Pagoda SL Group

W113 Pagoda SL Group => Drive train, fuel, suspension, steering & brakes => Topic started by: jcochran@cox.net on June 03, 2014, 02:08:59

Title: Fuel Pump noises on 1967 250SL
Post by: jcochran@cox.net on June 03, 2014, 02:08:59

Hi,
 I have had a high frequency noise from the fuel pump of my 250SL since I purchased it (I am the second owner - 94,000 miles) and was wondering if that is normal or perhaps is a warning. I recently had the car restored and was wondering if the fuel pump was partially responsible for the poor performance of the FIP. My mechanic tells me that the pump is working fine but at the same time advises me that I need to think about replacing it soon. I appreciate your comments/advice.

Thanks,
Jim Cochran

Title: Re: Fuel Pump noises on 1967 250SL
Post by: ja17 on June 03, 2014, 05:40:37

Any restrictions in the supply or return fuel line will make the pump work harder and may cause it to sound differently. A fuel pressure and volume check will quickly reveal any of these conditions.

Title: Re: Fuel Pump noises on 1967 250SL
Post by: jcochran@cox.net on June 03, 2014, 19:10:35

Thanks for the advice, I'll ask my mechanic to test it.

Thanks,
Jim

Title: Re: Fuel Pump noises on 1967 250SL
Post by: ja17 on June 03, 2014, 21:19:52

You can easily unhook the metal fuel line going to the  starting solenoid on the intake. Connect a pressure gauge to it. Normal pressure in the system is 15 to 19 psi.  Problems usually start after it drops under 10 psi. The volume check can also be made at this location.

Title: Re: Fuel Pump noises on 1967 250SL
Post by: garymand on June 03, 2014, 21:41:09

The pump is audibly whiny or buzzy.  I have gotten used to listening for the whine with the key in the on 2 position.  It is a diagnositc tool.  If the car has sat for a few months you can hear it spinning with no back pressure until the lines are full and regulators up to pressure, the tone goes higher.  Then you know you have fuel, some battery, and ready to go to starter position.

I had the pump fuse go out on the freeway.  I coasted to a safe stop just at an off ramp.  It wouldn't start and I couldn't tell why until I got it home and it was quiet:  When I turned the key I heard no pump.  Checked the fuse and it had fatigue broken open at the bottom pad.  It was so noisy on the freeway I couldn't hear the pump was not whining.

Title: Re: Fuel Pump noises on 1967 250SL
Post by: enochbell on June 03, 2014, 21:52:53

The whine is audible and normal unless, as ja17 points out, you have a restriction somewhere.  I listen to mine every time I turn the key.  In fact, I usually let it run a bit as there are several weeks between my enjoying a ride, and letting the pump run makes me confident that everything is in order.  if you go to this site:
http://onlinetonegenerator.com/
...and type in "830hz" you will hear, approximately, the whine-tone my pump makes.

Hope that helps,
g