Mercedes Repair Questions? Ask a Mechanic for Answers ASAP
Hello, my name is Bobby. Thank you for the question. From what you are explaining, if the vehicle runs with starting fluid then you have a fuel system issue. It is more than likley a bad fuel pump, but it may also be an issue with the control circuit for the pump also. Did you plan on fixing this yourself?
Do you have an RPM signal when cranking the engine over?
I am curious to know if the scan tool will communicate with the computer when this occurs. It sounds like the PCM may be losing power.
If you are getting an rpm reading then the sensor should be reading fine. Do you have a noid light to see if the injectors are being powered up?
No. We just need to start by checking to see if the injectors are coming on. I am concerned about the fuel pressure being at the lower end of the specification, but I do not think that it is the issue either.
You can use a voltage meter set on AC and see if there is a reading while cranking.
Does the voltage fluctuate or hold steady?
If it wanst fluctuating then that tells me that the injectors are not cycling. A noid light is needed to be able to tell for sure. if that is the case then the computer is not opening and closing the injectors. When you crank the engine over and over and then pull a spark plug is it dry ot does it smell like raw fuel?
Have you checked to see if the fuel pressure reading is the same when it runs for those 2-3 seconds as opposed to when it does not run? Also, have you checked to see what the air flow reading is when cranking the engine?
If it is not reading correctly then it can keep the vehicle from running. Try unhooking it to see if it attempts to start any differently.
Thank you. It appears to be getting spark and fuel pressure and is lacking getting the fuel into the engine. It sounds like the injectors are not cycling. It is possible that the computer is failing or that there is a missing input, possibly a cam sensor.
The noir light to see if the injectors are firing. If your scan tool is capable also see if there is a cam sensor reading.
Please let me know when you can and we can continue as needed. Thanks and have a great night.
If you are not getting any light from the noise light then you have an issue with the injectors powering and opening. Did you happen to check the smell of the spark plugs like I had previously mentioned?
No problem. Just let me know when you can
If they smell like fuel then there is fuel getting into the cylinder. I know you said there is spark. When it does start momentarily does it run good or very poorly.
We may have been looking into the wrong things. It sounds like something that possibly may be electrical shutting down. It may be the fuel or engine relay or a failing ignition switch.
Hi, my name is***** can help. If you have power to one of the terminals at the injectors when you turn the key on but you are getting no injector pulse when you crank the motor but the car will fun if you spray ether into the intake it tells you that the crank sensor is good and you have spark to the plugs. Since you have already confirmed that you have fuel pressure the problem is going to be with the anti theft system. The first thing you should do is try another key if you have one. Also try locking and unlocking the car with the remote. You can also try disconnecting the negative battery cable for 30 minutes then try starting the car.
Let me know if you have any questions.
How do you turn the alarm off once it starts?
Are you able to test for 12V to the injectors?
If it ran on it's own for 10 - 15 seconds you were getting injector pulse. Would it have continued to run if you didn't let it idle? Have you tried running it with the mass air flow sensor disconnected?
Ok, first check for 12V to the injectors and let me know what you find. Connect your black lead to ground and probe the terminals of the injector with the red lead. One terminal should have 12V with the key on. Also see if it will run again in the morning with the mass air flow sensor disconnected.
Can you give me the history of this problem?
As in how this all started.