel coming out when I cranked over the motor (nothing came out). I have now concluded that the cold start system is at fault. I went into the trunk to find the fuel pump relay (K27) and there was none to be found in either vehicle. Am I not finding them due to their being from Europe? Here is where I checked http://www.classic-roadster.de/cgi-bin/showitemlocation.cgi?TYPE=R129&X=8&Y=20&SORT=LOCATION&START=&ITEM=K27

I am also not sure where the cold start relay is located, or is it part of the fuel pump relay?

Any help would be greatly appreciated!!

[ctaylor738]

The cold start valve just provides a quick spurt of gas to get the engine started. The fact that even once your car starts it warms up poorly makes me think that the coolant sensor in the intake manifold, or the wires that run to it are bad.