Fuel Pump Stopped....

[rogerh113]

Hello,

Went out to start up my '66 this morning - no ticking, no fuel, no start.  Drove the car yesterday with no problem. Did check the fuse, cleaned up a bit or corrosion, but didn't make a difference.  

Before I crawl under the back end, pull the can, and start poking around I was wondering if anyone could suggest a methodical approach to figuring out why it is not working.  

I was planning to check that it is getting voltage, but aside from that not sure if there is anything else I can check short of pulling it out. Could it have stopped from clogging??  Are rebuild kits available/suggested??

Any help or suggestions would be appreciated.

Regards -- Roger

PS - Of course, I filled up yesterday when I was out, so the gas tank is FULL....

[J. Huber]

Hi Roger. Bummer. Are you saying there is no whining of the fuel pump when you turn key? Or that the car is cranking but not starting? or both or neither?

James
63 230SL

[ja17]

Hello Roger,

Good plan, check for voltage and ground. Try tapping it with a wooden hammer handle with the ignition on. It may just start up and run. If so you could have worn brushes or crud.

Joe Alexander
Blacklick, Ohio

[rogerh113]

Hi,

Just no whining of the fuel pump with the ignition on - pretty quiet in the garage, so the lack of fuel pump whine was immediately obvious.  It'll crank over ok, but won't catch.  I drive the car a fair bit, so it usually catches almost immediately (if it is going to start).

Thanks for the tapping suggestion - that was a common persuasion for my old Austin Healey...

[mdsalemi]

Roger,

You need to check not only the voltage at the pump, but check the wiring back to the harness in the trunk.  Been there, done that.

What happened with me last year is as follows: I was having intermittant problems which all pointed to the fuel pump.  Problem is the voltage measured fine.

During the restoration the wires to the pump were cut and when replaced, were crimped OUTSIDE the car body.  When I went to install the new pump, the problem was shown: the + wire was corroded causing a poor connection; it actually pulled out of the crimp with but a small tug of my hand.  Could not even support the weight of the pump!

The actual "take off" from the harness should be in the trunk, under the mat, upper left corner above the fuel pump area.  The wires go from the harness, through a long grommet-strain relief tube to the pump.

Don't worry about the full tank; have a clamp and bolt ready (as well as a container to hold the spilled fuel) and plug up the line from the tank as soon as you remove it.  You'll only lose a few ounces if you are quick.

Ensure that the the wires attached to the pump are sound--I believe there are ring terminals crimped on the ends.  Crimps are not forever.  Wires get corroded, yes, even copper--particularly those outside the car body and also if you are missing the fuel pump protective cage, which a lot of cars are.  You may need to cut off the old terminal, and crimp AND SOLDER a new terminal in place.  If the thought of a soldering iron around fuel scares you, you are not alone: I did the soldering work in the trunk and pushed the wires back out.  Really make sure that the wiring is sound.  You need all that voltage, all the time, at 100% reliability.  My car would stumble at high speed; almost certainly caused by the pump cutting out just enough to impair fuel delivery a little bit.

BEFORE you pull the fuel pump, better get some new fuel pump mount screws and have these on hand.  These are double ended rubber mounts.  Mine disintegrated and my car was out of service for 3 days while I waited for the new ones to arrive.  I used SS hardware and anti-seize on them when I put them together again.

Michael Salemi
1969 280SL
Signal Red 568G w/Black Leather (Restored)
President, International Stars Section
Mercedes-Benz Club of America

[rogerh113]

Hello,

The fuel pump is working now.  I pulled the can, and the electrical connections seemed fine (and plenty of fuel coming out of the line from the tank, even though I thought it was pretty well clamped....).  I then pulled the 6 screws on the bottom of the pump, and every thing looked really clean.  Also rotated the mechanism to assure it wasn't bound up.  I then turned on the ignition for a sec to see if it was working, and it was.  With any luck a long term solution, although I like to find out what was wrong. Hopefully it is not the motor brush issue, and by rotating the shaft put them in a more favorable position.

Easy to access the pump, in case anyone else has a problem.

Thanks for the input -- Roger

[glennard]

Roger, In "Start" did the starter run?(question is - did the other "Start" circuits work-CSV, FI pump start solenoid, etc).  Ignition switches seem to fail in the "Start" position.  Look at the wiring diagram for ignition sw circuit.  I think the pump runs in both "Start" and "Run", but MB doesn't make the sw logic easy to follow on the diagram.  ---PPP-  Pleasant Pagoda Promenading

[rogerh113]

Yes, the starter and the entire car ran just fine (several stops, and no fuel pump issue).  Even when the problem arose (the fuel pump was not ticking), I was able to use the starter to turn the engine over - it just would not catch because of no fuel.