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Discussion Starter #1
Over the last month I have been trying to trouble shoot randlom stalls in my SLK 320. Its a 2002 and about a month ago she started stalling out of the blue and on random occurances when at idle, i.e. while waiting at a traffic light.

The engine would cut off and for a second all electrical would die. If I put the car in park, took the key out and replaced it, it would start right up. After the first three times I took it to my mechanic and he saw no codes being thrown. He did indicate that he'd seen this and thought it was the Cam positioning switch. We replaced it and thought that did it, but the next week the car started stalling again.

Next I had him order a Mercedes K40 relay and I replaced it this weekend. When I removed the old one, it had a manufacture date of 2011, the new one was 2013. I thought it unlikely that it was bad, but popped in the new one anyway. Over the weekend I test drove the car with no stalls, but this morning on my way to work it stalled in traffic, on the busiest road in town. Again, park, key out and back in and it fired right up.

I am about to just take the car and leave it with my mechanic, but am already out nearly $400 in parts and labor between the Cam positioning switch an K40. Does anyone have any ideas of areas this could be?
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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You never mentioned how old the battery is/has it been tested or if the alternator has been tested.
 

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Premium Member 2005 SLK55 AMG; 2005 SLK350
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Does it only happen after the car warms up, and Is it predictable how soon it happens after starting from cold (i.e. always within 15 minutes?)

If yes, and In the absence of any codes (you did check with STAR, right?), my guess: Replace the CPS proactively, if that doesn't help, replace the fuel filter and pump.
 

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Discussion Starter #4
Alternator is less than 9 months old, battery??? I am not sure... I do have a voltage meter in my stereo head unit and when this all first started happening the voltage never dropped below about 13.3 while car was running. I'm not sure how accurate the volt meter in a Pioneer stereo is....

I'm not sure what STAR is but am assuming CPS is the cam positing sensor which is what we replaced initially when the stalling started. In every case the stall occurs after I have driven anywhere from 5 to 10 miles, but always within that window... before I replaced the Cam sensor and ran a bottle of fuel system cleaner through the car there seemed to be a rough idle or hesitation right before it stalled, and in some instances would feel like it was going to stall but wouldn't. Now there is no warning and it just cuts off, almost as if there is a loss of voltage or something to either the fuel pump, or another component which is making it stall. In the instance the "stall" occurs. Everything in the car shuts off, a/c radio, lights, etc. but immediately comes back on. Everything that is but the engine, which must be re-fired.

At this point I've tossed money at the "CPS" and the Engine Management Relay and its still occurring. It would be great if it was just battery, but I am not certain. I had thought it might be the fuel pump, but in putting the whole scenario to pen for this post am now thinking it might be electric since everything in the car shuts off, as if the alternator died, or there is no power being generated.
 

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Have you checked the earth lead from the battery, I had a similar problem, not with an SLK, an auto election found a corroded contact on an earth lead, sandpaper and Vaseline cured the problem


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Discussion Starter #6
I finally got the car to my local independent Merc mechanic, he put the car on his computer and we did a load test on the battery. Other than a few old codes (Which we cleared out) there were none which would indicate what the problem was. The battery and alternator came out fine and we were left with me having to try and replicate the stall, which couldn't be done after an hour in the shop.

I have taken the car home, with the instructions that if it stalls again, get it back to the shop ASAP. I can only hope that if it happens again, it remains the same scenario... all cuts off, and I can immediately restart it. That being said, on my morning commute I left off all accessories (lights, a/c, etc.) and tossed the car in neutral at every light and kept the RPM's up... to say the least it didn't stall out.

I realize I need to try and replicate it, but rush hour is not the time to be sitting in the middle of an intersection with a stalled car. My other option is to leave the car with the mechanic and have them go through the whole thing part by part.... which even with the shop owner being a good friend will cost me. So I guess its time to get brave and try and break it myself, traffic or no traffic.

Stay tuned....
 

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Discussion Starter #7
I just thought I would give an update. After a week of commuting I have not had the car stall since the mechanic cleared all the stored codes and load tested the electrical system. Despite my initial concerns with the battery/alternator, I have not had any issues with the car shutting off while at traffic lights, etc. Although I have to admit I have not really allowed the car to idle like I would normally, in fear of it stalling in traffic.

I usually left foot brake and give the car about 200 rpm of gas pedal while I am waiting at traffic lights. Whether this has prevented me from stalling or is a placebo, I can't say. I acknowledge that such a practice doesn't help me resolve the issue definitively, but it has save me the headache and embarrassment of stalling in rush hour. Due to weekend travel, without the car I have yet to be able to run around and do errands on less traveled roads to try and replicate the original problem.

My mechanic thinks it could be the throttle body/MAS, but I replaced it about a year ago. Since the car is over due for its regular service, I may go ahead and do a fuel filter when I next do the oil/filter just to relieve any idea of it being that. I am still at a loss, but knock on wood I have yet to be stranded.
 

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I just thought I would give an update. After a week of commuting I have not had the car stall since the mechanic cleared all the stored codes and load tested the electrical system. Despite my initial concerns with the battery/alternator, I have not had any issues with the car shutting off while at traffic lights, etc. Although I have to admit I have not really allowed the car to idle like I would normally, in fear of it stalling in traffic.

