Hard starting on my C240 W202
10-05-2011, 03:09 PM
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1999 C240 (W202)
Hard starting on my C240 W202
I'm posting this in the hope that it might save someone lots of trouble and swearing, not to mention money !
For a couple of months I had starting problems with this car, sometimes it would take up to a dozen attempts before it started othet times it started on the first swing. Obviously I searched through these forums and various others, coming up with umpteen solutions none of which worked. They ranged from a bad battery to the CPS (L05 sensor) - nothing showed up on the OBD either apart from a misfire on cylinders 1 & 6 (more about that later).
Anyway it all came to a head when the little 'black box' that controls the cooling fan packed up and the car seriously overheated in heavy traffic. So seriously that it blew a side tank on the radiator. I won't go into the sordid details of why. The car went in to have the radiator replaced (one day). While it was there they discovered it had also blown a head gasket - not a DIY job, not for me anyway with my limited resources at home. Off it went to a highly recommended workshop. They duly got the heads skimmed and replaced the valve guides, a job I knew needed doing as I was getting the occaisional puff of smoke, and while the heads were off .....
I mentioned to them about the starting problem and a bad misfire and asked them to take a look. The cause of the misfire became obvious - two plugs were cracked. One vertically all the way fromn the top to the bottom, and the other horizontally. I collected the car and it started perfectly. We surmised it was the plugs, although why two out of twelve would have given such massive problems we couldn't explain. That was Friday afternoon. On Saturday morning I had to try a couple of times before it started. By Sunday it refused point blank to start.
Monday they collected the car again. They couldn't get it started so had to tow it. When it reached the workshop it started fine. But out came the OBD and everything got tested. Not a thing showed up, clean as the proverbial whistle. I actually had doubts at this point as this car has done 180,000 Km. Perfect ? Possible, but let's face it highly unlikely ! Anyway they had access to an ex-Mercedes mechanic and got him to bring his diagnostic tools around and check it out. His verdict ? The CPS was at fault. OK, I thought at this mileage it could be, so it was replaced. It also places serious doubts on the trustworthiness of the workshop's equipment. Any way, off I drove - the car started fine again. The following morning the air around my garage turned blue - it wouldn't start.
An arrangement was made that if I could get it started I was to return it to the workshop and they would check it again. Managed eventually and of I drove - luckily it was only a couple of Km away.
When I got there the guy who had been working on the car said that his Merc contact had said that the relay in the boot (trunk to you, I guess) was black and should be green. What the Hell - the rest of the car is black !?! He gave me a relay (a green one) and I swapped it over right there. They both had Mercedes part numbers but they were different. Ever since, about 4 days now, not a single problem. I have no idea what the part cost as he gave it to me, but I'm sure it was a lot less than the cost of a CPS, new battery, new fuel pump, new filter and all the other possibilities listed.
In retrospect I should have wondered about the fuel system as sometimes I could hear the fuel pump priming the system and other times I couldn't. Listen for that nice satisfying buzz as the pump builds up the pressure. If it's not there, check out the relay before going the route I did. It took a month of waiting and returning the car before it was sorted out. By the way we pulled the old relay apart and it looks as though it has a dry joint so maybe a spot of solder would have cured the problem !
For a couple of months I had starting problems with this car, sometimes it would take up to a dozen attempts before it started othet times it started on the first swing. Obviously I searched through these forums and various others, coming up with umpteen solutions none of which worked. They ranged from a bad battery to the CPS (L05 sensor) - nothing showed up on the OBD either apart from a misfire on cylinders 1 & 6 (more about that later).
Anyway it all came to a head when the little 'black box' that controls the cooling fan packed up and the car seriously overheated in heavy traffic. So seriously that it blew a side tank on the radiator. I won't go into the sordid details of why. The car went in to have the radiator replaced (one day). While it was there they discovered it had also blown a head gasket - not a DIY job, not for me anyway with my limited resources at home. Off it went to a highly recommended workshop. They duly got the heads skimmed and replaced the valve guides, a job I knew needed doing as I was getting the occaisional puff of smoke, and while the heads were off .....
I mentioned to them about the starting problem and a bad misfire and asked them to take a look. The cause of the misfire became obvious - two plugs were cracked. One vertically all the way fromn the top to the bottom, and the other horizontally. I collected the car and it started perfectly. We surmised it was the plugs, although why two out of twelve would have given such massive problems we couldn't explain. That was Friday afternoon. On Saturday morning I had to try a couple of times before it started. By Sunday it refused point blank to start.
Monday they collected the car again. They couldn't get it started so had to tow it. When it reached the workshop it started fine. But out came the OBD and everything got tested. Not a thing showed up, clean as the proverbial whistle. I actually had doubts at this point as this car has done 180,000 Km. Perfect ? Possible, but let's face it highly unlikely ! Anyway they had access to an ex-Mercedes mechanic and got him to bring his diagnostic tools around and check it out. His verdict ? The CPS was at fault. OK, I thought at this mileage it could be, so it was replaced. It also places serious doubts on the trustworthiness of the workshop's equipment. Any way, off I drove - the car started fine again. The following morning the air around my garage turned blue - it wouldn't start.
An arrangement was made that if I could get it started I was to return it to the workshop and they would check it again. Managed eventually and of I drove - luckily it was only a couple of Km away.
When I got there the guy who had been working on the car said that his Merc contact had said that the relay in the boot (trunk to you, I guess) was black and should be green. What the Hell - the rest of the car is black !?! He gave me a relay (a green one) and I swapped it over right there. They both had Mercedes part numbers but they were different. Ever since, about 4 days now, not a single problem. I have no idea what the part cost as he gave it to me, but I'm sure it was a lot less than the cost of a CPS, new battery, new fuel pump, new filter and all the other possibilities listed.
In retrospect I should have wondered about the fuel system as sometimes I could hear the fuel pump priming the system and other times I couldn't. Listen for that nice satisfying buzz as the pump builds up the pressure. If it's not there, check out the relay before going the route I did. It took a month of waiting and returning the car before it was sorted out. By the way we pulled the old relay apart and it looks as though it has a dry joint so maybe a spot of solder would have cured the problem !
10-06-2011, 01:53 PM
#2
Super Moderator
Great - it had to be no 3.8 bar when cranking or CPS. CPS will be next.
04-07-2013, 11:59 AM
#3
regarding the relay in the trunk
I am having a hard time starting up the 2004 C240 during the first time of the day. After a full major tuneup and changing all the filters and plugs, plus replacing the crank positioning sensor & cam sensor, I still having a problem starting up my C240. Can anyone explain to me this green vs. black relay in the trunk. If I can have some more information on this, I can pass it along to my mechanic and have him check it out.
04-08-2013, 08:21 AM
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1999 C240 (W202)
Sorry mlee, I can't give you any more info on the relays. But I suggest you check out that relay, maybe you can borrow one for a couple of days ? The car has done 198 thousand kilos now and it's still starting fine. When you consider that a relay is nothing more than a switch it can only be a bad joint or dirty contacts. You could probably open your existing one and clean it up. If, like mine, it is an intermittent fault, the relay hasn't completely failed and a little judicious use of fine sand paper could solve the problem. If it does, at least you'll know where the problem is and can consider your options from there on. Good luck.
