1999 e320 blows fuel pump fuse
 

Cars is well maintained, 100k miles. Garage kept, no water damage, operated in relatively dry LA environment.

Parked car and next morning wouldn't start. Tracked it down to blown 25A fuel pump fuse #6, located under rear seat by battery. Replaced fuse and it blows when the car is cranked. Wiggled the fuel pump wires, tapped the pump gently and replaced fuse again but it blows immediately with ignition on. Is this a known problem with this car?

The only drawing i came up with shows simply that the fuse powers the #30 leg of the fuel pump relay but no details on more wiring info. Will try to bridge the relay (pin 30 to 87) and see if it blows another fuse and will report back.

Thanks.

$1000 question
 

I disconnected the positive terminal from the pump and wired it direct to the positive battery and the pump kicked on. then reconnected the wire to the pump and put in a 25A fuse and now it runs and doesn't blow the fuse. i checked some of the visible wire and see no cut/chafing. can a pump on the brink cause fuses to blow? should i change the pump even though it's huming quiet and fine and the fuse is holding. Don't have an ameter that goes to 25A but should I borrow/buy one and test the pump draw? What should it be, its listed as a Piersburg E3L in my shop manual? Any suggestions regarding tests or likely fail scenarios?

5.5A current draw
 

i found a spec for the fuel pump. Current draw is 5.5-8Amps. i put my 15A ammeter in line and record 5.5A so the pump is not drawing too much at least not now when it's warmed up. Can the pump motor have a bad spot on it (i don't know what it's called; aramature, brush; stator?) that could cause me to blow fuses until the pump passes that bad spot. Any one have any experience with this? Don't want to change the pump unnesesarily but definetly don't want it to happen again.

The motor was probably stuck which would cause it to draw a lot of current trying to get started. Maybe somethink like a piece of rust or debris got caught in the impeller. Maybe it is a sign of a failing motor. Your bypassing the fuse allowed it to break free and start running again...will it continue to run like this and not get stuck again? Maybe.

If it was me I would continue to drive like nothing happened...if it happens again you'll know what to do and will probably have to bite the bullet and replace it then.

Thanks NHDOC, will do. I didn't see your response before posing my question again in another post.

Hi erubin, it's only a matter of time until the problem comes back. The fact that the pump hung up and blew a 25A fuse is all you need to know. I doubt that the condition will improve as time goes by, and you certainly don't want to get stuck (it'll happen at the worst time possible). This is exactly the type of problem that should be addressed immediately if you wish to keep your "well maintained" MB well maintained.