Help! Fuel Pump fuse keeps blowing

[jjtrucker 5]

So I just bought a 2006 cdi with 89000 k ran like a charm 57 mpg so far,,,winter here in sk starting to love the little guy but,,, started it up the other day and put it in gear and it ran and stopped,,,after finding the fuse panel layout,,fun yah... i found the fuse and it was blown..replaced it  and car started and ran flawlessly...until i stopped..checked the fuse again and it was blown...so i robbed the fuse from the stability control and brought it home,,,so any ideas wiring short plugged fuel filter, weak pump??

[LooseLugNuts 557]

probably needs a fuel pump

 

might as well do the external relays fix while youre at it (for fuel pump and headlights)

 

first job though is figure out why its drawing enough to pop the fuse...maybe a check the harness for short to ground

[jjtrucker 5]

Thanx..just wondering is there a fuel restriction idiot light? Wondering if a plugging filter would cause the pump to work harder and blow the fuse? Going to start with the obvious the sam module is loose..thinking of disconecting it checking the conections reinstalling it. Also put a new filter on and see..

[smartdriver 49]

This is purely speculation, but because of the pump's high current and corrosion problems on the SAM connector, the connector frequently melts.

 

Assuming that the pump motor is OK, if the connector is corroded and is limiting the pump motor startup current so that the motor sometimes doesn't start, it seems a possibility to me that the constant high current from a stalled pump motor might be enough to blow the fuse.

Edited February 18, 2017 by smartdriver

[AHZELA 12]

There are issues at the SAM that will cause the fuel pump to short. Usually the connection just becomes unstable and will show itself as a dead fuel pump, but not blow the fuse. I will look at changing the N11 plug I think it is if I remember correctly. There is also a fix that involves opening the sam to sort out some solder joints. I added some wires that bypass the factory connection. there are a few threads on this in here..

 

closing in on 300000km and I have never had an issue with the pump itself.

[jjtrucker 5]

Thank to all!! for your interest and suggestions..Have been going to "Smart Car U" on this forum since i bought this little guy...It's been quite an education. My first Idea as to the fuel pump blowing fuses was restriction/plugging filter..So I figured I'd start by changing the fuel filter...but how do i get under the little guy...well you could buy a couple of jacks,stands ect.like a normal person, but lets face it guys normal people don't buy 10 year old diesel smart cars LOL, or you could go to the lumber store...see below. Now that my little smarty is comfortable 2 feet of the ground under I went under to take off the belly pans and change the fuel filter as per CANMAN's

excellent tutorial. But when I got under the car I noticed the belly pans were all broken up along with the fuel cooler box..$500 for the belly pans and MB in their wisdom doesn"t sell just  the box Oh NO! you have to buy the box and cooler $898...now i see why the guy sold this little guy with only 88k he took it 4x4 ing...moron !!. Anyway I'll deal with that later, wrecker parts or another smarty parts car..any suggestions would be appreciated on that. Well we finally got the fuel filter swapped out, can't tell if that made any difference as smarty"s still in the air, while i try to find belly pans. Did a thorough under the body inspection (like i should have done b4 i bought it) checked for obvious wiring problems and all seems good! I guess its time to pull the sam check the connections like AHZELA suggests and due the external rely upgrade...by then I should have sourced the parts belly pan ect, Well my wife said I needed a hobby..LOL

 

[jjtrucker 5]

Update..I changed the fuel filter, Inspected the wiring don't see anything obvious ,  dropped the SAM all connections are pristine...will probably still do relays BUT am running out of ideas an why the fuel pump is blowing fuses??? Are there any weak places on the harness under the body that i should focus on?? continuity test fuel pump to ground?? ohm resistance fuel pump to ground??

 

Edited March 3, 2017 by jjtrucker
spelling error

[jjtrucker 5]

On 2017-02-16 at 11:26 PM, LooseLugNuts said:

probably needs a fuel pump

 

might as well do the external relays fix while youre at it (for fuel pump and headlights)

 

first job though is figure out why its drawing enough to pop the fuse...maybe a check the harness for short to ground

tggg

[jjtrucker 5]

Any ideas on were to look?? inspected wiring from tank to were they disappear in rear but all looks good SAM and connectors are mnt.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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[tolsen 630]

Somebody ought to dig out a wiring diagram.

[jjtrucker 5]

Been searching for one..no luck ...wires from the top of the fuel tank were I assume the fuel pump is go back into the engine compartment..there is a red black wire the in the bundle...which is the color at the SAM but its going in the wrong direction...:( which leads me to believe there is some electronic "box" in the engine compartment that the fuel pump goes to...possibly an engine ecm and then comes back to the front of the car in one of the covered looms...will have to dig around in the engine compartment...which will be a pain since I have her up on ramps!! Waiting for belly pans. On a positive note I found all the belly pans and fuel box from a guy wrecking a Smarty for $150 which beats MB"s $1400 I guess I'l; be able to eat for another month LOL

[tolsen 630]

Here is a wiring diagram showing arrangement on my 2002 Smart Cdi.  Little use for you since different to yours.  Mine has a ZEE unit instead of a SAM and a separate relay box behind driver's seat where relays are socketed and can be replaced with ease.

 

Power feed to fuel pump is 1.5 mm2 and red/black.

