brettleasure

my fiances 07 clk550 has been dealing with her car taking multiple attempts at starting, which can take 2 times or 7 to 8 times. then, recently, the car will die. i've had it into autohaus in scottsdale and the first time there a bunch of codes came up, mostly all having to do with low voltage.

now, i replaced her battery 3 months ago, so that shouldn't be the issue, but i suspect it to be the cables as they were really corroded. autohaus replaced the negative cable, which i could've done, but didn't do the positive cable. i asked on here a couple weeks ago about how to install it, but didn't get alot of responses, so im hoping this is good news that it's not a prevalent problem as there's also little to nothing on this on youtube either. now, im thinking that it may only be the bad cable, but im also hoping that it's not a starter or alternator.

i plan to take it in again to see if they can test those two components, but in case they need replaced, has anybody had any experience replacing the cable, starter or alternator before? because if this is doable by myself, i could likely save quite a bit of money. that cable alone is like $110, and remanufactured starters are about the same price, if that's ok with these cars.

Rudeney

I put a reman starter on my SL550 and it starts better than OEM - much faster rotation, plus lifetime warranty through Autozone.

But I doubt this is the problem - if your engine rotates, it's not the starter nor the battery. It could be a CPS or fuel pump problem.

91ser

Ive never had any of those fail on mine yet, so no experience. As Rudeney suggested, it could be CPS or fuel pump. Do you have a fuel pressure tester? If so, Mercedes has an easy access location at the front of the fuel rail to test the pressure. I believe you can "rent" (for free) the fuel pressure testing tool at Advanced, Napa, or Autozone.

For the CPS, has this problem been getting consistently worse? Does it have any problems with starting up cold vs. hot?

As for DIY, all three of those (cable, alt, starter) are doable by somebody with average mechanical skills, and could save you some money. However, if you arent confident, Id take it to a shop, as they will have some sort of "warranty" on their work at least.

brettleasure

well, i'm leaning toward it being the cable itself, or at least that's what i'm hoping for. when autohaus replaced the negative cable, it apparently cleared most, if not all, the codes , or at least the ones specifying issues due to low voltage.

my plan, as i think i'm fairly capable of this, is to try and tackle this myself. i'll order the factory cable, but if i see, once im down there, that i can make a cable and save myself $150, then i will, because from every diagram i see, it's just cabling and connection points.

but, as far as symptoms go, it feels electrical to me. it takes a while for it to start sometimes, but others it starts right up. now, i would think maybe starter, but then i can't figure out why it dies while it's running?

Yidney

You don't do a very good job of describing the symptoms. When it takes 7 or 8 attempts, is the engine turning over but just not starting? If it is turning over, it is turning over at what seems like a normal speed - not the little lurches of a nearly dead battery? If it is turning over but just not starting, then, as Rodney says, your battery, cables and starter have nothing to do with it. They are doing their job. Also, if it dies after starting, then that is further evidence they have nothing to do with it. Once the car starts, your starter is having a cigarette and enjoying the ride. Could be an alternator, but I'm guessing not. I'd also vote for CPS or fuel issue. I'm pretty sure you cannot just test fuel pressure and conclude that is the issue. If the CPS is bad, I think it cuts off the fuel pump. Is there any difference in symptoms - how many tries to start or when it dies - depending on if the engine is hot or cold? If if it is worse when hot, then it is almost certainly your CPS. Really not that hard to do if you have reasonably skinny hands and forearm. No joke, but if you have large forearms, I'm not really sure it would be possible to do yourself.

91ser

Lol, hes not kidding about the skinny forearms!!! I have forearms like a woman and even I was having a tough time with the cps! Hahahaha

You mentioned that it dies after it starts? This is troubling because it rules out the starter. I wouldnt say it completely rules out the cable, but damn near.

I agree, you probably cant test only the fuel pressure and make a conclusion. Unless you measure it and its below a certain level (is mercedes 44psi or 52 psi?) If its at, say, 20psi, you have a fuel issue for sure. But if it measure nominal, that doesnt necessarily mean fuel is ruled out.

If the CPS is bad, I believe the fuel pump should still work. The fuel pump will start and pressurize before you even try to start the car. It runs for a few seconds to build up the correct pressure, and then turns off until you start the car, or relieve the pressure. For example, if you have the car in the "on" position but not running, and then you push on the fuel testing valve, it will shoot out fuel and then you will hear the pump kick back on.

Agreed, probably not the alternator, as that doesnt really prevent the car from starting. Its soley on the battery at that time.

I would guess the same thing as Yidney, CPS or fuel.

Although, could it possibly be the MAF? If it were, I would think it would throw the code for it tho..........

Amir_AMG

Voltage regulator? Rear Sam? Fuel pump? CPS?

brettleasure

ok, so the more i think about this, it might indeed be the cps. does anybody know the part number for the cps on a 07 clk550?

Yidney

I'm sure somebody can give you the actual part number, but I bought mine about a month ago w/o knowing the part number. If you are buying online, most any place that sells MB parts you can just search by the part description. Bought mine from Pelican parts. I bought the genuine MB version, as I usually do with stuff like sensors and seals. I think it was $45.

