Short Fuel Pump Problem

[chuckywoody]

Hello - I just rebuilt the short fuel pump on my 1970 280sl.  After reinstalling I verified that the pump motor was working but the vehicle wouldn't start. Checked the filter screen on the pump and it was fine. Plenty of gas in the tank. Checked output line from pump and no gas.  Mine has the "T" fitting from the fuel return line back to the bypass connection on the pump.  Pretty sure there is no gas at all in the hard lines from the tank forward. I've read that these pumps don't need to be primed, but maybe my configuration does?  Any help would be appreciated.

[dirkbalter]

Are you sure the pump is connected properly? Try switching the two wires going to the pump.

[chuckywoody]

I thought about that and checked the terminals and they are correct. I also thought I might have put the impeller in backwards so I pulled the pump and checked it as well.  Does anyone know how long it should take after switching on the ignition (just so the pump runs) for the pump to prime and get to the fuel injection system?  I'm afraid of letting it run for fear of burning up the pump.

[dirkbalter]

I tested mine while the pump was out with a bucket and some tubing. Fluid will flow almost instantly.  (Also described TM)

[chuckywoody]

Thank you for your prompt replies - I tested mine on the vehicle, just pulled the outlet line and no flow.  I also tested the check valve but it seemed ok (just blowing through it in each direction). Not sure what else it could be unless the output line is blocked, but it's brand new.

[chuckywoody]

So today I pulled the pump (again) and separated the upper and lower section to test the motor. It is spinning in the wrong direction (counterclockwise when looking at the rotor from the bottom, vs the clockwise direction of the arrow on the impeller cover that I assume is correct). Checked the terminals and it is correctly wired. The only thing I can think of is that something went wrong when I soldered the terminal wires back after replacing the o-rings , but there's no way I reversed them as I would've had to stretch the negative terminal wire across the housing, and I know that didn't happen. Before I take apart the upper housing to double check, is there anything else I could be missing? 

[chuckywoody]

I figured it out.  When you re-assemble the pump, if you rotate the upper housing body 180 degrees from how it was previously installed, the motor will run in the opposite direction.  The housing is the "stator" and the magnets have opposite polarity, so if you change the orientation it changes the spin direction. I haven't seen this mentioned in any posts or instructional videos, so hopefully it will help someone else who has this issue.

[dirkbalter]

Good to know. Thanks