Hard Start, Occasional Stall, Emotional Support - Mercedes-Benz Forum
 
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post #1 of 10 (permalink) Old 07-02-2019, 06:41 AM Thread Starter
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Hard Start, Occasional Stall, Emotional Support

Friday evening noticed the car took a little longer to fire up on our way out to dinner, and then took 3 tries in the parking garage after dinner. Threw some Techron in it Saturday morning and I personally haven't had a problem since. However, my son has driven the car twice since then and said it stalled once on each trip on him (two different days - but both after idling at a red light). Car seems to run as normal, no check engine light. My son said it fired right up after each stall and ran fine after.

The only thing I can think of is that I let the fuel tank run very low (basically on 'E') last week before all this started happening and then filled up with a no-name brand (but premium grade) gasoline. Could I have run too low and had lower-quality gas cause these issues? I have a fuel filter on order - the current one is a little less than 4 years old and about 35k miles.

Just wondering if there is anything else I should think about. Mental check list - I don't believe I have put a battery in it in my 4 years, but doubting that would cause these intermittent symptoms (drove it about 20 minutes last evening to run an errand and it started up and ran absolutely perfectly). MAF or other sensors? I have SDS but would that show anything considering no codes have been set?

appreciate in advance.
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post #2 of 10 (permalink) Old 07-02-2019, 04:19 PM
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post #3 of 10 (permalink) Old 07-02-2019, 07:37 PM
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I would fit a new Crank position sensor, easy Diy and very cheap just to rule it out. I am a believer in running some form of fuel system cleaner at regular intervals regardless.
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post #4 of 10 (permalink) Old 07-02-2019, 10:47 PM
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I would fit a new Crank position sensor, easy Diy and very cheap just to rule it out. I am a believer in running some form of fuel system cleaner at regular intervals regardless.


Agree sounds similar to my w211 would start when cold but once it heated up i would have to wait 20mins before it would fire up again. Put a new CPS in and boom fired up like normal.


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post #5 of 10 (permalink) Old 07-03-2019, 03:34 AM Thread Starter
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Hey thanks all. Would CPS failure be intermittent as it is needing replacement, or an all or nothing thing?

I ordered one and will pick up today - and bonus - found that there is a 24hr AutoZone (I got the Bosch part) near me, which will come in handy for those midnight parts runs.

Family is scattered on various vacations through the weekend - and the dog died a few weeks ago - so it is just me with tunes and the car on the lift all weekend doing some easy DIY. Heaven.
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post #6 of 10 (permalink) Old 07-03-2019, 06:14 AM
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Hey thanks all. Would CPS failure be intermittent as it is needing replacement, or an all or nothing thing?



I ordered one and will pick up today - and bonus - found that there is a 24hr AutoZone (I got the Bosch part) near me, which will come in handy for those midnight parts runs.



Family is scattered on various vacations through the weekend - and the dog died a few weeks ago - so it is just me with tunes and the car on the lift all weekend doing some easy DIY. Heaven.


Not quite sure what you mean but the car will still run with a bad cps but it will have trouble turning over but will crank as if itís out of petrol. If your r129 had the same v8 as my w211 then you can remove and install it from the top without jacking up the car


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post #7 of 10 (permalink) Old 07-03-2019, 06:24 AM Thread Starter
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Not quite sure what you mean but the car will still run with a bad cps but it will have trouble turning over but will crank as if itís out of petrol.
That is basically what I meant - will the car start and run with a bad CPS? Essentially wondering why isn't either bad or it isn't. Or why it is bad sometimes and not others.

Car will be up on the lift for the fuel filter - so changing from below or above not an issue.

Thanks
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post #8 of 10 (permalink) Old 07-03-2019, 07:14 PM
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The CPS is a well-documented failure, there is a full diy write up in the stickies. Basically, when they start to fail it's normally when the engine is hot, pull up at traffic lights and the car stalls, etc. Once cooled a bit the car will restart and off you go again. It gets worse and worse. The generic ones are so cheap I keep a spare in the car at all times.
here is a diy.. https://www.benzworld.org/forums/r12...ml#post3633863

Last edited by wayneg; 07-03-2019 at 07:22 PM.
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post #9 of 10 (permalink) Old 07-04-2019, 03:29 AM
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That is basically what I meant - will the car start and run with a bad CPS? Essentially wondering why isn't either bad or it isn't. Or why it is bad sometimes and not others.



Car will be up on the lift for the fuel filter - so changing from below or above not an issue.



Thanks


Yup the car will start when cold but when itís hot it wonít fire up, I had the same thought thinking I was out of petrol because it would crank but not fire up. Like the post above mentions itís a fairly cheap part and should be replaced.


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post #10 of 10 (permalink) Old 07-04-2019, 06:23 AM Thread Starter
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thanks folks - did the fuel filter and CPS last night - took it out for a test run and top off with a half tank of fuel. Seems to run fine, but then again it ran great except for the 4 occasions when it wasn't. So we will see.

CPS was a little bit of a pain just because of access. Basically had to tape the bolt/screw into the socket to get it threaded at first. But not horrible. I AM off to harbor freight to look for fuel line clamps for fuel filter jobs - no more gasoline baths for me and the fumes were not pleasant.

On to next task - fresh soft-top/roll bar fluid.
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