 

 

Wiring diagram rear fuse and relay box.pdf

[jjtrucker 5]

Update got all the belly pans and fuel cooler box installed lubed the clutch actuator and took Smarty out for a burn..ran like a top shifted much smoother...But the fuse blew again this time it turned on the check engine light. Checked the codes on reader and it  gave a "low pressure to the fuel rail" code, would this be due  to the electric pump in the tank not supplying the fuel to the engine? If so I guess its time to do the fuel pump in the tank must be not pumping correctly and drawing to much power blowing the fuse and not supplying the rail with fuel. That's my working theory...anybody smarter than me please tell me if I'm thinking this through correctly! If i am then its time to drop the tank< I have searched the forum for instructions/ tips and the closest I get is the post on full removal and replacement I was talking tho the guy I bought the belly pans from and he said the tank will drop low enough to get at the fuel pump for removal..any tips would be greatly appreciated!!

[tolsen 630]

There is something called an ammeter. Allows you to measure amps drawn by a consumer. 

[jjtrucker 5]

Tolsen  have one of those..any ideas on what the spec 's are. The problem with these little guys are no factory manuals...mb really missed there target demo ...if I was a young urban poffesional without a couple of $$ in tools this car would be in the wrecker..sad really it's well engineered and funner than all get out but fustrating that we have to figure it out with no support. 

 

[tolsen 630]

A new pump costs about £121 here. VDO 228-222-011-001Z. 

It is foolish in my humble opinion to replace pump without first confirming wiring to pump is sound and not the cause of blowing fuses. 

You will need a special tool and piping hot water to remove pump. Lower engine subframe before lowering tank.  Rear right wheel arch lining must come out. I have done it and did not need any special instructions or manual other than info available here. Dieselkiki, a club member, posted some details about how to do it. Search this forum.  

Edited March 13, 2017 by tolsen

[smartdriver 49]

In line with tolsen's thinking on this matter, you have indicated that you have checked the SAM, but have you looked inside?

 

Some have reported poor solder connections with the SAM pins on the PC board which can be fixed by re-soldering.

 

It seems to me that it might be possible and I had posted this earlier in this thread without a direct response, that a high resistance connection intermittently might not permit the pump to start but the pump will still draw a higher than normal current, which repeated over time could blow the fuse.

 

The first image below shows burnt pins. If you look closely at the left of the second image you will see that the pins at the left have become unsoldered, likely poor solder joints and damaged by the force of pushing in the connector.

Edited March 13, 2017 by smartdriver

[jjtrucker 5]

Thanks Tolsen ,Smartdriver for more things t look at...re special tool t pull fuel pump any ideas what it looks like or wear to find one?? if i kew what it loked like i can probably mcgiver or build something

[jjtrucker 5]

UPDATE...checked the interior sam..all good dropped the fuel tank removed the pump checked the wires to the pump for shorts all looks good..ran the fuel pump for 4 hrs with a 10 a fuse in line no problem blocked the flow outbound for over 1 min and fuse still wouldn't blow...so the only thing I can think of is to re assemble and run the external relay...as suggested on this site.. I just didn't want to do that until l  exhausted the obvious underlying causes...ps MB says if fuel pump runs its good no load testing...so they would have replaced it and still not have corrected the problem.

 

 

[jjtrucker 5]

Sorry for not updating. I did the external relay and the fuse kept blowing  when i hit  a bump. After consulting with MB I cut the power wire at the fuel pump and ran an new wire to the sam. Success!! apparentley there was a short in the power wire between the fuel pump and sam.

[zfan 2]

Hello jjtrucker, thank you for sharing your experience with this issue, your account has been very helpful in diagnosing my dad's fortwo.

 

Can you please tell me, do you have any tips for routing the bypass wire from the fuel pump to the sam?

 

Also, how/where did you mate the wire to the sam?

 

Any feedback is much appreciated.

[smart142 605]

Check out Evilutions fuse layout … https://www.evilution.co.uk/index.php?menu=info&mod=501  Run the wire to the 36 or 39 spot - switched power.

[zfan 2]

Thanks smart142, very helpful info, I did not know of that term, "switched power".  

 

Currently our smart fortwo is blowing fuse 16.  The fuse seems to be more prone to blow after going over a bump and is especially affected by the car accumulating heat.  For example, I was able to cold-start the car, and drive 5 miles, then the fuse blew.  I then replaced the fuse and drove 1.5 miles, then the fuse blew.  I replaced the fuse again, drove 0.75 miles, then the fuse blew.  I replaced the fuse again, drove 0.10 miles, then the fuse blew.  I replaced the fuse again, drove 10 Meters, then the fuse blew.  

 

Anyway, I will keep you all informed on my findings.

Edited July 19, 2018 by zfan

[smart142 605]

40-43 are ''live power''. Useful if you want to charge a phone without having the cars ignition on.

[jjtrucker 5]

I had the same problem.  Its a wiring short between the sam unit and fuel pump. I could not trace the wires from the fuel pump to the sam unit because they disappeared into the firewall motor area. So i dropped the tank and cut the power wire at the fuel pump and ran the power wire through a drain plug and under carpet to the sam unit or in my case s bypass   Hope this helps. Its been a while...over a year and no problems since