300TE Wagon Stalling 5 minutes after start

[Hugh E.]

I have a 1987 300TE wagon that starts fine and then stalls after 5 minutes of driving. It will restart once with a long and unpleasant amount of starter grinding, and then start no more. The next day however, it will spark right up and repeat same pattern.

It has a brand new rear fuel pump and the relay that works in conjunction with that pump. On a scale of 1 to 10, I'd rate myself a 6.5 in the handy department but this is my first Benz. I respect the engineering enough to want to get this thing reliable and am hoping that this problem is familiar to someone.

I should add. If I started the car and pulled out on the highway, it would run until the gas ran out but I live in Brooklyn and it's the low rev at lights and stop signs where the motor dies out.

Sequence - car fires up and runs fine through the first few streets...maybe a mile, then it starts to run real ruff as I slow down for an intersection so I put it in neutral and feather the accelerator up and down to keep the motor running. Light goes green, I let the RPMs down to get into drive and it bogs out.

[gatorblue92]

What is the condition of the spark plugs, wires, cap and rotor? These cars are very picky about the ignition system being in good condition and using the correct plugs.

[tecqboy]

Possible crankshaft position sensor failure. Heat sensitive; goes out of spec when engine gets to operating temp. You can do a search on this forum for more info on testing and location of sensor. Also, as noted above, inspect the rotor, distributor cap, wires and plugs. This engine will go through these parts faster than domestic engines and runs poorly or not at all if they are shot. Buy OEM or equiv, no URO parts.

[Frank Reiner]

Hugh E.:

Tecqboy's suggestion of the crankshaft ignition pickup seems a good starting point. In more sophisticated engine management systems, such as those with timed fuel injection and ignition all under computer control, sensors are used to determine the angular position of the crankshaft. In this case the pickup, which is called a variable reluctor (VR), provides a pulse three times per revolution which signals the ignition system to provide a spark. The VR consists of a permanent magnet surrounded by many, many turns of fine enameled copper wire. The flywheel has three short segments which pass close to the magnet as the flywheel turns, causing a variation in the magnetic field which surrounds the magnet. As the field changes a low voltage (~1-3V) current is induced in the windings. That current is the signal to create a spark. As the pickup ages, some of the insulating properties of the enamel deteriorate, and small fractures can also occur in the wire. When the pickup is cold, and the resistance of the wire is low, the voltage will be above the threshold to be recognized as a valid signal, and the ignition system will produce sparks. With increasing temperature the output can fall below the threshold due to increasing internal resistance. Why will the engine continue to run if the RPMs are up? Because the output of the pickup rises with the speed of the segments passing the VR. Once the pickup is warm, and engine speed drops to idle, the output is too low to be valid.

With all that said, the first steps will be to clean all the electrical connections that are associated with the VR, and check the cold resistance of the windings (700-1200 ohms).

[Marcel107]

A friend of mine has a 300 SL also with the M103 engine. He had a similar problem. The engine started right a way and was runing fine, the next stop at the trafficlight the engine stalls. No start at all, and no lights in the instrument cluster. After a few minutes the engine starts again.

The problem was a corroded and lose groundcable from batterie to chassis. This is wery short. After cleaning and installing it tight, the problem was gone.

Maybe you check your Batteriecables.
Execuse my english, my german is much better

From Cologne Germany
Marcel

[Hugh E.]

This is helpful. I really appreciate it. I'll be back after learning/checking.

[lsmalley]

Check the OVP and if that checks out fine then it's the EHA. It causes the fuel pressure to drop down to the point where your car stalls out instead of keeping it idling normally. What you can do is start the car up and then disconnect the plug to the EHA. Car should not stall out anymore after coming to an intersection, assuming the problem is the EHA. I guess you can drive like that until you get a new one. I ran mine like that for a week just to be sure it was the eha, after no more stalling I ended up getting a new one, although I probably could've just left it unplugged.