****Please Help If You Have Any Suggestion****
The 2004 C240 has only 45K miles and all the regular services were performed as required.

I have been having an extreme problem starting my 2004 C240. The morning start, it would crank and crank, and won't fire up. After quite a few attempts to start the C240 and when it seems to want to fire up, it sputters. After a few more time of trying to start the car, it eventually fires up. When I do get the C240 started, it runs beautifully.

Recently, I have done the following trying to fix my starting problem:
changed car battery.
complete tuneup (replaced plugs, oil/filter, gas filter, transmission fluid, coolant, brake fluid, air filter, and the cabin filter).
replaced the crank position sensor and cam sensor.

Prior to this problem with starting the car, the check engine light came on and the car had a problem with Mass Air Flow (being dirty). The mechanic cleaned the MAF and the car ran beautifully for over 3 months. Then, the cold winter came and my car started to have problems starting up in the morning. The car will crank and sputters when it tries to fire up. Even after doing a major tuneup and replacing the sensors, I am still having a problem starting up the car. BTW, the car is always garaged.

The strange thing is, when I do manage to start the car up, it runs beautifully on the road and freeway and the gas mileage is normal. I can even shut off the car for a hour or two and it will start up right away. And this includes multiple times shutting off the car and restarting it. Please, can anyone offer me any good suggestions to address my problem with starting the car. I really need help and any suggestions will be greatly appreciated because I am very worried about being stuck on the road.

I have asked my mechanic to think about cleaning out the throttle body to see it that will help. When I asked him about the fuel pump, he told me that's very unlikely because the C240 runs beautifully on the road and freeway. Another thing I am thinking is to have the MAF checked again. I have also read a post that mentioned the relay may need to be checked.

I forgot to mention that the mechanic also mentioned to me that when he serviced my C240, the throttle body didn't look dirty. The C240 was rechecked with a diagnostic machine and nothing showed up.

 

A dirty throttle body is not the cause of your no start situation. You wasted your $ on the crankshaft/camshaft position sensors. They only cause a stall/no start when the engine is hot. I suspect a fuel delivery issue. Hook up a fuel pressure gauge to the schrader valve. Make sure that you are seeing around 40psi when the engine is running. Turn the engine off. You shouldn't see a drop in pressure. Leave the fuel pressure gauge hooked up to the vehicle over night. Check the pressure again in the morning. Crank the engine. Check the gauge to make sure you are seeing good pressure.

A long cranking situation quite often indicates a drop in fuel pressure as the vehicle sits over night. After cranking for a while, the fuel pressure should have been able to build up and run normally.

First things first; Verify that you have good fuel pressure.

 

Your answer seems very logical and I will pass on your message to my mechanic. Thanks you, again.

 

***HELP****
My mechanic just finished checking the fuel pump's pressure and it is normal. He is going through and checking the voltages in the car. At this point, my mechanic is going through the car looking for the problem to fix the cold start problem. Any suggestions are greatly appreciated. Thanks.

 

I have read on another post about a relay in the trunk that cause his hard starting problem. Can anyone explain this relay and how to test it? Thanks.

 

Chris,

After weeks of testing the voltages, my mechanic is convinced I do have a problem with the fuel pump. He told me not to let the car sit and to drive it every day, until I get the fuel pump replaced. So, when I start the car, I would just turn it on for 10-15 seconds and then crank the car to start it. Works like a charm and without any problem starting. I personally want to thank you for the excellent advice. Thanks a million....Morris

 

I k ow the answer!!! The car is "programmed" to think it was burning E85. apparently the E85 does not like to fire in cold, so it basically "floods" the fuel injection system. I only had this issue while cold weather. Simply add some fuel injector cleaner to boost the fire in cold start or need to be reprogrammed my MB.

Hope this helps!!!

 

The car is finally running normal again. I will ask my mechanic about the fuel injector cleaner to boost the fire during a cold start. Thanks for the info....

 

My 2004 C240 was running very fine until this week. I was getting low on gas and I filled up with super at a Rotten Robbie gas station. Now, in the morning , I am having problems starting. It would crank and after awhile, sputters and won't fire up. After a few attempts, it will fire up and run just fine the whole day. I had about a 1/4 of a tank and refilled the gas with Chevron super....but, I am still having problems starting up in the morning (the 1st. start). Hopefully, with another fillup, I am praying it will starts up properly again. Thanks for the info.

btw, I had the mechanic replaced all the fluids, plugs, and filters. even replaced the CPS and CO sensors.

 

I am having the identical cold starting problem with my 2005 C240 Wagon. Did you ever figure out what the problem was?

 

My mechanic checked all the electrical voltages and the pressure in the fuel pump, and didn't find anything. He thought it may be a lazy fuel pump, but it is only a guess. Last year, my mechanic had me add an fuel additive to my fillup. Surprisingly, my car is starting up fine this year. The temperature has even dropped around the low 40's (maybe even high 30's) and even left sitting in the garage for a couple of days without any startups, and the car started up without any problem. For a piece of mind, radio/heater/lights are off, then I turn on the ignition and wait for the fuel pump to click on, then crank on the ignition.

Btw, the Crank sensor and Cam sensor were replaced during the full major service (all filters, fluids, plugs were replaced). Initially, I had the battery replaced thinking it was long overdue and wasn't getting enough juice to fire up the engine. But, that was not the case. Good luck.....

 

My mechanic replaced the crank position sensor. No change.


I then took it to the Mercedes Dealer. They decided it was the Mass Air Sensor. It was reading 0 degrees, when it was actually 28 degrees outside. They replace the Mass Air Sensor.


Took the car home. The next morning wouldn't start. Car got towed to the MB dealer this morning. Stay tuned......

 

So far, the car is doing really good during the cold morning start this year. From now on I will always buy top tier gas. If the problem acts up again, I will look into having it re-program for E85 gas. Thanks for the tip about he E85 gas.

 

Final update on my C240 Wagon cold start problem: After the dealer replaced the Air Mass Sensor, I took the car home and the next morning it wouldn't start. Ended up towing the car back to the dealer (paid for by Mercedes). They concluded the problem was the Engine Control Unit. Replaced the ECU and put the old Mass Air Sensor back in the car. Everything works great now!

The only way the Mercedes dealer could see the problem was to look at the temps from the Mass Air Sensor that the ECU was reporting. It was showing 0 degrees when the outside air temp was 28. With the Mass Air Sensor disconnected and shorted the values were also way off. The dealer had a special computer to see these values, that other mechanics don't have.

Note: This was NOT cheap ($1,400 part).

 

When I got the warning light for the MAF, my mechanic had it cleaned and re-installed it back in. Labor cost was less than a hour.

 

My C240 been doing great starting up in the cold until this week when it gotten even colder. Can you recommend a good fuel injector cleaner? I was thinking about trying Chevron Techron fuel injector cleaner.

Can an independent German mechanic shop "reprogram" the C240? I guess "reprogrammed" means a software update.

BTW,
one C240 owner, who has a cold start problem, the dealer changed the Engine Control Unit (expensive). :-(

Thanks for the advice.