sexyxe

Hey All, I'm really pitching to the brains trust with this one.

I can only assume since I replaced my fuel pumps and filter something has slowly began to die with my car. I'm making a guess it is either fuel pump or filter electrical connection due to the amount of fuel they were previously sitting in. Or even a bad pump.. Maybe.

I'm finding that seemingly randomly my car won't start. It will crank fine but no ignition. Other times it will start, come to idle then die - cleanly, no spluttering or coughing. Just stops.

This is when the car is cold, warm, hot, short or long trips. I'll take the key in and out a few times and then it will start and it's as though nothing happened. In as short as a few seconds between start attempts.

I took the rear seat out this arvo, and could hear the pumps prime. When the car wouldn't start the filter/sender unit wouldn't pump. Then, this happened(video) this is the first time that's ever happened. One of the times it did that, I heard the pump start and fuel came through and it was fine, the engine recovered and idled fine.

When the car is running, it is fine. It just needs to start. It is seemingly getting worse, and my patience for it is starting to wear. I also replaced the fuel relay with the pumps, but maybe I should replace it again? I was thinking I need to start with some dielectric grease on the connectors and then work up from there? Open to thoughts and help is appreciated!

StarvingArtist

Sounds like the CPS.

sexyxe

Really? I replaced it ~6 months ago. What a pain in the ****! I've got a spare, so I'll slap it in now and see how it goes. It is a genuine Merc part too (115 AUD ~70USD). What a bummer!

Would a failed CPS prevent the fuel pumps from running though?

StarvingArtist

No, it wouldn't. sorry not awake yet. Not reading clearly. Ok that sounds like fuel pump relay or bad connection.

sexyxe

Well, I just swapped the CPS anyway... Guess that's one less thing. I also checked the relay, appears fine on the outside.

I hope it isn't a filter issue, that'll boil my berries pretty good!

Yacht Master

I would think you are on the right track. CPS good first move. Then the fuel pump relay, and check the plug. It may be a good idea to check the fuel pressure at the fuel rail to help trouble shoot your intermintent problem.

moehler

I don't know how the idle control works on these cars, but it could be something with the TB, or an air bypass solenoid for idle. I would think that if it's a fuel problem, it would persist after the car is warmed up / driven (especially in a forced ind. car).

Hulk

Like has been said check fuel pressure at the rail, use star to see if any codes are stores also

Rocman8

Sounds like a fuel pump relay. Looks fine from the outside means nothing. Could you explain exactly which relay it is that you replaced already for the fuel pump. Unfortunately the fuse chart was wrong for a lot of e55's so most people don't know where the actual fp relay is located.

JoeNobody

Was fuel sender/pump replaced under extended warranty? Did they actually replace everything?

My buddy brought his E55 in and the dealer scammed him with a fraudulent invoice that showed both pump and sender were replaced, and then 3 months later his fuel pump went out because the dealer never changed the damn thing like they said they had.

Now his car is leaking fuel again, and it'll be one more trip to a different dealer.

bbirdwell

FWIW, here's a photo of my relay's location. Car would just randomly die and not restart for 10-15 minutes. Located in front of the fuel filler cap.

It's an easy check and the relay is inexpensive.

CarbonHan

the very same thing happened to my m5 and it turned out to be the fuel pump. The fuel filter was absolutely clogged up and the pump was working super over time trying to compensate and eventually gave out.

sexyxe

Rocman - I don't know the number off the top of my head, but the fuse box next to my Nav unit in the boot, second from he bottom.

Joe - I replaced them at home. Both the filter and pump were replaced (also a **** fight due to initially wrong parts).

Bbirdwell - do you have a larger photo? I'm unsure where I am looking in those pictures. I have a seperate set of fuses near my spare tyre, but they don't look like your picture. Mine is a Feb 05 built, 2004 model.

I am inclined to believe it is an electrical issue, as the pump can be heard and felt priming, then when they work, the very obvious and audible whir of fuel is heard. It is when they do nothing, or the car dies that they stay quiet. I cracked open the fuel line last night at the pump and it had good pressure. Doesn't mean much, but at least it wasn't dry!

Thanks for the suggestions, I'll get the fuel pressure measured and replace some more relays / have a look around for he one bbirdwell showed.

Denroll

This might be a long shot, but this is what happened to me. I swapped my fuel pumps out with a brand new OEM assembly. I put it all back together, the car would start, idle for about 10 seconds, then die. After some troubleshooting, I found that the pos/neg cables coming from the harness under the cap to one of the pumps was reversed, making the motor in the pump run backwards. After extracting the pins to swap the cables in the connector, it ran just fine.

bbirdwell

Sexyxe, here's a photo pulled back from the car. This is from a mid-2005 build so there may be some differences. The 2004 may have only had one relay. It's hidden behind the side panel with no access port. You have to pull the panel.

bbirdwell

And *that* is some great troubleshooting! One of the last things I would have expected.

sexyxe

Bbirdwell you glorious *******! After having the issue seemingly very rapidly deteriorate i opened that panel, which I never would have if you didn't post the pic, to find (picture). Interestingly my manual still has the fuel pump relay on the other side. Ive replaced some other systems relay, not the one I actually wanted to all those months ago.

The relay was visibly melted and damaged, new one in. Started straight away. I'm not an electrical guy, but is the clip itself now damaged? Does that need to be replaced? I replaced the pumps, so I'm assuming the current draw is normal again, and the new relay should help it out again. But is there damage to the wires or the housing? Once again, I don't know/like electrical stuff.

bbirdwell

Glad I could help you, Sir. See posts #7 and #8 in this thread. Bad relay was driving me crazy!


https://mbworld.org/forums/mercedes-...tcs-ideas.html


If the insulation is not melted off the wires, you can most likely get away with replacing the relay.


Items to confirm:
-check the insulation at the connector where it plugs into the fuel pumps under the back seat. I discovered mine had overheated and the insulation was cracked and flaking off. Electrical tape and an insulating cushion adhered to the underside of the metal cover where it pressed against the power cable to the pumps.
-the cause for my fuel pump over-current condition was almost certainly a clogged fuel filter accompanied by partially clogged inlet screens to the fuel pumps. I will now replace the fuel filter (an expensive piece!) every 100,000 km. FWIW, I could find no record of a fuel filter replacement by the previous two owners. My car failed at approximately 150,000 km.


Glad you found the issue. Replace the socket if needed but I could not find the plastic "positive lock" device on the stock Mercedes. I ended up using nylon ty-wraps to ensure mine were locked in place.


Happy motoring!

Max.H

I love it when a plan comes together