07 SL550 Vapor Lock
 

Greetings fellow Members,

I've been having a problem starting my engine after I shut it down for 10-20 minutes. The car is under MB warranty and has been to the dealer twice. They think the problem is caused by a vapor lock as a result of bad fuel. I'm using Chevron Premium.

They suggest that I use a medium grade fuel. Of course the manufacturer recommends premium, so I"m suspect of the recommendation.

Any help would be greatly appreciated since the dealer won't help; they blame the problem on Chevron.

Thanks for your help!!!

I believe the compression on the motor is over 10:1. I would not go mid grade. Change brand of gas. What happens to the car? Will it not start?

It won't start until the 4th or 5th try. It happens once or twice a week. I just picked up the car. The service agent wouldn't put anything in writing and wouldn't give me paperwork for the visit; said he would mail it to me.

I'm not willing to jeopardize the warranty by not using the approved fuel grade.

According to the agent, he hasn't seen this with an SL550 before but they want me to believe that the car is fine. Maybe I should talk to the service manager.

Fuel type wouldn't cause vapour lock. vapour lock is where fuel vapourises in the fuel rail due to engine heat. The main cause of this is the residual fuel pressure in the fuel rail dropping to 0psi. You need to get the fuel pressure checked to see what it is after the engine is shut down. It needs to reamin above 25psi for at least the first 20-30mins.

If there is a very quick pressure drop to 0psi then I'd be looking a the fuel pump as being fault (check valve or pressure reg), for a slow drop then it can still be the pump or a fuel injector.

The other more likely possibility is a faulty crank angle sensor, but this would log a fault code in the engine ecu.

Thank you. It's very nice to have your help.

There are no fault codes so the dealer won't work on it any more. By the way, they haven't ever seen another SL550 doing the same thing. That should tell them that something is wrong.

I need to escalate the issue until it gets fixed.