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Fuel Pump Failure - Burnt wire, needs new fuel tank?

15K views 45 replies 12 participants last post by  coolbep 
#1 ·
My car died immediately after starting up after filling fuel at a fuel station, then would not start. I had the car towed to the local dealer and they found the fuel pump to be faulty.

They also found this connector burned/damaged. They said this connector does not come with the fuel pump or the sender unit, and only comes with a new fuel tank.

Does anyone know what this connector is and if it's possible to repair or replace it without having to purchase a new fuel tank ($1000+.)

Thanks!

 
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#11 ·
MB has approved methods of repairing a wiring harness. It is hard to imagine that they can't cut out the damage wire and connector and replace it with new.

I think the bigger question is the source of the heat that did the damage. If it was an over current situation and the fuse for that circuit did not blow, then that needs to be addressed, otherwise the problem can be repeated.
One dealer said will order one for me but not sure. Worst I have to put two female connectors and connect to the two pins with new wires. Any input on this? I believe as long as good connection will be ok right, because all the wires and connectors are in the fuel. I'll make sure the connection won't fall off.
I wonder why they want us to buy new tank, because the wires is not even attach to the tank. Just from filter to pump. If they want to sell just the wire harnes will make more sense then force us to buy new tank.
I think the earlier replies are your best bet. (note that I know zip about electrics, except when it is a live wire).
The multi quotes might get the attention of the right people who are much more into this stuff, if you're lucky.
 
#3 ·
My car died immediately after starting up after filling fuel at a fuel station, then would not start. I had the car towed to the local dealer and they found the fuel pump to be faulty.

They also found this connector burned/damaged. They said this connector does not come with the fuel pump or the sender unit, and only comes with a new fuel tank.

Does anyone know what this connector is and if it's possible to repair or replace it without having to purchase a new fuel tank ($1000+.)

Thanks!
Mark,

Can you provide more detail? Where is the connector? What does it connect to? Can you find the other end of the wires and does it have a connector? MB lists and sells connectors, so if we can figure out exactly which one it is you should be able to order a new plastic connector and repair that portion of the wiring harness.
 
#4 ·
My service advisor told me that they are speaking directly with Mercedes USA to find a solution that doesn't involve me buying the entire tank assembly
 
#5 ·
MB has approved methods of repairing a wiring harness. It is hard to imagine that they can't cut out the damage wire and connector and replace it with new.

I think the bigger question is the source of the heat that did the damage. If it was an over current situation and the fuse for that circuit did not blow, then that needs to be addressed, otherwise the problem can be repeated.
 
#7 ·
Any updates? Or how do you get the new connector? I have the same prob. Fuse burned too. Changing pump and filter, but can't find this connector. I'm thinking of doing the new 14g wires and using a female connector to connect to the two pins.
Any help or info would be appreciated.
Thanks
 
#8 ·
#10 ·
Thanks Du and Mark, wow sound bad. I can't find the connector either. One dealer said will order one for me but not sure. Worst I have to put two female connectors and connect to the two pins with new wires. Any input on this? I believe as long as good connection will be ok right, because all the wires and connectors are in the fuel. I'll make sure the connection won't fall off.
I wonder why they want us to buy new tank, because the wires is not even attach to the tank. Just from filter to pump. If they want to sell just the wire harnes will make more sense then force us to buy new tank.
 
#12 ·
I had this exact same problem on my 55 a few months back. In my case it also happened directly after fueling up. The dealership said that was just coincidence but I'm not so sure.

Anyways, burnt wire, same exact thing. They ordered a harness for a 350 but it was not a match. Then went with entire fuel tank replacement ($$$!!!).

I know of at least one person that had the same issue, but in their case it happened in mid-flight on the freeway on a very hot day in Arizona. That was actually another thing we kind of had in common: when it happened to me after fueling, the outside temp was 110F (43 Celsius).
 
#13 ·
I come out of restaurant. Weather not hot, tank about 1/4. After it not start tow home.take it apart. See bad fuse, replace and crank back it starts. But I order pump and filter already so I decide to replace all. When open to pump I see it burned, really shock me.
First I can't find where the wires connect to but then realize it about 2' long, two wires connect from pump to filter. All connectors and wires are inside fuel.
I think just buy new connector and new wire should be fixed, but when I go to dealer, they can't find connector.
So the main concern is can I use the regular male female. Crimp to wires and connect to the two pins? I'll make sure it won't fall off. Is just the same as the original connector except the original have a case that snap in and hold the wires.
In theory, it should be ok, but because I never try so I kind of worry. Just want some opinions before I try it.
Thanks

P.s oh forgot to mention, they sell me the connector at the filter. So kind of funny that they sell one but not the other. Notice both connectors are inside the tank.
 
#14 ·
So this wire connects between the fuel filter and the fuel pump? The fuel filter has a four-wire connector on both the inside and the outside of the tank (two wires for pump, two wires for level sender). Does this wire attach to the four-wire connector inside the tank? And if yes, do you know any pin number?

