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Discussion Starter #1
My 2001 SLK stops running after a half hour or so and when it does you turn on the key and don't' hear the pump turn on for a second or so and then turn off pressurizing the rail. After 15 min,. or so turn on the key hear to pump do it's thing
and then the car will start and run again. Fuel pump? Relay?
By the way where is the fuel pump located on my 2001? Thanks!
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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Administrator 2009 SLK 55 AMG/Founding Member 2006
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Premium Member 2002 SLK320
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I think the K40 relay board contains the relay for the fuel pump. That'd be the first place I'd look. K40's are a common problem and only need re-soldering to fix the problem (usually). There's a sticky for it, otherwise do a search.
Good luck
 

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I pulled the K40 relay module and found a total of 5 relays. I didn't find any cold solder joints or anyplace on the module that looks burned or over heated. Re-installed the module and still have the same problem. Should I replace the module with a new one? It looks like it could be a little pricey. At this point I'm thinking that the fuel pump itself is probably not the problem but the fuel pump relay is most likely the culprit. Thanks!
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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reflow the solder on it first
you might not see it but the 'break' might be there :D
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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Administrator 2009 SLK 55 AMG/Founding Member 2006
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Premium Member 2002 SLK320
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Hi James,
Like Jeff says, it's not always easy to see any bad joints on the K40 relay. In my case I could see them - but only just. Bad K40 solder joints show up in several different symptoms; mine wasn't a fuel pump problem. If you are getting access to the fuel pump anyway, why don't you just check there's voltage on it before you lift it out? Obviously, voltage on the pump and pump not running; it's faulty. Voltage not present; you need to look elsewhere. Re-soldering a K40 doesn't cost anything if you're reasonably proficient with a soldering iron. Reading this forum suggests there's been many more faulty K40s, than fuel pumps (which doesn't mean it can't be the fuel pump, of course). I would suggest K40s are more likely than a fuel pump to show intermittent symptoms like you're having.

Do the cheap checks before buying parts. By the way, K40's aren't all that expensive - $100 to $150 on ebay.
Tony
 

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Discussion Starter #11
Well, I decided to eliminate the K40 relay module altogether and installed a new part. The car ran fine until I made a stop at the store. When I came out to car wouldn't start. Like before, you wait about 15 minutes and then you can hear the fuel pump kick in for a second or two and then shut off as normal when you turn the ignition switch on. Then the car started up and took me all the way home. I guess I have to get access to the fuel pump and check the connections for corrosion etc. and then make up my mind whether I need a new fuel pump and filter or not.
I want to thank everyone for all their help and input with this little problem of mine.
Thanks!
 

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Super Moderator UK SLK 55 AMG 2007
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Be aware not to overfill the tank.
That can cause almost similar, but not quite the same as you've had.
It can 'flood' the charcoal canister and may not show immediately.


Hope you get it fixed.
 

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Just a thought maybe the fault is not related to the pump. A failing crankshaft position sensor (CPS) will work when cold but once the engine warms up it breaks down and won't allow the engine to start. Once the car has cooled again it starts. This gets progressively worse until it fails completely. Worth checking as it's a realatiively easy fix.
 
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