Good morning fellas!
I'm brand new here and I live in Houston, TX. I'm hoping I can get little help/advice on my current "randomly wont start" issue from someone more experienced than myself on these cars.

I just recently purchased a 2003 E55 AMG (first Mercedes I've owned but I've always liked the E55's). I needed an affordable daily driver/work car that would still be nice and enjoyable to drive so I figured the E55 would be a solid bang for the buck option. Shortly after I began looking, this one popped up local at a good price.

I've had the car for about a week now. It has a few mods, mileage was reasonable at 103k. It seems to have been pretty well cared for. Price was more than fair at $6k for a clean title/clean history E55. 😬

Mods:
-74mm clutchless upper
-AMG belt wrap kit
-Aftermarket front mounted H/E
-Split cooling
-BMW power steering reservoir for additional coolant capacity
-BCracing coilovers
-Resonator/muffler delete with X pipe welded in
-KMC 19" wheels

Anyway, car has been great all week until this morning when it just randomly wouldn't start. The car turns over like it wants to start but just wont fire up. In the short time I had to mess with it before work, it seems like the fuel pumps are failing to prime/power up.

Previous owner said he just replaced the radiator, fuel pump setup and installed the coilovers not long before I bought the car.

Any ideas as to what my issue may be? My first thought was... fuel pump fuse/relay. I only had about 20 mins to mess with it before work. From what I googled, fuel pump fuse and relay are in the fuse box in the trunk but when I looked, I had a small 7.5 amp fuse in #004 which was still good and the relay in spot #A (without testing it) appeared to look normal. My car being an 03 E55 AMG, I read somewhere that those 2 spots are correct for non-AMG cars and that my fuel pump fuses are in a different location.

Can anyone point me to where they would be on my 03?

I plan to mess with it tonight after work. I'm mechanically inclined and I work on my own vehicles 90% of the time unless its something big that i dont have the space or time to mess with. On this E55 though, i just dont know much about them. This will def be a learning experience. Lol

I appreciate the help in advance!

 

Thats a nice car !

here you go

 

and here

 

Thank you! Def not too bad for its age. Has a few minor flaws but thats expected on a 100k+ mile car that's 17 years old. Lol

Thank you for the links!! I appreciate the help!

I've narrowed it down to 4 possibilities while I've been googling all day here at work.

-Crank position sensor
-Fuel pump relay
-Unplugged or damaged connection on fuel pump assembly on right side (was just replaced before I bought the car so maybe something came undone or got pinched under the cover.
-Sending unit/filter issue on the left side which I believe is still the factory unit.

I'm going to buy a couple necessary tools along with the fuel pump relay and crank position sensor after work and get to trouble shooting to see what the issue is. I'll just take back whatever I dont use or hold onto it for later.

 

and here

 

Little update...

So... I ran around after work grabbing a few specialty tools and the fuel pump relay.

I came home to start working on it and before I started, I figured I'd try one more time to see if it would start and boom... it fired right up. No check engine light or anything. 100% like it never happened in the first place. 🙄

So now... I'm assuming since there no light... CPS is prob ok. I'm assuming I have failing relay. Any other ideas as to what could cause a ghost symptom like that? Lol

 

The fuel pumps relay for your E55 is located in passenger side trunk. You will need to remove the paneling. The relay itself gets power from Z7/38 (circuit 81) and gets a ground activation from the engine control module. Fuel pump fuse is F90(40AMP) located in F33(rear pre-fuse box) if the vehicle was built up to Feb/2003. If the vehicle was built from March/2003 and up, then it get power from F82A which is located around the same area as the relay. I have had plenty of relay fail. If you can't get anywhere with it, you can bring it to me on the SW side of Houston.

 

Ok. Solid info! Thank you! I just checked my door jam and it was built 08/03.

When the relay fails, would it just randomly fail to start for several tries out of nowhere and then fire right up on the next attempt hours later?

Or... would that be more of a CPS intermittent failure as it's on it's way out?

I'm thinking at this point, I'll just replace both for peace of mind.

 

Another update...

The car started up on the first try this morning and I drove it to work. No issues. I haven't replaced anything yet. I ran out of time to mess with it last night.

From what I've read though, it seems the CPS going bad would cause the failure to start after the car is already warmed up at running temp or stalling when coming to a stop at a light. Mine doesn't do either of those things. Mine happened on a cold starting in the am with a 60* outside temp. Wish I would have realized 100% whether or not the fuel pump was priming at that time. I dont think it was but I could be mistaken. If the fuel pump was priming, it could very well be the crank position sensor. If the fuel pump was not priming, that should tell me my issues is fuel related and not CPS related right?

Would a failing CPS cause the fuel pump to fail to prime/come on?