_timothy

Hi all I have a weird problem. Twice in the past 2 weeks I have gone out to my car after about 6-8 hours of it being off and sitting. At each of the two occasions I have pushed start and it will crank 3-5 seconds longer than usual before firing. When it fires it is not with the same fierce sound. I shut it down and start it again and all seems well.

I just replaced my key less go unit battery fob before the last occurrence (just now)

I also leave my iPod plugged into the interface while its off.

There are no codes or lights

Is this a cps or battery prob? I have not consulted a dealer yet as I learning more before I do so I dont settle for their "go away " answer...... ideas?

natman316

I've had this problem once. hasnt happened to me again so I think it could be me not pressing the break enough when i start using keyless go. if you have keyless go this could be your problem. if not...i'm interested to see what your problem is

Roswell

If it only does it at the first attempt.. It sounds like a battery problem. Try unplugging ur iPod when ur car is off. Or get ur battery tested. GL

Mort

^^^+1 Testing the battery is a good place to start. Disconnect anything that will discharge the battery while the ignition is off.

dacls63amg

Maybe a vacuum leak?

_timothy

i did some errands this afternoon and did some driving after the occurence today. i came back and started it again. the crank took a bit longer than usual but it was shorter than the really long one i posted about. that seems to support the idea that the battery was drained, being that driving it for a bit improved the charge which later shortened crank time.

i disconnected my ipod after that start as recommended and will report back. subsequent starts were perfect. if it happens again with the ipod disconnected, then i guess we know its not battery drain.

do any of you leave the interface plugged up perpetually? is this bad? I dont recall anything about this in the manual but obviously an ongoing battery drain will have an effect...

Roswell

I'm glad to hear u r pin-pointing the problem to the battery.. Hope it's something simple as the iPod. Keep us posted.

Mort

The car will always have some millivolt draw on the battery when the key is off. When the battery gets weak this will be enough to cause problems until the battery fails. It would be best if you can get the battery charged back up to full capacity and see if that improves starting performance. Your battery may be past its prime. If you can get a battery maintenance charger plugged in when parked over night that may help prolong the life of your current battery and will also help on any replacement battery you get.

jim07

I though you were just bragging about your " Long crank" . I was wondering why that would be a problem???

_timothy

I wanted to bump this thread again. this has happened several more times since I last posted and it has been in the dealer. they were unable to reproduce the issue nor were they able to diagnose.

most recently, once on 5/17 and once today on 5/22.

almost all of the time (except for once), the car had been sitting outside for 4-6 hours in the hot sun (85F+) with varying oil temps, varying gas tank levels (from 9.5/10 to 1/4) and with the nose on a slight incline.

the issue appears to be described exactly by this video. 2011 c61 non p31 with 8900 miles, keyless go. first started occurring around 4000 miles.

_timothy

Just to be more specific, does any one have any suggestions?

Merc63

Have you seen the size of this battery??? Its HUGEEEE I highly doubt a little ipod is effecting it.. I leave my ipod in all the time and I use a Braille B2015 15lbs battery 24/7.

It starts the car just fine with my standard tune and with a race tune the first start is a big sluggish for some reason. My best guess, would be ignition timing advanced more making it harder to turn over.

You can have your battery tested. I doubt that's the problem. From the video the car is turning over just fine but not firing.. Could be crank position sensor or something is off.

_timothy

Yeah its definitely not the battery. I haven't had my iPod in there for weeks and have had several rough starts since

AMG-010

I had a similar issue a while ago, dealer replace fuel pump and battery which didn't fix the problem. I had the car reflashed back to standard (removed the tune) and all fixed.
Is your car tuned?

_timothy

As far as I know its not tuned. I bought a used 11 and haven't made any performance mods at all. The car is carrying a full warranty. The prior owner might have tuned it...,.. is there a way for me to check?

AMG-010

Might be worth getting all the latest software updates and re flshed if the dealer will do that

c63edition1

sounds like trying to start a boat engine :P

shades

Sounds like a crank sensor to me. Have them check it for you. Then have them see if there is any updates to the ecu.

Jim Brady

Could be your CPS (crank positon sensor). I'd clean the Mass flow sensor first with CRC and if it still does happens have the dealer check it out. You did say you didn't have a tune. Dealer will likely flash back to stock.

BK63amg

i agree with the crank position sensor assessment...mine was damaged recently and i experienced the same long cranking issue.

Merc63

That crank sensor is known to be weak and problematic according to my tech friend. They are easy to replace too.

natman316

I don't think the tune is a problem since that video is of my car and my car is 100% stock 2012 that I bought new.

Like I said in pm though, I haven't had that weak start happen since.

vtmbdlr

My 12 has done it a few times too ! Same hot conditions after sitting. Cranks just long enough to make you start to wonder if it might be a problem and then fires softly compared to normal. Mine has done it maybe 2-3 times in 1400 miles.
Crank sensor makes sense

jpsingh

Hello! Sorry to revive a 3 years old tread but this issue is really starting to bother me.

Is there someone that actually had this problem and managed to find out exactly what was causing this issue?

I have the exact same issue as the video above with my car for the last two years now (2011 C63 P31), happen only when temperature is hot outside (80-85 fahrenheit and up) and only on cold start (car must be parked 3-4 hours).

I searched a lot on this forum and thought it was the crank position sensor so I asked my dealer to replace it 2 months ago.

Unfortunately, it was really hot today and I still experienced this issue while starting my car in my garage, even with my replaced Crank position sensor.

I would like to bring it back to the dealer but I don't know what to suggest them... They can't reproduce the issues because it's really random and I brought them my car for this issue about 3 times now. The only time they did something was when I asked them to replace the crank position sensor since a lot of people was suggesting this here.

If anyone have any update on this issue and could provide any help I would be super happy. Thank you

HBC350

Leaky fuel injector allowing fuel pressure to bleed down over time?