alleymadison

Hi everyone,

Last summer my aunt gave me her 1999 Mercedes ML320 after my Jetta finally gave up on me. It had, and still has, just over 100k miles as I've only used it to commute to school and other nearby places. Neither of us had had any problems with it until recently.

I noticed this summer that it would turn over several times before actually starting about a third of the time. I could leave the key in the ignition and without touching it and it would continue revving sometimes. I didn't think much of it, until recently when I was driving on the freeway going about 68 MPH and it started decelerating. All of my indicator lights came on and my steering wheel sort of locked up. The accelerator had no power whatsoever, and it quickly began decelerating. needless to say, I pulled onto the shoulder and called Triple A. However, while I was waiting, I decided to try starting it up again. About ten minutes after the initial incident it started back up, and I called to cancel the tow truck. I turned the car off to do this and when I tried to restart it after the phone call, all it would do was rev again. I waited another ten minutes and it started turning over, after which I was able to make it about 15 miles back to my house, where it repeated the whole deceleration-light up-steering wheel lock thing again.

My mechanic came over and decided it was the fuel pump, which he then replaced last week. He also said I had an oil leak, and needed the O-ring replaced, so I drove to my his house the next day to get that done. After replacing the O-ring, I tried to start my car, but it had the same behavior as before. That is, trying to turn over but never actually starting. I left it at my mechanic's house and he hasn't been able to figure anything out since Saturday, but it has started up several times- as it had before replacing the fuel pump. I'm assuming I'll have to take it into the shop to do a diagnosis but I was just wondering if anyone's had a similar or experience or might know what's causing my automotive troubles. My brother has said he thinks it might be the fuel filter, or it could have something to do with the oil leak. I'm not sure. I would really appreciate any relevant feedback! Thanks!

LocalGhost

I'd say start with the infamous CPS, Crankshaft Position Sensor. I've seen exactly the same behavior before, in my friend's ML320. It would die randomly. It wouldn't accelerate at random. Sometimes it would start right after it stalled, sometimes only after it cooled down. Total randomness :-) $40 in parts, 6-pack of beer, bruised knuckles and a lot of bad words took care of it perfectly :-)<br />
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Your mechanic should have at least basic OBD scanner, did he check the fault codes at all?

alleymadison

Thank you for your response! I will definitely have him take a look at that.

He was pretty certain it was a fuel problem, as was everyone else I described it to. So he just went ahead with that replacement, evidently a bit prematurely. I'm not sure if he checked the codes before, I would assume so, but he hasn't had a ton of time since after the replacement to check out any other possibilities.

However, now that the new pump isn't doing the job, I'll have him look at the crankshaft position censor. Is there any chance that it could be the fuel filter and/or lines?

LocalGhost

"Is there any chance that it could be the fuel filter and/or lines?"

I don't think so. Clogged fuel filter is unlikely to cause engine to die randomly. It would limit engine's power under heavy load and /or on higher revs due to non-sufficient fuel flow, but won't stall it completely. The only thing related to the filter I can think of is the fuel pressure regulator, which is integrated with the filter... but again, it's failing is rather unheard of, and I believe symptoms would still differernt than yours. Might be worth checking, though.

If replacement is needed, make sure your mechanic gets the updated filter (I believe MB updated it in 2001, it includes some additional / modified fuel lines, comes with conversion manual) - some info here:
Some more info on Crankshaft Position Sensor (CPS) here:
Good luck and report back!