Could use some assistance from y’all’s brain power.
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Junior Member
Joined: Feb 2021
Posts: 29
Likes: 7
09 s550 4matic
Could use some assistance from y’all’s brain power.
I have a 2009 s550 4matic with 137k on the clock. The car runs amazing. However I have on 3 different occasions had an intermittent starting issue. It’s frustrating cause it’s not consistent. Every single time I hit the starter when cold, the car fires flawlessly and without hesitation......and 99% of the time when hot.
However, this has happened a couple times when I drive the car somewhere and then come back out to leave. Today I ran to the grocery store, was inside for around 20 minutes.....hopped back in, hit the starter button and it fired, ran for a sec, then died. Try again, same thing...fires, runs for a sec, dies. I repeated the process 4-5 times and about the 4-5th time, it kinda stumbles but starts. I can then shut the car off and it’ll fire right back up. This has only happened 3 times in months of driving, but I’m well aware that one of these times it’s just not gonna fire.
I have a few ideas, but I don’t wanna pollute this thread with my amateur opinion. I have replaced pcv valve, spark plugs, filters and oil. I also have driven the car with an icarsoft MB ii plugged in the last 2000 miles, an the car has no codes at this time. The only code issue I have intermittently had is a gas cap loose warning. Whether this is totally unrelated an fully coincidental I don’t know. But I have replaced the cap with another one off my other s550, and I still get the code maybe once a week. Not saying this has anything to do with the starting issue, but just some additional information.
Anyway, just hate holding my breath everytime I hit the starter button and really wanna get this resolved.......any help would be greatly appreciated.
However, this has happened a couple times when I drive the car somewhere and then come back out to leave. Today I ran to the grocery store, was inside for around 20 minutes.....hopped back in, hit the starter button and it fired, ran for a sec, then died. Try again, same thing...fires, runs for a sec, dies. I repeated the process 4-5 times and about the 4-5th time, it kinda stumbles but starts. I can then shut the car off and it’ll fire right back up. This has only happened 3 times in months of driving, but I’m well aware that one of these times it’s just not gonna fire.
I have a few ideas, but I don’t wanna pollute this thread with my amateur opinion. I have replaced pcv valve, spark plugs, filters and oil. I also have driven the car with an icarsoft MB ii plugged in the last 2000 miles, an the car has no codes at this time. The only code issue I have intermittently had is a gas cap loose warning. Whether this is totally unrelated an fully coincidental I don’t know. But I have replaced the cap with another one off my other s550, and I still get the code maybe once a week. Not saying this has anything to do with the starting issue, but just some additional information.
Anyway, just hate holding my breath everytime I hit the starter button and really wanna get this resolved.......any help would be greatly appreciated.
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Joined: Jul 2014
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From: Tucson, AZ
'20 X5 M50i; '17 Ram 3500; Golf Cart; Bikes; Scooters
Hot running/starting issues are many times related to the Crankshaft Position Sensor (CPS). They work fine cold, but fail hot.
DIY Replacement is less than an hour and $50. No codes will be shown with this fault.
I have had these fail on my MB cars, and now replace them at 50K miles as preventative maintenance. I would start here. Only use genuine parts.
The next item I would check is fuel pressure at the injector rail. Low pressure & hot engine can cause the fuel to boil, then injectors inject air, not fuel.
This will cause intermittent running until the air is purged and fuel pressure restored. Can be caused by leaky injectors, or poor fuel pump. Not as common as CPS, and may shown a code.
Keep us posted on the results and cure.
DIY Replacement is less than an hour and $50. No codes will be shown with this fault.
I have had these fail on my MB cars, and now replace them at 50K miles as preventative maintenance. I would start here. Only use genuine parts.
The next item I would check is fuel pressure at the injector rail. Low pressure & hot engine can cause the fuel to boil, then injectors inject air, not fuel.
This will cause intermittent running until the air is purged and fuel pressure restored. Can be caused by leaky injectors, or poor fuel pump. Not as common as CPS, and may shown a code.
Keep us posted on the results and cure.
