My car was running fine and all of a sudden it stopped. A guy who was close by stopped to help me out. He said he heard the car sputter just before I pulled over. I checked the battery and this wasn't the issue. He says he thinks its the fuel pump or the ECU. When I try to start it acts like it wants to turn over but it doesn't. Some threads I have read said it could be the CPS. Has anyone has this issue before?

Thanks,
Bryan

 

change CPS then go from there..

 

Check the fuses in the trunk. The fuel pumps' fuse is by the big battery. Check fuse #90, its a big 30 amp one. Good luck.

 

Any check engine lights? Get an OBD reader and see if there are any codes. When you say "turn over" it's like it's trying to start, but never fires up? Does it eventually start like on the fourth try?

 

There were no check engine lights....how much is the OBD reader and where do you buy it from? It hasn't started yet but I am about to try soon (the car is at my girlfriends house). Its like it wont start at all.

 

You can borrow an OBD reader at most parts stores (Autozone, OReilly, Pepboys, etc.) for free. The trick is getting the car there. Mine freaked out a few weeks ago and wouldn't start. After the 4th try it would usually start in "limp home" mode and drive just fine. Cars in the shop now with some electrical issues being sorted out. I'll post the details when I get them.

 

I checked the fuses and they look fine but the car still wont start. I ordered the CPS since it was only 40 dollars. Now I have to figure out how to remove the airbox. Is this something that is easy and what tools do I need?

 

If your car is cool/cold and you can't start it up, cps is not your problem.

And as far as the air boxes go, just pull them straight up and they'll come right off. Just becareful with the y pipe. No special tool needed.

 

Could it be the fuel pump? or fuel sending unit?

 

How many miles are on this car? Have you ever replaced the fuel pump (under the DS rear seat)? Normal service calls for replacement at 60K miles IIRC.... A failing pump would result in low fuel pressure, or sporadic pressure issues. As other people have discovered, a failing pump also causes a LOT of resistance which can melt the electrical connectors under the rear seat as well.

-G

 

I'm having the same problem right now, but only difference is my car starts after I let it sit for abt 30 mins & I changed my cps 3 months ago. Other than those things my problem is identical

I put some Sea Foam in my tank & filled it up, drove it hard in 90 degree temps, never shutdown. Tomorrow I'm gonna change the fuses to be sure. I'm hoping its not the sending unit & just the fuses.

 

GregMB: I just bought the car a month and a half ago. It has 67000 miles. I'm not sure if the fuel pump has ever been replaced. How do you know if you have low fuel pressure?

IkeLuv: you are still having the same issue after you already replaced the cps? if so that is weird. which fuses will you change? I need to do that. I only looked at a couple of the fuses.

 

Usually when its the fuel sending unit or fuel pump you smell gas right? Or is this only when there is a fuel leakage?

 

would your car start after a few hours/minutes? what did you do?

 

There seems to be a misnomer that the fuel pump needs replacing as a regular service interval. This isn't correct according to Mercedes' USA Maintenance System. Every 60K miles or 5 years, the FILTER assembly needs replaced. This is a rather expensive part (appx. $500) with an easy DIY procedure.

DO IT!! I logged a significant increase in my AF/R at WOT, just by replacing mine at 50K!

 

My understanding is that the unit under the rear seat (drivers side) is the fuel pump/filter and sender unit. This is the one that usually leaks for most people too.... The unit under the passenger side is an additional sender unit.

Either way, it seems that most people aren't aware that some of those hidden parts need to be replaced at the 60K service interval. It's an expensive part (as you mentioned) so its easy to understand why people try to avoid replacing it... I could understand how a clogged filter could increase the load on the factory fuel pump (causing overheating and melted wires)... And obviously a clogged filter is going to kill fuel flow and pressure also, and that's bad news for a car that sees a lot of WOT pulls.

To the OP: I'm not sure what the best way is to check fuel pressure and flow, but there might be some kind of port on the fuel rail that would allow the service tech to connect a pressure gauge

-G

 

If your car has 40K+, I'd replace it. If it's too expensive, then the price of admission is too high for you... it's a LOT cheaper than a nuked motor from running too lean and/or replacing both fuel pumps!!

Forget MB recommendation of waiting 'til 100K to replace your plugs too...they get toasty well before 50K. For any cars with more than a mod or two, I'd certainly replace both at 25K intervals or so. It's an easy way to take two more uncertainties out of the equation.

 

The pumps are on the passenger side, the sending unit is on the driver side.

There's a port that you can check for fuel pressure. It's on the fuel rail by cyclinder #1. You need to remove the air filter box to access it. It's at the end of the fuel rail.

 

Interesting.

So which item number on this sheet is the fuel filter that needs to be replaced at 60K? It seems like most people have replaced #55 (Driver's Side), and the passenger side sender is #40.....








-G

 

ok before replacing parts. you need to check your fuel pressure, they key in position 2 it should be 80 psi

 

55 is the fuel filter/sender assembly. It is replaced in it's entirety and the hoses go over to the other side (#40) to the pumps. #55 is specified to be replaced in the regular service interval, without mention of #40. Unless they fail, can't see a reason to.

Get #70 and 80 for each side too. Unless you have the special tool, you'll likely booger-up #80 when removing it. (they are like $5-6 ea and the seal is about $25).

 

any updates, seems like I have similar issues

 

You want to look for fuel pump activation signal,this eliminates fuses as the problem.Also , if live data shows a fluctuating rpm count, cps is good.
A bad cps won't necessarily set a code.

 

Is the engine cranking or not?

 

It was the Fuel pump. One was damaged and the other was almost dead. I got them both replaced. I'm sure they were already bad when I bought the car (it had 63,000 miles). It costs me 1,800 dollars (with tax). :-(