1989 300se 6cy engine will not restart after driving util 15 min later
 

I can start the car and drive , but when i shut her down I haved to wait 15 min to restart her. it will turn over and crank but won't start until about 15 min. new plugs , cap rotor,ovr, alternator regulator.could it be the crank position sensor? this car has 89000 miles.this 6 has two sensors, one at the flywheel and the other at the front of the engine.camshaft sensor I believe. the rear crankshaft sensor goes from the ezl to the flywheel. any suggestions? could the fuel relay cause this also. the car starts every moring with no problem until I shut her down, then must wait 15 min to restart.the fuel regulator seems to be ok. no fuel leaking after idle ( a few min when i pull the rubber hose from the regulator.?thanks

I had 'more difficult' starting when hot and new injectors, sleeves and seals solved the problem 100% 500€ for me but I think yours are about half that.

I'd also ensured that all the HT was 100% with MB cap and rotor, NGK copper plugs, Beru wires. Still going fine.

Good luck.

RayH

Crank position sensor
 

Something is getting "hot" temperature wise that is causing the computer to shut the starting down.

Perhaps you car has the system that shows trouble codes. What codes are showing up (DTC's)?

When I had this problem, I found that the CPS (the one at the flywheel just below the oil filter tube) was loose. I cleaned it, tightened it down, and solved the problem. Remove it, clean it thoroughly, it's just a magnetic sensor, and re-install. If you need to replace it, replace it with a genuine German part. Yes, it's more expensive than the off-brand names from China, but they really work and work for a real long time. This is one of those parts that will strand you. It's worth the extra money to not have it happen to you. Because I changed mine as an abundance of caution, I keep the spare in the car with all my other "anti-standed emergency spare parts".

If it's not starting due to the crank sensor there will be no spark or fuel, if its not starting due to the fuel pump relay there will be spark and no fuel. The easiest way to sort this out is to ,carefully, hit it with a shot of brake cleaner with the air cleaner off and see if it starts up and stalls, if it does, you know its not getting fuel, if it doesn't then pull a plug wire off and put a spare spark plug into the resistor end and lay it on the bare metal of the head, get an assistant to crank the engine while you look to see if the plug is firing.

Generally hot soak problems occur after the hot engine sits ("soaks") for 10 min or so after running. Are you saying you cannot restart it even immediately after turning it off?

A bad check valve in the fuel system could cause the fuel system to lose pressure after shutdown. This lets the fuel in the engine compartment vaporize, leading to a no start condition. Check your fuel pressure running and after stopping.

Another point... Spraying fast start into the intake to check for fuel/spark can lead to a false result. It's possible for the engine to "run" on fast start alone, without the aid of working spark plugs, on compression ignition alone, leading to the false assumption that the ignition system is working.

Jim

A bad crank position sensor generally will cause the car to stall, and then won't restart until it cools down. If you can get the car hot, and keep driving, I don't think the sensor is bad.
A hard start after shutdown sounds like a leaky injector or two causing a flood situation.

check valve
 

Check valve on pump? Or fuel line to tank?