I'm not seeing any up-side to replacing the tank itself.
 
#16 ·
The wire that burns is the one that is inside the tank, submerged in fuel. Yes, that feel very scary, but I guess since there's no oxygen it is not actually dangerous (unless the tank was near empty? I dunno).

And yeah, noone wants to buy a new tank assembly, but the problem is that the wiring harness is not available as a separate part with its own part number. So you can make a custom harness but the dealers won't touch that. Or order the smallest part that contains the harness, which happens to be the tank assembly (which also includes filter and pump).

The root cause of the entire problem seems to be the pump seizing and the subsequent current draw making a roast out of the wiring harness.
 
#18 ·
Fuses or fusable links are supposed to blow in the event of shorts or seized and stalled motors. Surely there is a problem beyond the seized pump?? And a serious one I would think!

Could a previous owner have "upgraded" a fuse 'cause it kept popping? I think I would check the rating on the relevant fuse against the spec.

tn
 
#20 ·
I keep looking for a solution or part that can be fixed, but forgot to ask about the wire. Does it have to be some special fuel resistant wire or any wire for auto will be ok?

Because it submerged for a long time so I just wonder if regular wire can stand the fuel or there is a wire fuel alone.
Once again thanks
 
#22 ·
The picture isn't great but it looks like the terminal/pin has burnt out and melted the connector?

If so, there isn't anything special about it, just a standard connector - you will normally find that particular connector is used elsewhere on the car multiple times so will be available it's just a case of finding out where else it is. Wiring repairs/ terminals are also readily available to make up bits of a loom.

I personally can't see why you can't just carry out a wiring repair using crimps/new terminals. Doesn't even have to be genuine - As long as connection is good and they are rated for correct amp usage. Merc have a habit of being awkward with things like looms etc that they are unavailable separately as you have seen. I certainly wouldn't be spending thousands on a tank to just to get a bit of loom!
 
#23 ·
Well nuts.

I am another SLK55 AMG owner (2006) with this exact same problem. Also happened at the 1/4 tank fuel level, after having traveled maybe 3 minutes away from a 3 hour stop. No codes, no rough engine, no bucking ... just went from "perfect" to "dead" with all the warning lights on the dash lit up. Would crank, but not fire.

Some kind souls pushed me to a gas station parking lot, and I trouble shot as much as I could then and there. Was fast and easy to confirm that there was NO fuel pressure at shrader valve. Next I used Google to determine that fuse 4 in the rear SAM is the pump fuse. I noted that the fuse was blown (yay - found problem!). However, upon replacing with a spare (thanks for the baggie, MB!) it immediately blew again (boo, found symptom only!)

Towed home and tested the relay. Energized it on a 9v battery, and the closed circuit registered 0 ohms. Read up and then dug out the pump. Found a burned wire and partly melted connector.

I'm waiting in another thread for advice on how to disconnect the fuel line from the pump. Can't seem to get it to even budge! Nevertheless, I thought it wise to post here too since this thread is pointing to a possible failure trend.

tn

PS - I'll offer that there is no need to put the trunk in the service position to get all the panels out. The regular "fully open" position is just fine.
 
#25 ·
Agreed - Dislike ... with a big fat thumbs down!

But seriously
Does anyone know what this thing is? It came from the bottom of my fuel tank, directly under my pump. It is SOFT rubber, and was smearing red on my nitrile gloves as I pulled it out. In other words, it seemed like it was not chemically compatible with the fuel/injector cleaner combo in the tank.

I suspect that thingy caused the overamp situation. Here's why:

I pulled my pump and connected it to a 12v source. It spun up perfectly! So I immersed it in water to place a load on it and tried again. And it shot the water 2 feet in the air, emptying about 4 liters in 20 seconds or so, while drawing 6.5 - 7.5 amps. So basically about what I'd expect. So I progressively plugged the output with my finger, and watched the amps. The max was 10-11A, at which time the spring loaded relief valve on the pump relieved the back pressure. Sprayed water directly in my left nostril it did.

So, plugging the output circuit of the pump can't blow the 20A fuse. In my mind this rules out the filter and regulator as they are both downstream of the pump. But the pump could still be plugged on the suction side. So I went looking in the tank, using my iphone like a remote camera. Couldn't see much, but when I felt around below where the pump sits I found and removed this rubber diaphram/disk. It was just sitting there - I don't believe that I pulled it off anything. And it is certainly capable of being sucked into and plugging the pump inlet area.

Where did it come from? It certainly seems like it can't handle constant contact with gasoline, so what's up with that? And the little hole you see in one picture isn't actually a hole ... it's just a dimple.

Anyone recognize it? It looks to me like it could be a diaphram/seal in a one-way valve?

Thanks!

tn
 

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#26 ·
Looks like a carpet/plastic trim clip to me. Just not seen it red before. Maybe it was black once upon a time and the petrol has stripped it of colour?

Certainly wouldn't expect it to be just chilling in the bottom of your fuel tank.

