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!

 

Check fuel pressure at the rail.

 

Ok. I will check it after work. Is there a good spot to check pressure once I get the engine covers off?

Should the fuel pump be audibly priming and making pressure with the key in the on position?

 

There's a shared valve in the rail to connect a fuel pressure tester. Harbor Freight sell them pretty cheap.
Other possibility is a bad crank sensor.

 

Ok cool! I'll have to run by there today after work.

So far... I'll be picking up...

-Torx socket set for the E-8 I may need
-Fuel pressure tester
-Crankshaft position sensor
-Fuel pump relay.

I just want to have everything I might need and anything I dont use can either be returned or I'll keep them for spare parts.

 

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

 

I think you have a bad crank sensor. When they fail they can be intermittent. If it was a bad fuel pump you would be down on power if it started.

 

I'm thinking you're prob right. From everything I've researched today, that makes the most sense to me also. I didn't drive the car but I'm about to. The fuel pump was just replaced a month or so ago with a brand new OEM pump so it shouldn't be the pump.

 

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?

 

no.

 

Well there's the beginning to my process of elimination. Should it happen again, I'll check to see if the pumps prime or not when it fails to start and that will point me in the right direction.