I usually left foot brake and give the car about 200 rpm of gas pedal while I am waiting at traffic lights. Whether this has prevented me from stalling or is a placebo, I can't say. I acknowledge that such a practice doesn't help me resolve the issue definitively, but it has save me the headache and embarrassment of stalling in rush hour. Due to weekend travel, without the car I have yet to be able to run around and do errands on less traveled roads to try and replicate the original problem.

My mechanic thinks it could be the throttle body/MAS, but I replaced it about a year ago. Since the car is over due for its regular service, I may go ahead and do a fuel filter when I next do the oil/filter just to relieve any idea of it being that. I am still at a loss, but knock on wood I have yet to be stranded.
Might as well do the spark plugs too. In the 320 there are 12 of them.
 

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Premium Member 2005 SLK55 AMG; 2005 SLK350
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This is a worst case scenario, difficult to diagnose.

STAR is the dealer level diagnostics that allows you to retrieve all the extended codes. If your mechanic isn't using it, or equivalent, he's not seeing the whole picture.

Before I start blabbering aloud with my guesswork, I want to be sure I understand something. You said that at the moment of the stall, everything electrical (lights, AC blower, radio) stops working momentarily, and then immediately everything starts working again... do you have to cycle the key 1-0-1-2 for everything to start working again? Or if you just sit there like a statue do all those things start working again (obviously the engine is not turning at this point).
 

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I'm with efair on this. After reading all the posts, it keeps coming back to the key or ignition. Normal stalling would keep the electrical on. In this case everything is lost until you take the key out and start over. While in your driveway, crank it up and start messing with the ignition switch. You might get your answer...hopefully. Good luck!
 

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I have a 2002 SLK320. About a month or so ago, I noticed that the idle would suddenly drop when stopped and then resume normal idle. Then about 2 weeks ago, while in a drive thru, the car suddenly shut off. No warning, no nothing. The dash went dark, then relit. I put the car in park, turned the key to 0 and it fired right up. I thought it was a fluke and didn't worry about it until I was pulling into my garage a few days later when it did it again. Took to my mechanic who ran the diagnostic, which showed no thrown codes of any sort. We replaced the CPS sensor and kept our fingers crossed. Was fine for almost two weeks, then last night while stopped at a traffic light, it shut off. Same scenario, it fired right back up. We are scratching our heads on this one, anyone have updates/ideas?
 

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I just thought I would give an update. After a week of commuting I have not had the car stall since the mechanic cleared all the stored codes and load tested the electrical system. Despite my initial concerns with the battery/alternator, I have not had any issues with the car shutting off while at traffic lights, etc. Although I have to admit I have not really allowed the car to idle like I would normally, in fear of it stalling in traffic.

I usually left foot brake and give the car about 200 rpm of gas pedal while I am waiting at traffic lights. Whether this has prevented me from stalling or is a placebo, I can't say. I acknowledge that such a practice doesn't help me resolve the issue definitively, but it has save me the headache and embarrassment of stalling in rush hour. Due to weekend travel, without the car I have yet to be able to run around and do errands on less traveled roads to try and replicate the original problem.

My mechanic thinks it could be the throttle body/MAS, but I replaced it about a year ago. Since the car is over due for its regular service, I may go ahead and do a fuel filter when I next do the oil/filter just to relieve any idea of it being that. I am still at a loss, but knock on wood I have yet to be stranded.
I have a 2002 SLK320. About a month or so ago, I noticed that the idle would suddenly drop when stopped and then resume normal idle. Then about 2 weeks ago, while in a drive thru, the car suddenly shut off. No warning, no nothing. The dash went dark, then relit. I put the car in park, turned the key to 0 and it fired right up. I thought it was a fluke and didn't worry about it until I was pulling into my garage a few days later when it did it again. Took to my mechanic who ran the diagnostic, which showed no thrown codes of any sort. We replaced the CPS sensor and kept our fingers crossed. Was fine for almost two weeks, then last night while stopped at a traffic light, it shut off. Same scenario, it fired right back up. We are scratching our heads on this one, anyone have updates/ideas?
Might be worth checking your main fuse holder I had the same problem, found the main 200 amp fuse loose in the holder, wife closing the passenger door caused enough vibration to stop the car and loose all power.
Ends of the fuse looked like a set of ignition points.
Cleaned fuse and refitted, no more problems.
Regards Stuart

http://www.slkworld.com/attachments/slk-r170-general-discussion/245521d1448218391-total-power-loss-fobs-wont-work-episode-iii-end-imga0378.jpg
 

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Might be worth checking your main fuse holder I had the same problem, found the main 200 amp fuse loose in the holder, wife closing the passenger door caused enough vibration to stop the car and loose all power.
Ends of the fuse looked like a set of ignition points.
Cleaned fuse and refitted, no more problems.
Regards Stuart

http://www.slkworld.com/attachments/slk-r170-general-discussion/245521d1448218391-total-power-loss-fobs-wont-work-episode-iii-end-imga0378.jpg
mine totally died rolling up to a light.Not even emergency flashers.
I wiggled the battery terminals ,it restarted,went home,tightened terminals and my indy checked them out,no corrosion,recent battery BUT work done on roof so poss battery disconnected and not reconnected 100%.
I also checked the main 200 amp fuse,it was fine.A small box in front of battery with 3 big fuses.No further stops since then-about 20 trips stopping and starting
 
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