Yidney

Also, you might want to look at my thread from a couple weeks ago called something like "W209 CPS tips" or something close to that. Besides getting your arm between the firewall and the back of the engine, the hardest part of the job is getting the connector off the sensor - the little plastic lever on the connector has to be squeezed to the limit of its travel to clear the little tab it hooks over on the sensor. It may very well break from being brittle from age and heat. If it breaks, then your option is to use tape to hold the connector to the new sensor until you get a new connector. The dealer nearest me does not stock them, so it took a couple days to get one. For the $5 they cost, you might consider just having it on hand.

brettleasure

good looking out man, thanks! yeah, i've been trying to research and absorb as much as i can in preparation for this. lucky for me, i have small hands, so i'm gonna see if this can be done. and i've seen the tape solution before as well. might need to buy some new tools, which im always looking for excuses to do. i'm gonna try to do this stuff this weekend if i can because i tried to start it last night, which it ultimately did, but took like 12 tries and i had to give it gas to keep it going.

Yidney

Hmmm. Changing the CPS can't hurt - I did mine for no reason at all other than they often go bad - but if you could keep a car going that wanted to die by giving it gas, that may not be the CPS. The CPS is typically more of a go/no go situation. It is sensing the crank rotation. It either is or it isn't. If it isn't, then your ECU thinks the engine is not running and basically shuts everything off. I suppose it is possible the CPS is very sporadically reading the crank, and thus it runs but not well, but I do not think that is the typical symptom. So that one additional fact makes me lean more heavily towards a fuel supply issue. Perhaps a very dirty filter. You never did respond to the questions about whether heat affects things, but your last post makes me think you were trying when it was cold.

brettleasure

well, it's hard to get good diagnosis/symptoms as my fiance drives this and she works full time, and goes to school full time, so i have very limited exposure to this and have to rely on her testimony. i'll try to make a video of the attempts if i can remember to do so

brettleasure

ok, so im thinking it might actually be a cps or fuel pump as my fiance told me yesterday that it still wouldn't start (worse in the morning/cold), but when she pumped the gas, it started right up. i'm still going to try to replace the main battery cable as it's really corroded and looks rough. however, is it possible that low voltage would mimic, or cause those other issues to happen?

Yidney

The general consensus is that these cars are very sensitive to having a healthy battery and proper voltage. Almost every imaginable problem has been attributed to that issue at one time or another - "gremlins" is the term often used. But given what you describe, I think the CPS is not your issue. So change your cable and go from there. Sounds like you may have some throttle related issue.

brettleasure

im quickly starting to realize this, thanks yidney. just got a text that the same thing worked like a charm today; one pump of the gas, started right up

Rudeney

Pumping the gas pedal does nothing - this is not like an old carbureted engine.

brettleasure

got in today; big red battery warning display came up. it's still intermittently starting, but it helps to give it gas. was able to drive it to autozone to have them check the battery, which was low (65%), but tested good so the guy immediately thought alternator. now, it looks original and the car has 156k miles, so changing the alternator may need to be changed just because, but would a bad cable mimic a bad alternator is not properly charging? btw, the oem cable's been ordered and should be here tuesday.

Rudeney

Your car has a built-in voltmeter, so it's easy enough to check the alternator. Turn the key to position 1 and then used the steering wheel controls to scroll to the "main" screen on the MFD (showing outside temp or digital speedo, depending on your settings). Now press the trip reset stalk 3 times until you hear a beep. Start the car and you should now have an additional menu with an option for voltage. If you get 14v or so at idle, then the alternator is fine. If not, then start with checking wiring. Also, the regulator (inside the alternator) is a separately replaceable part, though often, with Auto Zone and Advance Auto, it's just as cheap for a lifetime warranty rebuilt full unit as opposed to just the regulator.

brettleasure

thanks, i'll try that tomorrow

brettleasure

didn't get a chance to check that, but this came to a head yesterday. car was dead, would not start at all. she was able to get it to a shop down the street from her work, where they replaced the alternator and battery today. apparently everything is working ok. i hope so, because i was told that it wasn't the alternator and the battery was replaced 5 months ago. we'll see if she drives it home tonight.

MacVidMB-V8

replacing battery and alternator at same time is shotgun method

waste of money

brettleasure

we didn't have much of a choice at the time. however, some more updates...

the day after the replacement, she had a no start, followed by a start and then immediately die. and then a complete start, no failure. ever since, the car starts right up as healthy as can be, so that's good. however, since she's been home in the last hour, the alarm has gone off twice, unprovoked for all i know since it's in the lot. is there some kind of reset needed for this or will this eventually go away assuming all systems are 'booting back up'? i honestly have no idea, so im just grabbing at straws here.

Rudeney

First of all, you have to define "start". If the engine rotates, then the battery and starter are probably OK. If there is no rotation, then one of those two is likely the problem, but it can also be caused by bad wiring, fuses or relays. So, if the engine rotates and does not fire, or fires and then dies shortly thereafter, it is probably not the battery at fault. This can often be a symptom of a bad CPS (crankshaft position sensor).

As for the ATA siren going off, it has a built-in backup battery. Those batteries tend to dis after 10 years or so, sooner if you drive in areas with a lot of road salt (it's located behind the front passenger wheel, under the fender shroud). If it is the ATA siren battery, you have to replace the whole unit - the battery is internal, soldered to its electronic. If you on;t care about having the siren, you can just unplug it.

Yidney

If the symptoms came back after the alternator and battery - and I'm not surprised one bit that they did because what you have been describing would unlikely be caused by that - then you still have the problem and it will come back. The systems are not "booting back up" - that is just wishful thinking. I think you have two choices - get it diagnosed by a place that knows what they are doing - or just replace the CPS yourself and see if that cures it.