Have you refitted it all, topped up petrol and checked it's all o.k after removal of that thing? Is it still blowing fuses or running ok now?
 
#29 ·
Hi Topaz

The part is super soft and rubbery. So much so that I really can't see it as being a clip of any sort. It was slightly less flimsy than a soft contact lens, if you can imagine that.

I was busy all day today, but will confirm continuity of the wires Monday. If everything makes sense then I'll put enough together to test the pump/filter wiring. If that looks good (no glowing wires/blown fuses & the pump spins up) then I'll install the pump and filter back in the tank and get my wife to turn the key while I listen for the pump, check for pressure at the fuel rail and so forth.

I'm optimistic now, at least.

Thanks for the feedback!

tn
 
#27 ·
Looks like one of those fasteners that holds the backrest of the seat inside its frame. Can't imagine what other kind of use it may have inside a fuel tank. It doesn't seem affected by the petrol though. Maybe it holds the wire connector that burned to some other part? That would be make for a challenging cause and effect: burned connector loosens it from its fastener and makes the fastener floating free?
 
#28 ·
Sorry for late reply, but at this point I believe you removed the clips. I know one of them is really hard to remove.

The red rubber you see, I throw it away too because I can't put it back. If you look closely inside the tank at the bottom of the filter, in the box. You will see the hole where the fuel will enter. I believe this rubber will prevent dirt or stuff from enter the filter when the filter pump hard.
It has a small pin to hold on top of the hole, but don't cover it.
If you need anything else let me know and good luck.
Sorry it happen to you too, but glad it happened sooner than you on the trip.

On the other hand, I think All our 55 will end up like this sooner or later.
 
#31 ·
Hi AMG9999

Thanks for sharing your experience here,
as well as earlier above. Both were helpful. Was also glad to hear you recognized the part, and even more so to hear that you reassembled everything without it. I will try the same tomorrow.

Question for everyone that had this happen to them: did you add fuel injector cleaner or some other chemical just prior to your failure?

tn
 
#32 ·
The only other thing I spotted whilst cleaning the car yesterday was it looks similar to the clip that holds the rubber strap on the petrol cap to the petrol flap door. Never had the clip out but similar shape... again not red however. Would also give a plausible reason as to why it's in the bottom of the tank if it fell down the filler neck.
 
#33 ·
Samething happen to me 09 55 AMG

Hi all, I'm surprised that many people had same issue.
Yes, it happened to me also, my mechanic told me that i need to order entire tank assembly for those small wiring harness.
Also he already report to MB Service Manager and it can be recall if many people report this unacceptable issue.

If you have same issue, please send an email or contact to your local service manager to make this issue.
 

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#35 ·
Okee dokee

Before I seal everything up and move on I thought I'd add pics of my connector to this thread, as well as my thoughts. You can clearly see how the heat melted the plastic, and how the one disconnect migrated across to its mate. Very similar to the other pics posted.

So, my read on this is as follows:
1. A foreign, rubbery 'doomahicky' in the tank finds its way to the inlet of the fuel pump and plugs it. Perhaps this item isn't fully compatible with gasoline, meaning it might take years before it relaxes and releases from it's intended location.
2. The extra load causes the contacts inside the electrical connector to heat up. These are of a very simple design, with little electrical contact area; Their current-carrying ability is way less than the adjoining wire, hence they become the hot point in the circuit.
3. Any more fuel than (say) 1/3 of a tank means this connector is submerged. In this case I believe the fuel acts as a heat sink, slowing or preventing the heavily loaded contacts inside the connector from melting the plastic. In any event, the load is less than the 20 amp fuse in the circuit.
4. At 1/4 tank or so the connector is no longer being cooled by fuel. Maybe the occasional splash/slosh contributes a bit. Eventually the heat build-up at the plug contacts causes the supporting plastic to relax, and in short order one contact migrates toward its mate, shorting the circuit and blowing fuse 4 in the rear SAM. I have trouble imagining that these wires did not spark as they touched. Insert exclamation point here.​

Also contributory;
I note that the wires to the pump are zip tied such that there is strain on the pump disconnects. The strain may further minimize the effective (electrical) areas in contact with each other, and contribute to the migration upon the plastic melting. I'm going to see what I can do about that strain when I reassemble.

Also, I noted absolutely NO driving symptoms of a partially plugged fuel pump. Mind you at less than a quarter of a tank I'm generally not on the gas that much. Anyone with this problem notice symptoms of fuel starvation prior to?

Ideally I'd run a current regulated supply across a test disconnect and see how hot things get at 20 amps. But I don't have one and time's a tickin' so I'll go with what I surmise at this point. I fly RC electric ducted fan jets (40A at 11V all the way up to 100A at 22V under load) and would NEVER use this kind of contact for 40A, probably not even 20A. I use Anderson Power Poles owing to their superior design in this very area. Bottom line; I "expect" the contacts at the pump connector did get HOT. Yes, hot enough to melt plastic. And then they shorted.

Finally, does anybody have any last words for me before I commit the next several hours to the R&R?

tn
 

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