Yesterday my daughter started her car before school ran in to grab her stuff came back out 10 minutes later car was stalled , she tried to restart but it would crank at first then the battery went to low and wouldnt crank at all.. I came home and tried to jump it...cranked over, would kinda sputter , but no start....put it on the charger ..4 hours later same thing , battery would always get low and i would stop trying..

after work I just went ahead and replaced the battery , it would try to start sputter for 5 seconds and die...giving it gas would make it die faster .....I also replaced the brake light switch because i was getting an ABS and ESP warning. ...I actually should have done that a month ago but work has been crazy and my daughter said the car had been running ok prior anyway, no change immediately after changing it out along with the battery.

no check engine light ...no codes

I can hear the fuel pump coming on. I took the relay out and looked at it but did not test it yet(more on that coming)

went ahead and ordered a CPS and was going to order a relay also BUT

went out this morning and tried the car ...damn thing started , ran like **** for 10 seconds or so , not as bad as before, just like a coil was bad, then settled down and ran perfect.

no check engine light still no weird messages on the dash ?...I let it run for 3 minutes but had to get to work but Im really confused at this point.

will try it again at lunch but im not comfortable letting my teenage daughter drive it again until I know whats up....we are getting a blizzard so working on it right now will not be easy unless it does start again and I can get it in my garage.....but with my luck that could be a big ask...

Anyway anyone have any insight or advice for me?....

Thank You!!!

 

Attach a fuel pressure gauge to the schraeder valve on the end of the fuel rail. I do not have the pressure spec for your car handy so you'll have to search for that. If car runs poorly and fuel pressure is low then examine fuel system. E.g. pump, filter, electrical actuation. If pressure good, that leaves spark and air to check.

 

Thank you !! I will get a fuel pressure gauge and see what I have...if you come across the specs that would be great!

 

Going to check the pressure this weekend, the car did start again and ran perfectly fine. One other bit of info I found is my daughter has been putting ethanol blended gas in the car...not sure if that could also be contributing to the issue?

 

Fuel pressure at 58 psi and held in the 50's for a half hour....no codes , no messages,nothing, car runs fine...Im going to pretend like it never happened unless by some miracle someone actually replies to this thread and gives me some info to further the investigation.

PS is there any othe MB forums where people actually respond to threads/questions?...just curious.

 

Dont pretend it never happened, it will leave you stranded. It's likely a failing fuel pump. They tend to die intermitantly at first. It will happen again.

 

Your previous additional posts provided insufficient data; I wait to reply until I see enough information to make an educated evaluation.

Pressure is in the proper range. Now you're going to have to wait for it to fail again. Intermittent problems are the worst. At that time recheck fuel pressure. Heck, fuel pump and filter are not that expensive for your car (at least compared to our E55). Takes a bit of time to replace but it is not awful so if they've never been replaced before and you're over 60,000 miles, look at replacing them as preventive maintenance.

Some like to wait until a part fails; I prefer to replace parts in my garage rather than on the side of the road. There is a 525-mile each way back and forth trip I make several times a year; at one point in the journey, it is 180 miles in either direction to the nearest Mercedes dealer/parts department. D**n right I replace preemptively.

Other possibility (less likely) could be plugs are wearing out. I made the one-time mistake of pulling my Bosch plugs at 100K miles and installing some Champion platinum plugs I found on sale. 25,000 miles later car begins misfiring, triggering the CEL, throwing codes, and was difficult to start. Those Champion plugs, when pulled, had gaps eroded to ~0.060" versus the initial install gap of 0.034" (possibly counterfeit plugs?). Spent the money on a set of Bosch plugs and almost 70,000 miles later all is still well.

Also, there is always the chance of moisture affecting the plug wires (multiple lengths so don't mix them up) or the coil connectors degrading (way low on the list). Also chance of moisture getting into the front Motor Electronics. It's hard to diagnose remotely unless the failure mode is active or a stored code is available.

 

So you replaced the CPS? And replaced it with a good quality part?

 

(Just realized your problem is last year)

but, wondering the outcome and why alternator and fuel filter were not raised in prior replies.

I understand responses focusing on fuel delivery. But the battery is draining based on the history. You have a 2004. If you have standard mileage you may have over 200,000 miles on the car. By comparison, I have 243,000 and wonder why my battery and alternator have lived such long lives to date. Only once on my 2007 did I have a fuel issue. It was a recall service on the tank.

I do not know if your car has a fuel filter external to the tank, but I would start with that normal maintenance repair.

 

As I recall, fuel filter is part of the fuel pump assembly. There are some guys on youtube who change the filter without changing the pump. I think there was a sawzall involved.